The Myc gene is a very important proto-oncogene that encodes the Myc transcription factor. The Myc gene is normally only expressed in response to the presence of growth factors, and once expressed the Myc protein promotes passage through the restriction point by activating the transcription of early cell cycle genes. As an indication of the importance of Myc, overexpression of the Myc protein is sufficient to cause tumorigenesis in many cell types. For example, Burkittâs lymphoma is the result of a chromosomal translocation that leads to increased myc expression in B-lymphocytes.
(A) (3 pts) What is the restriction point, and which CDK complex is most directly activated by passage through the restriction point?
(B) (10 pts) Describe how activation of the CDK complex from part (A) leads to entry of cells into S-phase. Your answer must indicate the protein(s) that this CDK directly acts on, the proteins that directly stimulate S-phase entry, and the mechanism that prevents premature entry into S-phase.
(C) (8 pts) Indicate whether each protein you mention in part (B) is a proto-oncoprotein (e.g. a protein encoded by a proto-oncogene) or a tumor suppressor. You can incorporate this into your answer to part (B) if you choose.
(D) (4 pts) Why does the overexpression of Myc lead to cancer, for example Burkittâs lymphoma?
The Myc gene is a very important proto-oncogene that encodes the Myc transcription factor. The Myc gene is normally only expressed in response to the presence of growth factors, and once expressed the Myc protein promotes passage through the restriction point by activating the transcription of early cell cycle genes. As an indication of the importance of Myc, overexpression of the Myc protein is sufficient to cause tumorigenesis in many cell types. For example, Burkittâs lymphoma is the result of a chromosomal translocation that leads to increased myc expression in B-lymphocytes.
(A) (3 pts) What is the restriction point, and which CDK complex is most directly activated by passage through the restriction point?
(B) (10 pts) Describe how activation of the CDK complex from part (A) leads to entry of cells into S-phase. Your answer must indicate the protein(s) that this CDK directly acts on, the proteins that directly stimulate S-phase entry, and the mechanism that prevents premature entry into S-phase.
(C) (8 pts) Indicate whether each protein you mention in part (B) is a proto-oncoprotein (e.g. a protein encoded by a proto-oncogene) or a tumor suppressor. You can incorporate this into your answer to part (B) if you choose.
(D) (4 pts) Why does the overexpression of Myc lead to cancer, for example Burkittâs lymphoma?
