Cell Cycle Regulatory Genes as Targets of Retinoids

Abstract

Retinoids are a large group of natural and synthetic derivatives of vitamin A. There are more than 4000 different compounds in this group. Vitamin A and its derivatives play an essential role in vision, immuno-modulation, reproduction, maintaining epithelial tissue, cell growth, and differentiation. Retinol, retinal, and retinoic acid (RA) are among the most important natural retinoids. Retinol is the alcohol form, and is the major transport form of vitamin A. Retinal is the aldehyde form. It is produced by an enzymatic oxidation of retinol in a variety of tissues or by a direct cleavage of dietary β-carotene in small intestine and liver. Retinal can be converted back to retinol through a reduction reaction. In contrast, further oxidation of retinal into retinoic acid (RA) is an irreversible step (Fig. 1). RA is effective therapeutically in the treatment of a variety of diseases involving cell proliferation, abnormal differentiation, and inflammation. 11-cis-retinal is the chromophore in the visual protein, rhodopsin. With the exception of vision and reproduction, all of the action of vitamin A can be accomplished by retinoic acid. 9-cis and 13-cis RA are natural isomers of all-trans RA (ATRA).