The EGF-receptor is a receptor tyrosine kinase that binds to epidermal growth fa

Question

The EGF-receptor is a receptor tyrosine kinase that binds to epidermal growth factor (EGF). In response to EGF binding, the EGF-receptor stimulates a signaling pathway that involves Ras. Ultimately, this signaling pathway leads to the upregulation of factors that promote cell division. As a result, in response to EGF, cells that express the EGF-receptor undergo cell division to produce more cells. If an inhibitor that inhibited all G proteins was added to cells, how would this affect the ability of these cells to respond to EGF?

1)The inhibitor would have no effect, because the EGF-receptor is not a G protein-coupled receptor.

2)While the receptor would dimerize and autophosphorylate in the presence of the inhibitor, downstream signaling would be prevented because the inhibitor would affect Ras activity.

3)In the presence of the inhibitor, the receptor could bind to EGF and dimerize, but it would not be able to autophosphorylate because this requires the activity of a G protein.

Explanation / Answer

Binging of EGF to EGFR stimulates homo and heterodimerization. These dimers, particularly the ErbB heterodimers, undergo auto and transphosphorylation on their tyrosine residues (tyrosine based activation motifs). This leads to generation of a converged group of molecules and interactions, which further start downstream signaling cascades to generate various physiological events.

One such important event is activation of Ras, which occurs through small GTPase enzymes, through transfer of a phosphate group to Ras-GDP.

In the presence of inhibitors to G proteins, this pathway is inhibited, and leads to inhibition of downstream pathway cascades.

Therefore, the correct answer is

2) )While the receptor would dimerize and autophosphorylate in the presence of the inhibitor, downstream signaling would be prevented because the inhibitor would affect Ras activity.

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