Soluble guanylyl (or guanylate) cyclases are heterodimeric enzymes consisting of an alpha and a beta subunit , which are activated by nitric oxide and which catalyze the conversion of GTP to 3-prime, 5-prime-cyclic GMP and pyrophosphate.
General function
Enzyme
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Cellular localization
Cytoplasmic
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Ovarian function
Follicle development, Ovulation
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Activation of soluble guanylyl cyclase inhibits estradiol production and cyclic AMP accumulation from cultured rat granulosa cells.
Tafoya MA, et al .
OBJECTIVE: To demonstrate the expression of soluble guanylyl cyclase (sGC) alpha and beta subunits in rat granulosa cells and determine the effects sGC activation on levels of cyclic GMP (cGMP), E(2), and cAMP. DESIGN: Basic research study. SETTING: University research laboratory. ANIMAL(S): Estrogen-treated immature Sprague-Dawley female rats from which primary cell culture of granulosa cells was obtained. INTERVENTION(S): Functionally immature rat granulosa cells were incubated for 48 hours with media alone, FSH, or FSH plus YC-1, a specific activator of sGC. MAIN OUTCOME MEASURE(S): Expression of sGC alpha and beta subunits was determined by immunoblot analysis. Media concentrations of E(2), cAMP, and cGMP were measured by radioimmunoassays. RESULT(S): Immunoblot analysis of granulosa cells revealed the expression of sGC alpha and beta subunits. While cGMP accumulation was low in cells incubated with media alone or with FSH, cotreatment with FSH plus YC-1 increased cGMP levels approximately five-fold. Incubation of cells with FSH stimulated E(2) production in a dose-dependent manner. However, cotreatment of cells with FSH plus YC-1 significantly decreased E(2) concentrations at all doses of FSH tested. Similarly, while FSH increased cAMP accumulation from granulosa cells, cotreatment with YC-1 markedly inhibited FSH-stimulated cAMP levels. CONCLUSION(S): These findings demonstrate the expression of sGC subunits in rat granulosa cells and indicate that activation of sGC increases cGMP levels, which are associated with inhibition of FSH-stimulated E(2) production and cAMP accumulation.
Expression regulated by
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Ovarian localization
Granulosa, Theca, Luteal cells
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Endocrine society meeting [P2-441] Regulated Expression of Soluble Guanylyl Cyclase Alpha and Beta Subunits in the Rat Ovary.
Fangxiong Shi, Robert L Stewart, Jr., Emerson Perez, Jean Y-H Chen, Philip S LaPolt Dept. of Biological Scis, California State Univ, Los Angeles, CA
Soluble guanylyl cyclase (sGC) is activated by nitric oxide (NO), resulting in the production of cyclic GMP. Recent studies indicate that NO and cyclic GMP may play important roles in ovarian functions. However, little information is available regarding the ovarian expression of sCG. The present study examined the cellular localization and regulated expression of sGC alpha and beta subunit proteins during ovarian follicular development, ovulation, and luteinization, and in cultured rat granulosa cells. Immature rats were treated with equine gonadotropin (eCG) to stimulate follicle growth, followed 52 h later by an ovulatory dose of hCG. Immunohistochemical analyses revealed that sGC alpha subunit levels were high in ovarian vascular endothelium, and low in germinal epithelium. Very intense sCG alpha subunit staining was observed in granulosa cells of primordial and primary follicles. In contrast, sGC alpha expression was low in granulosa cells of small antral and large antral follicles, and in atretic follicles. Theca cells of developing follicles demonstrated moderate sCG alpha levels. In preovulatory follicles, sGC alpha content was very low in granulosa cells, but remained high in theca cells 52 h after eCG treatment. Subsequently, sGC alpha immunoreactivity increased in corpora lutea by 72 h after hCG. Similar ovarian localization and expression patterns were seen for the sCG beta subunit, indicating regulated coexpression of the sCG subunits. Immunoblot analysis of whole ovarian homogenates revealed no significant changes in whole ovarian sCG alpha or beta subunit protein levels during treatments with eCG and hCG, presumably due to the cell-specific nature of sGC expression. Cultured granulosa cells were also used to examine the regulation of sGC subunit levels. While sGC alpha and beta subunit proteins were detectable in cultured rat granulosa cells by immunoblot analysis, there was no effect of treatments with FSH or with the NO generator, DETA/NO, on sGC levels, despite reported regulation of sGC levels by cyclic AMP and NO in nonovarian cells. Together, these results indicate that ovarian sGC subunit expression is regulated in a cell-specific manner, with highest levels observed in primordial and primary follicles, thecal cells, and corpora lutea. Further studies are required to determine whether these findings reflect potential roles of sGC in the process of follicular recruitment, and in thecal and luteal functions.