Activin-induced inhibin alpha-subunit production by rat granulosa cells requires endogenous insulin-like growth factor-I.
Inhibin-alpha subunit (Inh-alpha) gene expression is important for granulosa cell (GC) differentiation and prevention of ovarian tumorigenesis. Studies on Inh-alpha regulation have implicated activin and insulin-like growth factor-I (IGF-I) in the mechanisms of expression. Here we present evidence that endogenously produced IGF-I plays an obligatory role in activin-induced Inh-alpha production. Primary cultures of rat GC were incubated with increasing concentrations of various regulatory molecules, and the levels of Inh-alpha protein and its mRNA were measured in conditioned medium and cells, respectively. Recombinant activin A stimulated Inh-alpha expression, and the effects were dose- and time-dependent. The receptor tyrosine kinase inhibitor tyrphostin A23 caused a dose-dependent inhibition of activin-dependent Inh-alpha expression, whereas the inactive isomer, A63, had no effect. The stimulatory effect of activin was also blocked in a dose-dependent manner by added IGF binding protein-4 or -5, and the effects were reversed by IGF-I. Moreover, increasing concentrations of an anti-IGF-I antibody had a similar inhibitory effect on activin-stimulated Inh-alpha expression. Collectively, these results suggest, for the first time, that endogenously produced IGF-I is required for activin stimulation of Inh-alpha expression in cultured rat GC.
Kubo
T
T
Department of Reproductive Medicine, University of California, San Diego, La Jolla 92093-0674, USA.
Shimasaki
S
S
Kim
H
H
Li
D
D
Erickson
G F
GF
D028341:Activins; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006107:Granulosa Cells / Q000187:drug effects* / Q000378:metabolism*; D007265:Inhibins / Q000008:administration & dosage / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000378:metabolism / Q000494:pharmacology; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000378:metabolism / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats
D000906:Antibodies; D004791:Enzyme Inhibitors; D018974:Insulin-Like Growth Factor Binding Protein 4; D018975:Insulin-Like Growth Factor Binding Protein 5; D010455:Peptides; D012333:RNA, Messenger; C094377:inhibin-alpha subunit; D028341:Activins; D007265:Inhibins; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases