Effects of selective protein kinase c isozymes in prostaglandin2alpha-induced Ca2+ signaling and luteinizing hormone-induced progesterone accumulation in the mid-phase bovine corpus luteum

Influence of omega-3 polyunsaturated fatty acids from fish oil or meal on the structure of lipid microdomains in bovine luteal cells

Biological membranes are composed of a lipid bilayer and proteins that form lipid microdomains. This study examined the effects of fish byproducts on lipid-protein interactions within lipid microdomains of bovine luteal cells. In Exp. 1 and 2, luteal cells were prepared from corpora lutea (CL; n = 4 to 8) collected at an abattoir. Exp. 1 was conducted to optimize ultrasonication in a detergent-free protocol for isolation of lipid microdomains. A power setting of 10 to 20% was effective in isolating lipid microdomains from bulk lipid. In Exp. 2, cells were cultured in control medium or fish oil to determine influence of fish oil on distribution of lipid microdomain markers and prostaglandin F_2α (FP) receptors. Cells treated with fish oil had a smaller percentage of microdomain markers and FP receptor in microdomains (P < 0.05). In Exp. 3 and 4, cells were prepared from mid-cycle CL obtained from cows supplemented with corn gluten meal (n = 4) or fish meal (n = 4). Exp. 3 examined effects of dietary supplementation on distribution of lipid microdomain markers and FP receptor and Exp. 4 on fatty acid composition within lipid microdomains. A smaller percentage of lipid microdomain markers and FP receptor was detected in microdomains of cells collected from fish meal supplemented animals (P < 0.05). In Exp. 4, a greater percentage of omega-3 polyunsaturated fatty acids was detected in bulk lipid from fish meal supplemented cows (P < 0.05). Results show that fish byproducts influence lipid-protein interactions in lipid microdomains in bovine luteal cells.

The prostaglandin E2 receptor PTGER2 and prostaglandin F2α receptor PTGFR mediate oviductal glycoprotein 1 expression in bovine oviductal epithelial cells

Oviductal glycoprotein 1 (OVGP1), an oviductin, is involved in the maintenance of sperm viability and motility and contributes to sperm capacitation in the oviduct. In this study, the regulatory effects exerted by prostaglandin E₂ (PGE₂) and F_2α (PGF_2α) on OVGP1 expression via their corresponding receptors in bovine oviductal epithelial cells (BOECs) were investigated. BOECs were cultured in vitro, and their expression of receptors of PGE₂ (PTGER1, PTGER2, PTGER3, and PTGER4) and PGF_2α (PTGFR) was measured using RT-qPCR. Ca²⁺ concentration was determined with a fluorescence-based method and cAMP was quantified by enzyme-linked immunosorbent assays to verify activation of PTGER2 and PTGFR by their corresponding agonists in these cells. OVGP1 mRNA and protein expression was measured using RT-qPCR and western blotting, respectively, following PTGER2 and PTGFR agonist-induced activation. PTGER1, PTGER2, PTGER4, and PTGFR were found to be present in BOECs; however, PTGER3 expression was not detected. OVGP1 expression was significantly promoted by 10^–6 M butaprost (a PTGER2 agonist) and decreased by 10^–6 M fluprostenol (a PTGFR agonist). In addition, 3 μM H-89 (a PKA inhibitor) and 3 μM U0126 (an ERK inhibitor) effectively inhibited PGE₂-induced upregulation of OVGP1, and 5 μM chelerythrine chloride (a PKC inhibitor) and 3 μM U0126 negated OVGP1 downregulation by PGF_2α. In conclusion, this study demonstrates that OVGP1 expression in BOECs is enhanced by PGE₂ via PTGER2-cAMP-PKA signaling, and reduced by PGF_2α through the PTGFR-Ca²⁺-PKC pathway.

Activation of Adenosine Monophosphate-Activated Protein Kinase Is an Additional Mechanism That Participates in Mediating Inhibitory Actions of Prostaglandin F2Alpha in Mature, but Not Developing, Bovine Corpora Lutea

Elevated cytosolic calcium and protein kinase C are well-established mediators of luteolytic actions of prostaglandin F2alpha (PGF2alpha). The objectives of this study were to determine 1) if calcium/calmodulin-dependent kinase kinase 2 (CAMKK2) participates in mediating PGF2alpha actions in developing (Day [d]-4) and mature (d-10) bovine corpus luteum (CL), 2) distal targets of CAMKK2, 3) developmental expression of adenosine monophosphate-activated protein kinase (AMPK), and 4) effects of AMPK activation on progesterone (P4) production. Expression of AMPK increased as the CL matured. Activation of the prostaglandin receptor (FP) induced rapid phosphorylation of AMPK, which was blocked by a CAMKK2 inhibitor. Changes in basal P4 secretion in vitro were determined in response to AMPK activation via metformin (met) or 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) in d-4 and d-10 CL. Production of P4 in d-10 CL decreased with met or AICAR compared to control, similar to activation by PGF2alpha. Therefore, potential distal targets of AMPK in d-10 CL were examined during induced functional regression via exogenous PGF2alpha. Serum and luteal P4 decreased at 2 and 4 h after administration of PGF2alpha. Protein expression of LDLR decreased at 2 and 4 h, while those of ACAT1 and STAR increased 4 h after PGF2alpha. During induced regression, alterations of cholesterol transport proteins contributed to decreased luteal and serum P4. Therefore, developmental differences in signal transduction associated with FP, specifically CAMKK2 and AMPK, partially contribute to differences in the ability of PGF2alpha to induce regression in mature, but not developing, bovine CL. Multiple cholesterol transport proteins, including LDLR, were altered by PGF2alpha and could be potential AMPK targets.

Protein kinase C isoforms α, δ and ε are differentially expressed in mouse ovaries at different stages of postnatal development

Background

The protein kinase C (PKC) is a family of serine/threonine kinases that consists of 12 different isoforms. Since PKC isoform expressions are known to be specific for different cell types and postnatal developmental stages, we aimed to determine immunolocalizations and protein expression levels of different PKC isoforms in pre-pubertal, pubertal and adult mouse ovaries.

Methods

Ovaries were obtained from postnatal day 1 (PND1) and PND7 of pre-pubertal, PND21 of pubertal and PND60 of adult mice. Immunolocalizations of PKCα, PKCδ and PKCε isoforms were determined and immunostainings in different cellular components of all follicular stages were evaluated by H-Score. PKCα, PKCδ and PKCε protein expression levels were determined by Western blot. The bands were quantified via ImageJ software. The data obtained from H-Score and ImageJ evaluations were analyzed by ANOVA statistical test.

Results

PKCα immunostainings were more intense in oocytes when compared to granulosa and theca cells at different follicular stages of all groups. The Western blot analysis revealed that PKCα expression was significantly higher in PND60 adult ovaries. Conversely, PKCδ immunostainings were more intense in granulosa cells. According to the Western blot analysis, PKCδ protein expression was also higher in PND60 and significantly lower in PND1 ovaries. PKCε immunostaining was more apparent in oocytes. PKCε protein expression was significantly higher in adult PND60 and pubertal PND21 ovaries when compared to pre-pubertal PND7 and PND1 ovaries. Interestingly, PKCε immunostaining was significantly higher in primordial follicles, though PKCα and PKCδ immunostainings were more apparent in larger follicles. PKCα immunostainings of corpora lutea (CL) were significantly higher when compared to follicles in PND60 ovaries.

Conclusions

This study demonstrates that PKCα, PKCδ and PKCε isoforms are differentially expressed in particular cellular components of pre-pubertal, pubertal and adult mouse ovarian follicles. Therefore, we suggest that each PKC isoform has unique functions that are controlled by gonadotropin dependent mechanisms during follicular growth, oocyte maturation, ovulation and luteinization.

Tumor necrosis factor-α inhibits the stimulatory effect of luteinizing hormone and prostaglandin E(2) on progesterone secretion by the bovine corpus luteum

Tumor necrosis factor-α (TNF-α) is involved in the tissue remodeling that occurs in the corpus luteum (CL) during its development and regression. This cytokine is also implicated in the regulation of reproduction by its actions on ovarian steroidogenic cells. The aim of this study was to examine the influence of TNF-α on (1) progesterone (P(4)) output by the bovine CL and on (2) the responsiveness of the CL to LH or prostaglandin E(2) (PGE(2)) in vitro. In experiment 1, CL (days 8 to 10 of the estrous cycle) were perfused by using an in vitro microdialysis system with TNF-α (0.1, 0.5, or 1 μg/mL) alone or with TNF-α (1 μg/mL) followed by LH (1000 ng/mL) or PGE(2) (2 × 10(-5) M). Basal P(4) release (P < 0.05) was increased by TNF-α (0.5 or 1 μg/mL). Moreover, TNF-α (1 μg/mL) inhibited the stimulatory effect of LH or PGE(2) on P(4) output (P < 0.05). In experiment 2, 4 h after intrauterine infusion of TNF-α (0.01 μg/mL or 1 μg/mL), CL (days 8 to 10 of the estrous cycle) were collected by colpotomy, cultured, and stimulated with LH (10 ng/mL) or PGE(2) (10(-6) M). Intrauterine infusion of TNF-α at a concentration of 1 μg/mL increased basal P(4) output by CL (P < 0.05). Moreover, the intrauterine infusion of TNF-α at a concentration of 0.01 μg/mL inhibited the stimulatory effect of LH or PGE(2) on P(4) output (P < 0.05). These results indicate that TNF-α (1) does not have an effect on the autonomous, pulsatile release of P(4); (2) increases P(4) secretion by bovine CL with increasing doses, and (3) reduces in a dose-dependent manner the responsiveness of CL to luteotropic factors both directly (after infusion to CL) and indirectly (after intrauterine infusion).

The involvement of specific PKC isoenzymes in phorbol ester-mediated regulation of steroidogenic acute regulatory protein expression and steroid synthesis in mouse Leydig cells

Protein kinase C (PKC) is a multigene family of serine/threonine kinases. PKC is involved in regulating adrenal and gonadal steroidogenesis; however, the functional relevance of the different PKC isoenzymes remains obscure. In this study, we demonstrate that MA-10 mouse Leydig tumor cells express several PKC isoforms to varying levels and that the activation of PKC signaling, by phorbol 12-myristate 13-acetate (PMA) elevated the expression and phosphorylation of PKCα, -δ, -ε, and -μ/protein kinase D (PKD). These responses coincided with the expression of the steroidogenic acute regulatory (StAR) protein and progesterone synthesis. Targeted silencing of PKCα, δ, and ε and PKD, using small interfering RNAs, resulted in deceases in basal and PMA-mediated StAR and steroid levels and demonstrated the importance of PKD in steroidogenesis. PKD was capable of controlling PMA and cAMP/PKA-mediated synergism involved in the steroidogenic response. Further studies pointed out that the regulatory events effected by PKD are associated with cAMP response element-binding protein (CREB) and c-Jun/c-Fos-mediated transcription of the StAR gene. Chromatin immunoprecipitation studies revealed that the activation of phosphorylated CREB, c-Jun, and c-Fos by PMA was correlated with in vivo protein-DNA interactions and the recruitment of CREB-binding protein, whereas knockdown of PKD suppressed the association of these factors with the StAR promoter. Ectopic expression of CREB-binding protein enhanced the trans-activation potential of CREB and c-Jun/c-Fos in StAR gene expression. Using EMSA, a -83/-67-bp region of the StAR promoter was shown to bind PKD-transfected MA-10 nuclear extract in a PMA-responsive manner, targeting CREB and c-Jun/c-Fos proteins. These findings provide evidence for the presence of multiple PKC isoforms and demonstrate the molecular events by which selective isozymes, especially PKD, influence PMA/PKC signaling involved in the regulation of the steroidogenic machinery in mouse Leydig cells.

Prostaglandin F2alpha represses IGF-I-stimulated IRS1/phosphatidylinositol-3-kinase/AKT signaling in the corpus luteum: role of ERK and P70 ribosomal S6 kinase

Little is known about the early intracellular events that contribute to corpus luteum regression. Experiments were designed to determine the effects of prostaglandin F2alpha (PGF2alpha) on phosphatidylinositol-3-kinase (PI3K)/Akt signaling in the corpus luteum in vivo and in vitro. Treatment of midluteal-phase cows with a luteolytic dose of PGF2alpha resulted in a rapid increase in ERK and mammalian target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase (p70S6K1) signaling and a rapid suppression of Akt phosphorylation in luteal tissue. In vitro treatment of primary cultures of luteal cells with PGF2alpha also resulted in an increase in ERK and mTOR/p70S6K1 signaling and a diminished capacity of IGF-I to stimulate PI3K, Akt, and protein kinase C zeta activation. Accounting for the reductions in PI3K and Akt activation observed in response to PGF2alpha treatment, we found that PGF2alpha promoted the phosphorylation of serine residues (307, 612, 636) in the insulin receptor substrate 1 (IRS1) peptide sequence in vivo and in vitro. Serine phosphorylation of IRS1 was associated with reduced formation of IGF-I-stimulated IRS1/PI3Kp85 complexes. Furthermore, treatment with inhibitors of the MAPK kinase 1/ERK or mTOR/p70S6K1 signaling pathways prevented PGF2alpha-induced serine phosphorylation of IRS1 and abrogated the inhibitory actions of PGF2alpha on Akt activation. Taken together, these experiments provide compelling evidence that PGF2alpha treatment stimulates IRS1 serine phosphorylation, which may contribute to a diminished capacity to respond to IGF-I. It seems likely that the rapid changes in phosphorylation events are among the early events that mediate PGF2alpha-induced corpus luteum regression.

Protein kinase C isoforms in the porcine corpus luteum: temporal and spatial expression patterns

Porcine corpora lutea (CL) fail to show a luteolytic response to prostaglandin-F-2alpha (PGF-2alpha) (ie, luteolytic sensitivity, or LS) until approximately day 13 of the estrous cycle. In view of the importance of protein kinase C (PRKC) in PGF-2alpha signal transduction, it was hypothesized that limiting levels of 1 or more PRKC isoforms may explain the lack of LS before day 13. This hypothesis was tested by examining expression of mRNA and protein, and the cellular localization patterns of the 11 PRKC isoforms throughout the porcine estrous cycle, to determine whether PRKC expression correlates with and thus may be associated with the control of the acquisition of LS in the pig. The expression patterns show that for most PRKC isoforms (ie, PRKC alpha, beta 1, beta 2, delta, epsilon, theta, iota, and zeta), mRNA was maximally expressed on day 7 or day 10 (protein kinase D1 only) of the cycle, whereas PRKCs gamma, eta, and lambda were unchanged. At the protein level, only PRKC epsilon (PRKCE) significantly changed during the estrous cycle and was elevated on day 13 (versus days 4, 7, and 15; P<0.05). By immunofluoresence, most PRKC isoforms, including PRKCE, were localized to steroidogenic large luteal cells (LLC) and small (nonendothelial cell) luteal cell subtypes (SLC). In conclusion, since the increase in PRKCE protein expression (day 13) occurred coincidentally with the onset of LS (> or =day 12), these results support a potential role for PRKCE in control of the acquisition of LS in the pig.

Differential gene expression in the bovine corpus luteum during transition from early phase to midphase and its potential role in acquisition of luteolytic sensitivity to prostaglandin F2 alpha

Prostaglandin F2 alpha (PGF(2alpha)) brings about regression of the bovine corpus luteum (CL). This luteolytic property of PGF(2alpha) is used in beef and dairy cattle to synchronize estrus. A limitation of this protocol is insensitivity of the early CL to luteolytic actions of PGF(2alpha). The mechanisms underlying this differential luteal sensitivity are poorly understood. The developing CL has a maximum number of PGF(2alpha) receptors; therefore, differences in signaling events may be responsible for luteal insensitivity. Hence, differential gene expression at two developmental stages of CL, Day 4 (D-4) and D-10 after estrus, might account for differences in signal transduction pathways associated with luteal sensitivity. This possibility was examined in these studies. Microarray analysis (n = 3 cows per stage) identified 167 genes that were differentially expressed (P < 0.05). These were categorized into genes involved in protein biosynthesis and modification (18.5%), transcription regulation and DNA biosynthesis (18.5%), miscellaneous (17.0%), cell signaling (12.0%), steroidogenesis and metabolism (10.2%), extracellular matrix and cytoskeletal proteins (9.5%), unknown functions (6.0%), protein degradation (5.3%), and antioxidant property (3.0%). Real-time PCR confirmed the differential expression of nine selected genes, including tyrosine 3-monooxygenase/tryptophan 5-monooxygense activation protein zeta polypeptide (YWHAZ) and regulator of G protein signaling 2 24-kDa (RGS2), observed in microarray. Furthermore, the in vivo effect of exogenous PGF(2alpha) (n = 3 cows per stage) on selected genes that were found to be differentially expressed during this developmental transition was examined. PGF(2alpha) increased the expression of a guanine nucleotide-binding protein (G protein) beta polypeptide 1 (GNB1) in D-4 CL and calcium/calmodulin-dependent kinase kinase 2 beta (CAMKK2) in D-10 CL. Therefore, GNB1, CAMKK2, YWHAZ, and RGS2 are candidate genes that may have a significant role in acquisition of luteal sensitivity to PGF(2alpha). Additional evidence supporting the significance of the microarray data was obtained from the observation that the amount of CAMKK2 paralleled the differential mRNA expression observed for this gene when examined by microarray analysis and by real-time RT-PCR. Furthermore, the two types of luteal steroidogenic cells known to be targets for PGF(2alpha) actions were demonstrated to be a cellular source for CAMKK2.

Cocaine- and amphetamine-regulated transcript accelerates termination of follicle-stimulating hormone-induced extracellularly regulated kinase 1/2 and Akt activation by regulating the expression and degradation of specific mitogen-activated protein kinase phosphatases in bovine granulosa cells

Pleiotropic actions of cocaine- and amphetamine-regulated transcript (CART) are well described in the central nervous system and periphery, but the intracellular mechanisms mediating biological actions of CART are poorly understood. Although CART is not expressed in mouse ovaries, we have previously established CART as a novel intracellular regulator of estradiol production in bovine granulosa cells. We demonstrated that inhibitory actions of CART on estradiol production are mediated through inhibition of FSH-induced cAMP accumulation, Ca(2+) influx, and aromatase mRNA expression via a G(o/i)-dependent pathway. We also reported that FSH-induced estradiol production is dependent on Erk1/2 and Akt signaling, and CART may regulate other signaling proteins downstream of cAMP essential for estradiol production. Here, we demonstrate that CART is a potent inhibitor of FSH-stimulated Erk1/2 and Akt signaling and the mechanisms involved. Transient CART stimulation of bovine granulosa cells shortens the duration of FSH-induced Erk1/2 and Akt signaling whereas a prolonged (24 h) CART treatment blocks Erk1/2 and Akt activation in response to FSH. This CART-induced accelerated termination of Erk1/2 and Akt signaling is mediated both by induced expression and impaired ubiquitin-mediated proteasome degradation of dual specific phosphatase 5 (DUSP5) and protein phosphatase 2A. Results also support existence of a negative feedback loop in which CART via a G(o/i)-MAPK kinase dependent pathway activates Erk1/2, and the latter induces DUSP5 expression. Moreover, small interfering RNA mediated ablation of DUSP5 and/or protein phosphatase 2A prevents the CART-induced early termination of Erk1/2 and Akt signaling. Results provide novel insight into the intracellular mechanism of action of CART in regulation of FSH-induced MAPK signaling.

Luteolytic effect of prostaglandin F 2 alpha on bovine corpus luteum depends on cell composition and contact

Prostaglandin F(2 alpha) (PGF(2 alpha)) is a main luteolytic factor in vivo; however, its direct luteolytic influence on steroidogenic cells of bovine corpus luteum (CL) is controversial and not fully understood. The aim of the study was to clarify PGF(2 alpha) action on bovine CL in different in vivo and in vitro conditions and to examine whether the contact among all main types of CL cells is necessary for luteolytic PGF(2 alpha) action. In experiment 1, the bovine CL (day 15 of the oestrous cycle) was perfused using in vivo microdialysis system with dinoprost (an analogue of PGF(2 alpha)) for 0.5 h. Dinoprost caused a short-time increase in progesterone (P4), whose concentration decreased thereafter (at 6-, 10-, 12- and 24-h after treatment). In experiment 2, the direct effect of PGF(2 alpha) on P4 accumulation in CL steroidogenic cells cultured in monolayer (day 15 of the cycle) was determined. PGF(2 alpha) after 24 h of incubation increased P4 accumulation in steroidogenic CL cells. In experiment 3 steroidogenic, endothelial CL and immune cells (day 15 of the cycle) were incubated with PGF(2 alpha) in cocultures for 24 h in glass tubes and the levels of P4, stable metabolites of nitric oxide (NO) and leukotriene (LT) C(4) were determined. Although PGF(2 alpha) treatment increased P4 secretion in homogeneous steroidogenic CL cell culture, the decrease in P4 secretion in cocultures of all types of CL cells was observed. The secretion of NO and LTC(4) increased after the treatment of PGF(2 alpha) both in pure cultures of CL cells and in cocultures. The interactions between endothelial and immune cells with steroidogenic CL cells are needed for luteolytic PGF(2 alpha) action within the bovine CL. Our results indicate that the cell coculture model, including the main types of CL cells, is the most approximate to study PGF(2 alpha) role in vitro.

Cocaine- and amphetamine-regulated transcript regulation of follicle-stimulating hormone signal transduction in bovine granulosa cells

Regulation of estradiol production, central to ovarian follicular development and reproductive function, is mediated by a complex interaction of pituitary gonadotropins such as FSH with locally produced regulatory molecules. We previously demonstrated a negative association of expression of cocaine-and amphetamine-regulated transcript (CART) with follicle health status and a novel local negative role for CART in regulation of basal estradiol production by bovine granulosa cells. However, effects of CART on FSH-induced estradiol production and the underlying mechanism(s) mediating the physiological actions of CART on granulosa cells are not known. Objectives of the present study were to determine effects of CART on basal and FSH-induced intracellular cAMP levels, aromatase mRNA, estradiol accumulation, calcium signaling, and the intracellular signaling pathways involved using primary cultures of bovine granulosa cells. CART treatment potently inhibits the FSH-induced rise in granulosa cell cAMP levels, estradiol accumulation, and aromatase mRNA. Furthermore, results show that calcium is essential for FSH-induced cAMP and estradiol accumulation, and CART significantly inhibits FSH-induced calcium influx. Select G protein and protein kinase inhibitors were used to elucidate pathways involved in CART actions. The inhibitory actions of CART on FSH signaling and estradiol production are mediated via a G(o/i)-dependent pathway, whereas none of the other signaling inhibitors had any effect on CART actions. Results demonstrate novel potent inhibitory effects of CART on multiple components of the FSH signaling pathway linked to estradiol production and follicular development and shed new insight into the mechanism of action of CART potentially pertinent within and beyond the reproductive system.

PKC epsilon and an increase in intracellular calcium concentration are necessary for PGF2 alpha to inhibit LH-stimulated progesterone secretion in cultured bovine steroidogenic luteal cells

The hypotheses that PKC epsilon is necessary for: 1) PGF2 alpha to inhibit LH-stimulated progesterone (P4) secretion, and 2) for the expression of key prostaglandin synthesizing/metabolizing enzymes were tested in bovine luteal cells in which PKC epsilon expression had been ablated using a validated siRNA protocol. Steroidogenic cells from Day -6 bovine corpus luteum (CL) were isolated and transfected to reduce PKC epsilon expression after 48, 72 and 96 h. A third tested hypothesis was that an increase in intracellular calcium concentration ([Ca(2+)]i) is the cellular mechanism through which PGF2 alpha inhibits luteal progesterone. The hypothesis was tested with two pharmacological agents. In the first test, the dose-dependent effects on raising the [Ca(2+)]i with the ionophore, A23187, on basal and LH-stimulated P4 secretion in cells collected from early (Day -4) and mid-cycle (Day -10) bovine CL was examined. In the second test, the ability of PGF2 alpha to inhibit LH-stimulated P4 secretion in Day-10 luteal cells was examined under conditions in which an elevation in [Ca(2+)]i had been buffered by means of the intracellular calcium chelator, Bapta-AM.PKC epsilon expression was reduced 65 and 75% by 72 and 96 h after transfection, respectively. In cells in which PKC epsilon expression was ablated by 75%, the inhibitory effect of PGF2 alpha on LH-stimulated P4 secretion was only 29% lower than in the LH-stimulated group. In contrast, it was reduced by 75% in the group where PKC epsilon expression had not been reduced (P < 0.05). Real time PCR analysis indicated that there were no differences in the expression of cyclooxygenase-2 (COX-2), aldoketoreductase 1B5 (AKR1B5), prostaglandin E synthase (PGES), hydroxyprostaglandin-15 dehydrogenase (PGDH) and PGE2 -9-reductase as a function of PKC epsilon down-regulation. Finally, LH stimulated secretion of P4 at each luteal stage (Day -4 and -10), and PGF2 alpha inhibited this only in Day -10 cells (P < 0.05). When A23187 was used at concentrations greater than 0.1 mumol, the induced elevation in [Ca(2+)]i inhibited the effect of LH on secretion of P4 in Day -4 and -10 cells (P < 0.05, Fig. 5). The inhibitory effect of PGF2 alpha on LH-stimulated P4 in Day -10 cells was reduced if an increase in [Ca(2+)]i was prevented with Bapta-AM. These results support the hypothesis that differential expression of PKC epsilon and an elevation of [Ca(2+)]i are important for acquisition of luteolytic response to PGF2 alpha.

Participation of specific PKC isozymes in the inhibitory effect of ET-1 on progesterone accumulation in cells isolated from early- and mid-phase corpora lutea

Expression of PKC alpha, beta I, beta II, epsilon and micro has been demonstrated in the whole bovine CL with PKC epsilon being differentially expressed as a function of development. In experiment 1 we have investigated the amount of mRNA encoding PKC epsilon at different stages of luteal development (days 1, 4, 10 and 17). In experiment 2, the cellular source of luteal PKC isozymes was determined. Enriched steroidogenic (SC) and endothelial (EC) cells from day-10 CL were used to examine this question by Western blot analysis and immuno-histochemistry. In experiment 3, Western blot analysis was used to examine the ability of ET-1 to activate luteal PKC isozymes in day-10 CL. In experiment 4, the role of luteal PKC isozymes in the ET-1 mediated inhibition of P(4) accumulation in steroidogenic cell cultures from day-4 and day-10 CL was examined. Abundance of PKC epsilon mRNA gradually increased from day-1 to -10 with no further increase on day-17. In experiment 2, PKC epsilon was exclusively detected in SC (LLC and SLC). In contrast, PKC alpha, beta I and beta II were detected in both SC and EC, with EC expressing higher amounts of PKC isozymes. In day-10 CL, ET-1 induced cellular redistribution of PKC alpha, beta I, epsilon but not beta II. Inhibitors specific for conventional PKC isozymes as well as PKC epsilon were able to negate the inhibitory effects of ET-1 on P4 accumulation in the day 10 CL. In the day-4 CL, the inhibitory effect of ET-1 might be mediated via conventional PKC. Thus, an exclusive presence of PKC epsilon in luteal steroidogenic cells, its higher expression along with the ability of ET-1 to stimulate its activation in day-10 CL strongly suggests that this PKC isoform may play an important regulatory role in decreasing P(4) during luteal regression. Inhibition of P(4) by ET-1 in the early CL may be mediated via conventional PKC isozymes.

Prostaglandin involvement in follicle-stimulating hormone-induced proliferation of granulosa cells from chicken prehierarchical follicles

The aim of the present study was to evaluate the role of prostaglandin (PG) on proliferation of granulosa cells from prehierarchical small yellow follicles (SYF) of buff laying hens. The granulosa layers were separated by mechanic method and dispersed into single cells. After 16 h pre-incubation in 0.5% FCS medium, the medium was replaced with serum-free medium, which was supplemented with 10 microg/ml insulin, 5 microg/ml transferrin and 3 x 10(-8)M selenite. Cells were challenged with PGE1 and FSH for 24 h and then assessed for proliferation. The results showed that PGE(1) (0.1-10 ng/ml) had a similar proliferating effect as FSH on granulosa cells, and these stimulating effects were restrained by the PGE receptor antagonist SC19220 at 10(-7) to 10(-5)M. Prostaglandin synthase antagonist indomethacin (10(-7) to 10(-5)M) suppressed FSH-induced increase in the number of granulosa cells in a dose-dependent manner. Downstream activation of protein kinase A by forskolin-activated adenylate cyclase resulted in elevated proliferation of granulosa cells, an effect unobserved by phorbol-12-myristrate-13-acetate-activated protein kinase C. In addition, PGE1-stimulated proliferation of granulosa cells was hindered by H89 (PKA inhibitor) but not by H7 (PKC inhibitor). Furthermore, the proliferating cell nuclear antigen labeling index (PCNA-LI) of granulosa cells displayed similar changes with the number of cells. These results indicated that PGE1 promoted the proliferation of granulosa cells from SYF and was also involved in mediating FSH-stimulated intracellular PKA signal transduction.

Possible roles of intracellular cyclic AMP, protein kinase C and calcium ion in the apoptotic signaling pathway in bovine luteal cells

Structural luteolysis occurs by apoptosis of luteal cells. The present study examined the effects of activators of well-characterized second messengers on Fas and caspase-3 mRNA expression and on P4 production in luteal cells in order to trace the pro- and anti-apoptotic factors in the bovine corpus luteum (CL). Cultured bovine mid luteal cells were treated for 24 h with a cyclic AMP analogue (8-bromo cyclic AMP; 8br-cAMP; 2.5 mM), a protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate; PMA; 10 microM), or calcium ionophore (A23187; 10 microM). Fas and caspase-3 mRNA expression was inhibited by 8br-cAMP and PMA but was increased by A23187 (P<0.05). In addition, P4 production by bovine luteal cells was stimulated by 8br-cAMP and PMA, whereas it was inhibited by A23187, compared with untreated controls (P<0.05). The overall results suggest that cAMP and PKC suppress apoptosis in bovine luteal cells through inhibition of Fas and caspase-3 mRNA expression and through stimulation of P4 production. Therefore, substances that activate cAMP or PKC may act as survival factors in the bovine CL. Furthermore, substances that mobilize Ca2+ may act as apoptotic factors by stimulating Fas and caspase-3 expression in the bovine luteal cells.