Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In previous studies in porcine granulosa cell cultures, endothelin-1 (ET-1) was shown to inhibit FSH-stimulated cAMP and progesterone accumulation, and to increase inositol phosphate formation and cytosolic calcium ion concentration. The latter results suggest an action of ET-1 via the activation of phospholipase C. Here we have investigated the following experimental questions. (1) Does ET-1 activate PKC in ovarian cells? (2) Does the cellular mechanism(s) whereby ET-1 interferes with the steroidogenic action of FSH in granulosa cells involve an impairment of cAMP generation or action? And (3) how does the site(s) of the inhibitory effect(s) of ET-1 and TPA on FSH-stimulated progesterone accumulation in cultured granulosa cells compare? In the present investigation, ET-1 (1 microM) induced rapid cytosol-to-membrane translocation of [3H]phorbol 12,13-dibutyrate binding sites, indicating protein kinase C (PKC) activation. At 24 or 48 h, ET-1 inhibited FSH-, but not forskolin (1 microM)-induced, cAMP accumulation. Cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc) messenger RNA (mRNA) accumulation was stimulated by FSH, 8-bromo-cAMP (8Br-cAMP, 0.5 mM) and forskolin. ET-1 significantly inhibited this effect of FSH, but not the effects of 8Br-cAMP and forskolin. Progesterone production decreased commensurately with this inhibitory action of ET-1 on the FSH-stimulated accumulation P450scc mRNA. The PKC activator, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), suppressed steroidogenesis stimulated by forskolin and 8Br-cAMP as well as FSH. In conclusion, ET-1 inhibited FSH-stimulated cAMP accumulation, P450scc expression, and progesterone production in porcine granulosa cell cultures. The data are compatible with pre-adenylate cyclase site of action. Although ET-1 activated PKC, TPA, unlike ET-1, seems to inhibit steroidogenesis by interfering with cAMP action.
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PMID:Mechanisms underlying endothelin's inhibition of FSH-stimulated progesterone production by ovarian granulosa cells. 1061 35

This study was conducted to shed light on the so far unexplored intracellular mechanisms underlying negative modulation of Leydig cell steroidogenesis by histamine (HA). Using the MA-10 cell line and highly purified rat Leydig cells as experimental models, we examined the effect of the amine on biochemical steps known to be modulated by HA or involved in LH/hCG action. In agreement with previous findings, HA at 10 microM showed a potent inhibitory effect on hCG-stimulated steroid synthesis, regardless of the gonadotropin concentration used. Moreover, HA decreased not only LH/hCG-induced cAMP production but also steroid synthesis stimulated by the permeable cAMP analog dibutyryl cAMP (db-cAMP). Considering the post-cAMP sites of HA action, it is shown herein that HA markedly inhibited db-cAMP-stimulated steroidogenic acute regulatory (STAR) protein expression, as well as steps catalyzed by P450-dependent enzymes, mainly the conversion of cholesterol to pregnenolone by cholesterol side-chain cleavage enzyme (CYP11A). The antisteroidogenic action of HA was blocked by addition of the phospholipase C (PLC) inhibitor U73122, and HA significantly augmented inositol triphosphate (IP3) production, suggesting a major role for the PLC/IP3 pathway in HA-induced inhibition of Leydig cell function. Finally, HA increased nitric oxide synthase (NOS) activity, and the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) markedly attenuated the effect of the amine on steroid synthesis. On the basis of our findings, HA antagonizes the gonadotropin action in Leydig cells at steps before and after cAMP formation. NOS activation is the main intracellular mechanism by which HA exerts its antisteroidogenic effects.
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PMID:Involvement of nitric oxide synthase in the mechanism of histamine-induced inhibition of Leydig cell steroidogenesis via histamine receptor subtypes in Sprague-Dawley rats. 1876 16