Effect of protein kinase C modulation on gonadotrophin-induced granulosa cell steroidogenesis

PKC-βII is downregulated in the premature ovarian failure SD rat model

We investigated the role of protein kinase c (PKC) -α and -β during the ovarian follicular dynamics using estrous cycle, gonadotropin-induced ovulation, and antral follicle culture, 4-vinylcyclohexene diepoxide (VCD)-induced premature ovarian failure (POF) in the SD rat models. We found the higher activity of PKC during the proestrus stage along with expression of PKC-α during the estrus and metestrus stages of the estrous cycle while PKC-β expression was increased during the diestrus, proestrus, and estrus stages. In response to pregnant mare gonadotropin (PMSG)-induced follicular recruitment and ovulation, the phosphorylated (Thr-642) PKC-β was increased. PKC activity inhibition by hispidin during the proestrus stage resulted in decreased antral follicles and corpus luteum. Treatment with hispidin resulted in the downregulation of granulosa cell (GC) biomarker, follicle stimulating hormone receptor (FSHR) expression in the cultured pre-antral follicle. During the forskolin-induced luteinization of human granulosa cells, the expression level of PKC-α and β (I and II) was decreased. In the POF condition, the activity of total PKC and the expression levels of PKC-α and β (I and II) were increased. Immunostaining depicted ubiquitous expression of PKC-α in the ovary during the estrous cycle and POF conditions. Taken together, we conclude the association of PKC-α and -β (I and II) during ovarian follicular dynamics where the expression level of PKC-α is increased, but the expression level of PKC-β (I and II) is suppressed in the POF condition in the SD rat model.

Physiological and pathological functions of sphingolipids in pregnancy

Signaling by the bioactive sphingolipid, sphingosine 1-phosphate (S1P), and its precursors are emerging areas in pregnancy research. S1P and ceramide levels increase towards end of gestation, suggesting a physiological role in parturition. However, high levels of circulating S1P and ceramide are correlated with pregnancy disorders such as preeclampsia, gestational diabetes mellitus and intrauterine growth restriction. Expression of placental and decidual enzymes that metabolize S1P and S1P receptors are also dysregulated during pregnancy complications. In this review, we provide an in-depth examination of the signaling mechanism of S1P and ceramide in various reproductive tissues during gestation. These factors determine implantation and early pregnancy success by modulating corpus luteum function from progesterone production to luteolysis through to apoptosis. We also highlight the role of S1P through receptor signaling in inducing decidualization and angiogenesis in the decidua, as well as regulating extravillous trophoblast migration to anchor the placenta into the uterine wall. Recent advances on the role of the S1P:ceramide rheostat in controlling the fate of villous trophoblasts and the role of S1P as a negative regulator of trophoblast syncytialization to a multinucleated placental barrier are discussed. This review also explores the role of S1P in anti-inflammatory and pro-inflammatory signaling, its role as a vasoconstrictor, and the effects of S1P metabolizing enzymes and receptors in pregnancy.

The activity of human aquaporin 1 as a cGMP-gated cation channel is regulated by tyrosine phosphorylation in the carboxyl-terminal domain

In addition to a constitutive water channel activity, several studies suggest Aquaporin-1 (AQP1) functions as a nonselective monovalent cation channel activated by intracellular cGMP, although variability in responsiveness between preparations has led to controversy in the field. Data here support the hypothesis that responsiveness of the AQP1 ionic conductance to cGMP is governed by tyrosine phosphorylation. Wild-type and mutant human AQP1 channels expressed in Xenopus laevis oocytes were characterized by two-electrode voltage clamp and optical osmotic swelling analyses. Quadruple mutation by site-directed mutagenesis of barrier hydrophobic residues (Val50, Leu54, Leu170, Leu174) to alanines in the central pore induced inward rectification of the ionic current and shifted reversal potential by approximately +10 mV, indicating increased permeability of tetraethylammonium ion. Introduction of cysteine at lysine 51 in the central pore (K51C) in a cysteine-less template created new sensitivity to block of the conductance by mercuric ion. Mutations of candidate consensus sites and pharmacological manipulation of serine and threonine phosphorylation did not alter cGMP-dependent responses; however, mutation of tyrosine Y253C or pharmacological dephosphorylation prevented ion channel activation. Modification of Y253C by covalent addition of a negatively charged group [2-sulfonatoethyl methanethiosulfonate sodium salt (MTSES)] rescued the cGMP-activated conductance response, an effect reversed by dithiothreitol. Results support the proposal that phosphorylation of tyrosine Tyr253 in the carboxyl terminal domain, confirmed by Western blot, acts as a master switch regulating responsiveness of AQP1 ion channels to cGMP, and the tetrameric central pore is the ion permeation pathway. These findings advance resolution of a standing controversy and expand our understanding of AQP1 as a multifunctional regulated channel.

Downregulation of progesterone biosynthesis in rat granulosa cells by adlay (Coix lachryma-jobi L. var. ma-yuen Stapf.) bran extracts

Adlay (Coix lachryma-jobi L. var. ma-yuen Stapf.) has long been used as a traditional Chinese medicine for dysfunctions of the endocrine system and inflammation conditions. However, the effect of adlay seed on the endocrine system has not yet been reported. In the present study, the effects and the mechanisms of methanolic extract of adlay bran (ABM) on progesterone synthesis in rat granulosa cell were studied. ABM was further partitioned with different solvents including water, 1-butanol, ethyl acetate and n-hexane. Four subfractions named ABM-Wa (water fraction), ABM-Bu (1-butanol fraction), ABM-EA (ethyl acetate fraction) and ABM-Hex (n-hexane fraction) were obtained. ABM-Bu was further fractionated using Diaion HP-20 resin column chromatography with gradient elution. Granulosa cells were prepared from pregnant mare serum gonadotropin-primed immature female rats and challenged with different reagents including human chorionic gonadotropin (hCG 0.5 IU/ml), forskolin (10 microM), 8-bromo-adenosine-3',5'-cyclic monophosphate (8-Br-cAMP, 1 mM), A23187 (10 microM), phorbol 12-myristate 13-acetate (PMA, 0.01 microM), 25-OH-cholesterol (0.1-10 microM) and pregnenolone (0.1-10 microM) in the presence or absence of ABM-Bu (100 microg/ml). The functions of steroidogenic enzyme including protein expression of the steroidogenic acute regulatory protein (StAR) and cytochrome P450 side-chain cleavage enzyme (P450scc) protein were investigated. Expressions of both P450scc and StAR mRNA have also been explored. We found that ABM decreased progesterone production via an inhibition on (1) the cAMP-PKA and PKC signal transduction pathway, (2) P450scc and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) enzyme activity, (3) P450scc and StAR protein and mRNA expressions and (4) the phosphorylation of ERK1/2 in rat granulosa cells.

Regulation of granulosa cell-derived insulin-like growth factor binding proteins (IGFBPs): role for protein kinase-C in the pre- and posttranslational modulation of IGFBP-4 and IGFBP-5

A growing body of information suggests antigonadotropic and atretogenic roles for granulosa cell-derived insulin-like growth factor binding proteins (IGFBPs) 4 and 5 during ovarian folliculogenesis. Activation of protein kinase-A (PKA) in rat granulosa cells has been shown to modulate the relative expression of IGFBP-4 and -5 transcripts and proteins. In this article, we assess the role of protein kinase-C (PKC) in this regard. Provision of granulosa cells with phorbol 12-myristate 13-acetate (PMA) (but not 4alphaPMA, an inert analogue), a tumor-promoting phorbol ester and an established activator of PKC, was without significant effect on the expression of IGFBP-4 transcripts but resulted in biphasic dose-dependent alterations in IGFBP-5 transcripts and in the accumulation of the IGFBP-4 and -5 proteins. Comparable effects were noted for GnRH, an established PKC agonist. Provision of staurosporine, a potent inhibitor of the catalytic subunit of PKC, produced significant dose-dependent decrements in the relative expression of IGFBP-5 transcripts. Treatment with FSH (presumptively PKA-mediated) markedly attenuated the ability of PMA or GnRH to upregulate the accumulation of the IGFBP-5 (but not IGFBP-4) protein. Taken together, our present findings indicate that the modulation of rat ovarian IGFBP-4 and -5 is PKC as well as PKA dependent and that these two signaling pathways interact in a diametrically opposed and antagonistic fashion.

Cytokine regulation of the expression of estrogenic biosynthetic enzymes in cultured rat granulosa cells

Both P450 aromatase (P450arom) and 17beta-hydroxysteroid dehydrogenase (17HSD) type 1 are key enzymes in the ovarian E(2) biosynthesis. Cytokines have been suggested to be mediators between the immune and the reproductive systems, and they may play a role as paracrine or autocrine ovarian regulatory factors. Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) have been shown to modulate the FSH-induced E(2) production in immature rat granulosa cells. The aim of the present study was to investigate the effects of these cytokines on the activity and expression of the 17HSD type 1 enzyme in cultured undifferentiated granulosa cells. Furthermore, the expression of P450arom was also analyzed. The granulosa cells obtained from the ovaries of immature DES-treated rats were initially cultured for 48 h with no other treatment and then incubated with or without the test reagents for an additional 48 h. The treatment of the granulosa cells with cytokines alone did not affect the activity of 17HSD type 1 as assessed by the conversion of tritiated substrate. However, both TNFalpha and IL-1beta caused a dose-dependent inhibition of the recombinant FSH-induced enzyme activity and the Forskoline-induced expression of 17HSD type 1 and P450arom mRNAs. The cytokines only slightly inhibited the 8-Br-cAMP-induced P450arom expression. In contrast, the inhibitory cytokine effects on 17HSD type 1 expression and activity were not abolished by the presence of 8-Br-cAMP. Despite the presence of inhibitors of protein kinase C (staurosporine) or tyrosine kinases (genistein), the inhibitory effects of TNFalpha and IL-1beta on the Forskoline-induced expression of 17HSD type 1 and P450arom and the Forskoline-induced 17HSD activity were not blocked. The data show a dose dependent inhibitory effect of TNFalpha and IL-1beta on gonadotropin action, opposite to the follicular development by down-regulating the expressions of estrogen biosynthetic enzymes. The cytokine effects on P450arom expression are mainly derived from a decrease in gonadotropin-induced cAMP production, while the inhibitory mechanisms on 17HSD type 1 expression involve distal sites from cAMP generation. The protein kinase C and tyrosine kinase pathways are likely not to be involved in the latter mechanisms.

G protein-coupled receptors as targets for prolactin actions

Prolactin (PRL) is known to be involved in a wide range of biological functions including osmoregulation, lactation, reproduction, and immunomodulation. The first step in PRL action involves its interaction with a specific membrane receptor that belongs to the cytokine receptor superfamily. In spite of the lack of a kinase domain, receptors of the cytokine superfamily induce tyrosine phosphorylation of cellular substrates including the receptors. The role of PRL in female reproductive functions is well known and a direct effect on ovarian and testicular steroidogenesis has been established. In the ovary, PRL binds to a specific membrane receptor and exerts an inhibitory effect on follicular steroidogenesis. This effect is the result of an impairment involving FSH stimulation of G protein-coupled receptors (GPCR) and cyclic AMP-mediated activation of aromatase cytochrome P450 gene expression. This observation may indicate a direct connection between tyrosine phosphorylation and follicle-stimulating hormone (FSH) receptor (FSHR) transduction pathways, as is the case for growth factor receptors with intrinsic tyrosine kinase activity, which share several downstream signaling elements with GPCRs. Some studies leading to our understanding of these pathways are reviewed.

Growth factors and phorbol-12-myristate-13-acetate modulate the follicle-stimulating hormone- and cyclic adenosine-3',5'-monophosphate-dependent regulation of 17beta-hydroxysteroid dehydrogenase type 1 expression in rat granulosa cells

In the present study primary cultures of rat granulosa cells obtained from diethylstilbestrol (DES)-primed immature rats were used to study the regulation of 17beta-hydroxysteroid dehydrogenase (17HSD) activity and type 1 expression via protein kinase A (PKA)- and C (PKC)-dependent pathways, and by several autocrine and/or paracrine growth factors. Follicle-stimulating hormone (FSH), 8-bromo-cyclic adenosine-3',5'-monophosphate (8-Br-cAMP) and transforming growth factor beta1 (TGFbeta1) strongly enhanced 17HSD activity and type 1 expression. The stimulatory effects of FSH and 8-Br-cAMP were further potentiated by TGFbeta1. In contrast, neither phorbol-12-myristate-13-acetate (PMA), epidermal growth factor (EGF), transforming growth factor alpha (TGFalpha) nor fibroblast growth factor (bFGF) affected 17HSD activity or type 1 expression when given alone. However, they effectively neutralized the stimulatory effects of 8-Br-cAMP and FSH. The present data suggest that, in rat granulosa cells 17HSD type 1 expression is primarily induced by FSH acting via PKA-dependent pathway and the extent of the induction is modulated by PKC-dependent inhibition and autocrine/paracrine growth factors present in the ovary.

Differential responses of post-natal rat ovarian cells to FSH and activin

A role for activin in the acquisition of gonadotropin responsiveness by the post-natal rat ovary was investigated. The inhibin/activin subunits in terms of protein and mRNA, were localised in granulosa cells of the rat ovary at days 4, 8 and 12 after birth. A characteristic pattern of responses to FSH for inhibin and progesterone (P) production was established using a dispersed ovarian cell bioassay. P production by day 4, 8 and 12 cultures was stimulated by FSH, but only when iso-butyl-methyl-xanthine (MIX) was present. In contrast, a basal level of inhibin production was measured in day 4 cultures which was not responsive to FSH or MIX. In day 8 and 12 cultures, inhibin production was FSH-responsive, but only in the absence of MIX. The addition of activin to cultures of day 4, 8 and 12 ovarian cells induced FSH-responsive P production and stimulated both basal and FSH-stimulated inhibin production. These studies indicate a differential response of neonatal ovarian cells to FSH in terms of P and inhibin production. Activin may play a role in facilitating the effects of FSH on signal transduction pathways leading to inhibin and steroid production and therefore be part of the mechanism which determines responsiveness of granulosa cells to FSH.