Figure 6.

Cellular uptake by target cells and intracellular receptors for vitamin A. Once in the cytoplasm, retinol undergoes several oxidation steps, which end up forming ATRA, which can follow different fates inside the cell. ATRA can mediate both genomic and non-genomic functions. The non-genomic functions are less known and include regulation of phosphorylation of target proteins (CREB) and cytoplasmic translation regulation. Genomic functions are more common and include the binding of ATRA to nuclear receptors (RAR, PPAR, RXR, ROR), which have a direct influence on gene regulation. In the absence of a ligand, gene transcription is repressed. For this to happen, ATRA must be transported to the nucleus, which is mediated by cellular retinoic acid-binding proteins (CRABP) or fatty-acid-binding protein (FABP). CREB—cAMP response element-binding protein.