Regulation of inhibin alpha- and beta A-subunit messenger ribonucleic acid levels by chorionic gonadotropin and recombinant follicle-stimulating hormone in cultured human granulosa-luteal cells.
We studied the effects of recombinant human FSH (rhFSH) and purified hCG on the steady state messenger ribonucleic acid (mRNA) levels of inhibin alpha- and beta A-subunits in cultured granulosa-luteal cells of preovulatory ovarian follicles obtained from women undergoing in vitro fertilization. Specific mRNA transcripts for the alpha- and beta A-subunits were detected in Northern and dot blot filter hybridization analyses, and the levels of these mRNAs were induced by rhFSH and hCG in a distinct concentration- and time-dependent manner. The basal and hCG-stimulated alpha-subunit mRNA levels were first determined at 2- to 3-day intervals over a 3- to 10-day culture period after the initiation of the cultures. Both the basal and hCG-stimulated alpha-subunit mRNA levels declined steadily during culture, but the maximal relative stimulatory effect of hCG was observed on day 7 of culture. All subsequent experiments, therefore, were performed on days 6-8 of culture. Both gonadotropins induced alpha-subunit mRNA levels with slower kinetics than those of the beta A-subunit. Varying between experiments, rhFSH and hCG increased the expression of the alpha-subunit with a maximal effect of 2.5- to 5.7-fold and 1.7- to 7.2-fold, respectively, above basal levels 24-48 h after stimulation. rhFSH and hCG induced beta A-subunit mRNA levels with 3.0- to 5.8-fold and 2.3- to 8.6-fold increases above basal levels, respectively, at 2 h; thereafter, only moderate or no stimulation of the beta A-subunit mRNA levels could be detected at 7-48 h. Treatment of the cells with the RNA synthesis inhibitor actinomycin-D prevented the induction of alpha-subunit mRNA levels by hCG, and no significant differences were detected in the stability of alpha-subunit mRNA transcripts in hCG-treated cells vs. untreated cultures. This indicates that hCG induces transcription of the alpha-subunit gene rather than maintains the levels of preexisting transcripts. As the kinetics of induction of alpha- and beta A-subunit mRNAs by gonadotropins were different, we examined how the inhibition of protein synthesis affects the induction of alpha- and beta A-subunit mRNAs by hCG. Cycloheximide had no effect on basal alpha-subunit mRNA levels at 2 or 24 h. However, it inhibited at 24 h the induction of the alpha-subunit by hCG.(ABSTRACT TRUNCATED AT 400 WORDS)
Erämaa
M
M
Department of Bacteriology and Immunology, University of Helsinki, Finland.
Tuuri
T
T
Hildén
K
K
Ritvos
O
O
D015152:Blotting, Northern; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007265:Inhibins / Q000235:genetics*; D007700:Kinetics; D008184:Luteal Cells / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis*; D011994:Recombinant Proteins / Q000494:pharmacology; D013997:Time Factors
D006063:Chorionic Gonadotropin; D012333:RNA, Messenger; D011994:Recombinant Proteins; D003609:Dactinomycin; D007265:Inhibins; D005640:Follicle Stimulating Hormone; D003513:Cycloheximide