Institute of Radiation Biology. Oncogenes and tumour suppressor genes DoReMi Course 2014

Transcription

1 Institute of Radiation Biology Oncogenes and tumour suppressor genes DoReMi Course 2014

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3 Hippocrates: Cause is systemic excess of black humor. Paracelsus challenges the humor theory. Suggests external influences. Müller & Virchow Propose a cellular basis of cancer. Boverie Proposes normal cells become tumour cells 4 th Ch. BC 16 th Ch 18 th Ch 19 th Ch. 20 th Ch. John Hunter suggest cancer is not a systemic disease. Rous discovers chicken sarcoma virus. First evidence against Hippocratic concept. Later Rous & Freidwald proposed 2-stage model. Vogelstein, Weinberg and many others associate genetic alterations with phenotypic changes of cancer

4 Georg Bauer (Agricola) described Bergsucht: An occupational disease of miners. Paracelsus suggests cause is inhalation of metal vapours Curie lab discovers Radium. Begin to develop leukemia Pirchan & Sikl identify Radon as the cause of Bergsucht Argonne studies suggest genetic variation changes chronic radiation response 16 th Ch. 19 th Ch Röntgen discovers X- rays. Becquerel discovers natural radiation Martland identifies osteosarcoma in radium workers as an occupational disease Manhatten project initiate radiation effects studies Hiroshima & Nagasaki victims develop an excess of cancers

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6 Effect Risk extends into the low dose range Intentional release Accidental release Space flight Radiotherapy Air travel Workplace Natural radiation Cosmic sources Diagnostics & Imaging Dose

7 negative effect I 2mGy 0,1Gy 2Gy I I positive effect

8 Radiation protection conflict: If dose limits too high restrict development of nuclear technologies and medical applications. If dose limits too low failure to protect the population, but maybe not all individuals have the same risk.

9 Baby is sent through X-ray machine at LAX A woman places her month-old grandson in a bin for carry-on items. Doctors later determine he did not get a dangerous dose of radiation. By Jennifer Oldham, Times Staff Writer December 20, 2006

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11 Two stage clonal expansion model (W. Heidenreich, H. Paretzke and others)

12 Mechanisms: Cancer is genetically programmed

13 Mendelian (familial) cancer syndromes (e.g. retinoblastoma) Malignant phenotype is transmitted during cell division Retroviral genomes can be oncogenic (Rous, Waterford etc) Naked tumour DNA can transform cells Genetic alterations accompany tumour progression DNA damage is evident in irradiated cells Genetic alterations accompany tumour progression Germ-line manipulation of oncogenes or tumour supressor genes is tumorigenic

14 Cancer is a multistage disease driven by an accumulation of genetic changes Attachment or capture in blood /lymph vessel Exit into peripheral tissue Proteolysis Loss of cell-cell and cell-matrix adhesion Angiogenesis

15 Hanahan/ Weinberg model places pathway events before individual gene functions From: Hanahan D., Weinberg RA. (2011) Cell 144:646-74

16 The original mutation A clear DNA damage signature in that mutation (radiation fingerprint) A mechanistic link between this mutation and the cancer Other mutations that accumulate may be random, driven by the first mutation, caused by additional carcinogenic factors (including radiation

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18 Cancer is a disturbance of cell kinetics Cell proliferation Balanced Cell death/loss Reduced loss Increased production Combination

19 Oncogenes Gain of function mutations leading to up-regulated proliferation. Tumour suppressor genes Loss of function mutation causing loss of control over proliferation But not all gene functions fit in these boxes

20 Oncogenes: Dominant action, only one mutation (hit) needed Gain of function (upregulation) Stimulate cell division by excess positive signal Mutation is amplification, point mutation or translocation e.g. c-myc, Ret, ras, sis

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23 Tumour Suppressor genes: Recessive action, two mutations needed (NB genetic inheritance appears as a dominant trait) Loss of function Repress cell division Non-classical suppressor inactivation Imprinting & LOH (p73 paternal allele 1p) p53 binding by MDM2, TAg, papilloma E6 & Adenovirus E1B RB1 binding by TAg, papillopma E7

24 An example of a classical Tumour Suppressor Gene

25 Retinoblastoma (RB1) RB1 tumor suppressor gene regulates cell cycle entry. 1: frequency. Loss of function leads to sporadic retinoblastoma and osteosarcoma. In radiation field the risk of osteosarcoma rises many-fold. Mouse model does not develop retinoblastoma. Sensitivity to radiationinduced osteosarcoma

26 Biological mechanisms of Rb1 action M G 0 RB-1 P G 2 G 1 E2F-1 RB-1 E2F-1 S p16 CycD1 P CDK 4,6

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29 Cum. Survival The Retinoblastoma gene (Rb1) is associated with an increased sensitivity to radiation-induced cancer Osteosarcoma induction in Th 227 -injected mice P= Rb1 BALB/c BALB/c Rb1 BALB/c CBA

30 Oncogenes Gain of function Dominant action Excess positive signalling Point mutation, amplification, translocation

31 Suppressor genes Recessive inheritance, dominant, LOH Imprinting & LOH (p73 paternal allele 1p) p53 binding by MDM2, TAg, papilloma E6 & Adenovirus E1B RB1 binding by TAg, papillopma E7

32 Oncogenes are activated, suppressors are inactivated

33 Oncogenes and TSGs can interact

34 Gene mutations during cancer Vogelstein Model non-linear Model

35 Do cancer genes only regulate cell cycle? Non-classical cancer genes are neither oncogenes or suppressor genes) Cell adhesion (E-cadherin) DNA damage repair (ATM, XP) DNA mismatch repair (MSH1) Apoptosis (Bcl2) Developmental pathways (PAX, Patched) Tumor susceptibility genes

36 Viral carcinogenesis via TSG inactivation

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39 As with all cancers, radiation cancers involve gene mutations. If DNA damage causes a gene mutation leading to clonal expansion where are the smoking guns?

40 In vivo evidence of this is shown by: Translocations in leukemia (misrepair of radiation-induced breaks?) Loss of the wild type allele in radiation-induced cancer models where the first hit is given by a germ line mutation Ptch1 +/- mutant cells show loss of wild type allele during preneoplastic growth Pazzaglia S. et al Oncogene (2006) 25,

41 p53 suppressor gene in man Radon-associated lung tumors Codon 249 mutation in 16/52 (31%) lung tumors (Taylor et al Lancet 343: ) 12/69 (23%) lung tumors with mutation (no codon 249 mutation) (Vahakangas et al Lancet 339: , Hollstein et al Carcinogenesis 18: ) Mutation rate of p53 in lung cancer of 26% in non-smokers (Takagi et al Br J Cancer 77: )

42 But: Changes in genome for the second hit are not really identifiable as direct radiation effects.

43 A genomic mechanism does seem probable for radiation-induced cancer Gene mutations are present in key genes. Clonal evolution is accompanied by transmission of a basic set of mutations, plus new acquired mutations. But the number of radiation hits not enough to account for the probability of specific genes being hit ( 1base in 3 billion!) SSB and 100 DSB per Gy. Genomic instability / bystander has been suggested as a driving force in radiation-induced cancer. Not clear if this is a cause or a consequence!

44 Non-genomic effects A host of stoichimetric events accompany irradiation. The tissue response includes cell death, cell dedifferentiation and proliferation to replace lost cells, release of mediators of proliferation, infiltration etc. Some of these may produce the so-called bystander effect, where an irradiated cell can influence non-irradiated neighbours. Non-genomic effects (epigenetic) on gene expression (methylation, acetylation, mirna)??? Non-cancer effects????