Activation of protein kinase in the bovine corpus luteum by phospholipid and Ca2+

Early Warning for Ovarian Diseases Based on Plasma Non-esterified Fatty Acid and Calcium Concentrations in Dairy Cows

Inactive ovaries (IO) and ovarian (follicular or luteal) cysts (FC or LC) are two common ovarian diseases leading to infertility in dairy cattle. Both disorders are associated with altered metabolites and hormones. There are currently no known effective biomarkers that can be used for early diagnosis of ovarian diseases. The purpose of this study was to identify the plasma biomarkers of ovarian diseases in Holstein dairy cows that facilitate an early diagnosis of the diseases and control its progression. The experiment was performed from 3 weeks postpartum and last for 7 weeks. Seventy-six multiparous Holstein cows (mean age, 4.36 years; weight, 635.63 kg) were divided into healthy control group (HC, n = 22), FC group (n = 18), LC group (n = 18) and IO group (n = 18) by rectal palpation or ultrasonography during the last 2 weeks before trial end. Blood was collected via tail vein for measurement of plasma energy metabolites, liver function indicators, minerals, and hormones at 3 and 8 weeks postpartum. Data were analyzed by Mann-Whitney U, Kruskal-Wallis, Spearman correlation, binary logistic regression analysis and receiver operating characteristic analysis, where applicable. At 8 weeks postpartum, FC cows had a more severe body condition score loss and these had greater levels of non-esterified fatty acids (NEFA) and estradiol, and lesser levels of alanine aminotransferase (ALT), progesterone and insulin-like growth factor 1 (IGF-1) levels than HC cows (P < 0.05). LC cows had a lower milk yield, higher NEFA and progesterone levels, and lower calcium, phosphorus and magnesium levels than HC cows (P < 0.05). IO cows had a lower body condition score, higher NEFA levels, and lower ALT, calcium, phosphorus, magnesium, estradiol, progesterone and IGF-1 levels than HC cows (P < 0.05). At 3 weeks postpartum, cows with ovarian diseases had greater (P < 0.05) concentrations of NEFA, and lesser concentrations of ALT, calcium, phosphorus and IGF-1 than HC cows. Early warning values for ovarian diseases were plasma NEFA concentrations >0.50 mmol/L, or calcium concentrations <2.02 mmol/L. Therefore, plasma NEFA and calcium could be used as early-warning indicators for ovarian diseases in dairy cows.

Protein Kinase C-ζ stimulates colorectal cancer cell carcinogenesis via PKC-ζ/Rac1/Pak1/β-Catenin signaling cascade

Colorectal cancer (CRC) is the second most common cancer in the world and death from CRC accounts for 8% of all cancer deaths both in men and women in the United States. CRC is life-threatening disease due to therapy resistant cancerous cells. The exact mechanisms of cell growth, survival, metastasis and inter & intracellular signaling pathways involved in CRC is still a significant challenge. Hence, investigating the signaling pathways that lead to colon carcinogenesis may give insight into the therapeutic target. In this study, the role of atypical Protein Kinase C (aPKC) on CRC was investigated by using two inhibitors of that protein class: 1) ζ-Stat (8-hydroxynaphthalene-1,3,6-trisulfonic acid) is a specific inhibitor of PKC-ζ and 2) ICA-I 5-amino-1-(2,3-dihydroxy-4-hydroxymethyl)cyclopentyl)-1H-imidazole-4-carboxamide) is a specific inhibitor of PKC-ι. The cell lines tested were CCD18CO normal colon epithelial and LOVO metastatic CRC cells. The inhibition of aPKCs did not bring any significant toxicity on CCD18CO normal colon cell line. Although PKC-ι is an oncogene in many cancers, we found the overexpression of PKC-ζ and its direct association with Rac1. Our findings suggest that the PKC-ζ may be responsible for the abnormal growth, proliferation, and migration of metastatic LOVO colon cancer cells via PKC-ζ/Rac1/Pak1/β-Catenin pathway. These results suggest the possibility of utilizing PKC-ζ inhibitor to block CRC cells growth, proliferation, and metastasis.

Mechanisms of intracellular calcium homeostasis in developing and mature bovine corpora lutea

Although calcium (Ca(2+)) is accepted as an intracellular mediator of prostaglandin F2 alpha (PGF2alpha) actions on luteal cells, studies defining mechanisms of Ca(2+) homeostasis in bovine corpora lutea (CL) are lacking. The increase in intracellular Ca(2+) concentration ([Ca(2+)]i) induced by PGF2alpha in steroidogenic cells from mature CL is greater than in those isolated from developing CL. Our hypothesis is that differences in signal transduction associated with developing and mature CL contribute to the increased efficacy of PGF2alpha to induce a Ca(2+) signal capable of inducing regression in mature CL. To test this hypothesis, major genes participating in Ca(2+) homeostasis in the bovine CL were identified, and expression of mRNA, protein, or activity, in the case of phospholipase Cbeta (PLCbeta), in developing and mature bovine CL was compared. In addition, we examined the contribution of external and internal Ca(2+) to the PGF2alpha stimulated rise in [Ca(2+)]i in LLCs isolated from developing and mature bovine CL. Three differences were identified in mechanisms of calcium homeostasis between developing and mature CL, which could account for the lesser increase in [Ca(2+)]i in response to PGF2alpha in developing than in mature CL. First, there were lower concentrations of inositol 1,4,5-trisphosphate (IP3) after similar PGF2alpha challenge, indicating reduced phospholipase C beta (PLCbeta) activity, in developing than mature CL. Second, there was an increased expression of sorcin (SRI) in developing than in mature CL. This cytoplasmic Ca(2+) binding protein modulates the endoplasmic reticulum (ER) Ca(2+) release channel, ryanodine receptor (RyR), to be in the closed configuration. Third, there was greater expression of ATP2A2 or SERCA, which causes calcium reuptake into the ER, in developing than in mature CL. Developmental differences in expression detected in whole CL were confirmed by Western blots using protein samples from steroidogenic cells isolated from developing and mature CL. Localization of these genes in steroidogenic luteal cells was confirmed by immunohistochemistry. Therefore, it is concluded that the cellular mechanisms that allow PGF2alpha to induce a calcium signal of greater magnitude in mature than in developing CL involve 1) greater PLCbeta activity with enhanced generation of IP3, 2) an enhanced Ca(2+) release from the ER via unrestrained RYR2 due to a decrease in SRI expression, and 3) a reduction in calcium reuptake to the ER due to lower expression of ATP2A2. Accordingly, the increase in [Ca(2+)]i induced by PGF2alpha in mature large steroidogenic cells had less dependency from extracellular calcium than in those isolated from immature CL.

Regulation of Cdk7 activity through a phosphatidylinositol (3)-kinase/PKC-ι-mediated signaling cascade in glioblastoma

The objective of this research was to study the potential function of protein kinase C (PKC)-ι in cell cycle progression and proliferation in glioblastoma. PKC-ι is highly overexpressed in human glioma and benign and malignant meningioma; however, little is understood about its role in regulating cell proliferation of glioblastoma. Several upstream molecular aberrations and/or loss of PTEN have been implicated to constitutively activate the phosphatidylinositol (PI) (3)-kinase pathway. PKC-ι is a targeted mediator in the PI (3)-kinase signal transduction repertoire. Results showed that PKC-ι was highly activated and overexpressed in glioma cells. PKC-ι directly associated and phosphorylated Cdk7 at T170 in a cell cycle-dependent manner, phosphorylating its downstream target, cdk2 at T160. Cdk2 has a major role in inducing G(1)-S phase progression of cells. Purified PKC-ι phosphorylated both endogenous and exogenous Cdk7. PKC-ι downregulation reduced Cdk7 and cdk2 phosphorylation following PI (3)-kinase inhibition, phosphotidylinositol-dependent kinase 1 knockdown as well as PKC-ι silencing (by siRNA treatment). It also diminished cdk2 activity. PKC-ι knockdown inhibited overall proliferation rates and induced apoptosis in glioma cells. These findings suggest that glioma cells may be proliferating through a novel PI (3)-kinase-/PKC-ι/Cdk7/cdk2-mediated pathway.

PKC-ι promotes glioblastoma cell survival by phosphorylating and inhibiting BAD through a phosphatidylinositol 3-kinase pathway

The focus of this research was to investigate the role of protein kinase C-iota (PKC-ι) in regulation of Bad, a pro-apoptotic BH3-only molecule of the Bcl-2 family in glioblastoma. Robust expression of PKC-ι is a hallmark of human glioma and benign and malignant meningiomas. The results were obtained from the two human glial tumor derived cell lines, T98G and U87MG. In these cells, PKC-ι co-localized and directly associated with Bad, as shown by immunofluorescence, immunoprecipitation, and Western blotting. Furthermore, in-vitro kinase activity assay showed that PKC-ι directly phosphorylated Bad at phospho specific residues, Ser-112, Ser-136 and Ser-155 which in turn induced inactivation of Bad and disruption of Bad/Bcl-XL dimer. Knockdown of PKC-ι by siRNA exhibited a corresponding reduction in Bad phosphorylation suggesting that PKC-ι may be a Bad kinase. PKC-ι knockdown also induced apoptosis in both the cell lines. Since, PKC-ι is an essential downstream mediator of the PI (3)-kinase, we hypothesize that glioma cell survival is mediated via a PI (3)-kinase/PDK1/PKC-ι/Bad pathway. Treatment with PI (3)-kinase inhibitors Wortmannin and LY294002, as well as PDK1 siRNA, inhibited PKC-ι activity and subsequent phosphorylation of Bad suggesting that PKC-ι regulates the activity of Bad in a PI (3)-kinase dependent manner. Thus, our data suggest that glioma cell survival occurs through a novel PI (3)-kinase/PDK1/PKC-ι/BAD mediated pathway.

A novel PKC-ι inhibitor abrogates cell proliferation and induces apoptosis in neuroblastoma

Protein Kinase C-iota (PKC-ι), an atypical protein kinase C isoform manifests its potential as an oncogene by targeting various aspects of cancer cells such as growth, invasion and survival. PKC-ι confers resistance to drug-induced apoptosis in cancer cells. The acquisition of drug resistance is a major obstacle to good prognosis in neuroblastoma. The focus of this research was to identify the efficacy of [4-(5-amino-4-carbamoylimidazol-1-yl)-2,3-dihydroxycyclopentyl] methyl dihydrogen phosphate (ICA-1) as a novel PKC-ι inhibitor in neuroblastoma cell proliferation and apoptosis. ICA-1 specifically inhibits the activity of PKC-ι but not that of PKC-zeta (PKC-ζ), the closely related atypical PKC family member. The IC(50) for the kinase activity assay was approximately 0.1μM which is 1000 times less than that of aurothiomalate, a known PKC-ι inhibitor. Cyclin dependent kinase 7 (Cdk7) phosphorylates cyclin dependent kinases (cdks) and promotes cell proliferation. Our data shows that PKC-ι is an in vitro Cdk7 kinase and the phosphorylation of Cdk7 by PKC-ι was potently inhibited by ICA-1. Furthermore, our data shows that neuroblastoma cells proliferate via a PKC-ι/Cdk7/cdk2 cell signaling pathway and ICA-1 mediates its antiproliferative effects by inhibiting this pathway. ICA-1 (0.1μM) inhibited the in vitro proliferation of BE(2)-C neuroblastoma cells by 58% (P=0.01). Additionally, ICA-1 also induced apoptosis in neuroblastoma cells. Interestingly, ICA-1 did not affect the proliferation of normal neuronal cells suggesting its potential as chemotherapeutic with low toxicity. Hence, our results emphasize the potential of ICA-1 as a novel PKC-ι inhibitor and chemotherapeutic agent for neuroblastoma.

Protein kinase Calpha-induced derepression of the human luteinizing hormone receptor gene transcription through ERK-mediated release of HDAC1/Sin3A repressor complex from Sp1 sites

LH receptor (LHR) gene transcription is subject to repression/derepression through various modes and multiple effectors. Epigenetic silencing and activation of the LHR is achieved through coordinated regulation at both histone and DNA levels. The LHR gene is subject to repression by deacetylation and methylation at its promoter region, where a HDAC/mSin3A repressor complex is anchored at Sp1 sites. The present studies revealed that protein kinase C (PKC) alpha/ERK signaling is important for the activation of LHR promoter activity, and the increase of endogenous transcripts induced by phorbol-12-myristate-13-acetate (PMA) in HeLa cells. Whereas these effects were attributable to PKCalpha activity, the ERK pathway was the downstream effector in LHR activation. PMA caused a significant enhancement of Sp1 phosphorylation at serine residue (s), which was blocked by PKCalpha or ERK inhibition. The interaction of activated phosphorylated ERK with Sp1 and ERK's association with the LHR promoter points to Sp1 as a direct target of ERK. After Sp1 phosphorylation, the HDAC1/mSin3A repressor complex dissociated from Sp1 sites, histone 3 was acetylated, and transcription factor II B and RNA polymerase II were recruited. In addition, overexpression of a constitutively active PKCalpha (PKCalpha CA) strongly activated LHR transcription in MCF-7 cells (devoid of PKCalpha), induced Sp1 phosphorylation at serine residue (s) and caused derecruitment of HDAC1/mSin3A complex from the promoter. These effects were negated by cotransfection of a dominant-negative PKCalpha. In conclusion, these studies have revealed a novel regulatory signaling mechanism of transcriptional control in which the LHR is derepressed through PKCalpha/ERK-mediated Sp1 phosphorylation, causing the release of HDAC1/mSin3A complex from the promoter.

Relationships between the conception rate of estrus synchronization using estradiol benzoate and CIDR (progesterone) and other parameters in holstein lactating dairy cows

The purpose of this study was to determine the relationships between conception rate and other parameters before estrus synchronization with a Controlled Internal Drug Release Device (CIDR) and estradiol benzoate (EB). In the estrus synchronization program, animals were injected with 2 mg EB and then received a CIDR. Seven days later, the CIDR was removed and the animals were given an injection of Prostaglandin F(2alpha). Twenty-four hours later, they received an injection of 1 mg EB, and they were artificially inseminated 24 h after that. This program was applied to 258 Holstein cows in Tohoku-machi (Aomori, Japan). Blood was collected at the beginning of the program, and the conception rate was determined about 40 days after insemination. The relationships among conception rate, blood biochemical values, age, body condition score and days in milk were statistically analyzed to determine better conditions for cow conception. The conception rate of the cows in the high progesterone group (more than 1 ng/ml, P(4)+) was significantly higher than that of the low progesterone group (less than 1 ng/ml, P(4)-; 47.9% vs. 28.6% P<0.01). In the P(4)- groups, the serum phospholipid level was significantly higher in the conception group than in the non-conception group, and the same tendency was seen in the P(4)+ groups. Blood urea nitrogen (BUN), albumin (Alb), and total cholesterol (TChol) were significantly higher in the conception group compared with the non-conception group, but no with P(4) was observed. We concluded that 1) the conception rate of the P(4)- group was remarkably low, that 2) the low conception rate and low P(4) level was related to a low PL level and that 3) BUN, Alb and TChol were higher in the conception group, although no relation with P(4) was found.

Human glioma PKC-iota and PKC-betaII phosphorylate cyclin-dependent kinase activating kinase during the cell cycle

Cell cycle phase transition is regulated in part by the trimeric enzyme, cyclin-dependent kinase activating kinase (CAK) which phosphorylates and activates cyclin-dependent kinases (cdks). Protein kinase C (PKC) inhibitors prevent cell cycle phase transition, suggesting a fundamental role for PKCs in cell cycle regulation. We report that in glioma cells, CAK (cdk7) is constitutively associated with PKC-iota. In vitro phosphorylation, co-immunoprecipitation, and analysis of phosphorylated proteins by autoradiography indicate that CAK (cdk7) is a substrate for PKC-iota and PKC-betaII hyperphosphorylation. These results establish a role for PKC-iota and PKC-betaII in the activation of CAK during the glioma cell cycle.

Effects of interferon and PKC modulators on human glioma protein kinase C, cell proliferation, and cell cycle

The in-vitro effects of human interferon alpha-2b (HuIFN alpha-2b), protein kinase C (PKC) agonist [TPA (12-0-tetra-decanoyl-phorbol-13-acetate)] and PKC inhibitor (calphostin C) on human glioma (U-373 MG) PKC activity, cell proliferation and cell cycle were compared. HuIFN alpha-2b and TPA increased PKC activity, elevated the number of cells in DNA synthesis (S) phase and decreased cell proliferation by similar magnitudes. Calphostin C inhibited PKC activity, increased the number of cells in S phase and produced strong cytotoxic effects (IC50 150 nM). Higher concentrations of calphostin C with or without serum induced an additional block in gap2 and mitosis. We conclude that HuIFN alpha-2b's mode of action may be directly or indirectly affecting PKC. The response produced by HuIFN alpha-2b is similar to TPA (potent PKC activation and S phase arrest).

Gap junctional intercellular communication of bovine luteal cells from several stages of the estrous cycle: effects of prostaglandin F2 alpha, protein kinase C and calcium

Cellular interactions mediated by both contact-dependent and contact-independent mechanisms are probably important to maintain luteal function. The present studies were performed to evaluate the effects of luteotropic and luteolytic hormones, and also intracellular regulators, on contact-dependent gap junctional intercellular communication (GJIC) of bovine luteal cells from several stages of luteal development. Bovine corpora lutea (CL) from the early, mid and late luteal phases of the estrous cycle were dispersed with collagenase and incubated with no treatment, LH, PGF or LH + PGF (Experiment 1), or with no treatment, or agonists or antagonists of protein kinase C (TPA or H-7) or calcium (A23187 or EGTA; Experiment 2). After incubation, media were collected for determination of progester-one concentrations. Then the rate of GJIC was evaluated for small luteal cells in contact with small luteal cells, and large luteal cells in contact with small luteal cells by using the fluorescence recovery after photobleaching technique and laser cytometry. Luteal cells from each stage of the estrous cycle exhibited GJIC, but the rate of GJIC was least (P < 0.05) for luteal cells from the late luteal phase. LH increased (P < 0.05) GJIC between small luteal cells from the mid and late but not the early luteal phase. PGF increased (P < 0.05) GJIC between small luteal cells from the mid luteal phase and diminished (P < 0.05) LH-stimulatory effects on GJIC between small luteal cells from the late luteal phase. Throughout the estrous cycle, TPA decreased (P < 0.05) the rate of GJIC between large and small, and between small luteal cells, and A23187 decreased (P < 0.05) the rate of GJIC between large and small luteal cells. LH and LH + PGF, but not PGF alone increased (P < 0.05) progesterone secretion by luteal cells from the mid and late luteal phases. Agonists or antagonists of PKC or calcium did not affect progesterone secretion by luteal cells. These data demonstrate that both luteal cell types communicate with small luteal cells, and the rate of communication depends on the stage of luteal development. LH and PGF affect GJIC between small luteal cells during the fully differentiated (mid-luteal) and regressing (late luteal) stages of the estrous cycle. In contrast, at all stages of luteal development, activation of PKC decreases GJIC between small and between large and small luteal cells, whereas calcium ionophore decreases GJIC only between large and small luteal cells. Luteotropic and luteolytic hormones, and intracellular regulators, may be involved in regulation of cellular interactions within bovine CL which likely is an important mechanism for coordination of luteal function.

Regulation of delta protein kinase C during rat ovarian differentiation

Studies were undertaken to classify protein kinase C (PKC) forms present in rat corpora lutea and to begin to evaluate their regulation during ovarian differentiation. Hydroxyapatite (HAP) column chromatography of rat luteal tissue revealed the presence of multiple forms of PKC (alpha, beta, delta, zeta). Identification of the PKC isoforms was based upon elution positions from HAP column chromatography and immunoreactivity. The delta PKC isoform was identified as the major Ca(2+)-independent form of PKC present in rat luteal tissue. The Ca(2+)-independent, lipid-dependent phosphorylation of the 80-kDa delta PKC was readily detectable in soluble luteal extracts and was shown to reflect autophosphorylation of delta PKC. To evaluate the regulation of PKC isoforms during ovarian differentiation, PKC protein levels were compared between preovulatory follicle-enriched ovaries and corpora lutea obtained on day 16 of pregnancy. Levels of delta PKC protein were greatly elevated in corpora lutea compared to levels in preovulatory follicles. In contrast, levels of alpha and beta PKC protein remained constant while levels of zeta PKC were slightly higher in the follicular than the luteal extract. Levels of delta PKC mRNA were also higher in corpora lutea than in preovulatory follicles. These results are the first to demonstrate the physiological regulation of delta PKC with follicular differentiation into corpora lutea and implicate a role for this prominent PKC form in the corpus luteum during pregnancy.

Hormonal regulation of the type III isoform of C-kinase in porcine ovarian tissues

C-kinase activity is notably increased in corpora lutea (CL) compared to preovulatory follicles of porcine ovaries. Our purpose was to identify the C-kinase isoform(s) involved in this increase and to examine the expression of C-kinase in ovarian tissues at different stages. The major component of C-kinase activity in the CL was isoform III, with a molecular weight (M(r)) of 80,000. Minor activities were attributed to the type II isoform (M(r) = 80,000) and an unidentified C-kinase activity (M(r) = 77,000). C-kinase was not partitioned differently in preovulatory follicles and CL as demonstrated by tissue homogenization in the presence of a detergent and increased chelators. A 3-fold increase in immunoreactive C-kinase was detected in postovulatory follicles relative to preovulatory. A second, nearly 3-fold increase in C-kinase was detected in mature CL relative to postovulatory follicles. These increases are examined in the context of the complex hormonal regulation of the porcine CL.

Protein kinase C stimulatory activity in the pseudopregnant rat ovary

Ovarian cytosol from pseudopregnant rats was heated to 80-90 degrees C for 2 min and precipitated proteins removed by centrifugation. The supernatant of the heated ovarian cytosol contained no protein kinase C activity but when added to a control preparation containing protein kinase C, enzyme activity was increased to 200% of control. The stimulatory activity was stable to heating for 10 min, was retained on a centrifugal filtration device with a 100,000 M(r) cut-off, did not affect cAMP-dependent protein kinase, was not extractable in petroleum ether or chloroform/methanol (2:1), and enhanced the phosphorylation of protein kinase C-specific peptide substrates. The stimulatory factor was calcium-dependent and could substitute for phosphatidylserine and diacylglycerol in the protein kinase C assay. This stimulatory factor may provide a mechanism whereby the response of protein kinase C to hormonal activation could be regulated by the cell.

Intragonadal signalling mechanisms in the control of steroid hormone production

In the gonads, there are two recognized signal transduction mechanisms which operate in the processing of hormonal stimuli. The gonadotropins, follicle stimulating hormone and luteinizing hormone, act primarily through the generation of cyclic AMP. Several other hormonal regulators in the ovary and the testis, such as gonadotropin releasing hormone and prostaglandin F2 alpha stimulate inositol lipid metabolism following receptor binding. This triggers a cascading mechanism which ultimately results in the generation of increased cytosolic free calcium levels, enhanced protein kinase C activity, and liberation of arachidonic acid. There is also evidence that luteinizing hormone shares in the activation of this pathway. In this review, the significance of these signal transduction pathways is discussed in relation to the effects of various hormones on steroid biosynthesis in the gonads.

Neomycin, an inhibitor of phosphoinositide hydrolysis, inhibits the resumption of bovine oocyte spontaneous meiotic maturation

The possibility that the intracellular signals generated upon phosphoinositide hydrolysis are involved in regulating bovine oocyte spontaneous meiotic resumption was investigated. Oocytes were mass-harvested and cultured in 2A-BMOC medium supplemented with 0.5% bovine serum albumin in the presence or absence of neomycin (an inhibitor of phosphoinositide hydrolysis) or phorbol myristate acetate (an activator of protein kinase C). The role of intracellular calcium was examined by preloading with BAPTA/AM (a calcium chelator) prior to culture. Meiotic maturation was scored cytogenetically. 1) Neomycin induces an irreversible inhibition of germinal vesicle breakdown which does not exceed 60% and is apparent at concentrations of 5 mM or above. Progression of meiosis past metaphase I is inhibited at concentrations of 2.5 mM or above. The full effect of neomycin is only apparent if it is presented to the oocytes within 3 h of follicular release, although germinal vesicle breakdown is not observed until 9 h culture under control conditions. 2) PMA alone has negligible effect on germinal vesicle breakdown, but it acts synergistically with 2 mM IBMX to inhibit this process. PMA has a dual effect on the progression of meiosis past metaphase I: 1 nM PMA has a stimulatory effect while 1 microM PMA blocks the ability of oocytes to reach anaphase I or beyond. These observations are not found with a non-tumor-promoting phorbol ester. 3) Spontaneous meiotic resumption is not significantly affected in the absence of added exogenous calcium. However, oocytes preloaded with BAPTA/AM exhibit a dose-dependent inhibition of germinal vesicle breakdown, even in the presence of extracellular calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium-independent phospholipid/diolein-dependent phosphorylation of a soluble ovarian Mr 80,000 substrate protein: biochemical characteristics

Soluble ovarian extracts were incubated with protein kinase effectors in the presence of [gamma 32P]ATP and proteins were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Autoradiograms revealed phosphorylation of an ovarian Mr = 80,000 substrate in the presence of EGTA ([ethylenebis(oxyethylenenitrilo)]tetraacetic acid), phosphatidylserine and 1,2-diolein. In contrast to a classical response pattern to C-kinase effectors, the ovarian Mr = 80,000 phosphorylation was inhibited by 2 x 10(-7) M or greater free Ca2+. The ovarian Mr = 80,000 substrate was distinguished from the myristoylated acidic Mr = 80,000 C-kinase substrate of brain tissue on the basis of heat stability and phosphorylative response to effectors. Phosphorylation of the exogenous substrate myelin basic protein by DEAE-resolved ovarian kinase showed the variant effector dependence, maximal in the presence of EGTA, phosphatidylserine and 1,2-diolein. Finally, the effect of Ca2+ on ovarian Mr = 80,000 [32P]phosphate content could not be accounted for by post-phosphorylation activities, or by DEAE-resolvable or hydroxylapatite-resolvable inhibitory activities.

Phorbol ester receptors in bovine luteal cells: relationship to protein kinase C

We investigated the binding kinetics of the tumor-promoting phorbol ester, phorbol-12,13-dibutyrate (PBt2) to dispersed total bovine luteal cells, purified small luteal cells, and purified luteal protein kinase C (PKC). Saturation analysis and competitive displacement techniques were used. Binding of [3H]PBt2 to total luteal cell preparations resulted in two distinct affinities. The high affinity component was characterized by a Kd of 4.5 +/- 1.5 nM. Analysis of [3H]PBt2 binding to total cells using competitive displacement demonstrated that the low affinity binding was specific and displaceable but dependent on concentrations of [3H]PBt2 far above the Kd for the high affinity binding. In contrast to the total cell preparations, only high affinity binding was observed in intact purified small luteal cells (Kd = 0.96 +/- 0.04 nM). Partial purification of luteal cytosolic PKC by DEAE-Sephadex chromatography resulted in co-elution of PKC enzyme activity and the [3H]PBt2 binding activity. Under conditions of saturating calcium (0.1 mM) and phosphatidylserine (PS) (100 micrograms/tube) concentrations, binding to the partially purified PKC preparation was found to be of a single high affinity and exhibited a Kd (1.3 +/- 0.2 nM) similar to the high affinity binding observed in intact cells. These results suggest that the primary phorbol ester receptor in luteal cells is PKC. However, a low affinity, high capacity [3H]PBt2 binding site also exists within the corpus luteum, either in the large cells or in the accessory cell fraction which consists mainly of endothelial cells.

Phorbol ester- and luteinizing hormone-induced phosphorylation of membrane proteins in bovine luteal cells

In this study we have investigated the protein phosphorylation pattern in the membrane fraction prepared from bovine luteal cells. The phosphorylation reaction was carried out in vitro, under defined conditions, using either [gamma-32P]ATP or [gamma-35S]ATP as the phosphate donor. The results obtained show that [gamma-35S]ATP was a suitable phosphate donor for performing in vitro phosphorylation studies, and that thiophosphorylation of at least eight protein bands (120 kDa to 18 kDa) was observed. The extent of phosphorylation was dependent upon the duration of incubation and the amount of membrane protein used. The presence of Ca2+ was obligatory for phosphorylation and an enhanced phosphorylation was observed in the presence of Ca2+, phosphatidyl serine and phorbol 12-myristate 13-acetate (PMA), agents known to activate protein kinase C. Interestingly, when phosphorylation was carried out in the presence of luteinizing hormone (LH), a phosphorylation pattern was obtained which was similar to that obtained in the presence of calcium and phospholipid. Furthermore, in the case of two protein bands corresponding to 80-82 and 44-46 kDa, an additive phosphorylation was observed when the phosphorylation reaction was carried out for 5 min in the presence of both LH and Ca2+, phosphatidyl serine and PMA. To conclude, we have demonstrated a calcium- and phospholipid-dependent endogenous protein phosphorylation in the membrane fraction prepared from bovine luteal cells and the data obtained suggest that LH is able to stimulate this endogenous protein phosphorylation via a protein kinase C-mediated mechanism.

Suppression of LH-stimulated prostaglandin and progesterone accumulation in rat granulosa cells by isoquinolinesulfonamide protein kinase inhibitors

Rat granulosa cells were incubated with isoquinolinesulfonamide inhibitors of protein kinases A and C and/or LH, dibutyryl cAMP (dbcAMP), tetradecanoylphorbol acetate (TPA), cholera toxin, or forskolin for 5 h. H7 (25 microM) was observed to inhibit LH, cholera toxin or dbcAMP stimulation of prostaglandin (PGE), and progesterone accumulation. H7 produced inhibition when added as little as 2 min before and as long as 1 h after LH. HA1004 was ineffective against LH or cholera toxin stimulation of PGE or progesterone at up to 100 microM. H9 blocked some LH and forskolin responses at 25 microM, but required a 50 microM concentration to minimally affect TPA stimulation. Cytotoxicity was not observed at the concentrations and times of isoquinolinesulfonamides tested. H7 and H9, therefore, suppress LH stimulation of granulosa cell functions in a dose- and time-dependent manner consistent with inhibition of protein kinases A and/or C, and consonant with a requirement for such kinases in LH action.

Nonsteroidal antiestrogen inhibition of protein kinase C in human corpus luteum and placenta

These studies were undertaken to determine whether nonsteroidal antiestrogens would inhibit the calcium/lipid-dependent protein kinase (protein kinase C) activity in hormonally-responsive human reproductive tissues. Cytosol was prepared from human corpus luteum and term placenta. Protein kinase C activity was examined with various antiestrogens, estrogens, and catecholestrogens. The nonsteroidal antiestrogens tamoxifen, clomiphene and Z-4-hydroxytamoxifen inhibited protein kinase C in cytosol from human corpora lutea and placentae in a concentration-dependent manner. The IC50 values were 35-45 microM for tamoxifen, 58-66 microM for clomiphene, and 88 microM for hydroxytamoxifen. Protein kinase C purified 600-fold from human placenta was also inhibited by tamoxifen. The estrogens, estradiol and diethylstilbestrol (DES), and the catecholestrogens, 2-hydroxyestradiol and 4-hydroxyestradiol, had no effect on protein kinase C activity, nor were they able to prevent the inhibition of protein kinase C by the antiestrogens. Inhibition of the enzyme by the antiestrogens was competitive with phosphatidylserine and 1,2-diolein. In addition, tamoxifen inhibited enzyme activity stimulated by the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA). The data suggest that the action of these antiestrogens on protein kinase C was a direct inhibition of the enzyme. Furthermore, the site of interaction showed markedly different structural specificity from that of the estrogen receptor.

Mechanism(s) by which activation of protein kinase C is coupled to prostacyclin synthesis in granulosa cells

We examined the mechanisms by which the phospholipid-sensitive, calcium-dependent protein kinase (protein kinase C) regulates prostacyclin synthesis by ovarian cells. In monolayer cultures of swine granulosa cells, specific phorbol esters significantly augmented production of the stable immunoreactive metabolite of prostacyclin, 6-keto-prostaglandin F1 alpha by 3- to 8-fold. These stimulatory actions were dose (0.03-30 ng/ml) and time (24-96 h) dependent, could be reproduced by non-diterpene activators of protein kinase C, and were corroborated by high performance liquid chromatography and mass spectrometry. The rank order of potency of phorbol esters was 12-O-tetradecanoylphorbol 13-acetate (TPA) greater than phorbol 12,13-dibenzoate greater than phorbol 12,13-dibutyrate greater than pure phorbol base. TPA enhanced de novo synthesis of prostacyclin, and synergized with the divalent cation ionophore, A23187. Although prostacyclin synthetase activity was not induced, microsomal cyclooxygenase activity was significantly increased by phorbol treatment. Moreover, TPA doubled the intracellular accumulation of free arachidonic acid. An inhibitor of phospholipase A2 (quinacrine 100 microM) impeded, whereas melittin (0.01 microM), an activator of cellular phospholipase A2, and purified bacterial phospholipase A2 (5 and 50 mU/ml) both augmented prostacyclin production. RH 59022 (30 microM), an inhibitor of diacylglyceride lipase, also suppressed prostacyclin synthesis. We conclude that the protein kinase C effector pathway is functionally coupled to de novo prostacyclin production in the swine granulosa cell. Increased eicosanoid synthesis can be accounted for by enhanced phospholipase A2 and diacylglyceride lipase-mediated availability of arachidonic acid substrate and an activated cyclooxygenase enzyme without a change in prostacyclin synthetase activity.

Protein kinase A and C activities and endogenous substrates in ovine small and large luteal cells

Protein kinase A (cAMP-dependent) and C (calcium, phospholipid-dependent) activities were measured and in vitro phosphorylation of endogenous proteins by these kinases were observed by SDS-PAGE in 100,000 x g supernatant (soluble) fractions of ovine small (12-22 microns) and large (greater than 22 microns) luteal cells. No differences in stimulation (P less than 0.05) of A kinase activity between small and large cells were detected. Protein kinase C activity was stimulated (P less than 0.05) 2.9-fold in small cells but not significantly enhanced above basal (P greater than 0.05) in large cells. By direct comparison, greater stimulation (P less than 0.05) over basal of A versus C kinase (6.1- versus 2.9-fold) was measured in small cells. These stimulations were greater than those observed in large cells (A kinase, 4.8-fold; C kinase, 1.8-fold). Maximal specific activities of both kinases (per mg protein) were greater (P less than 0.05) in small than in large cells. Endogenous proteins that could serve as substrates for phosphorylation by A and C kinases differed between small and large cells. Phosphorylation of six proteins by A kinase was consistently greater in small than in large cells. One endogenous protein (37 kDa) appeared to serve as a preferred substrate for phosphorylation by A kinase in small cells and C kinase in large cells. One protein (81 kDa) was predominantly phosphorylated in large rather than small cells by a calcium-dependent, C kinase-independent mechanism. These results support the accepted role of cAMP via A kinase and a possible role for C kinase in regulating steroidogenesis in ovine small luteal cells. The inability of large cells to respond to cAMP with enhanced secretion of progesterone may be due to an unavailability of phosphoprotein substrates for A kinase. Furthermore, protein kinase C activity and available protein substrates display quantitative and qualitative differences between small and large cells. Differences in regulation of steroidogenesis between the cell types may be due to these observed differences.

Isolation and characterization of protein kinase C from Y-1 adrenal cell cytoskeleton

The cytoskeletons of Y-1 mouse adrenal tumor cells contain a calcium and phospholipid-dependent protein kinase (protein kinase C) that is bound sufficiently tight to resist extraction by 0.5% Triton but not by 1.0% Triton. The enzyme has been purified to near homogeneity from cytoskeleton and cytosol. It shows features typical of this type of kinase, namely a requirement for Ca2+ and phospholipid, stimulation by tumor promoters but not by nontumor-promoting phorbol esters, and inhibition by trifluoperazine. The enzyme shows specificity for four substrates found in the cytoskeleton, namely 80, 33, 20, and 18 kD. The first three substrates are phosphorylated by the enzyme; the fourth is dephosphorylated and is therefore affected by the kinase indirectly. The 80-kD protein is the kinase enzyme itself which is autophosphorylated in vitro and in the cytoskeleton. The 20-kD protein is myosin light chain. The 33- and 18-kD proteins are unidentified. The same substrates were phosphorylated when Y-1 cells were permeabilized with digitonin and incubated with [gamma-32P]ATP and phorbol-12-myristate-13-acetate. Partly purified protein kinase C changes the extent of phosphorylation of the same substrates when added to cytoskeletons previously extracted to remove endogenous protein kinase C. Addition of Ca2+, phosphatidylserine, and phorbol-12-myristate-13-acetate to cytoskeletons, and addition of these three agents plus protein kinase C to extracted cytoskeletons, causes these structures to undergo a rapid and extensive rounding. A similar change is induced in intact cells by addition of phorbol ester. It is concluded that protein kinase C is capable of changing the shape of adrenal cells by an action that involves autophosphorylation and phosphorylation of myosin light chain. This response may in turn be related to the steroidogenic responses to ACTH and cyclic AMP.

Purification of three forms of chromatographically distinct protein kinase C from the swine ovary

A calcium-sensitive, lipid-dependent protein kinase (protein kinase C) modulates physiological function in a variety of cells. In certain tissues, multiple forms of this key regulatory enzyme exist. To examine the nature of ovarian protein kinase C, swine luteal cytosol (1000 mg protein) was applied and eluted from DE-52 cellulose. The pooled active fractions were sequentially purified further by threonine- (TS) and phenyl-Sepharose (PS) affinity chromatography in a buffer of 20 mM Tris, 0.5 mM EDTA, 0.5 mM EGTA, 5 mM dithiothreitol and 250 micrograms/l leupeptin. Protein kinase C activity was eluted with NaCl gradients of 0.075-125 M (DE-52), 0.1-1 M (TS) and 0.6-0.0 M (PS). This purification scheme yielded three distinct peaks of highly purified protein kinase C activity and an overall enrichment in protein kinase C activity of approximately 1000-fold. Inasmuch as control of steroidogenesis or peptide hormone production in the ovary via the Ca2+-protein kinase C pathway could occur at several different levels, we postulate that the demonstrated presence of isoforms of this enzyme in ovarian tissue offers a means for selective spatial and temporal compartmentalization of the endocrine stimulus with correspondingly distinct changes in cellular function.

Inhibition of follicle-stimulating hormone- and adenosine-3',5'-cyclic monophosphate-induced progesterone production by calcium and protein kinase C in the rat ovary

In this study we examined the effects of A23187 (a calcium ionophore) and 12-O-tetradecanoyl phorbol-13-acetate, a known activator of protein kinase C, on progesterone production. Granulosa cells obtained from pregnant mare serum gonadotropin-primed rats were maintained in primary culture. Treatment with follicle-stimulating hormone (0.5 microgram/ml), 8-bromo-adenosine-3',5'-cyclic monophosphate (2 mmol/L), or cholera toxin (0.1 microgram/ml) for 5 hours or 24 hours markedly stimulated progesterone production. The concomitant presence of A23187 attenuated the elevated levels of progesterone induced by follicle-stimulating hormone, 8-bromo-adenosine-3',5'-cyclic monophosphate, or cholera toxin, with or without the presence of a phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine (0.2 mmol/L). Likewise, treatment of the cells with 12-O-tetradecanoyl phorbol-13-acetate suppressed follicle-stimulating hormone-induced progesterone production, whether or not 1-methyl-3-isobutylxanthine was present in the cultures. The effect of 12-O-tetradecanoyl phorbol-13-acetate was not mimicked by phorbol-13-monoacetate or 4 alpha-phorbol-12, 13-didecanoate. These results indicate that both A23187 and 12-O-tetradecanoyl phorbol-13-acetate inhibit follicle-stimulating hormone-induced progesterone production, in part at a step or steps beyond adenosine-3',5'-cyclic monophosphate generation and degradation. They further support a role of calcium and protein kinase C in the intraovarian action of luteinizing hormone-releasing hormone.

Gonadotropin-releasing hormone agonist activates protein kinase C in rat Leydig cells

Gonadotropin-releasing hormone (GnRH) has specific receptor sites in rat Leydig cells and has direct effects on their steroidogenesis. The purpose of the present study was to examine whether activation of the calcium- and phospholipid-dependent protein kinase C (PK-C) is involved in GnRH effects on rat Leydig cells, as has been shown in pituitary gonadotrophs. Testosterone production of Percoll-purified Leydig cells was similarly stimulated (about 50-100%) by a GnRH agonist (buserelin, maximum effect at concentration of 10(-9) mol/l and above) and a tumor promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA, maximum effect at 10(-8) mol/l), which is known to activate PK-C. In contrast, a GnRH antagonist (10(-5) mol/l) and an inactive phorbol ester, 4 alpha-phorbol-12,13-didecanoate (10(-6) mol/l), were without effect on testosterone. None of these substances had clear effects on cAMP production. The maximum steroidogenic effects of GnRH agonist and TPA were the same whether used separately or together, suggesting that they share a common mechanism of action. TPA translocated the cytosolic proportion of Leydig cell PK-C activity to a membrane-associated form almost instantaneously, within 0.5-1 min. A similar translocation, though less complete, was observed in the presence of buserelin in 1-4 min. Inclusion of a 100-fold excess of a potent GnRH antagonist completely prevented the translocation of PK-C. These results provide evidence that GnRH agonist activates PK-C also in the testis tissue, and this may be the mechanism whereby it affects Leydig cell endocrine function.

Prostaglandin F2 alpha initiates polyphosphatidylinositol hydrolysis and membrane translocation of protein kinase C in swine ovarian cells

The biochemical mechanisms subserving the inhibitory actions of prostaglandin F2 alpha on ovarian cells are not known. Since the protein kinase C pathway is coupled to steroidogenesis in an inhibitory fashion in pig granulosa cells, we have tested the hypothesis that prostaglandin F2 alpha activates this phospholipid-dependent, calcium-stimulated effector pathway. Using monolayer cultures of swine granulosa cells, we now report that prostaglandin F2 alpha is capable of activating critical components of the protein kinase C pathway, including the production of water-soluble inositol phosphates, liberation of free arachidonic acid, release of endogenous diacylglycerol, and translocation of cytosolic protein kinase C to the phospholipid-enriched membrane microenvironment.

Effects of phorbol esters on steroidogenesis in small bovine luteal cells

The possible influence of an activator of protein kinase C, the tumor-promoting phorbol ester, PMA (phorbol-12-myristate-13-acetate), upon small bovine luteal cell steroidogenesis was investigated in vitro, PMA had no significant effect on basal and dibutyryl cyclic AMP (dbcAMP)-stimulated progesterone production but markedly modulated the LH-stimulated progesterone and cAMP productions. PMA potentiated the LH-stimulated cAMP accumulation whatever the dose of LH used. It also potentiated the LH-induced progesterone production in the presence of low doses of LH. Paradoxically, in the presence of maximal or submaximal effective doses of LH, PMA exerted a time- and dose-dependent inhibition of progesterone synthesis. Diacylglycerol was able to mimic the effects of PMA on LH-induced steroidogenesis. These observations suggest that the Ca2+- and phospholipid-dependent protein kinase C can modulate the regulation by LH of small bovine luteal cell steroidogenesis at a step before the synthesis of cAMP. They also suggest that the interaction between LH and its receptor is able to trigger a negative regulatory signal which would be only expressed for high doses of LH and in the presence of an activator of PKC.

Desensitisation of LH-stimulated cyclic AMP accumulation in isolated bovine luteal cells--effect of phorbol ester

In this study, we have characterized the LH-mediated desensitisation of receptor-linked cAMP generation in bovine luteal cells. Furthermore, the possibility that protein kinase C could play a role in this process has been investigated. The results obtained, show that the preincubation of Percoll-purified bovine luteal cells with LH diminished the cAMP response during reincubation with LH, depending upon the duration of prior exposure to LH and the concentration of LH used in the first incubation. This desensitisation was specifically dependent upon the prior exposure of the cells to the hormone only, as preincubation with either forskolin or cholera toxin did not result in a desensitised cAMP response to subsequent LH stimulation. On the other hand, LH-desensitised cells retained undiminished responsiveness to restimulation with cholera toxin. Neither the maximum binding capacity nor the affinity of the LH-receptor was affected by exposure of the cells to a desensitising dose of LH. The results demonstrate that in bovine luteal cells, LH produces a homologous desensitisation of the cAMP response which is not mediated by cAMP and that a hormone-receptor interaction appears to be a prerequisite for this process. Preincubation of the cells with varying concentrations of the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) did not result in any reduction of LH-induced cAMP response during reincubation. The affinity of LH-receptor was also not affected by PMA pretreatment. In contrast, PMA-pretreated cells consistently produced increased amounts of cAMP when challenged with any of the agonists, LH, cholera toxin or forskolin. The preincubation of the cells with LH in the presence of PMA appears to prevent, at least partially, the desensitising effect of LH. It is concluded that in bovine luteal cells there is no evidence for a role of protein kinase C in LH-induced desensitisation. On the contrary, PMA pretreatment increased the response of adenylate cyclase to a subsequent hormonal stimulation without changing the affinity of the receptors for the hormone. Either an attenuation of the inhibitory N protein or a direct activation of the catalytic unit of adenylate cyclase could be the explanation for the observed effects of PMA. However, available data at present do not offer a choice between the two possibilities.

Role of protein kinase C in luteinizing hormone-releasing hormone (LHRH)-stimulated progesterone production in rat granulosa cells

Treatment of rat granulosa cells with LHRH or the phorbol ester TPA stimulated progesterone (P) production during a 5-h incubation. The concomitant presence of a potent inhibitor of protein kinase C attenuated the LHRH effect by ca. 60% and completely blocked the stimulatory effect of TPA. Addition of TPA (10(-9), 10(-8) or 10(-7) M) or dioctanylglycerol (100 micrograms/ml) increased P production; these stimulatory effects were not potentiated by the concomitant presence of a calcium ionophore (A23187, 10(-7) or 10(-6)M). These data support the hypothesis that protein kinase C activation have a role in the steroidogenic action of LHRH in the ovary.

Activation of protein kinase C is coupled to prostaglandin E2 synthesis in swine granulosa cells

We have examined the role of phospholipid-sensitive calcium-dependent protein kinase (protein kinase C) in prostaglandin E2 synthesis by monolayer cultures of swine granulosa cells. Specific phorbol ester derivatives known to activate protein kinase C significantly augmented the production of prostaglandin E2. These stimulatory actions were dose and time-dependent, and could be abolished by the cyclooxygenase inhibitor, indomethacin, or the protein synthesis inhibitor, cycloheximide. Moreover, the rank order of potency of phorbol esters in enhancing prostaglandin E2 production was concordant with that demonstrated for activation of protein kinase C. Phorbol ester in conjunction with the divalent cation ionophore, A23187, increased prostaglandin E2 production synergistically. In addition, a non-phorbol stimulator of protein kinase C, 1-octanoyl-2-acetylglycerol, also significantly enhanced prostaglandin E2 biosynthesis. The stimulated synthesis of prostaglandin E2 was confirmed by high-pressure liquid chromatographic purification of this radiolabeled metabolite of 3H-arachidonic acid, and by capillary gas chromatography high-resolution mass spectrometry. Thus, the present studies indicate that the protein kinase C effector pathway is functionally coupled to prostaglandin E2 production in the swine granulosa cell.

Muscarinic receptors in human SH-SY5Y neuroblastoma cell line: regulation by phorbol ester and retinoic acid-induced differentiation

The specific binding of the muscarinic ligand [3H](-)quinuclidinyl benzilate [( 3H]QNB) to cell membranes of human SH-SY5Y neuroblastoma cells was studied. Saturation isotherms yielded a Kd = 0.28 +/- 0.06 nM and a Bmax of 337 +/- 47 pmol/g protein. Pirenzepine inhibited [3H]QNB binding; inhibition data showed best fit to a 2-site binding model revealing both a high affinity pirenzepine site (34%, KH = 10 nM) and a low affinity site (66%, KL = 1 microM). These results indicate that muscarinic receptors on SH-SY5Y cells may be subclassified as M1/M2 subtypes. Morphological and biochemical differentiation of these cells after treatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or retinoic acid (RA) resulted in a decrease and an increase in the number of muscarinic binding sites, respectively. Furthermore, TPA- and RA-treated cells showed a significant increase in acetylcholinesterase activity compared with non-treated cells. However, only RA-treated cells showed significant increase in choline acetyltransferase activity compared to non-treated cells. These findings demonstrate that TPA and RA can regulate both the number of muscarinic receptors and the acetylcholinesterase activity in human SH-SY5Y neuroblastoma cells.

Prostaglandin F2 alpha stimulates phosphatidylinositol 4,5-bisphosphate hydrolysis and mobilizes intracellular Ca2+ in bovine luteal cells

The present studies were conducted to determine whether prostaglandin F2 alpha (PGF2 alpha) stimulates the production of "second messengers" derived from inositol phospholipid hydrolysis and increases intracellular free Ca2+ ([Ca2+]i) in isolated bovine luteal cells. PGF2 alpha provoked rapid (10 sec) and sustained (up to 60 min) increases in the levels of inositol mono-, bis-, and trisphosphates (InsP, InsP2, and InsP3, respectively). InsP3 was formed more rapidly than InsP2 or InsP after PGF2 alpha treatment. In addition, PGF2 alpha increased inositol phospholipid turnover, as evidenced by increased 32PO4 incorporation into phosphatidic acid and phosphatidylinositol. LiCl (1-20 mM) enhanced inositol phosphate accumulation in response to PGF2 alpha. Maximal increases in InsP3 occurred at 1 microM PGF2 alpha, with half-maximal stimulation occurring at 36 nM. The acute effects of PGF2 alpha on InsP3 levels were independent of reductions in extracellular calcium. Prostaglandins E1 and E2 also stimulated increases in inositol phosphate levels, albeit to a lesser extent. PGF2 alpha also induced rapid and concentration-dependent increases in [Ca2+]i as measured by quin-2 fluorescence. The PGF2 alpha-induced increases in [Ca2+]i were maximal within 30 sec (approximately 2- to 3-fold), and [Ca2+]i remained elevated for 8-10 min. The PGF2 alpha-induced increases in [Ca2+]i were also independent of extracellular calcium. These findings demonstrate that the action of PGF2 alpha is coupled to the phospholipase C-InsP3 and diacylglycerol second messenger system in the corpus luteum.

Luteinizing hormone-releasing hormone (LHRH)-induced arachidonic acid release in rat granulosa cells. Role of calcium and protein kinase C

In rat granulosa cells prelabeled with [3H]arachidonic acid, addition of LHRH, A23187 or 12-0-tetradecanoyl phorbol-13-acetate (TPA) enhanced the release of [3H]arachidonic acid into the culture medium. The effect of A23187 was significant as early as 5 min and the lowest effective dose was 5 X 10(-8)/M. On the other hand, TPA was effective only at dosages greater than 10(-6)M. These results suggest that the stimulatory effect of LHRH on arachidonic acid release is coupled more tightly to a Ca2+-dependent rather than a protein kinase C-mediated pathway.

Catalytic and receptor-binding properties of the calcium-sensitive phospholipid-dependent protein kinase (protein kinase C) in swine luteal cytosol

We have evaluated the catalytic and receptor-binding properties of protein kinase C in swine luteal cytosol using two complementary approaches: assay of catalytic activity assessed as the enzymatic transfer of radiolabeled phosphate to histone III-s acceptor protein in the presence of specific phospholipid, diacylglycerol, or phorbol ester and ionic calcium; and, the high-affinity binding of [3H]phorbol-12,13-dibutyrate ([3H]PDB) to the protein kinase C receptor. Catalytic properties of pig luteal protein kinase C included: absolute dependence on calcium ions for maximal activation (approximate ka = 0.5 microM); synergistic activation by 1,2-sn-diolein, phospholipid and calcium ions; and rank order of specific phospholipid activational potency: phosphatidylserine greater than phosphatidic acid greater than phosphatidylinositol greater than phosphatidylethanolamine greater than phosphatidylcholine. The enzyme was also activated by specific phorbol esters at the following half-maximally effective (ED50) concentrations: 12-O-tetradecanoylphorbol-13-acetate (TPA) 11 nM; phorbol-12,13-dibenzoate (PDBe) 26 nM; phorbol-12,13-dibutyrate (PDBu) 33 nM; mezerein 65 nM; and phorbol-12,13-diacetate (PDA) 130 nM. Phorbol-ester receptor properties of protein kinase C included specific, high-affinity (kd congruent to 19 nM), saturable, low-capacity (congruent to 44 pmol/mg protein) [3H]PDB binding sites. Moreover, the rank order of the equilibrium binding ID50s for various phorbol compounds was similar to that of catalytic ED50s: viz. 3 nM TPA; 8 nM PDBe; 16 nM PDBu; 19 nM mezerein; and 590 nM PDA. Thus, swine luteal cytosol contains catalytically active protein kinase C with specific phospholipid sensitivity, synergistic activation by diacylglycerol, phospholipid and calcium, and a strict dependence on ionic calcium concentrations that is influenced markedly by the presence of diacylglycerol.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of protein kinase C is coupled to prostaglandin F2 alpha synthesis in the ovary: studies in cultured swine granulosa cells

We have investigated the role of phospholipid-sensitive calcium-dependent protein kinase (protein kinase C) in prostaglandin F2 alpha synthesis by monolayer cultures of swine granulosa cells. In this system, specific phorbol ester derivatives known to activate protein kinase C significantly augmented the production of prostaglandin F2 alpha. Phorbol ester in conjunction with the ionophore A23187 synergistically increased prostaglandin F2 alpha production. These stimulatory actions were dose- and time-dependent, and could be abolished by the cyclooxygenase inhibitor, indomethacin, or the protein synthesis inhibitor, cycloheximide. Moreover, the rank order of potency of phorbol esters in enhancing prostaglandin F2 alpha production was concordant with that demonstrated for activation of protein kinase C in the swine ovary. In addition, a nonphorbol stimulator of protein kinase C, 1-octanoyl-2-acetylglycerol, also significantly enhanced prostaglandin F2 alpha biosynthesis. The synthesis of immunoassayable prostaglandin F2 alpha was confirmed by high-pressure liquid chromatographic purification of this radiolabeled metabolite of [3H]arachidonic acid. Thus, the present studies indicate that the protein kinase C effector pathway in the swine granulosa cell is functionally coupled to prostaglandin F2 alpha production.

Demonstration of protein kinase C activity in crustacean Y-organs, and partial definition of its role in regulation of ecdysteroidogenesis

Ecdysteroid-producing Y-organs from the crab Cancer antennarius were shown to possess enzyme activity that was stimulated in vitro by addition of Ca2+, phosphatidylserine, or the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA; ED50, 4 nM). In the presence of calcium and phosphatidylserine, PMA increased protein kinase C activity dose-dependently to a maximum 4-fold increase at 100 nM PMA. Stimulated protein kinase C activity was unaffected by calmodulin (100 nM) but was inhibited by 100 nM trifluoperazine. Pretreatment of cultured Y-organ segments with PMA elevated basal protein kinase C activity, whereas molt-inhibiting hormone (MIH) and calcium ionophore A23187 did not affect activity. PMA (1-100 nM) increased Y-organ steroidogenesis dose-dependently and alleviated suppression due to MIH or lysine vasopressin; PMA effects on steroidogenesis became evident after 2 h of incubation. Another phorbol activator of protein kinase C (phorbol 12, 13-dibutyrate) and a permeable synthetic diacylglycerol (1-oleoyl-2-acetyl-glycerol) stimulated ecdysteroidogenesis while an inactive phorbol (4 alpha-phorbol 12,13-didecanoate) and diolein were ineffective. The inhibitory effects on steroidogenesis of cholera toxin, forskolin, dibutyryl cAMP, and 3-isobutyl-1-methylxanthine were countered by PMA, but PMA did not alter basal or peptide hormone-stimulated Y-organ cAMP levels. Stimulatory effects on steroidogenesis of PMA and of A23187 were not additive, and PMA did not alter inhibition caused by lanthanum (calcium channel blocker) or trifluoperazine (calmodulin inhibitor). PMA increased the incorporation of [3H]leucine into Y-organ protein by 112%, and countered the suppressive effect of MIH on protein synthesis; PMA did not affect RNA synthesis. When Y-organs were suppressed with cycloheximide, PMA was unable to stimulate steroidogenesis. Actinomycin D alone had no effect on steroidogenesis but prevented stimulation by PMA. The results indicate that Y-organs contain protein kinase C activity which stimulates ecdysteroid production and protein synthesis by a mechanism not directly interactive with the cAMP or Ca2+-calmodulin systems.

Distribution and activation of protein kinase C in the rat testis tissue

The distribution and role of the calcium-activated, phospholipid-dependent protein kinase C (PK-C) was studied in rat testis. When testis tissue was homogenized in the presence of 2 mmol/l EDTA and EGTA, the majority (greater than 70%) of the PK-C activity was soluble, the rest was released from the particulate fraction by solubilization with 0.3% Triton X-100. Without chelating agents the soluble PK-C activity was undetectable, and only partially recovered from solubilized membranes. Preincubation of the tissue with the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA, 10(-7) mol/l) translocated PK-C to the membranes, and the majority of this activity was recovered by solubilization. Mobility of testicular soluble PK-C activity in HPLC-DEAE cellulose chromatography was similar to that of the brain enzyme. This single step purified testicular PK-C activity 140-fold. The specific activity and subcellular distribution of PK-C was similar in whole testis tissue and separated seminiferous tubules (160-210 pmol 32P X mg protein-1 X min-1 in the soluble and particulate fractions), but 2- to 3-fold higher in purified Leydig cells. However, the majority of total testicular PK-C activity appeared to be of tubular origin. Unilateral cryptorchidism for 1 week reduced PK-C of the abdominal testis by 50%, and the activity of dissected seminiferous tubules varied according to the epithelial wave. Both findings suggest that the bulk of the activity resides in the seminiferous epithelium. Involvement of PK-C in Leydig cell function was demonstrated using the TPA, which at 10(-7) mol/l inhibited basal cAMP production by 50% (P less than 0.01) but increased that of testosterone by 2- to 3-fold (P less than 0.01). On the other hand, when incubated with hCG, TPA inhibited both cAMP and testosterone production; the ED50s of hCG stimulation increased 4- to 10-fold with both parameters. It is concluded that PK-C activity is present in both the seminiferous tubules and Leydig cells, and is involved in the regulation of these testicular compartments. Its total activity and subcellular distribution are at variance according to the functional state and endocrine milieu of the testis.

Human chorionic gonadotropin activates the inositol 1,4,5-trisphosphate-Ca2+ intracellular signalling system in bovine luteal cells

Human chorionic gonadotropin, hCG, a hormone which increases intracellular cAMP, provoked rapid (30 s) and sustained (up to 30 min) increases in the levels of inositol mono-, bis- and trisphosphates (IP, IP2 and IP3, respectively) in bovine luteal cells. LiCl (10 mM) enhanced inositol phosphate accumulation in response to hCG. Concentration-dependent increases in inositol phosphates, cAMP and progesterone accumulation were observed in hCG-treated luteal cells. hCG also induced rapid and concentration-dependent increases in cytosolic free Ca2+ as measured by quin 2 fluorescence. These findings demonstrate that hCG stimulates the phospholipase C-IP3 and diacylglycerol 'second messenger' system in the bovine corpus luteum.

Postsynaptic effects of the phorbol ester TPA on frog end-plates

The effects of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a specific activator of protein kinase C (PKc), were examined on the frog neuromuscular junction. The depolarization elicited by iontophoretically applied acetylcholine (ACh) was reversibly decreased by 20-60% when muscle fibres were exposed to 1-5 X 10(-7) M TPA. Liposome-delivered phosphatidylcholine (100 micrograms/ml) prevented this effect. A similar decrease in ACh-sensitivity was produced by diacylglycerol (diolein), a physiological activator of PKc, but in this case the decrease was only partially reversible. In TPA-Ringer, the peak size of miniature end-plate potentials exhibited a small decrease; miniature end-plate currents were reduced in size and their decay time constant became longer and relatively independent of membrane potential. The possibility that these TPA-induced actions are mediated by activation of PKc is discussed.

Recent advances in corpus luteum physiology

Development, maintenance, and regression of the corpus luteum have been investigated for many years. However, endocrine and cellular mechanisms regulating progesterone synthesis and secretion remain unclear. Because comprehensive reviews of factors affecting luteal function have been published recently, this paper discusses several emerging concepts that may be important in understanding the regulation of luteal progesterone synthesis and secretion. Concepts discussed include preovulatory follicular determinants of subsequent luteal function, hormonal stimulation of progesterone synthesis, effect of different luteal cell types on progesterone secretion, and role of secretory granules in luteal function.

Mechanisms of action of gonadotropin releasing hormone on rat granulosa cells

To elucidate the mechanisms of stimulatory actions of GnRH on rat granulosa cells (GC), we have compared the actions of a GnRH agonist with those of a tumor-promoting phorbol ester, 12-0-tetradecanoylphorbol 13-acetate (TPA) and Ca+2 ionophore, A23187. GC were obtained from immature (28-29 days old) rats 48 h after injection of 20 IU PMSG. Following prelabeling with 3[H]arachidonic acid (AA), the cells were incubated with the test substances for 10 min and AA release determined. A GnRH agonist, [D-Ala6, des-Gly-NH2(10)] GnRH ethylamide (GnRHa; 10 ng/ml) increased AA release 175% compared to the control value. AA release in the presence of GnRHa was larger than that due to 1 microM A23187 or 40 nM TPA alone. A23187 or TPA increased GnRHa-stimulated AA release further. GC were incubated with the test substances for longer time periods, i.e., up to 5 h. GnRHa caused a 4-fold increase in prostaglandin (PG) synthase activity at 5 h. GnRHa increased PGE accumulation to the same extent as TPA, but only increased PG synthase activity about half as much. In combination with TPA, GnRHa had no influence on TPA-stimulated PG synthase activity, but increased PGE accumulation to levels comparable to those with A23187 plus TPA. GnRHa caused a 2.5 fold increase in progesterone (P) accumulation, which was the same as TPA. P accumulation in the presence of GnRHa was affected by neither A23187 nor TPA. These data indicate that the combination of TPA and A23187 can substitute for GnRH action on PGE and P accumulation in rat GC.

Protein kinase C in adrenal cells: possible role in regulation of steroid synthesis

Y-1 adrenal tumor cells and rat fasciculata cells were shown to possess an enzyme with the properties of protein kinase C. Activity was stimulated by Ca2+ and phospholipid (specifically phosphatidylserine). Enzyme activity was stimulated by addition of phorbol ester to a cell homogenate (ED50 10 nM) and inhibited by trifluoperazine (ID50 10 microM). ACTH and cyclic AMP added to Y-1 cells increased the activity of protein kinase C. Dose-response curves with ACTH showed that the hormone was effective in stimulating protein kinase C at lower concentrations than those required to increase steroid synthesis. When phorbol ester was added to Y-1 cells, total kinase C activity was diminished. Neither phorbol ester nor ACTH causes redistribution of protein kinase C between membranes and cytosol. Phorbol ester also stimulates steroid production by Y-1 cells. Protein kinase C phosphorylates 5 proteins in Y-1 cells (67, 61, 32, 16 and less than 14.4 kDa). Puromycin and cycloheximide increase the activity of protein kinase C in adrenal cells. It is concluded that protein kinase C may play an ancillary role in regulation of adrenal steroid synthesis but does not mediate the classical steroidogenic response that results from activation of adenylate cyclase by ACTH.

Gonadotropin-releasing hormone as a modulator of ovarian function

GnRH and its agonist analogs exert direct inhibitory and stimulatory effects on the ovaries of animals from several species. In the immature follicle, GnRH inhibits the actions of FSH on an integrated array of biochemical responses that lead to follicular development and corpus luteum formation. GnRH also suppresses gonadotropin action in mature follicles, and stimulates certain ovarian processes such as steroidogenesis and oocyte maturation. The inhibitory and stimulatory effects of GnRH are mediated through the binding of the peptide to high-affinity receptors in granulosa and thecal cells. Recent studies have shown that GnRH action in the ovary is dependent upon calcium mobilization and probably operates through stimulation of phospholipid turnover and activation of protein kinase C.