GATA-4 is a granulosa cell factor employed in inhibin-alpha activation by the TGF-beta pathway.
Part of heterodimeric inhibin, inhibin-alpha is crucial for mammalian ovarian function. Regulation of inhibin-alpha expression in granulosa cells is both endocrine, primarily by follicle-stimulating hormone (FSH), and paracrine, primarily by members of the transforming growth factor beta (TGF-beta) superfamily. Smad proteins transmit TGF-beta signals to the nucleus, but the cooperating transcription factors involved in inhibin-alpha promoter activation remain unknown. Transcription factor GATA-4 regulates inhibin-alpha in gonadal cells, and the FSH cascade activates GATA-4. We hypothesized that the TGF-beta signalling cascade and GATA-4 also cooperate to regulate inhibin-alpha expression. In KK-1 granulosa tumour cells, which resemble normal granulosa cells and express inhibin-alpha, we found that TGF-beta upregulated GATA-4 expression. Transient transfection experiments in KK-1 cells demonstrated that dominant negative GATA-4 variants or mutations of GATA-binding sites in the inhibin-alpha promoter attenuated TGF-beta-induced gene activation. In GATA-4-deficient COS-7 cells, TGF-beta enhanced the expression of the inhibin-alpha promoter only in the presence of exogenous GATA-4. Smad3, but not Smad2, cooperated with GATA-4 in the transcriptional activation of the inhibin-alpha promoter, and immunoprecipitation experiments in KK-1 cells revealed a physical Smad3:GATA-4 interaction. Our data suggest that GATA-4, interacting with Smad3, is a cofactor for TGF-beta signalling to activate inhibin-alpha in granulosa cells.
Anttonen
M
M
Program for Developmental and Reproductive Biology, Biomedicum Helsinki, Finland.
Parviainen
H
H
Kyrönlahti
A
A
Bielinska
M
M
Wilson
D B
DB
Ritvos
O
O
Heikinheimo
M
M
D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D005260:Female; D050991:GATA4 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006107:Granulosa Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D007265:Inhibins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D015398:Signal Transduction / Q000502:physiology*; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D050991:GATA4 Transcription Factor; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; C094377:inhibin-alpha subunit; D007265:Inhibins