INSULIN-LIKE GROWTH-FACTOR-I INCREASES EXPRESSION OF THE PORCINE P-450 CHOLESTEROL SIDE-CHAIN CLEAVAGE GENE THROUGH A GC-RICH DOMAIN

The promoter/regulatory region of the porcine P-450 cholesterol side c hain cleavage (P450scc) gene was cloned from a porcine genomic library . This gene contains a GC-rich region (-130-100) that mediates insulin like growth factor I (IGF-I) and cAMP stimulation of gene expression i n porcine granulosa cells. Stimulation of gene expression by cAMP occu rs in 6 h, while IGF-I stimulation occurs in 24-48 h. This region is a lso responsive to insulin but not fibroblast growth factor. The effect s of IGF-I and cAMP on gene expression in porcine granulosa cells are additive. In Y1 adrenal cells, the same region is responsive to cAMP b ut not to IGF-I. Gel shift assays using an oligonucleotide of this reg ion and nuclear extract protein from porcine granulosa and Y1 adrenal cells identified three DNA protein complexes (C-1-C-3). The binding ac tivity of the complexes did not change with IGF-I or forskolin treatme nt of granulosa cells. Mutational analysis results were consistent wit h IGF-I regulating gene expression through the C-2 DNA protein complex . Moreover, this complex binds differently in gel shift assay to mutan t oligonucleotides with porcine and Y1 and nuclear extract protein. We conclude that IGF-I stimulates porcine P450scc gene expression throug h a distinct, cell-specific protein complex binding to a GC-rich domai n.