Institute of Radiation Biology

Oncogenes and tumour suppressor genes DoReMi Course 2014

4th Ch. BC

16th

Ch

18th Ch

19th Ch.

20th Ch.

Hippocrates: Cause is systemic excess of black humor.

John Hunter suggest cancer is not a systemic disease.

Vogelstein, Weinberg and many others associate genetic alterations with phenotypic changes of cancer

Müller & Virchow Propose a cellular basis of cancer.

Paracelsus challenges the humor theory. Suggests external influences.

Rous discovers chicken sarcoma virus. First evidence against Hippocratic concept. Later Rous & Freidwald proposed 2-stage model.

Boverie Proposes normal cells become tumour cells

16th Ch. 19th Ch. 1910 1930 1950 1970 1990

Georg Bauer (Agricola) described Bergsucht: An occupational disease of miners. Paracelsus suggests cause is inhalation of metal vapours

Argonne studies suggest genetic variation changes chronic radiation response

Martland identifies osteosarcoma in radium workers as an occupational disease

Hiroshima & Nagasaki victims develop an excess of cancers

Röntgen discovers X-rays. Becquerel discovers natural radiation

Curie lab discovers Radium. Begin to develop leukemia

Pirchan & Sikl identify Radon as the cause of Bergsucht

Manhatten project initiate radiation effects studies

Accidental

release

Risk extends into the low dose range

Intentional

release

Radiotherapy

Diagnostics

& Imaging

Workplace

Air travel

Cosmic

sources Natural

radiation

Dose

Effec

t

Space

flight

negative

effect

positive

effect

I I 2mGy 0,1Gy 2Gy

I

• 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.

Radiation protection conflict:

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

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

Mechanisms: Cancer is genetically programmed

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

Cancer is a multistage disease driven by an accumulation of genetic changes

Proteolysis Loss of cell-cell and cell-matrix adhesion

Attachment or capture in blood /lymph vessel

Exit into peripheral tissue

Angiogenesis

From: Hanahan D., Weinberg RA. (2011) Cell 144:646-74

Hanahan/ Weinberg model places pathway events before individual gene functions

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

Cell proliferation Cell death/loss

Cancer is a disturbance of cell kinetics

Balanced

Reduced loss

Increased production

Combination

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

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

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

An example of a classical Tumour Suppressor Gene

Retinoblastoma (RB1)

RB1 tumor suppressor gene regulates cell cycle entry. 1:23 000 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 radiation- induced osteosarcoma

RB-1

P

E2F-1 RB-1 E2F-1

P

CDK 4,6

CycD1

p16

G0

G1 G2

M

S

Biological mechanisms of Rb1 action

0

0.2

0.4

0.6

0.8

1.0

Cu

m. S

urv

ival

0 100 200 300 400 500 600 700 800 900

P=0.0007

The Retinoblastoma gene (Rb1) is associated with an increased sensitivity to radiation-induced cancer.

Osteosarcoma induction in Th227-injected mice

Rb1 BALB/c BALB/c

Rb1 BALB/c CBA

Oncogenes

• Gain of function

• Dominant action

• Excess positive signalling

• Point mutation, amplification, translocation

• 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

Suppressor genes

Oncogenes are activated,

suppressors are inactivated

Oncogenes and TSGs can interact

non-linear Model

Gene mutations during cancer

“Vogelstein” Model

1 2 3 4 5 6

1

2

3

4

5 6

Cell adhesion (E-cadherin)

DNA damage repair (ATM, XP)

DNA mismatch repair (MSH1)

Apoptosis (Bcl2)

Developmental pathways (PAX, Patched)

Tumor susceptibility genes

Non-classical cancer genes are neither

oncogenes or suppressor genes)

Do cancer genes only regulate cell cycle ?

Viral carcinogenesis via TSG inactivation

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?

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, 5575–5580

p53 suppressor gene in man

Radon-associated lung tumors

Codon 249 mutation in 16/52 (31%) lung tumors

(Taylor et al Lancet 343:86 1994)

12/69 (23%) lung tumors with mutation (no codon 249 mutation)

(Vahakangas et al Lancet 339:576 1992, Hollstein et al Carcinogenesis 18:511 1997)

Mutation rate of p53 in lung cancer of 26% in non-smokers

(Takagi et al Br J Cancer 77:1568 1998)

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

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!). 1000 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 !

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 ????