Besmer lecture2009

8/8/2019 Besmer lecture2009

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DISEASE GENES

Peter Besmer

Developmental Biology ProgramSloan Kettering Institute

New York


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BEHAVIOR OF CANCER CELLS

Do not obey signals that regulate cell proliferation

Circumvent programmed limitations to proliferation,escaping replicative senescence and avoidingdifferentiation

Tend to avoid suicide by apoptosis

They are genetically unstable

Escape from home tissues, they are invasive

Survive and proliferate in foreign sites (metastasis)


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Normal cellular processes are controlled by signaling networks


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Why are these cellular processes not working properly ?


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Mutations carcinogen induced

radiation spontaneous


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Tumor progression involves successive rounds ofmutation and natural selection


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Somatic mutations - germline mutations


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-Gain of function mutations - oncogenesoveractivity mutation

-Loss of function mutations

- tumor suppressor genesunderactivity mutation


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Proto-oncogene can be converted into an oncogene indifferent ways:

1. Point mutation or deletion in coding sequence produces hyperactiveprotein in normal amounts

2. Gene amplification - normal protein is overproduced

3. Chromosome rearrangement - nearby regulatory sequence causesoverproduction of normal protein

4. Chromosome rearrangement produces fusion protein that isoverexpressed or produces a fusion-protein that is hyperactive


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Schematic of regulation ofRas activation

Crystal structureof Ras

decrease

increase


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Amplification of Myc:Double Minutes - Homogenously Staining Region


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Conversion of Abl proto-oncogene into anOncogene by Translocation


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Conversion of Abl proto-oncogene into anOncogene by Translocation


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Tumor suppressor genes can be inactivated in different ways:(both alleles need to be inactivated)

1. The first allele may be inactivated by a point mutation or smalldeletion

2. Epigenetic changes can inactivate a gene through DNA methylation

in the promoter region, or the gene packed into heterochromatin

3. The second allele may be inactivated similarly but more often thechromosome is lost or the gene is replaced by mutant gene by mitotic

recombination or gene conversion


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Tumor suppressor genes can be inactivated indifferent ways (both alleles need to be inactivated)


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Figure 9.8 The Biology of Cancer( Garland Science 2007)


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Table 9.2 The Biology of Cancer( Garland Science 2007)


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p53 tumor suppressor gene

cell cycle control apoptosis

genetic stability (DNA damage)


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Mutations that inactivate p53in human tumors


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DNA tumor viruses sequester p53

and activate cell proliferation


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Pathway That Controls Cell CycleProgression via Rb Protein


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Identification of oncogenes and tumor suppressor genes

1. Capture of oncogenes by retroviruses

2. DNA transfection


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CAPTURE OF ONCOGENES BY RETROVIRUSES


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Identification of oncogenesby DNA transfection


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Dominant familial cancer syndromes are very rare


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Kit

Structural Characteristics of Receptor TyrosineKinase Subclasses

adapted from T. Hunter


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The Kit RTK and KitL are encoded at the murineWhite Spotting (W) and Steel (Sl) loci

Chabot et al., 1988; Geissler et al., 1988; Tan et al., 1990Huang et al, 1990; Copeland et al., 1990; Zsebo et al.1990


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Schematic histologic representation of intestinal tract

longitudinal musclelayer

circular musclelayer

myenteric plexus


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Gastro-intestinal stromal tumors, (GIST) Mastocytosis

Acute Myelogenous Leukemia Germ Cell Tumors

contain activating Kit mutations

Nagata et al., 1995 PNAS 92, 10560-10564

Hirota et al. 1998 Science 279, 577-580

Kit in Human Malignancies


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Schematic Representation of Gain of Function

Mutations in Kit Protein

exon 9 GISTexon 10 hMC

JM (exon 11) GIST& cMC, hMC

exon 13 GIST

exon 17 hMC, seminoma, GIST

Extra cellularDomain

KinaseDomain

TMS


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The Juxta-Membrane Domain is an Autoinhibitory

Domain of the Kit Kinase

Mol et al. JBC 2004


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Human Familial GIST-Syndromecontaining Germline Mutation in Kit gene

Nishida et al., Nature Gen. 1998


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homologous recombination

cre recombinase

Kit Locus:

= loxP Site

12 13 14

Targeted Kit Locus:

Kit loxP-neo locus:

10 1198

NEO

12 13 1410 119

NEO

12 1310 119 DT-A

12 13 1410 119

Targeting construct:

Targeted Mutation in Kit gene: V558


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Gross Pathological Findings in GastrointestinalTract of KitV558/ + Mice


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GIST in KitV558/+ mice and human familial GISTare histologically indistinguishable

Sommer et al., PNAS100, 6706-11 (2003)


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We have produced a mouse model for the study of constitutiveactivation of Kit in oncogenesis by a knock-in strategy introducingthe exon 11 KitV558 activation mutation into mouse Kit gene.

Histological findings indicate patchy hyperplasia of Kit positive cellswithin the myenteric plexus of the entire gastrointestinal tract (loweresophagus, stomach, proximal duodenum, cecum and large intestine).

Neoplastic lesions indistinguishable from human GIST were observedin the cecum and sometimes in the large intestine.

Constitutive Kit signaling is critical and sufficient for induction

of GIST and ICC hyperplasia

SUMMARY


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Targeted drug therapy


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TYROSINE KINASE INHIBITOR IMATINIB - GLEEVEC

specific inhibitor of ABL, KIT and PDGFR

is used to treat CML (BCR-ABL) and GIST (KIT)

inhibits inactive form of the kinases


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P-Y

PtdInsP2PtdInsP3

PI-3K

AKT PDK1

PTENmTOR

TSC1

TSC2

S6K4E-BP PP2A

eIF4E S6

translation

Imatinib


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Untreated 6h Imatinib

mTOR250

Akt50

150100

P-719 Kit

P-mTOR250

pAkt50

GAPDH37

Kit150100

37

25P-S6 Protein

Comparison of treated & untreated tumors Imatinib


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In patients with GIST imatinib therapy achieves a partial responseor stable disease in 80% of patients. However some patients developresistance to imatinib therapy.

What is the mechanism of resistance to imatinib?


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In part imatinib resistance in GIST patients may ariseas a result of acquisition of secondary KITmutations

Antonescu et al. 2005

Debiec-Rychter et al. 2005

Documents

Besmer lecture2009