Question

Platelet-derived growth factor (PDGF) is a mitogen that activates tyrosine kinase receptors and this leads to the proliferation of cells. Signaling downstream from the PDGF receptor does what to stimulate proliferation?

a-phosphorylates the Rb protein which then turns on the transcription of cyclins
b-degrades p53 to alleviate cell cycle arrest
c-phosphorylates the Rb protein to relieve inhibition of cell proliferation genes
d-causes the activation of intracellular mitogens
e-activate apoptosis

Answer 1

Signaling from the PDGF receptor phosphorylates the Rb protein, which in turn releases E2F transcription factors, stimulating the transcription of cell cycle progression genes and leading to cell proliferation.

Step-by-step explanation:

Signaling downstream from the Platelet-Derived Growth Factor (PDGF) receptor stimulates cell proliferation by phosphorylating the Rb protein to relieve inhibition of cell proliferation genes. Specifically, phosphorylation inactivates the Rb protein, which normally functions to restrain the cell cycle by preventing the transcription of certain genes necessary for cell cycle progression.

The inactivation of Rb releases E2F transcription factors, allowing them to turn on genes essential for the cell transit from the G1 to the S phase of the cell cycle, including those encoding for various cyclins and cyclin-dependent kinases (CDKs). This phosphorylation cascade is part of a complex network of signaling pathways that include the activation of RAS and MAP kinase, ultimately leading to cell growth and division.