Molecular identification of adenylyl cyclase 3 in bovine corpus luteum and its regulation by prostaglandin F2alpha-induced signaling pathways.

The involvement of cAMP in various aspects of ovarian steroidogenic cells functions has been extensively studied. However, the adenylyl cyclase (AC) types expressed in ovarian cells, of any species, are not yet determined. The present study was undertaken to identify AC types present in bovine luteal cells and their regulation by various stimuli. AC isoforms 2, 3, 5, 6, 7, 8, and 9 were detected in the bovine brain by Northern blotting analysis, whereas the bovine corpus luteum (CL) only expressed AC3 and 6 mRNAs, with AC3 being more abundant than AC6. The use of AC3-specific primers in RT-PCR reaction verified the presence of AC3 mRNA in both bovine and rat CL tissue as well as in bovine steroidogenic luteal cells. Because these two AC isoforms, AC3 and 6, exhibit distinct regulatory patterns we have next examined the effects of various signaling pathways on AC activity in luteal cells. These studies have shown that: 1) prostaglandin (PG) F2alpha and phorbol 12-myristate 13-acetate markedly elevated agonist-stimulated cAMP synthesis (these effects were inhibited by addition of highly specific PKC inhibitor, bisindolylmaleimide); 2) depletion of Ca2+ from the incubation medium inhibited AC activity; 3) physiological concentrations of Ca2+ ions (up to 5 mM) significantly stimulated cAMP production in luteal cells; and 4) the effects of Ca2+ on cAMP synthesis were evident only in the presence of forskolin. These regulatory characteristics of AC activity are consistent with the molecular identification of ACs indicating the presence of AC3 in luteal cells. The reported data may delineate the cross-talk between physiological activators of AC in the CL (such as LH, PGE2, and PGI2) and other ligands (such as PGF2alpha and endothelin-1), which indirectly modulate AC activity. Therefore, the identification of AC isoforms present in luteal cells is an important step toward understanding the mode of action of a wide array of hormones regulating ovarian cells.