Oncogene and Cancer

Chen-Kung Chou

6-16-2009

The Biology of Cancer (© Garland Science 2007)

正常老鼠細胞癌化需要二個致癌基因的合作Nature 312:649-51 (1984)

What happen in the normal fibroblast when an oncogenic ras is ov

erexpressed?

Oncogenic ras induces growth arrest in mouse or human fibroblasts

Oncogenic Ras induces cell cycle inhibitors and

marker of senescence in normal fibroblasts

One question needs to be answered!

Ras cooperates with E1A to immortalize MEF and Ras induces senescence is p53 and p16 dependent

Cellular senescence

Human diploid fibroblast has limited replicative life span, termed replicative senescence or cellular senescence. Human diploid fibroblasts can divide ~60-80 times.

Young vs. senescent fibroblasts

Telomere: structure and function

CentromereAGGGTTAGGGTTAGGG-3’ TCCC-5’

Telomere

Telomere

1. Maintaining the integrity of chromosomes.

2. Prevent end-to-end fusion of chromosome ends.

3. Facilitate complete replication of chromosomes.

End-to-end fusion

(In Greek, Telos means end; meros, part)

Telomere, cancer, and cellular senescence

Cell divisions

Cell divisions

Cell cycle arrest (M1)

Catastrophe (M2)

Telomerase activation

Telomerase is expressed in immortal and cancer cells

Oncogenic ras provokes premature cell senescence associated with accumulation of p53

and p16INK4a.

Cell 88: 593–602 (1997)

Senescence: a natural defense mechanism against cancer formation!

New England J. of Med. P1037-46 September 7, 2006

RASV12-induced premature senescence can be used to identify novel factors that interfere with tumor

suppressor pathways

New oncogenic pathway!

Functional screen with retroviral cDNA expression libraries,

two interesting genes are identified:

1, Peeper, D. S. et al. A functional screen identifies hDRIL1 as an oncogene that rescues RAS-induced senescence. Nature Cell Biol. 4, 148–153 (2002).2, Rowland B. D.,Bernards R & Daniel S. Peeper D. S. The KLF4 tumour suppressor is a transcriptional repressor of p53 that acts as a context-dependent oncogene. Nature Cell Biology 7, 1074 - 1082 (2005)

The Biology of Cancer (© Garland Science 2007)

正常老鼠細胞癌化需要二個致癌基因的合作Nature 312:649-51 (1984)

Different combination of myc family members promotes or suppresses cell proliferation through transcriptional control of specific gene expression

What might happen in the normal fibroblasts when myc along is overexpressed?

Can overexpression of myc prevent low serum induced growth arrest of normal fibr

oblasts?

Constitutively express of myc does not prevent low serum induced growth arrest of normal rat-1 fibroblasts

But overexpression of myc indeed increase DNA replication (% of cell in S phase of cell cycle) of rat-1 fibroblasts in low s

erum!

Why?

Viewing cells cultured in 0.1% FCS medium under time-lapse cinemicroscope at one frame per every 30 seconds

Induction of apoptosis infibroblasts by c-myc protein.

Cell 69, 119–125 (1992).

What cytokines in serum prevent apoptosis?

How myc induce apoptosis?

C-myc strongly induced expression of ARF, p53, and p53 targets in normal MEFs.

Figure 9.14 The Biology of Cancer (© Garland Science 2007)

ARF is the alternative spliced product of p16INK4A gene (coded for CDK inhibitor). However, the function of ARF has nothing to do with CDK !

Figure 9.15a The Biology of Cancer (© Garland Science 2007)

ARF is induced by E2F, bound to Mdm2 and prevent p53 from Mdm2 mediated degradation!

Signaling pathway of wild type and Burkitt’s lymphoma derived MYC mutants (T58A and P57S)

Induction of apoptosis infibroblasts by c-myc protein.

Cell 69, 119–125 (1992).

Is this observation relevant to tumor formation in vivo?

Of course, yes!

Oncogene addiction hypothesis

For each human cancer cell, there is a specific set of genes which are essential to

maintain viability of that cancer cell!

One Step Remedy!

Clin Cancer Res. 2005 May 15;11(10):3750-7.

  Mutation in the tyrosine kinase domain of epidermal growth factor receptor is a predictive and prognostic factor for gefitinib treatment in patients with non-small cell lung cancer.Chou TY, Chiu CH, Li LH, Hsiao CY, Tzen CY, Chang KT, Chen YM, Perng RP, Tsai SF, Tsai CM.Department of Pathology and Chest Department, Taipei Veterans General Hospital, School of Medicine and Institute of Genetics and Genome Research Center, National Yang-Ming University, Taiwan.

Feb. 24 2005

Multi-steps genetic alteration are required for a successful cancer cell formation –promote cell proliferation + inhibit cell death genes and/or

increase anti-apoptosis gene etc.

Weinberg R. et al Nature 400: 464-8; 1999

Cancer Stem Cells

What it is and is it real?

Huntly and Gilliland (2005) NRC 5: 311-321

A subset of cancer cells seem capable of self-renewing and producing tumors either in vitro or in vivo.

1994 - first real identification of a true “cancer stem cell” (AML), which can repeatedly confer disease in recipient mice.

How do stem cells relate to cancer?

Traditional cancer therapies (top) kill rapidly dividing tumor cells (blue) but may spare stem cells (yellow) that can give rise to a new tumor. In theory, killing cancer stem cells (bottom) should halt a tumor's growth lead to its disappearance.

Concept of cancer stem cells

Figure 11.15 The Biology of Cancer (© Garland Science 2007)

Where would a cancer stem cell come from? Transformation of normal SC or “dedifferentiation” of a committed progenitor

In either case, multiple additional mutations are almost certainly needed to create full-blown cancer stem cell…

Can we correct the misbehavior of cancer stem cells?

Pardal, Clarke, Morrison NRC 2003

Mouse teratocarcinoma cell is a totipotent cells

Is cancer stem cell real?

Cancer stem cell was defined by its behavior in mice!

What problem of human cell should be overcome in order to grow in mice?

Limitation of xenotransplant model

• Residual elements of the recipient immune system

• The absence of cross species reactivity of some cytokines

• Other components of the murine microenvironment (CD133 positive helper)

Efficient tumour formation by single human melanoma cells

Nature 456: 593-599; 2008

How to intervene apoptotic pathway by small molecules?

To enhance apoptosis in cancer cells!

Truncated Bid (tBid) evokes a rapid and complete release of cytochrome C and Smac from mitochondrio

n and initiates apoptosis.

Could we block this pathway by small chemicals which interact with tBid and prevent

apoptosis occur?

Targeting Apoptosis via Chemical Design: Inhibition of Bid-Induced Cell Death by Small Organic Molecules

Chemistry & Biology, 11, 1107–1117, 2004

A small molecule Smac mimic potentiates TRAIL and TNF a-mediated cell death.

Science 305, 1471–1474 (2004)

C2-symmetric compound 3 is a potent Smac mimetic in vitro

Why some cells are so sensitive to Smac mimic alone?

Autocrine TNFα signaling renders human cancer cells susceptible to Smac

mimetic-induced apoptosis.

Cancer Cell 12, 445–456 (2007)