GROWTH-HORMONE AND VITAMIN-A INDUCE P4502C7 MESSENGER-RNA EXPRESSION IN PRIMARY RAT HEPATOCYTES

The effects of growth hormone (GH) and retinoids on P4502C7 mRNA level s were investigated in cultured primary hepatocytes from normal female rats. Northern blot analysis of total nucleic acids from hepatocytes maintained in culture for 90 hr showed low basal levels of P4502C7 mRN A, which were marginally increased after continuous treatment with GH. Retinol treatment gave a slightly higher induction than GH, whereas t reatment with all-trans retinoic acid alone or with GH in combination with retinol induced P4502C7 mRNA to levels about one-third of those i n normal female rat liver. The effects of retinoids on P4502C7 mRNA we re dependent on both the dose and type of retinoid used. All-trans ret inoic acid produced a saturable dose-response curve with a 50% maximal induction of P4502C7 mRNA at 1.5 muM. The isomer 9-cis retinoic acid showed a dose-dependent activation of P4502C7 mRNA similar to that of all-trans retinoic acid. Retinol gave a 50% maximal response at approx imately 5 muM. In the presence of GH, the induction of P4502C7 mRNA ap peared additive to the effect of retinol at all concentrations used an d to all-trans retinoic acid at concentrations up to 1 muM. As determi ned by a quantitative solution hybridization assay, P4502C7 mRNA level s were induced 3-fold by GH, 5-fold by retinol, and 19-fold by all-tra ns retinoic acid. In the presence of GH, P4502C7 was induced 8-fold by retinol, whereas the induction by saturating concentration of all-tra ns retinoic acid showed no significant additional effect of GH. The im portance of vitamin A for the expression of P4502C7 in vivo was confir med by the low abundance of P4502C7 mRNA in vitamin A-deficient animal s as compared with vitamin A-adequate control rats. Nuclear run-on exp eriments performed in cultured primary hepatocytes showed that both GH and retinoic acid exert their effects at the transcriptional level. W e conclude that both GH and retinoids can induce P4502C7 mRNA in rat l iver hepatocytes, retinoic acid being the dominant inducer.