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. 2022 Mar 31;14(7):1456. doi: 10.3390/nu14071456

Figure 1.

Figure 1

Model of Intracellular Retinol Metabolism and Molecular Actions. Retinoic acid (RA), the endogenous agonist for the three retinoic acid receptors (RARα, β, and γ), moves to the nucleus where it binds an RAR in a heterodimer with an RXR. This results in transcriptional activation of primary target genes that contain a retinoic acid response element (RARE) on DNA. A metabolite of RA, 4-OxoRA, can also act as an agonist for RARs. RARα can move to the cytoplasm, actively transported out of the nucleus, where RARα can regulate the rate of translation of target mRNAs into proteins, with different effects if the ligand RA is bound to RARα. RARα, without the ligand RA, can also inhibit ERK and mTORC1 signaling. The cytoplasmic actions of RARα have only been shown to date in neurons. Abbreviations: RDHs: retinol dehydrogenases; ALDH: aldehyde dehydrogenase; CYP26: Cytochrome P450 family 26 subfamily A member 1; ERK: extracellular signal-regulated kinase; mTORC1: mammalian target of rapamycin complex 1; LRAT: lecithin retinol acyltransferase; REH: retinyl ester hydrolase; S6K1: 40S ribosomal protein S6 kinase p70/p85.