TGF-beta binds its type II receptor on an epithelial cell. Which sequence correctly describes the downstream signal transduction?

• A Type II receptor autophosphorylates tyrosine residues that bind Grb2-Sos to activate Ras
• B Type II receptor recruits JAK kinases, which activate STAT3 homodimers
• C Type II receptor generates cAMP through an associated Gs protein
• D Type II receptor phosphorylates type I receptor, which phosphorylates R-SMADs that complex with SMAD4 and enter the nucleus ✓

Explanation

TGF-beta receptors are serine/threonine kinases. Type II receptor first phosphorylates the type I receptor, which then phosphorylates receptor-regulated SMADs (SMAD2/3). These form a complex with the common mediator SMAD4 that translocates to the nucleus to regulate transcription. Option B describes the GH-leptin cytokine pathway, and option A describes RTK-Ras signalling. The distinguishing feature examined here is serine/threonine rather than tyrosine kinase specificity.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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