Regulation of inhibin beta B-subunit mRNA expression in rat Sertoli cells: consequences for the production of bioactive and immunoreactive inhibin.
In Sertoli cells from 21-day-old rats, the expression of the mRNA encoding the alpha-subunit of inhibin, and the production of immunoreactive inhibin are stimulated by follicle-stimulating hormone (FSH). In contrast, the amount of beta B-subunit mRNA is not increased after FSH treatment of the cells, and the ratio between bioactive and immunoactive inhibin decreases after stimulation with FSH. These data suggest that the beta B-subunit is the limiting factor in the production of bioactive inhibin. The aim of the present experiments was to investigate the effect of changes in the amount of beta B-subunit mRNA on the production of bioactive and immunoreactive inhibin. During early postnatal testicular development, the relative amounts of the 4.2 kb and 3.5 kb mRNAs encoding the beta B-subunit of inhibin changed markedly. The meaning of this changing ratio between beta B-subunit mRNAs is not clear, since both mRNAs are actively translated, as demonstrated by polysomal analysis. The total amount of beta B-subunit mRNA correlated with the in vitro production of bioactive inhibin as published earlier. Prolonged stimulation of cultured Sertoli cells from 14-day-old rats with 4 beta-phorbol 12-myristate 13-acetate (PMA) caused a decreased expression of the beta B-subunit mRNAs, presumably by down-regulation of protein kinase C. A similar effect was obtained after addition of the calcium ionophore A23187. Concomitantly, a decreased production of bioactive inhibin was observed. Furthermore, Western blotting revealed that secretion of the 32 kDa inhibin alpha beta-dimer was decreased, whereas secretion of the combination of the C-terminal part with the pro-region of the alpha-subunit was increased. It is concluded that the level of the beta B-subunit of inhibin is rate-limiting for the production of bioactive inhibin in cultured Sertoli cells, and that its expression can be influenced by modulation of protein kinase C, and/or intracellular calcium levels.
Klaij
I A
IA
Department of Endocrinology and Reproduction, Medical Faculty, Erasmus University Rotterdam, Netherlands.
Timmerman
M A
MA
Blok
L J
LJ
Grootegoed
J A
JA
de Jong
F H
FH
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D007265:Inhibins / Q000096:biosynthesis* / Q000235:genetics; D008297:Male; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D011919:Rats, Inbred Strains; D012708:Sertoli Cells / Q000378:metabolism*; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000470:Alkaloids; D012333:RNA, Messenger; D000001:Calcimycin; D007265:Inhibins; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium