RETINOIC ACID INCREASES HYDROXYINDOLE-O-METHYLTRANSFERASE ACTIVITY AND MESSENGER-RNA IN HUMAN Y-79 RETINOBLASTOMA CELLS

Hydroxyindole-O-methyltransferase (HIOMT) plays an important role as t he final enzyme in the synthesis of melatonin. Here we present the fir st evidence that retinoic acid (RA) stereoisomers are potent regulator s of HIOMT in the human retinoblastoma-derived Y-79 cell line. Treatme nt with all-trans-, 13-cis-, and 9-cis-RA induced a gradual IO-fold in crease in HIOMT activity and mRNA, without changing the levels of mRNA encoding glyceraldehyde-3-phosphate dehydrogenase, actin, S-antigen, and interphotoreceptor retinoid-binding protein. These findings point to the possibility that RA may play a physiological role in the regula tion of human HIOMT.