Growth hormone binds its receptor on hepatocytes, leading to dimerization of the receptor chains. Which kinase is activated by this dimerization and phosphorylates STAT5?

• A Janus kinase 2 (JAK2) ✓
• B Receptor tyrosine kinase domain intrinsic to the receptor
• C Protein kinase A
• D Phosphoinositide 3-kinase directly bound to ligand

Explanation

The growth hormone receptor has no intrinsic kinase domain. Ligand binding induces receptor dimerization, which brings two constitutively associated JAK2 molecules together so they transphosphorylate and activate each other. Activated JAK2 then phosphorylates STAT5, which dimerizes, enters the nucleus and drives transcription of genes including IGF-1. This distinguishes GH from insulin, whose receptor carries its own tyrosine kinase domain.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.