Biochemical properties, tissue expression, and gene structure of a short chain dehydrogenase/reductase able to catalyze cis-retinol oxidation

We have identified a retinol dehydrogenase (cRDH) that catalyzes the oxidat ion of 9-cis- but not all-trans-retinol and proposed that this enzyme plays an important role in synthesis of the transcriptionally active retinoid, 9 -cis-retinoic acid. There is little information regarding either the bioche mical properties of cRDH or how its 9-cis-retinol substrate is formed, We n ow report studies of the properties and expression of human and mouse cRDH and of the characteristics and location of the murine cRDH gene, Additional ly, we report mouse hepatic 9-cis-retinol concentrations and demonstrate th at 9-cis-retinol is formed in a time- and protein-dependent manner upon inc ubation of all-trans-retinol with cell homogenate, Human and mouse cRDH dis play similar substrate specificities for cis-isomers of retinol and retinal dehyde, Moreover, human and mouse cRDH show marked sensitivity to inhibitio n by 13-cis-retinoic acid, with both being inhibited by approximately 50% b y 0.15 mu M 13-cis-retinoic acid (for substrate concentrations of 10 mu M) Lesser inhibition is seen for 9-cis- or all-trans-retinoic acids, Immunoblo t analysis using antiserum directed against human cRDH demonstrates cRDH ex pression in several tissues from first trimester human fetuses, indicating that cRDH is expressed early in embryogenesis, Adult mouse brain, Liver, ki dney and to a lesser extent small intestine and placenta express cRDH, The murine cRDH gene consists of at least 5 exons and spans approximately 6 kb of genomic DNA, Backcross analysis mapped the mouse cRDH gene to the most d istal region of chromosome 10.1 Taken together, these data extend our under standing of the properties of cRDH and provide additional support for our h ypothesis that cRDH may play an important role in 9-cis-retinoic acid forma tion.