Figure 2. Simplified schematic of the all-trans retinoic acid (ATRA) signaling pathway.

ATRA is synthesized from retinol (Vitamin A) in a two-step oxidation process which takes place in the cytoplasm. To induce transcription, retinoic acid receptors (RARs) need to be activated by ATRA binding, and both RARs and retinoid X receptors (RXRs) need to bind retinoic acid response elements (RAREs) in the vicinity of target genes. Several CYP26 isoforms are responsible for ATRA degradation. Due to its small size and hydro- and lipophilic properties, ATRA is able to cross cell membranes and thus act in other cells.