Figure 1: The effects of RA production and other metabolic factors on the activities of transcription factors associated with a retinoic acid-responsive element (RARE) in the promoter of an RA-targeted gene. In primary hepatocytes, RA is produced from retinal derived from retinol. Retinol can be esterified into retinyl ester (RE) or oxidized into retinal. The RARE can be occupied by retinoic acid receptor (RAR), retinoid X receptor (RXR), hepatocyte nuclear factor 4α (HNF4α), chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII), and peroxisome proliferator-activated receptor β/δ (PPARβ/δ) in the forms of heterodimers or homodimers. These transcription factors receive signals from RA and metabolic pathways and regulate the expression of the RA-responsive gene.