Genetic change that lead to development of cancer Carcinogenesis is a multistep process, interaction between environment and genetic factors. It consist of three stages. Carcinogen such as physical(UV ray), biological (virus-HIV,EB,bacteria) and chemical (bezene) with the inherited gene cause Initiation, promotion -further acquisition of genetic errors and defect.Progression- gain metastatic potential lead to genome instability or become cancer. Hallmark of cancer (a) evading apoptosis (b) self sufficiency in growth signal (c) insensitivity to antigrowth signals (d) sustained angiogenesis (e) tissue invasion and metastasis (f) emerging hallmarks- deregulating cellular energetics,avoiding immune destruction (g) enabling character- genome instability and mutation,tumor promoting inflammation Common genetic changes that occur in cancer (A) Mutation (deletion,duplication,amplification,truncation) (B) DNA damages to a small set of gene that control cell proliferations and cell death- oncogene,tumor suppressor gene and DNA repair pathways gene. Imbalance between oncogene and TS result in cancer. Oncogene are mutated form of normal cellular gene (proto-oncogene), due to gain of function; their protein product stimulate cell division and/or inhibit cell death. Cell environment signal regulate the activity of protooncogene, oncogene are defective and they are ‘on’ even when they do not receive the appropriate signals.they help ignore negative signals that would prevent the cell from dividing. TSG protein product prevent directly or indirectly cell division or lead to cell death .eg. p53, RB,APC,BRCA (PRAB) P53- regulate gene control cell division and death Rb- regulate altering TF activity.inhibitor of cell division. APC- protein bind and stimulate degradation of TF BRCA- repair DNA damage and regulation of gene expression. !

cancer cells/tumors arise from ancestral cell acquiring 7-12 genetics changes over 20-50 years. !Oncogenes are derived from the normal viral or chromosomal genes -become “ACTIVATED” by mutation (e.g. a constitutively active growth receptor in absence of growth factor) or ENHANCED by mutation (e.g. simple over-expression of normal growth factor receptors makes them much more sensitive to growth factor) or self-expression of growth factors Mutant gene function is dominant to WT gene (proto-oncogene) Principally, they are intracellular signal transduction proteins (receptors), or transcription factors. Oncogene are functionally defined by transformation assays,by increasing the plating efficiency of P rat embryo fibroblasts and in combination with other oncogene cause transformation of cells(immortalisation). Alteration in GF regulatory control circuit cause ligand independent firing. All components of signalling pathway are potential oncogenes,when they are over expressed,mutated or fused with other genes. Five class of oncogene secreted growth factor growth factor receptor intracellular signal transduction DNA binding protein/TF cell cycle proteins -cyclins,cyclin dependent kinases and CDK inhibitors !

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Cancer Genetics – an overviewDr. S.M. Picksley

(s.m.picksley@bradford.ac.uk)

14 Learning Objectives• Understand cancer is a genetic disease, whereby a single

progenitor cell has acquired 6-12 genetic (and/or epigenetic) events that affect proto-oncogenes & tumour suppressors. Some progress has been made in identifying these successive genetic events (e.g. colon cancer)

• Understand proto-oncogenes, oncogenes & tumour suppressors, and their functional definition.

• Understand the common genetic events that affect proto-oncogenes & tumour suppressors.

• Understand that individual oncogene activation is not sufficient to cause cancer (several defense mechanisms are in place)

• Understand that all agents including viruses that cause cancer result in genetic changes that affect oncogene or tumoursuppressors (directly or indirectly)

References

The lecture was adapted from the course recommended text “Human Molecular Genetics”, Chp 17 by T. Strachan & Read (4th

Edition). It is a wealth of information and is highly recommended, - a source of extra reading

Some material was also sourced from “Biology of Cancer” R.A. Weinberg

For illustration only

CANCER CELLS / TUMOURS ARISE

FROM A SINGLE ANCESTRAL CELL

ACQUIRING 7-12 GENETIC CHANGES

OVER 20 to 50 YEARS!

Aims of cancer genetics• To to identify the

mutations within pathways that allow normal cells to found/produce a population of proliferating and invasive cancer cells.

• To evaluate whether these genetic events have therapeutic or diagnostic or prognostic potential

For illustration only

Some progress identified in molecular genetics of some cancers, e.g. colon cancer (but really a simple overview)

A useful figure!

!1 genomic instability cause gene amplification !!!!!!!!!!!

Tumor suppresor gene encode protein that restore the growth control function to cancer cells by -prevent inappropriate entry into cell cycle -promote cancer cell death by apoptosis -maintainance of genomic stability (accurate replication,DNA repair,segregation of daughter DNA molecules) Both allele LOST/INACTIVAATED to see changes in cell properties,WT function is dominant to mutant. Knudson’s 2 hit hypothesis on Rb gene studies. TS are inactivated by - Mutation followed by loss of remaining WT allele through deletion, known as LOH - Mutation followed by loss of remaining WT allele by epigenetic silencing DNA is methylated at CG sequences known as CpG island. Sometimes these regions are methylated in tumour suppressor promoters and is known to switch off OR silence gene expression. Activation of oncogenes is not enough to cause cancer,it is in turn control by TSG and other cell cycle regulatory proteins. Viral protein also target and inactivate TSG. All DNA tumour viruses have viral trans-acting genes that target the pRB and p53 tumour suppressors How virus interact with genetics factors contributing to cancer. !!!!!!!!!!!!Instability of genome EITHER chromosomal instability or microsatellite instability that occur during tumorigenesis microsatellite instability, ie, alterations in the length of short repetitive sequences (microsatellites) e.g. colon cancers A change in chromosome number, or aneuploidy, is a defining characteristic of many types of cancer. The other common chromosomal abnormalities identified in cancers include translocations, deletions, and amplifications. The loss or gain of whole chromosomes results from defective mitosis, involving chromosomal nondisjunction in which sister chromatids are not properly segregated to the daughter cells. CML 95% pt bcr-abl reciprocal translocation long arm of chromosome 9,22 Gleevec (imitinib mesylate) tyrosine kinase inhibitor,successful development of rationally designed drug !

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Viral mechanisms src avian sarcomacarry oncogene in genome

Insert strong viral promoter ALV virus avian modelnext to proto-oncogene insert next to myc

Make viral proteins that SV40 MesotheliomasInactivate tumour suppressors TAg

More copies of the gene!

(leads to constitutive activity of signal transduction system!)

1. Activation of oncogenes by gene amplification

Oncogenes can be activated by gene amplification thatarises from genome instability.These extra copies of genes are present on small paired minute chromosomes (double minute chromosomes)Extra copies = great increase in [gene product]

FISH study showing: mycn gene amplified on double minute chromosomes in neuroblastoma

For illustration only

Molecular Oncology Volume 4, Issue 3 2010 255 -266

2. Activation of oncogenes by point mutation

Growth factor signaling triggers GTP to bind to RAS protein.GTP-RAS complex is an active tyrosine kinase that activates downstream molecules by a signaling cascade. Hydrolysis of GTP leaves a GDP-RAS complex that is inactive as a tyrosine kinase.Mutations are common at aa12, 16 or 61 in RAS protein in many cancers (colon, lung breast and bladder) and all decrease the intrinsic GTPases activity of RAS protein, so that the RAS protein remains in an active complex with GTP for longer.

For illustration only

3. Activation of oncogenes by formation of a chimeric proteinvia chromosomal translocation

The Philadelphia Chromosome, Ph1, represents a balanced translocation between chrm 9 & 21 to generate a fusion gene that encodes a fusion protein BCL-ABL1 that is a tyrosine kinase with abnormal transforming properties found in Chronic Myeloid Leukemia.

For illustration only

Just for reference only

18/12/2012

4

Viral mechanisms src avian sarcomacarry oncogene in genome

Insert strong viral promoter ALV virus avian modelnext to proto-oncogene insert next to myc

Make viral proteins that SV40 MesotheliomasInactivate tumour suppressors TAg

More copies of the gene!

(leads to constitutive activity of signal transduction system!)

1. Activation of oncogenes by gene amplification

Oncogenes can be activated by gene amplification thatarises from genome instability.These extra copies of genes are present on small paired minute chromosomes (double minute chromosomes)Extra copies = great increase in [gene product]

FISH study showing: mycn gene amplified on double minute chromosomes in neuroblastoma

For illustration only

Molecular Oncology Volume 4, Issue 3 2010 255 -266

2. Activation of oncogenes by point mutation

Growth factor signaling triggers GTP to bind to RAS protein.GTP-RAS complex is an active tyrosine kinase that activates downstream molecules by a signaling cascade. Hydrolysis of GTP leaves a GDP-RAS complex that is inactive as a tyrosine kinase.Mutations are common at aa12, 16 or 61 in RAS protein in many cancers (colon, lung breast and bladder) and all decrease the intrinsic GTPases activity of RAS protein, so that the RAS protein remains in an active complex with GTP for longer.

For illustration only

3. Activation of oncogenes by formation of a chimeric proteinvia chromosomal translocation

The Philadelphia Chromosome, Ph1, represents a balanced translocation between chrm 9 & 21 to generate a fusion gene that encodes a fusion protein BCL-ABL1 that is a tyrosine kinase with abnormal transforming properties found in Chronic Myeloid Leukemia.

For illustration only

Just for reference only