Vitamin A (retinol) is converted intracellularly to retinoic acid, which binds to a specific nuclear receptor that heterodimerizes with retinoid X receptor (RXR) to regulate gene transcription. Which nuclear receptor is primarily responsible for mediating the effects of retinoic acid on epithelial differentiation?

• A Vitamin D receptor (VDR)
• B Thyroid hormone receptor (TR)
• C Retinoic acid receptor (RAR) ✓
• D Peroxisome proliferator-activated receptor gamma (PPAR-γ)

Explanation

Retinoic acid binds to RAR, which then heterodimerizes with RXR to regulate genes involved in epithelial cell differentiation, immune function, and embryonic development. VDR binds 1,25-(OH)2D3, TR binds T3, and PPAR-γ is involved in adipogenesis. Confusing RAR with VDR is a common error because both are nuclear receptors, but they bind different ligands.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.