Figure 2: Pathway of retinoic acid metabolism and signaling effector function. Vitamin A (provided by β-carotene) is metabolized by retinyl ester hydrolases to retinol. Retinol/RBP4 complexes enter cells via STRA6-mediated endocytosis or via diffusion. Inside the cell, retinol is oxidized to retinal which is subsequently oxidized by RALDHs (also known as ALDH1A isoforms) to retinoic acid. CRABP2 binds retinoic acid and delivers it to RARs within the nucleus. RA-bound RARs and RXRs heterodimerize to activate transcription of genes containing RAREs.