Biosynthesis of catalytically active rat testosterone 5 alpha-reductase in microinjected Xenopus oocytes: evidence for tissue-specific differences in translatable mRNA.

Publisher Website
Google Scholar
Abstract
The enzyme 4-ene-3-ketosteroid-5.alpha.-oxidoreductase [5.alpha.-reductase; 3-oxo-5.alpha.-steroid .DELTA.4-dehydrogenase, 3-oxo-5.alpha.-steroid: (acceptor) .DELTA.4-oxidoreductase, EC 1.3.99.5] plays a key role in androgen-dependent target tissues, where it catalyzes the conversion fo testosterone to the biologically active dihydrotestosterone. The regulation of 57a-reductase expression has not been studied at the molecular level as the enzyme is a membrane protein that is labile in cell-free homogenates. We developed a sensitive bioassay of the enzyme activity expressed in Xenopus oocytes microinjected with rat liver and prostate mRNA. After microinjection, incubation of intact oocytes in the presence of [3H]testosterone revealed the in ovo appearance of active 5.alpha.-reductase. Polyadenylylated RNA was fractionated by sucrose gradient centrifugation, and the enzymatic activity was shown to be encoded by a 1600- to 2000-base-pair fraction of hepatic poly(A)+ RNA. 5.alpha.-Reductase mRNA was most efficiently translated when up to 80 ng of RNA was injected per oocyte. In the injected oocytes, 5.alpha.-reductase mRNA was found to be a short-lived molecule (t1/2 = 2 hr), whereas its in in ovo translatable 5.alpha.-reductase protein exhibited stable enzymatic activity for over 40 hr. Moreover, the levels of translatable tissue-specific 5.alpha.-reductase mRNAs as monitored in the Xenopus oocytes correlated with the variable 5.alpha.-reductase activities in female rat liver, male rat liver, and prostate homogenates; the ratio of their specific activities was of 2500:630:1, respectively. Altogether, these results provide supporting evidence in favor of the transcriptional control of 5.alpha.-reductase expression in rat tissues.

This publication has 36 references indexed in Scilit: