1. The Biology of Cancer Second Edition CHAPTER 4 Cellular Oncogenes
Robert A. Weinberg
The Biology of Cancer
Second Edition
CHAPTER 4
Cellular Oncogenes
Copyright © Garland Science 2014

2. Oncogenes
Oncogenes : Originally identified as the transforming genes of viruses
: The dorminantly acting transforming genes
: Altered forms of normal cellular genes called proto-oncogenes
Tumor suppressor genes : function normally to constrain cell growth
Proto-oncogenes and their products
Highly conserved in evolution
Important regulators of normal cell growth and differentiation.
Maintain the ordered progression of the cell cycle, cell division, and differentiation
In the cancer cell, the ordered progression is partially lost
Mutation that alter the structure, levels, or sites of expression of the gene products activates oncogenic potential
Extracellular cytokines, Growth factors, Transmembrane growth factor receptors, Cytoplasmic proteins that act to transmit the signal to the nucleus, Nuclear proteins that include transcription factors and proteins involved in the control of DNA replication

3. Can cancers can be triggered by the activation of endogenous retrovirus ?
No tumor virus in the majority of human cancer in the mid 1970.
Endogenous provirus can become infectious retrovirus, thus inducing tumors ?
No, because no reports if infectious retroviral particles in human tumors were not be verified
Thus, research suspected that most of human cancer could be induced by mutagens which mutate normal growth-controlling genes such as cellular oncogenes
Figure 4.1 The Biology of Cancer (© Garland Science 2007)

4. DNA transfection assay is a new stragegy for detecting nonviral oncogens
To verify this model, they asked question whether transformed cells carried mutated genes functions as oncogenes
New experimental methods were developed to prove this model.
DNA from chemically transformed cells was introduced into normal cells by transfection and determine whether these recipient cells become transformed
NIH3T3 cells: mouse fibroblasts in origin, contact-inhibited, nontumorigenic cell lines.
Transformation of NIH3T3 cells by gene transfer changes in cell morphology in culture, loss of contact inhibition, focal areas of dense layers termed foci.
Figure 4.2 The Biology of Cancer (© Garland Science 2007)

5. Transforming genes of a human bladder and lung carcinoma :
Genomic DNA from human tumors or tumor cell lines is transferred to NIH3T3 cells foci formation of morphologically altered cells that have tumorigenic properties.
Molecular cloning of human transforming genes using human repetitive DNA sequences (alu).
Transforming genes of a human bladder and lung carcinoma :
homologous to c-H-ras and c-K-ras.
N-ras from human neuroblastoma tumor cell line and human promyelocytic leukemia cell line.
neu, met, trk, mas, erbB-2/HER-2, ret, hat, KS3 oncogenes
Figure 4.2 The Biology of Cancer (© Garland Science 2007)

6. Virus-associated Oncogenes were mutated in many human tumors
Figure 4.4 The Biology of Cancer (© Garland Science 2007)

8. Activation of oncogenes
Via retroviral transduction (Acute transforming retrovirus)
During viral replication, viral sequences are lost and replaced with a cellular proto-oncogene.
Rapid numerous mutational events that occur during viral replication, and a high level of expression driven by retroviral transcriptional enhancers.
Transforming potential of the transduced proto-oncogene
By proviral insertion (The slowly transforming retrovirus)
Retrovirus integration into or adjacent to host cellular proto-oncogenes enhance proto-oncogene expression.
low probability long latency period
First, Avian leukosis virus-induced bursal lymphomas
- Provirus insertion upstream from the c-myc proto-oncogene locus
50- to 100- fold transcription of the c-myc gene
- Also provirus insertion downstream of c-myc or upstream in the opposite orientation oncogene activation.

9. Proto-oncogenes to Oncogenes conversion mechanisms
1) Recombination between retroviral DNA and a proto-oncogene
2) Deletion or point mutation in coding sequence
3) Chromosome rearrangement
4) Gene amplification

10. Gene amplification Proto-oncogene amplilfication
Cellular proto-oncogenes in multiple copies in various tumors and transformed cell lines
Increased expression of amplified proto-oncogenes : a role in the development and progression of these tumors
Amplification of erbB2/neu in breast cancers

11. Figure 4.7 The Biology of Cancer (© Garland Science 2007)

12. Myc amplification
In situ hybridization of myc genes with fluorescent probe
Microscopic chromosomal changes
1) Homogeneously staining chromosomal regions
2) Double-minute chromosomes
N-Myc amplification in neuroblastoma by increasing copy number
Myc transcriptional up regulation by integrated strong viral promoter
Myc transcriptional up regulation by strong promoter with translocation
Figure 4.11a The Biology of Cancer (© Garland Science 2007)

13. Table 4.4 The Biology of Cancer (© Garland Science 2007)

14. Chromosomal translocation in Burkitt’s lymphoma Malarial parasites and EBV virus are an etiologiocal factor ?
Figure The Biology of Cancer (© Garland Science 2007)

15. Table 4.3 The Biology of Cancer (© Garland Science 2007)

16. Mutations in coding sequence affect structural change to activate the oncoprotein
Figure 4.8 The Biology of Cancer (© Garland Science 2007)

17. Discovery of a point mutation in oncogenes.
Point mutation by Chemical carcinogenes
Genes activated in chemically induced tumor were identified by DNA transfection assay;
In human tumors, the activated ras genes by single point mutations show a mutation in codon 12, 13, 59, and 61
Biochemical mechanisms by which proto-oncogenes act
1) Phosphorylation of proteins on serine,
threonine, or tyrosine residues
Two basic purpose of phosphorylation in signal transduction
Conformational change and activation of the
kinase activity
Docking sites to target proteins
2) GTPase (ras gene family)
3) Proteins that localized in the nucleus
Figure The Biology of Cancer (© Garland Science 2007)

19. Deregulated firing of growth factor receptors
Figure The Biology of Cancer (© Garland Science 2007)

20. Translocation Chromosomal rearrangement at Chromosomal breakpoints
In situ hybridization of cellular proto-oncogenes : at or near chromosomal translocation break points
Cytogenetic analysis of leukemias and myelodysplasias : tumor-specific chromosome translocation
95% of Chronic myelogenous leukemia (CML) :the Philadelphia (Ph) chromosome translocation between chromosome 9 and 22, t(9;22) (q34;q11)
- chimeric gene expressing fusion protein, bcr-abl ; increased kinase activity-tranform cells
c-Myc and immunoglobulin genes on the chromosome translocation 2:14, 8:14, 22:14 in lymphomas; constitute expression of c-Myc gene
Figure 4.15a The Biology of Cancer (© Garland Science 2007)

24. Summary
The mutations in oncogenes were also found in many human tumors (DNA hybridization method).
Gene amplification of oncogenes. Ex) erbB2/neu/HER2 genes in breast cancer
Viral promoter enhance the transcriptional rate of cellular oncogene nearby insertional genomic sites. Ex) Myc: Provirus
integration, gene amplification, chromosomal translocation
Single mutation of proto-oncogene become converted into active oncogenes. Ex) H-ras, EFG receptor