Activin and inhibin exert their effects on granulosa cells through a class of receptors distinct from G protein-coupled and tyrosine kinase receptors. These receptors signal intrinsically through which pathway?

• A Coupling to Gq and generation of IP3 and diacylglycerol
• B Activation of phospholipase C-gamma through SH2 domain recruitment
• C Intrinsic serine/threonine kinase activity leading to SMAD protein phosphorylation ✓
• D Direct activation of a cytoplasmic tyrosine kinase of the Src family

Explanation

TGF-beta superfamily members including activin, inhibin, anti-Mullerian hormone and MIS bind type II receptors that phosphorylate type I receptors on serine and threonine residues. The activated type I receptor then phosphorylates receptor-regulated SMADs (SMAD 2/3), which complex with SMAD 4 and move to the nucleus. This distinguishes them sharply from RTK pathways, which use tyrosine phosphorylation and SH2 adaptors.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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