Involvement of cyclic adenosine 3',5'-monophosphate in the differential regulation of activin betaA and betaB expression by gonadotropin in the zebrafish ovarian follicle cells.
Activin is a dimeric protein consisting of two similar but distinct beta-subunits, betaA and betaB. In our previous studies, both activin A (betaAbetaA) and activin B (betaBbetaB) have been demonstrated to stimulate oocyte maturation and promote oocyte maturational competence in the zebrafish. Follistatin, a specific activin-binding protein, can block both activin- and gonadotropin-induced final oocyte maturation in vitro, suggesting that activin is likely a downstream mediator of gonadotropin actions in the zebrafish ovary. In the present study, a full-length cDNA encoding zebrafish ovarian activin betaA was cloned and sequenced. The precursor of zebrafish activin betaA consists of 395 amino acids and its mature region exhibits about 78% homology with that of mammals. Using an in vitro primary culture of the ovarian follicle cells and semiquantitative RT-PCR assays, we examined the regulation of activin betaA and betaB expression by human chorionic gonadotropin (hCG) and its intracellular signal transduction mechanisms. hCG (15 IU/ml) increased the mRNA level of activin betaA-subunit; however, it significantly down-regulated the steady-state expression level of activin betaB in a time- and dose-dependent manner. The differential regulation of the two beta-subunits by hCG could be mimicked by 3-isobutyl-1-methylxanthine, forskolin, and dibutyryl-cAMP, suggesting involvement of the intracellular cAMP pathway. Interestingly, H89 (a specific inhibitor of protein kinase A, PKA) could effectively block hCG- and forskolin-stimulated activin betaA expression at 10 micro M, but it was unable to reverse the inhibitory effects of hCG and forskolin on betaB expression. This suggests that the hCG-stimulated activin betaA expression is dependent on the activation of the cAMP-PKA pathway, whereas the inhibitory effect of hCG on activin betaB expression is likely mediated by PKA-independent pathway(s).
Wang
Yajun
Y
Department of Biology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
Ge
Wei
W
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D003001:Cloning, Molecular; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D018076:DNA, Complementary; D005260:Female; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D006062:Gonadotropins / Q000494:pharmacology*; D006801:Humans; D028322:Inhibin-beta Subunits / Q000235:genetics*; D008969:Molecular Sequence Data; D006080:Ovarian Follicle / Q000166:cytology / Q000502:physiology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D015203:Reproducibility of Results; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000592:standards; D015027:Zebrafish
D018076:DNA, Complementary; D006062:Gonadotropins; C422402:INHBB protein, human; D010726:Phosphodiesterase Inhibitors; C103008:inhibin beta A subunit; D005576:Colforsin; D003994:Bucladesine; D028322:Inhibin-beta Subunits; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D015056:1-Methyl-3-isobutylxanthine