Question

Explain how mutations affecting both growth-promoting and growth-inhibiting processes can result in cancerous cell proliferation. Give specific examples.

Answer 1

In growth promoting processes: Mutation results in activation of oncogenes which promote cell proliferation of the cell resulting in its transformation into cancer cell. Example of oncogene is Bcr-Abl which is found on the Philadelphia chromosome. It is activated by translocation of pieces of genetic material from chromosomes 9 and 22. Bcr-Abl codes for a tyrosine kinase, which is constitutively active, leading to uncontrolled cell proliferation.

In growth inhibiting processes: Mutation results in inactivation of tumor suppressor genes which control the cell growth and hence prevent excessive cell proliferation. Example of tumor suppressor gene is p53 which activates transcription of p21 (a CDK inhibitor) resulting in inhibition of cell cycle. When p53 is mutated it loses its function and cell cycle becomes unregulated resulting in tumor formation.