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A REPORT ON

“STUDY OF SIGNALLING CASCADES IN CANCER AND

GROWTH FACTOR SIGNALLING AND ONCOGENES”

PREPARED IN THE PARTIAL FULFILLMENT OF

SPECIAL PROJECT, BIO C491

(APRIL, 2012)

NAME OF THE STUDENT IDNO.

B SRIMAN 2009B1A8319G

PROJECT INSTRUCTOR: Dr. VIJAY SHREE NAYAK

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ACKNOWLDGEMENT

First and foremost, I am grateful towards Dr. Vijay shree nayak for providing

such a great opportunity. She has given a constant support, guidance and

motivation throughout the project and providing relevant study materials.

We would like to conclude by thanking our instructor and mentor Dr. Vijay

shree nayak once again for giving us this invaluable learning opportunity of a

lifetime.

We thank Dr.utpal Roy (Instructor in charge) for providing such a

valuable study oriented project.

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Abstract:

The main aim of this project is to study the different types of cancer,

how cancer is formed and different pathways related to cancer.

During this Project I will review basic research articles and molecular aspects of

cancer. Topics of discussion may include cancer development and progression,

oncogenes and tumour suppressor genes, cell cycle control, apoptosis,

angiogenesis, cell migration/metastasis, and the future of cancer treatment.

To develop a clear appreciation that cancer is not one disease; rather the

mechanism, cause and therapy of cancer are variable depending on the cellular

origin of the disease.

To gain a thorough understanding of the types of molecules and pathways

involved in the process of converting a normal cell into a cancer cell and how

this knowledge has improved over time.

To understand the relationship between knowledge of the detailed mechanism

of cancer, the development of plausible drug therapies and the improvement of

quality of life for individuals with this disease.

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TABLE OF CONTENTS

ACKNOWLEDGEMENT

ABSTRACT

1. INTRODUCTION

1.1 WHAT IS CANCER??

1.2 DIFFERENT TYPES OF CANCER

1.3 INFLUENTIAL FACTORS AFFECTING CARCINOGENESIS

2. REGULATION OF GENE EXPRESSION

2.1 GENE STRUCTURE

2.2 MOLECULAR TARGETS IN CANCER THERAPHY

3. GROWTH FACTOR SIGNALLING AND ONCOGENES

3.1 EGF PATHWAY

3.2 RAS-MAP KINASE PATHWAY

3.3 JAK-STAT PATHWAY

3.4 HEDGEHOG PATHWAY

3.5 WNT SIGNALLING PATHWYA

4. GROWTH INHIBITION AND TUMOUR SUPRESSOR GENES

4.1 P53 PATHWAY

4.2 RETINOBLASTMO PATHWAY

5. CELL CYCLE

5.1 CDC DEPENDENT KINASE,CDK REGULATION

5.2 PROGRESSION OF CANCER THROUGH CHECK POINTS

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6. APOPTOPSIS

6.1 MOLECULAR MECHANISM

6.2 APOPTOTOIC DRUG

7. STEM CELL AND CANCER

7.1 DIFFERNTAION AND REGULATION OF CANCER

8. CANCER IN FUTURE

8.1 CANCER VACCINE, CANCER TREATMENT

8.2 TREATING CANCER SYMPOTOMS,

8.3 IMAGING AND CANCER NANOTECHNOLOGY TECHNIQUES

9. CONCLUSIONS AND RECOMMENDATIONS

10. SCOPE FOR FUTURE WORK

11. REFERENCES

12. APPENDIX

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INTRODUCTION

CANCER:

Cancer known medically as a malignant neoplasm, is a broad group of

various diseases, all involving unregulated cell growth. In cancer, cells divide and

grow uncontrollably, forming malignant tumours, and invade nearby parts of

the body. The cancer may also spread to more distant parts of the body

through the lymphatic system or bloodstream. Not all tumours are

cancerous. Benign tumours do not grow uncontrollably, do not invade

neighbouring tissues, and do not spread throughout the body. There are over

200 different known cancers that afflict humans.

Determining what causes cancer is complex. Many things are known to increase

the risk of cancer, including tobacco use, certain infections, radiation, lack of

physical activity, obesity, and environmental pollutants. These can directly

damage genes or combine with existing genetic faults within cells to cause the

disease.[3] Approximately five to ten per cent of cancers are entirely hereditary.

Cancer can be detected in a number of ways, including the presence of

certain signs and symptoms, screening tests, or medical imaging. Once a

possible cancer is detected it is diagnosed by microscopic examination of a tissue

sample. Cancer is usually treated with chemotherapy, radiation

therapy and surgery. The chances of surviving the disease vary greatly by the

type and location of the cancer and the extent of disease at the start of

treatment. While cancer can affect people of all ages, and a few types of cancer

are more common in children, the risk of developing cancer generally increases

with age. In 2007, cancer caused about 13% of all human deaths worldwide

(7.9 million). Rates are rising as more people live to an old age and as mass

lifestyle changes occur in the developing world

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Legend: → tumour ←, ✱ central pleural effusion, 1 & 3 lungs, 2 spine, 4 ribs,

5 aorta, 6 spleen, 7 & 8 kidneys, 9 liver.

DIFEFRNT TYPES OF CANCER:

Breast Cancer

Breast cancer is the most common cancer in women, being responsible for

almost 20 percent of all cancer deaths in women. It ranks second after lung

cancer. Roughly 180,000 women are diagnosed with this disease each year, of

which 44,000 will die. With increased awareness and increased use of

routine mammograms, more women are diagnosed in the earlier stages of this

disease, at which time a cure may be possible. For every 100 women, one man

is diagnosed with this disease. The disease is more common in women after age

40. It is also more frequent in women of a higher social-economic class

.

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Many factors are known to increase the risk of development of breast cancer:

Genetic predisposition. A few genetic markers have been linked to development

of breast cancer.

History of breast cancer in the same patient, in the opposite breast

Onset of menstruation in early ages

Late onset of menopause

Radiation exposure

Heavy alcohol consumption

High fat diet

Obesity

First pregnancy after age of 30

Very tall women

Colon Cancer

Colorectal cancer is the third most common cancer in men and women. An

estimated 131,000 Americans are diagnosed with this disease each year and

some 55,000 die as a result of it. Certain genetic factors play a role in the

development of this cancer. The specific cause of colorectal cancer is unknown;

however, environmental, genetic, familial factors and pre-existing Ulcerative

Colitis have been linked to the development of this cancer. It is more common

among African-Americans.

Risk Factors

Age: Average age at the time of diagnosis is between 60-65, and the older we

get the higher our risk of colorectal cancer.

Family History of colorectal cancer increases the risk of developing this illness in

first- degree relatives. Certain familial conditions, like Familial Polyposis, is

associated with a much higher risk.

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Genetic factors clearly play a role in the development of colorectal cancers.

Several genetic and inherited illnesses carry a very high risk of colorectal cancer:

Familial Polyposis, Turcot syndrome, Gardner syndrome, Peutz-Jeghers

syndrome, Juvenile Polyposis, Cowden's disease, Neurofibromatosis.

Ulcerative colitis , High Dietary Fat and Low Dietary Fiber can each increase the

risk of this cancer.

Signs and Symptoms

This cancer may exhibit no signs in its early stages. Gradually, as the disease

progresses, any of the following may be seen;

Blood in the stool

Diarrhea

Constipation

Bowel obstruction, causing nausea, vomiting and abdominal distention

Abdominal pain

Pelvic pain

Anaemia due to blood Loss

Weight loss

Loss of appetite

Fatigue

Lung cancer:

Lung cancer is the second most common malignancy affecting both sexes.

Roughly 180,000 Americans are diagnosed with this illness ever year. It is

considered the most rapidly increasing cause of death from cancer. Since 1987,

lung cancer has been the leading cause of cancer death in women, surpassing

breast cancer. And while lung cancer incidence has levelled off among men, it

continues to rise steadily among women. The average age of patients with lung

cancer is 60 years. It is more common in African-Americans and Hawaiians.

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Causes:

Cigarette smoking is the number one cause of this disease. Even passive

inhalation of the smoke increases the chance of developing this illness. Radon

exposure is another cause of lung cancer, killing 14,000 Americans every year.

Asbestos exposure also increases Lung cancer risk. The risk becomes astronomical

in exposed individuals who also smoke.

Signs and Symptoms

Patients do not manifest any signs in the very early stages. Cough, shortness of

breath, chest pain or blood in the sputum is among the early warning signs.

Other signs of this illness could be a change of voice, hoarseness, weakness,

fatigue, and weight loss.

Establishing Diagnosis

When the diagnosis is suspected, patients must be examined carefully by a

qualified physician. A chest x-ray along with studying a sample of sputum are

the very first steps in establishing a diagnosis. If the study sputum does not

confirm the diagnosis, then Bronchoscopy and biopsy are the next steps. In

certain patients, cancer may have already spread to lymph glands in the neck.

In such cases, a Fine needle aspiration of the lymph gland should be performed.

This is a fairly easy procedure. Unfortunately, most doctors avoid the simple

test of sputum study. There is no reason not to perform this test, since it

establishes the diagnosis in about 30% of patients. In a small percentage of

patients, none of the above tests will lead into a diagnosis and there will be a

need to proceed with more invasive procedures, and perhaps surgery.

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Different Types of Lung cancer

There are two basic kinds of lung cancer:

Small cell or oat cell, that occurs in one-third of all patients with lung cancer

Non-small cell in two-thirds of patients.

This distinction is rather important, because the treatment for the two kinds is

very different. Small cell cancers are primarily treated with Chemotherapy.

Surgery does not play a role in this type of lung cancer. On the other hand,

Non-small cell lung cancer is treated primarily with surgery.

Another type of cancer that can develop in the lungs is Carcinoid Tumour.

RTK (RECEPTOR TYROSINE KINASE) PATHWAY

Four common structural features shared among RTKs:

Extracellular ligand-binding domain

Single trans membrane domain

Cytoplasmic tyrosine kinase domain(s)

Regulatory domains

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Ligand-induced RTK activation induces Receptor dimerization, leading to

activation of catalytic domains

Receptor auto Tran’s phosphorylation:

Stimulates kinase activity Leads to phosphorylation of additional proteins

involved in receptor signalling pathway .Provides “docking sites” for

downstream signaling proteins (Grb2, PI3-kinase, phospholipase Cg, etc.)

Map kinase pathway:

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Jak stst pathway:

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JAK-STAT pathway

Binding of erythropoietin causes dimerization of receptors and recruitment of

soluble JAK kinase to cytosolic domain

JAKs are phosphorylated (activated) and phosphorylate receptors

STATs bind to receptors (SH2) and become phosphorylated

Phosphorylated STATs form dimers activating NLS (nuclear localization)

STAT dimers activate transcription of EPO specific genes

Wnt pathway

Wnt proteins released from or presented on the surface of signaling cells act on

target cells by binding to Frizzled (Fz)/LDL-related protein (LDR) complex at

the cell surface.

Receptors

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Frizzled receptors, like GPCRs, are transmembrane proteins that span 7 times

the plasma membrane.

Their ligand-binding site is exposed outside the surface of the cell.

Their effector site extends into the cytosol.

Fz receptors transduce signals to intra-cellular proteins including Dsh, GSK-3ß,

Axin, APC and ß-catenin

Nuclear ß-catenin interacts with lymphoid enhancer-binding factor 1/T cell-

specific transcription factor (LEF/TCF) to affect transcription

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The APC gene was originally discovered to be the culprit in a hereditary cancer

syndrome termed familial adenomatous polyposis (FAP).

FAP patients, inheriting one defective APC allele, develop large numbers of colon

polyps, or adenomas, early in life.

Individual polyps are clonal outgrowths of epithelial cells in which the second

APC allele is inactivated.

Mutational inactivation of APC leads to the inappropriate stabilization of b-

catenin, implying that the absence of functional APC transforms epithelial cells

through activation of the Wnt cascade.

In some cases of colorectal cancer in which APC is not mutated, the scaffolding

protein axin 2 is mutant, or activating (oncogenic) point mutations in b-

catenin remove its N-terminal Ser/Thr destruction motif.

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Growth inhibition and tumour suppressor genes:

Carcinogenesis or oncogenes is or tumorigenesis is literally the creation

of cancer. It is a process by which normal cells are transformed into cancer cells.

It is characterized by a progression of changes at the cellular, genetic

and epigenetic level that ultimately reprogram a cell to undergo

uncontrolled cell division, thus forming a malignant mass.

Cell division is a physiological process that occurs in almost all tissues and under

many circumstances. Under normal circumstances, the balance between

proliferation and programmed cell death, usually in the form of apoptosis, is

maintained by tightly regulating both processes to ensure the integrity of organs

and tissues. Mutations and epimutations in DNA that lead to cancer (only

certain mutations and epimutations can lead to cancer and the majority of

potential mutations and epimutations will have no bearing) disrupt these

orderly processes by disrupting the programming regulating the processes.

Carcinogenesis is caused by mutation and epimutation of the genetic material of

normal cells, which upsets the normal balance between proliferation and cell

death. This results in uncontrolled cell division and the evolution of those

cells by natural selection in the body. The uncontrolled and often rapid

proliferation of cells can lead to benign tumors; some types of these may turn

into malignant tumors (cancer). Benign tumors do not spread to other parts of

the body or invade other tissues, and they are rarely a threat to life unless they

compress vital structures or are physiologically active, for instance, producing a

hormone. Malignant tumors can invade other organs, spread to distant

locations (metastasis) and become life-threatening.

More than one mutation is necessary for carcinogenesis. In fact, a series of

several mutations to certain classes of genes is usually required before a normal

cell will transform into a cancer cell. On average, for example, 15 "driver

mutations" and 60 "passenger" mutations are found in colon cancers. Mutations

in those certain types of genes that play vital roles in cell division, apoptosis (cell

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death), and mutations and epimutations (see article Genome instability) in DNA

repair genes will cause a cell to lose control of its cell proliferation.

Oncovirinae, viruses that contain an oncogene, are categorized as oncogenic

because they trigger the growth of tumorous tissues in the host. This process is

also referred to as viral transformation.

Cancer is fundamentally a disease of regulation of tissue growth. In order for a

normal cell to transform into a cancer cell, genes that regulate cell growth and

differentiation must be altered.[3] Genetic and epigenetic changes can occur at

many levels, from gain or loss of entire chromosomes, to a mutation affecting

a single DNA nucleotide, or to silencing or activating microRNA that controls

expression of 100 to 500 genes.[4][5] There are two broad categories of genes

that are affected by these changes. Oncogenes may be normal genes that are

expressed at inappropriately high levels, or altered genes that have novel

properties. In either case, expression of these genes promotes the malignant

phenotype of cancer cells. Tumor suppressor genes are genes that inhibit cell

division, survival, or other properties of cancer cells. Tumor suppressor genes are

often disabled by cancer-promoting genetic changes. Typically, changes in many

genes are required to transform a normal cell into a cancer cell.

There is a diverse classification scheme for the various genomic changes that

may contribute to the generation of cancer cells. Many of these changes

are mutations, or changes in the nucleotide sequence of genomic DNA. There are

also many epigenetic changes that alter whether genes are expressed or not

expressed. Aneuploidy, the presence of an abnormal number of chromosomes, is

one genomic change that is not a mutation, and may involve either gain or loss

of one or more chromosomes through errors in mitosis.

Large-scale mutations involve the deletion or gain of a portion of a

chromosome. Genomic amplification occurs when a cell gains many copies (often

20 or more) of a small chromosomal region, usually containing one or more

oncogenes and adjacent genetic material. Translocation occurs when two

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separate chromosomal regions become abnormally fused, often at a

characteristic location. A well-known example of this is the Philadelphia

chromosome, or translocation of chromosomes 9 and 22, which occurs

inchronic myelogenous leukemia, and results in production of the BCR-

abl fusion protein, an oncogenic tyrosine kinase.

Small-scale mutations include point mutations, deletions, and insertions, which

may occur in the promoter of a gene and affect its expression, or may occur in

the gene'scoding sequence and alter the function or stability of

its protein product. Disruption of a single gene may also result from integration

of genomic material from a DNA virus or retrovirus, and such an event may

also result in the expression of viral oncogenes in the affected cell and its

descendants.

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Tumor suppressor genes

Many tumour suppressor genes effect signal transduction pathways that

regulate apoptosis, also known as "programmed cell death".

Tumor suppressor genes code for anti-proliferation signals and proteins that

suppress mitosis and cell growth. Generally, tumor suppressors are transcription

factors that are activated by cellular stress or DNA damage. Often DNA damage

will cause the presence of free-floating genetic material as well as other signs,

and will trigger enzymes and pathways that lead to the activation of tumor

suppressor genes. The functions of such genes is to arrest the progression of the

cell cycle in order to carry out DNA repair, preventing mutations from being

passed on to daughter cells. The p53 protein, one of the most important

studied tumor suppressor genes, is a transcription factor activated by many

cellular stressors including hypoxia and ultraviolet radiation damage.

Despite nearly half of all cancers possibly involving alterations in p53, its tumor

suppressor function is poorly understood. p53 clearly has two functions: one a

nuclear role as a transcription factor, and the other a cytoplasmic role in

regulating the cell cycle, cell division, and apoptosis.

The Warburg hypothesis is the preferential use of glycolysis for energy to sustain

cancer growth. p53 has been shown to regulate the shift from the respiratory

to the glycolytic pathway.

However, a mutation can damage the tumor suppressor gene itself, or the

signal pathway that activates it, "switching it off". The invariable consequence of

this is that DNA repair is hindered or inhibited: DNA damage accumulates

without repair, inevitably leading to cancer.

Mutations of tumor suppressor genes that occur in germ line cells are passed

along to offspring, and increase the likelihood for cancer diagnoses in subsequent

generations. Members of these families have increased incidence and decreased

latency of multiple tumors. The tumor types are typical for each type of tumor

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suppressor gene mutation, with some mutations causing particular cancers, and

other mutations causing others. The mode of inheritance of mutant tumor

suppressors is that an affected member inherits a defective copy from one

parent, and a normal copy from the other. For instance, individuals who inherit

one mutant p53 allele (and are therefore heterozygous for mutatedp53) can

develop melanomas and pancreatic cancer, known as Li-Fraumeni syndrome.

Other inherited tumor suppressor gene syndromes include Rb mutations, linked

to retinoblastoma, and APC gene mutations, linked to adenopolyposis colon

cancer. Adenopolyposis colon cancer is associated with thousands of polyps in

colon while young, leading to colon cancer at a relatively early age. Finally,

inherited mutations in BRCA1 and BRCA2 lead to early onset of breast cancer.

Development of cancer was proposed in 1971 to depend on at least two

mutational events. In what became known as the Knudson two-hit hypothesis,

an inherited, germ-line mutation in a tumor suppressor gene would cause

cancer only if another mutation event occurred later in the organism's life,

inactivating the other allele of that tumor suppressor gene.

Usually, oncogenes are dominant, as they contain gain-of-function mutations,

while mutated tumor suppressors are recessive, as they contain loss-of-function

mutations. Each cell has two copies of the same gene, one from each parent,

and under most cases gain of function mutations in just one copy of a

particular proto-oncogene is enough to make that gene a true oncogene. On the

other hand, loss of function mutations need to happen in both copies of a

tumor suppressor gene to render that gene completely non-functional.

However, cases exist in which one mutated copy of a tumor suppressor gene can

render the other, wild-type copy non-functional. This phenomenon is called

the dominant negative effect and is observed in many p53 mutations.

Knudson's two hit model has recently been challenged by several investigators.

Inactivation of one allele of some tumor suppressor genes is sufficient to cause

tumors. This phenomenon is called haplo insufficiency and has been

demonstrated by a number of experimental approaches. Tumors caused

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by haplo insufficiency usually have a later age of onset when compared with

those by a two hit process.

Cell cycle:

DNA damage and deficient DNA repair in carcinogenesis

The central role of DNA damage and epigenetic defects in DNA repair genes in

carcinogenesis

DNA damage is considered to be the primary cause of cancer. [13] More than

10,000 new naturally occurring DNA damages arise, on average, per human

cell, per day, due to endogenous cellular processes (see article DNA damage

(naturally occurring).

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Additional DNA damages can arise from exposure to exogenous agents. As one

example of an exogenous carcinogenic agent, tobacco smoke causes increased

DNA damage, and this DNA damages likely cause the increase of lung cancer

due to smoking. In other examples, UV light from solar radiation causes DNA

damage that is important in melanoma, helicobacter pylori infection produces

high levels of reactive oxygen species that damage DNA and contributes to

gastric cancer, and the Aspergillus metabolite, aflatoxin, is a DNA damaging

agent that is causative in liver cancer.

DNA damages can also be caused by endogenous (naturally occurring) agents.

Katsurano et al. indicated that macrophages and neutrophils in an inflamed

colonic epithelium are the source of reactive oxygen species causing the DNA

damages that initiate colonic tumorigenesis, and bile acids, at high levels in the

colons of humans eating a high fat diet, also cause DNA damage and contribute

to colon cancer.

Such exogenous and endogenous sources of DNA damage are indicated in the

boxes at the top of the figure in this section. The central role of DNA damage in

progression to cancer is indicated at the second level of the figure. The central

elements of DNA damage, epigenetic alterations and deficient DNA repair in

progression to cancer are shown in red.

A deficiency in DNA repair would cause more DNA damages to accumulate, and

increase the risk for cancer. For example, individuals with an inherited

impairment in any of 34 DNA repair genes (see article DNA repair-deficiency

disorder) are at increased risk of cancer with some defects causing up to 100%

lifetime chance of cancer (e.g. p53 mutations [74]). Such germ line mutations

are shown in a box at the left of the figure, with an indication of their

contribution to DNA repair deficiency. However, such germ line mutations

(which cause highly penetrant cancer syndromes) are the cause of only about 1

percent of cancers.

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The majority of cancers are called non-hereditary or "sporadic cancers". About

30% of sporadic cancers do have some hereditary component that is currently

undefined, while the majority, or 70% of sporadic cancers, have no hereditary

component.

In sporadic cancers, a deficiency in DNA repair is occasionally due to a mutation

in a DNA repair gene, but much more frequently reduced or absent expression

of DNA repair genes is due to epigenetic alterations that reduce or silence gene

expression. This is indicated in the figure at the 3rd level from the top. For

example, for 113 colorectal cancers examined in sequence, only four had

a missense mutation in the DNA repair gene MGMT, while the majority had

reduced MGMT expression due to methylation of the MGMT promoter region

(an epigenetic alteration).[23] Five reports present evidence that between 40%

and 90% of colorectal cancers have reduced MGMT expression due to

methylation of the MGMT promoter region.

Similarly, out of 119 cases of mismatch repair-deficient colorectal cancers that

lacked DNA repair gene PMS2 expression, Pms2 was deficient in 6 due to

mutations in the PMS2 gene, while in 103 cases PMS2 expression was deficient

because its pairing partner MLH1 was repressed due to promoter methylation

(PMS2 protein is unstable in the absence of MLH1).[29] In the other 10 cases,

loss of PMS2 expression was likely due to epigenetic overexpression of the

microRNA, miR-155, which down-regulates MLH1.

In further examples [tabulated in the article Epigenetics (see section “DNA

repair epigenetics in cancer”)], epigenetic defects in cancers were found at

frequencies of between 13%-100% for the DNA repair

genes BRCA1, WRN, FANCB, FANCF, MGMT, MLH1, MSH2, MSH4, ERCC1,

XPF, NEIL1 and ATM in cancers including those in breast, ovarian, colorectal,

and the head and neck areas. In particular, two or more epigenetic deficiencies

in expression of ERCC1, XPF and/or PMS2 were shown to occur simultaneously

in the majority of the 49 colon cancers evaluated by Facista et al.

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When expression of DNA repair genes is reduced, this causes a DNA repair

deficiency. This is shown in the figure at the 4th level from the top. With a DNA

repair deficiency, more DNA damages remain in cells at a higher than usual

level (5th level from the top in figure), and these excess damages cause

increased frequencies of mutation and/or epimutation (6th level from top of

figure). Experimentally, mutation rates increase substantially in cells defective

in DNA mismatch repair[32][33] or in Homologous recombination repair

(HRR).[34] Chromosomal rearrangements and aneuploidy also increase in HRR

defective cells during repair of DNA double strand breaks, or repair of other

DNA damages, incompletely cleared sites of repair can cause epigenetic gene

silencing.[36][37]

Many studies of heavy metal-induced carcinogenesis show that such heavy

metals cause reduction in expression of DNA repair enzymes, some through

epigenetic mechanisms. In some cases, DNA repair inhibition is proposed to be a

predominant mechanism in heavy metal-induced carcinogenicity. For example,

one group of studies shows that arsenic inhibits the DNA repair genes PARP,

XRCC1, Ligase 3, Ligase 4, DNA POLB, XRCC4, DNA PKCS, TOPO2B, OGG1,

ERCC1, XPF, XPB, XPC XPE and P53.[38][39][40][41][42][43] Another

group of studies shows that cadmium inhibits the DNA repair genes MSH2,

ERCC1, XRCC1, OGG1, MSH6, DNA-PK, XPD and XPC[44][45][46][47][48]

The somatic mutations and epigenetic alterations caused by DNA damages and

deficiencies in DNA repair accumulate in field defects. Field defects are normal

appearing tissues with multiple alterations (discussed in the section below), and

are common precursors to development of the disordered and improperly

proliferating clone of tissue in a cancer. Such field defects (second level from

bottom of figure) may have multiple mutations and epigenetic alterations.

It is impossible to determine the initial cause for most specific cancers. In a few

cases, only one cause exists; for example, the virus HHV-8 causes all Kaposi's

sarcomas. However, with the help of cancer epidemiology techniques and

information, it is possible to produce an estimate of a likely cause in many more

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situations. For example, lung cancer has several causes, including tobacco use

and radon gas. Men who currently smoke tobacco develop lung cancer at a rate

14 times that of men who have never smoked tobacco, so the chance of lung

cancer in a current smoker being caused by smoking is about 93%; there is a 7%

chance that the smoker's lung cancer was caused by radon gas or some other,

non-tobacco cause.[49] These statistical correlations have made it possible for

researchers to infer that certain substances or behaviours are carcinogenic.

Tobacco smoke causes increased exogenous DNA damage, and these DNA

damages are the likely cause of lung cancer due to smoking. Among the more

than 5,000 compounds in tobacco smoke, the genotoxic DNA damaging agents

that occur both at the highest concentrations and which have the strongest

mutagenic effects are acrolein, formaldehyde, acrylonitrile, 1,3-butadiene,

acetaldehyde, ethylene oxide and isoprene.

Using molecular biological techniques, it is possible to characterize the

mutations, epimutations or chromosomal aberrations within a tumor, and rapid

progress is being made in the field of predicting prognosis based on the

spectrum of mutations in some cases. For example, up to half of all tumors have

a defective p53 gene. This mutation is associated with poor prognosis, since

those tumor cells are less likely to go into apoptosis or programmed cell

death when damaged by therapy. Telomerase mutations remove additional

barriers, extending the number of times a cell can divide. Other mutations

enable the tumor to grow new blood vessels to provide more nutrients, or

to metastasize, spreading to other parts of the body. However, once a cancer is

formed it continues to evolve and to produce sub clones. For example, a renal

cancer, sampled in 9 areas, had 40 ubiquitous mutations, 59 mutations shared

by some, but not all regions, and 29 “private” mutations only present in one

region.[

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Apoptosis:

Multiple mutations

Multiple mutations in cancer cells

In general, mutations in both types of genes are required for cancer to occur.

For example, a mutation limited to one oncogene would be suppressed by

normal mitosis control and tumor suppressor genes, first hypothesised by

the Knudson hypothesis.[93] A mutation to only one tumor suppressor gene

would not cause cancer either, due to the presence of many "backup" genes that

duplicate its functions. It is only when enough proto-oncogenes have mutated

into oncogenes, and enough tumor suppressor genes deactivated or damaged,

that the signals for cell growth overwhelm the signals to regulate it, that cell

growth quickly spirals out of control. Often, because these genes regulate the

processes that prevent most damage to genes themselves, the rate of mutations

increases as one gets older, because DNA damage forms a feedback loop.

Usually, oncogenes are dominant alleles, as they contain gain-of-function

mutations, whereas mutated tumor suppressors are recessive alleles, as they

contain loss-of-function mutations. Each cell has two copies of a same gene, one

from each parent, and, under most cases, gain of function mutation in one

copy of a particular proto-oncogene is enough to make that gene a true

oncogene, while usually loss of function mutation must happen in both copies of

a tumor suppressor gene to render that gene completely non-functional.

However, cases exist in which one loss of function copy of a tumor suppressor

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gene can render the other copy non-functional, called the dominant negative

effect. This is observed in many p53 mutations.

Mutation of tumor suppressor genes that are passed on to the next generation

of not merely cells, but their offspring, can cause increased likelihoods for

cancers to be inherited. Members within these families have increased incidence

and decreased latency of multiple tumors. The mode of inheritance of mutant

tumor suppressors is that affected member inherits a defective copy from one

parent, and a normal copy from another. Because mutations in tumor

suppressors act in a recessive manner (note, however, there are exceptions), the

loss of the normal copy creates the cancer phenotype. For instance, individuals

that are heterozygous for p53 mutations are often victims of Li-Fraumeni

syndrome, and that are heterozygous for Rb mutations develop retinoblastoma.

In similar fashion, mutations in the adenomatous polyposis coli gene are linked

to adenopolyposis colon cancer, with thousands of polyps in the colon while

young, whereas mutations in BRCA1 and BRCA2 lead to early onset of breast

cancer.

A new idea announced in 2011 is an extreme version of multiple mutations,

called chromothripsis by its proponents. This idea, affecting only 2–3% of cases

of cancer, although up to 25% of bone cancers involve the catastrophic

shattering of a chromosome into tens or hundreds of pieces and then being

patched back together incorrectly. This shattering probably takes place when

the chromosomes are compacted during normal cell division, but the trigger for

the shattering is unknown. Under this model, cancer arises as the result of a

single, isolated event, rather than the slow accumulation of multiple mutations.

Cell types involved in cancer growth

There are several different cell types that are critical to tumour growth. In

particular endothelial progenitor cells are a very important cell population in

tumour blood vessel growth.[84][85] The hypothesis that endothelial progenitor

cells are important in tumour growth, angiogenesis and metastasis has been

30

supported by a recent publication in Cancer Research (August 2010). This

paper argues that endothelial progenitor cells can be marked using the Inhibitor

of DNA Binding 1 (ID1). This novel finding meant that investigators were able

to track endothelial progenitor cells from the bone marrow to the blood to the

tumour-stroma and vasculature. This finding of endothelial progenitor cells

incorporated in tumour vasculature gives evidence for the importance of this

cell type in blood vessel development in a tumour setting and metastasis.

Furthermore, ablation of the endothelial progenitor cells in the bone marrow

lead to a significant decrease in tumour growth and vasculature development.

The continued research into the importance of endothelial progenitor cells may

present novel therapeutic targets.

Oncogenes

Oncogenes promote cell growth through a variety of ways. Many can

produce hormones, a "chemical messenger" between cells that encourage mitosis,

the effect of which depends on the signal transduction of the receiving tissue or

cells. In other words, when a hormone receptor on a recipient cell is stimulated,

the signal is conducted from the surface of the cell to the cell nucleus to affect

some change in gene transcription regulation at the nuclear level. Some

oncogenes are part of the signal transduction system itself, or the

signal receptors in cells and tissues themselves, thus controlling the sensitivity to

such hormones. Oncogenes often produce mitogens, or are involved in

transcription of DNA in protein synthesis, which creates

the proteins and enzymes responsible for producing the products and bio

chemicals cells use and interact with.

Mutations in proto-oncogenes, which are the normally quiescent counterparts

of oncogenes, can modify their expression and function, increasing the amount

or activity of the product protein. When this happens, the proto-oncogenes

become oncogenes, and this transition upsets the normal balance of cell

cycle regulation in the cell, making uncontrolled growth possible. The chance of

31

cancer cannot be reduced by removing proto-oncogenes from the genome, even

if this were possible, as they are critical for growth, repair and homeostasis of

the organism. It is only when they become mutated that the signals for growth

become excessive.

One of the first oncogenes to be defined in cancer research is the Ras oncogene.

Mutations in the Ras family of proto-oncogenes (comprising H-Ras, N-Ras and

K-Ras) are very common, being found in 20% to 30% of all human

tumours.[87] Ras was originally identified in the Harvey sarcoma virus genome,

and researchers were surprised that not only is this gene present in the human

genome but also, when ligated to a stimulating control element, it could induce

cancers in cell line cultures.

Proto-oncogenes

Proto-oncogenes promote cell growth in a variety of ways. Many can

produce hormones, "chemical messengers" between cells that encourage mitosis,

the effect of which depends on the signal transduction of the receiving tissue or

cells. Some are responsible for the signal transduction system and

signal receptors in cells and tissues themselves, thus controlling the sensitivity to

such hormones. They often produce mitogens, or are involved in transcription of

DNA in protein synthesis, which create the proteins and enzymes is responsible

for producing the products and bio chemicals cells use and interact with.

Mutations in proto-oncogenes can modify their expression and function,

increasing the amount or activity of the product protein. When this happens,

they become oncogenes, and, thus, cells have a higher chance to divide

excessively and uncontrollably. The chance of cancer cannot be reduced by

removing proto-oncogenes from the genome, as they are critical for growth,

repair and homeostasis of the body. It is only when they become mutated that

the signals for growth become excessive. It is important to note that a gene

possessing a growth-promoting role may increase carcinogenic potential of a

cell, under the condition that all necessary cellular mechanisms that permit

32

growth are activated.[89] This condition includes also the inactivation of specific

tumor suppressor genes (see below). If the condition is not fulfilled, the cell may

cease to grow and can proceed to die. This makes knowledge of the stage and

type of cancer cell that grows under the control of a given oncogene crucial for

the development of treatment strategies.

Apoptosis:

Apoptosis (is the process of programmed cell death (PCD) that may occur

in multicellular organisms.[4] Biochemical events lead to characteristic cell

changes (morphology) and death. These changes include blebbing, cell

shrinkage, nuclear fragmentation, chromatin condensation, and

chromosomal DNA fragmentation. (See also apoptotic DNA fragmentation.)

In contrast to necrosis, which is a form of traumatic cell death that results

from acute cellular injury, apoptosis generally confers advantages during an

organism's life cycle. For example, the differentiation of fingers and toes in a

developing human embryo occurs because cells between the fingers apoptosis;

the result is that the digits are separate. Unlike necrosis, apoptosis produces cell

fragments called apoptotic bodies that phagocytic cells are able to engulf and

quickly remove before the contents of the cell can spill out onto surrounding

cells and cause damage

33

The process of apoptosis is controlled by a diverse range of cell signals, which

may originate either extra cellular (extrinsic inducers) or intra cellular (intrinsic

inducers). Extracellular signals may include toxins, hormones, growth

factors, nitric oxide or cytokines, that must either cross the plasma membrane

or transduce to effect a response. These signals may positively (i.e., trigger) or

negatively (i.e., repress, inhibit, or dampen) affect apoptosis. (Binding and

subsequent trigger of apoptosis by a molecule is termed positive induction,

whereas the active repression or inhibition of apoptosis by a molecule is

termed negative induction.)

34

A cell initiates intracellular apoptotic signalling in response to a stress, which

may bring about cell suicide. The binding of nuclear receptors

by glucocorticoids, heat, radiation,[15] nutrient deprivation,[15] viral

infection,[15] hypoxia[15] and increased

intracellular calcium concentration,[16] for example, by damage to the

membrane, can all trigger the release of intracellular apoptotic signals by a

damaged cell. A number of cellular components, such as poly ADP ribose

polymerase, may also help regulate apoptosis.[17]

Before the actual process of cell death is precipitated by enzymes, apoptotic

signals must cause regulatory proteins to initiate the apoptosis pathway. This

step allows apoptotic signals to cause cell death, or the process to be stopped,

should the cell no longer need to die. Several proteins are involved, but two

main methods of regulation have been identified: targeting

mitochondria functionality, or directly transducing the signal via adaptor

proteins to the apoptotic mechanisms. Another extrinsic pathway for initiation

identified in several toxin studies is an increase in calcium concentration within

a cell caused by drug activity, which also can cause apoptosis via calcium

binding protease calpain.

Mitochondrial regulation

The mitochondria are essential to multicellular life. Without them, a cell ceases

to respire aerobically and quickly dies. This fact forms the basis for some

apoptotic pathways. Apoptotic proteins that target mitochondria affect them in

different ways. They may cause mitochondrial swelling through the formation of

membrane pores, or they may increase the permeability of the mitochondrial

membrane and cause apoptotic effectors to leak out.[15] These are very closely

related to intrinsic pathway, and tumors arise more frequently through

intrinsic pathway than the extrinsic pathway because of sensitivity.[18] There is

also a growing body of evidence indicating that nitric oxide is able to induce

apoptosis by helping to dissipate the membrane potential of mitochondria and

35

therefore make it more permeable.[14] Nitric oxide has been implicated in

initiating and inhibiting apoptosis through its possible action as a signal molecule

of subsequent pathways that activate apoptosis.[19][citation needed]

Mitochondrial proteins known as SMACs (small mitochondria-derived activator

of caspases) are released into the cytosol following an increase in permeability.

SMAC binds to inhibitor of apoptosis proteins (IAPs) and deactivates them,

preventing the IAPs from arresting the apoptotic process and therefore allowing

apoptosis to proceed. IAP also normally suppresses the activity of a group of

cysteine proteases called caspases,[20] which carry out the degradation of the

cell, therefore the actual degradation enzymes can be seen to be indirectly

regulated by mitochondrial permeability.

Cytochrome c is also released from mitochondria due to formation of a channel,

the mitochondrial apoptosis-induced channel(MAC), in the outer mitochondrial

membrane,[21] and serves a regulatory function as it precedes morphological

change associated with apoptosis.[15] Once cytochrome c is released it binds

with Apoptotic protease activating factor - 1 (Apaf-1) and ATP, which then

bind to pro-caspase-9 to create a protein complex known as an apoptosome.

The apoptosome cleaves the pro-caspase to its active form of caspase-9, which

in turn activates the effector caspase-3.

MAC, also called "Mitochondrial Outer Membrane Permeabilization Pore" is

regulated by various proteins, such as those encoded by the mammalian Bcl-2

family of anti-apoptotic genes, the homologs of the ced-9 gene found in C.

elegans.[22][23] Bcl-2 proteins are able to promote or inhibit apoptosis by

direct action on MAC/MOMPP. Bax and/or Bak form the pore, while Bcl-2,

Bcl-xL or Mcl-1 inhibits its formation.

36

Stem cell cancer:

A new way of looking at carcinogenesis comes from integrating the ideas

of developmental biology into oncology. The cancer stem cell hypothesis proposes

that the different kinds of cells in a heterogeneous tumor arise from a single

cell, termed Cancer Stem Cell. Cancer stem cells may arise from transformation

of adult stem cells or differentiated cells within a body. These cells persist as a

subcomponent of the tumor and retain key stem cell properties. They give rise

to a variety of cells, are capable of self-renewal and

homeostatic control.[98] Furthermore, the relapse of cancer and the emergence

of metastasis are also attributed to these cells. The cancer stem

cell hypothesis does not contradict earlier concepts of carcinogenesis.

37

Cancer stem cells (CSCs) are cancer cells (found

within tumors or haematological cancers) that possess characteristics associated

with normal stem cells, specifically the ability to give rise to all cell types found

in a particular cancer sample. CSCs are therefore tumorigenic (tumor-forming),

perhaps in contrast to other non-tumorigenic cancer cells. CSCs may generate

tumors through the stem cell processes of self-renewal and differentiation into

multiple cell types. Such cells are proposed to persist in tumors as a distinct

population and cause relapse and metastasis by giving rise to new tumors.

Therefore, development of specific therapies targeted at CSCs holds hope for

improvement of survival and quality of life of cancer patients, especially for

sufferers of metastatic.

Existing cancer treatments have mostly been developed based on animal models,

where therapies able to promote tumor shrinkage were deemed effective.

However, animals could not provide a complete model of human disease. In

particular, in mice, whose life spans do not exceed two years, tumor relapse is

exceptionally difficult to study.

The efficacy of cancer treatments is, in the initial stages of testing, often

measured by the ablation fraction of tumor mass (fractional kill). As CSCs would

form a very small proportion of the tumor, this may not necessarily select for

drugs that act specifically on the stem cells. The theory suggests that

conventional chemotherapies kill differentiated or differentiating cells, which

38

form the bulk of the tumor but are unable to generate new cells. A population

of CSCs, which gave rise to it, could remain untouched and cause a relapse of

the disease.

Both tumor models may play role in the maintenance of tumor. Initially,

tumor growth assures specific CSC (CSC1). With tumor progression, another

CSC (CSC 2) may arise due the clonal selection. Development of new more

aggressive CSC may be result from acquisition additional mutation or epigenetic.

Pathways

The design of new drugs for the treatment of CSCs will likely require an

understanding of the cellular mechanisms that regulate cell proliferation. The

first advances in this area were made with hematopoietic stem cells (HSCs) and

their transformed counterparts in leukemia, the disease for which the origin of

CSCs is best understood. It is now becoming increasingly clear that stem cells of

many organs share the same cellular pathways as leukemia-derived HSCs.

Additionally, a normal stem cell may be transformed into a cancer stem cell

through deregulation of the proliferation and

differentiation pathways controlling it or by inducing on coprotein activity.

Bmi-1

The Poly comb group transcriptional repressor Bmi-1 was discovered as a

common oncogene activated in lymphoma[74] and later shown to specifically

39

regulate HSCs.[75] The role of Bmi-1 has also been illustrated in neural stem

cells.[76] The pathway appears to be active in CSCs of pediatric brain

tumors.[77]

Notch

The Notch pathway has been known to developmental biologists for decades. Its

role in control of stem cell proliferation has now been demonstrated for several

cell types including hematopoietic, neural and mammary [78] stem cells.

Components of the Notch pathway have been proposed to act as oncogenes in

mammary [79] and other tumors.

A particular branch of the Notch signalling pathway that involves the

transcription factor Hes3 has been shown to regulate the number of cultured

cells with cancer stem cell characteristics obtained from glioblastoma

patients.[80]

Sonic hedgehog and Wnt

These developmental pathways are also strongly implicated as stem cell

regulators.[81] Both Sonic hedgehog (SHH) and Wnt pathways are commonly

hyper activated in tumors and are required to sustain tumor growth. However,

the Gli transcription factors that are regulated by SHH take their name

from gliomas, where they are commonly expressed at high levels. A degree

of crosstalk exists between the two pathways and their activation commonly

goes hand-in-hand.[82] This is a trend rather than a rule. For instance, in

colon cancer hedgehog signalling appears to antagonise Wnt.[83]

Sonic hedgehog blockers are available, such as cyclopamine. There is also a new

water soluble cyclopamine that may be more effective in cancer treatment.

There is also DMAPT, a water soluble derivative of parthenolide (induces

oxidative stress, inhibits NF-κB signalling[84]) for AML (leukemia), and possibly

40

myeloma and prostate cancer. A clinical trial of DMAPT is to start in England

in late 2007 or 2008. Finally, the enzyme telomerase may qualify as a study

subject in CSC physiology.[85] GRN163L (Imetelstat) was recently started in

trials to target myeloma stem cells. If it is possible to eliminate the cancer stem

cell, then a potential cure may be achieved if there are no more CSCs to

repopulate a cancer.

Hedgehog pathway:

Embryonic development:

41

Insect cells express a full size zinc-finger transcription factor Cubits interrupt’s

(Ci), which forms a complex with the kinesin- like protein Costal-2 (Cos2) and

is localized in the cytoplasm bound to cellular microtubules (Figure 2). The SCF

complex targets the 155 kDa full length Ci protein for proteasome- dependent

cleavage, which generates a 75 kDa fragment (CiR). CiR builds up in the cell

and diffuses into the nucleus, where it acts as a co-repressor for Hh target

genes.[6] The steps leading to Ci protein proteolysis include phosphorylation of

Ci protein by several protein kinases; PKA, GSK3β and CK1(Figure

2).[7] The Drosophila protein Slimb is part of an SCF complex that targets

proteins for ubiquitylation. Slimb binds to phosphorylated Ci protein.

In the absence of Hh, a cell-surface trans membrane protein

called Patched(PTCH) acts to prevent high expression and activity of a 7

membrane spanning receptor[8] called Smoothened (SMO). Patched has

42

sequence similarity to known membrane transport proteins. When extracellular

Hh is present (Figure 3), it binds to and inhibits Patched, allowing Smoothened

to accumulate and inhibit the photolytic cleavage of the Ci protein. This process

most likely involves the direct interaction of smoothened and Costal-2 and may

involve sequestration of the Ci protein-containing complex to a micro domain

where the steps leading to Ci protein proteolysis are disrupted.[6] The

mechanism by which Hh binding to Patched leads to increased levels of

Smoothened is not clear (Step 1 in Figure 3). Following binding of Hh to

Patched, Smoothened levels increase greatly over the level maintained in cells

when Patched is not bound to Hh.[9] It has been suggested that phosphorylation

of Smoothened plays a role in Hh-dependent regulation of Smoothened

levels.[10]

In cells with Hh-activated Patched (Figure 3), the intact Ci protein accumulates

in the cell cytoplasm and levels of CiR decrease, allowing transcription of some

genes such as decapentaplegic (dpp, a member of the BMP growth factor

family). For other Hh-regulated genes, expression requires not only the loss of

CiR but also the positive action of uncleaved Ci to act as a transcriptional

activator.[7] Costal-2 is normally important for holding Ci protein in the

cytoplasm, but interaction of Smoothened with Costal-2 allows some intact Ci

protein to go to the nucleus. The Drosophila protein Fused (Fu in Figure 3) is a

protein kinase that binds to Costal-2. Fused can inhibit Suppressor of Fused

(SUFU), which in turn interacts with Ci to regulate gene transcription in some

cell types.[

Hedgehog has roles in larval body segment development and in formation of

adult appendages. During the formation of body segments in the

developing Drosophila embryo, stripes of cells that synthesize the transcription

factor Engrailed can also express the cell-to-cell signalling protein Hedgehog

(green in Figure 4). Hedgehog is not free to move very far from the cells that

make it and so it only activates a thin strips of cells adjacent to the Engrailed-

expressing cells. Only cells to one side of the Engrailed-expressing cells are

43

competent to respond to Hedgehog following interaction of Hh with the

receptor protein Patched .

Cells with Hh-activated Patched receptor synthesize the Wingless protein (red

in Figure 4). If a Drosophila embryo is altered so as to produce Hh in all cells, all

of the competent cells respond and form a broader band of Wingless-expressing

cells in each segment. The wingless gene has an upstream transcription

regulatory region that binds the Ci transcription factor in a Hh-dependent

fashion resulting in an increase in wingless transcription (interaction 2 in Figure

3) in a stripe of cells adjacent to the stripe of Hh-producing cells.[12]

Wingless protein acts as an extracellular signal and patterns the adjacent rows

of cells by activating its cell surface receptor Frizzled. Wingless acts on Engrailed-

expressing cells to stabilize the stripes of engrailed expression. Wingless is a

member of the Wnt family of cell-to-cell signaling proteins. The reciprocal

signaling by Hedgehog and Wingless stabilizes the boundary between Para

segments . The effects of Wingless and Hedgehog on other stripes of cells in each

segment establishes a positional code that accounts for the distinct anatomical

features along the anterior-posterior axis of the segments [13]

The Wingless protein is called "wingless" because of the phenotype of

some wingless fly mutants. Wingless and Hedgehog functioned together

during metamorphosis to coordinate wing formation. Hedgehog is expressed in

the posterior part of developing Drosophila limbs. Hedgehog also participates in

the coordination of eye, brain, gonad, gut and tracheal development. Hedgehog

has been implicated in reduced eye development in the amphipod Gammarus

minus. Specifically, down regulation of hedgehog results in reduced eyes. [14]

Cancer treatment:

The existence of CSCs has several implications in terms of future cancer

treatment and therapies. These include disease identification, selective drug

44

targets, prevention of metastasis, and development of new intervention

strategies.

Normal somatic stem cells are naturally resistant to chemotherapeutic agents-

they have various pumps (such as MDR[citation needed]) that pump out drugs,

DNA repair proteins and they also have a slow rate of cell turnover

(chemotherapeutic agents naturally target rapidly replicating cells)[citation

needed]. CSCs that have mutated from normal stem cells may also express

proteins that would increase their resistance towards chemotherapeutic agents.

These surviving CSCs then repopulate the tumor, causing relapse. By selectively

targeting CSCs, it would be possible to treat patients with aggressive, non-

resectable tumors, as well as preventing the tumor from metastasizing. The

hypothesis suggests that upon CSC elimination, cancer would regress due to

differentiation and/or cell death [citation needed]. What fraction of tumor cells

are CSCs and therefore need to be eliminated is not clear yet.

A number of studies have investigated the possibility of identifying specific

markers that may distinguish CSCs from the bulk of the tumor (as well as from

normal stem cells).[11] Proteomic and genomic signatures of tumors are also

being investigated.[70][citation needed]. In 2009, scientists identified one

compound, Salinomycin, that selectively reduces the proportion of breast CSCs

in mice by more than 100-fold relative to Paclitaxel, a commonly used

chemotherapeutic agent.[71]

The cell surface receptor interleukin-3 receptor-alpha (CD123) was shown to

be overexpressed on CD34+CD38- leukemic stem cells (LSCs) in acute

myelogenous leukemia (AML) but not on normal CD34+CD38- bone marrow

cells.[72] Jin et al., then demonstrated that treating AML-engrafted

NOD/SCID mice with a CD123-specific monoclonal antibody impaired LSCs

homing to the bone marrow and reduced overall AML cell repopulation

including the proportion of LSCs in secondary mouse recipients.[73]

45

He concept of migrating cancer stem cells (MSC).

Stationary cancers stem cells are embedded in begin carcinomas and these cells

are detectable in the differentiated central area of tumor. The important step

toward malignancy is the induction of epithelial mesenchyme transition (EMT)

in the stationary cancer stem cells (SCS), which become mobile or migrating

cancer stem cells. MCS cells divide asymmetrically. One daughter cell starts

proliferation and differentiation. The remaining MCS migrates a short distance

before undergoing new asymmetric division, or starts dissemination through

Blood vessel blood or lymphatic vessels and produces a metastatic.

CONCLUSIONS:

Finally studied different signalling pathways which are related to cancer

and development if cancer.

Different oncogenes and proto oncogenes, which are responsible for the

cancer

And while studying the cell cycle, different check points, and which are

affecting the cell cycle.

Study related to different therapies, drugs, and different several

treatments related to cancer.

Finally how to reduce the cancer using herbs, and many other techniques

are well studied and included in it.

Study of gene expression, and DNA damage, and different tumour

suppressor genes.

Study of different types of molecules and pathways involved in the

process of converting a normal cell into a cancer cell.

46

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