Follicle-stimulating hormone induction of ovarian insulin-like growth factor-binding protein-3 transcription requires a TATA box-binding protein and the protein kinase A and phosphatidylinositol-3 kinase pathways

The current study was done to elucidate the mechanism of the FSH stimulation of IGF-binding protein 3 (IGFBP-3) expression and map the FSH response element on the pig IGFBP-3 promoter. Forskolin induced IGFBP-3 reporter activity in transiently transfected granulosa cells. The protein kinase A (PKA) inhibitor [N-[2-(p-bromocinnamyl)amino)ethyl]-5- isoquinolinesulfonamide, 2HCl] ( and cotransfection with a PKA inhibitor expression vector), the phosphatidylinositol-3 kinase inhibitor [2-(4morpholinyl)-8-phenyl-4H-1-benzopyran-4-one], and the ERK inhibitor[1,4- diamino-2,3-dicyano-1,4-bis(2aminophenylthio) butadiene], all blocked FSH stimulation. Use of serial deletion constructs and site-directed mutagenesis show that a TATA box-binding protein site is required for FSH stimulation and that specific protein 1 (Sp1) site is required for basal transcription. Gel shift assays of nuclear protein with a -61/-25 probe detected four protein-DNA complexes, with bands I and II having significantly higher intensities in FSH-treated cells than in controls. Mutation of the Sp1 site prevented formation of bands I and II whereas mutation of the TATA box-binding protein site prevented formation of band IV. Use of specific antibodies showed that Sp1 participates in formation of band I, Sp3 band II, and p300 in both I and II. Band III was nonspecifically competed out. We conclude that FSH stimulation of IGFBP-3 transcription is mediated by cAMP via the PKA pathway and requires the P1-3 kinase and likely the MAPK pathways.