How do retinoids work?

The main physiological function of natural retinoids, i.e. the dietary micronutrient retinol and its metabolite retinoic acid, is in proper differentiation and maintenance of differentiated state of many if not all epithelia. Also, it appears that the metabolism of nonepithelial cells can be affected by these compounds. The effects are diverse. Although the exact molecular mechanism causing these effects remain to be elucidated, recent research indicates that both retinol and retinoic acid affect genomic expression by activating and simultaneously repressing specific genes. Such action results in the appearance and disappearance of more than 40 specific proteins. The effect on the genomic expression is time-dependent. Some of the genes are influenced very soon in a matter of a few hours. Effects on other genes require considerable time. Whether natural retinoids interact with the genome directly remains to be shown. How such interactions could occur is discussed.