When activated by the extracellular signal protein platelet-derived growth facto

ID: 7233 • Letter: W

Question

When activated by the extracellular signal protein platelet-derived growth factor (PDGF), the PDGF receptor

phosphorylates itself on multiple tyrosines (as indicated in Figure 16-46A by the circled Ps; the numbers next to

these Ps indicate the amino acid number of the tyrosine). These phosphorylated tyrosines serve as docking sites for

proteins that interact with the activated PDGF-receptor. These proteins are indicated in the figure, and include the

proteins A, B, C, and D. One of the cell’s responses to PDGF is an increase in DNA synthesis, which can be

measured by the incorporation of radioactive thymidine into the DNA.

To determine which protein or proteins, A, B, C, or D, are responsible for the activation of DNA synthesis, you

construct mutant versions of the PDGF receptor that retain one or more tyrosine phosphorylation sites. You

express these mutant versions in cells that do not make their own PDGF receptor. In these cells, the various mutant

versions of the PDGF receptor are expressed normally, and, in response to PDGF binding, become phosphorylated

on whichever tyrosines remain. You measure the level of DNA synthesis in cells that express the various mutant

receptors and obtain the data shown in Figure 16-46B.

A. From these data, which, if any, of proteins A, B, C, and D are involved in the stimulation of DNA synthesis by

PDGF?

Explain your answer.

B. Which, if any, of these proteins inhibit DNA synthesis? Explain your answer.

Kindly post the 16-46B diagram, otherwise we cannot answer your questions.

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