FOLLICLE-STIMULATING HORMONE-REGULATED EXPRESSION OF SERUM GLUCOCORTICOID-INDUCIBLE KINASE IN RAT OVARIAN GRANULOSA-CELLS - A FUNCTIONAL-ROLE FOR THE SPL FAMILY IN PROMOTER ACTIVITY/

Recently, a family of novel, serine/threonine protein kinases has been identified. One of these transcriptionally inducible, immediate-early genes encodes serum/glucocorticoid inducible-protein kinase, sgk. By in situ hybridization, we show that sgk expression in the rat ovary is selectively localized to granulosa cells. In culture, FSH or forskoli n, activators of the protein kinase A (PKA) pathway, rapidly (2 h) and transiently increased sgk mRNA levels in undifferentiated granulosa c ells. Sgk mRNA exhibited a biphasic expression pattern, with maximal l evels observed at 48 h of FSH/forskolin as granulosa cells differentia te to the preovulatory phenotype. Deletion analyses using sgk promoter -reporter constructs (-4.0 kb to -35 bp) identified a region between - 63 and -43 bp that mediated FSH and forskolin-responsive transcription in undifferentiated and differentiated granulosa cells. This G/C-rich region 1) conferred both basal and inducible transcription to the min imal -35 sgk promoter chloramphenicol acetyltransferase reporter const ruct, 2) specifically bound Sp1 and Sp3 present in granulosa cell extr acts, and 3) bound recombinant Sp1. Mutation of 2 bp in this region no t only prevented Sp1 and Sp3 binding, but also abolished the PKA-media ted transactivation observed when using the wild type construct. Sp1 a nd Sp3 DNA-binding activity acid protein levels did not change signifi cantly during sgk induction. Collectively, these data indicate that Sp 1/Sp3 transactivation of the sgk promoter likely involves regulated, p hosphorylation-dependent interaction with other factors. Thus the nove l, biphasic induction of sgk that correlates with granulosa cell progr ession from proliferation to differentiation appears to involve sequen tial, coordinated actions of FSH, PKA, and transcription factors, incl uding Sp1 and Sp3.