Prostaglandin F2alpha stimulates the Raf/MEK1/mitogen-activated protein kinase signaling cascade in bovine luteal cells

Expression patterns of chemokine (C-C motif) ligand 2, prostaglandin F2A receptor and immediate early genes at mRNA level in the bovine corpus luteum after intrauterine treatment with a low dose of prostaglandin F2A

The present study evaluated expression patterns of chemokine (C-C motif) ligand 2 gene/Monocyte chemoattractant protein-1 gene (CCL2/MCP-1), prostaglandin F2 alpha receptor gene (PTGFR) and immediate early genes including nuclear receptor subfamily 4, group A, member 1 (NR4A1), early growth response 1 (EGR1) and FBJ murine osteosarcoma viral oncogene homolog (FOS) in cells of the bovine corpus luteum after intrauterine infusion of a low dose of prostaglandin F2α (PGF2A) aimed at enhancing our understanding of the mechanisms of luteolysis. Holstein dairy cows were superovulated (>6 corpora lutea [CL]) and on day 9 of the estrous cycle were infused with a low dose of PGF2A (0.5 mg PGF2A in 0.25 ml phosphate buffered saline) into the greater curvature of the uterine horn ipsilateral to the CL. Ultrasound-guided biopsy samples of different CL were collected at 0 min, 15 min, 30 min, 1h, 2h and 6h after PGF2A infusion. Expression profiles and localization of mRNA for PTGFR, CCL2/MCP-1, and immediate early genes (NR4A1, EGR1 and FOS), were investigated by using qPCR and in situ hybridization. The concentrations of early response genes including FOS, NR4A1, and EGR1 exhibited the greatest increase at 30 min after PGF2A, compared to other time points. Expression profile of CCL2 mRNA increased gradually after intrauterine infusion of PGF2A with maximal up-regulation for CCL2 at 6h. Abundance of PTGFR mRNA only increased at 15 min and significantly decreased at 6h, compared to 0 min. Cellular localizations of all studied genes except CCL2 (primarily localized to apparent immune cells) were predominantly visualized in large luteal cells. Interestingly, early response genes demonstrated a changing profile in cellular localization with initial responses appearing to be in both large luteal cells and endothelial cells, although no staining for PTGFR mRNA was observed in endothelial cells. Later, sustained responses, were only observed in large luteal cells, although PTGFR mRNA was decreasing in large luteal cells over time after PGF2A. The involvement of the immune system was also highlighted by the immediate increases in CCL2 mRNA that became much greater over time as there was an apparent influx of CCL2-positive immune cells. Thus, the temporal and cell-specific localization patterns for the studied mRNA demonstrate the complex pathways that are responsible for initiation of luteolysis in the bovine CL.

A phosphorylation of RIPK3 kinase initiates an intracellular apoptotic pathway that promotes prostaglandin2α-induced corpus luteum regression

Receptor-interacting serine/threonine-protein kinase 3 (RIPK3) normally signals to necroptosis by phosphorylating MLKL. We report here that when the cellular RIPK3 chaperone Hsp90/CDC37 level is low, RIPK3 also signals to apoptosis. The apoptotic function of RIPK3 requires phosphorylation of the serine 165/threonine 166 sites on its kinase activation loop, resulting in inactivation of RIPK3 kinase activity while gaining the ability to recruit RIPK1, FADD, and caspase-8 to form a cytosolic caspase-activating complex, thereby triggering apoptosis. We found that PGF2α induces RIPK3 expression in luteal granulosa cells in the ovary to cause luteal regression through this RIPK3-mediated apoptosis pathway. Mice carrying homozygous phosphorylation-resistant RIPK3 S165A/T166A knockin mutations failed to respond to PGF2α but retained pro-necroptotic function, whereas mice with phospho-mimicking S165D/T166E homozygous knock-in mutation underwent spontaneous apoptosis in multiple RIPK3-expressing tissues and died shortly after birth. Thus, RIPK3 signals to either necroptosis or apoptosis depending on its serine 165/threonine 166 phosphorylation status.

Luteinizing hormone regulates the phosphorylation and localization of the mitochondrial effector dynamin-related protein-1 (DRP1) and steroidogenesis in the bovine corpus luteum

The corpus luteum is an endocrine gland that synthesizes and secretes progesterone. Luteinizing hormone (LH) activates protein kinase A (PKA) signaling in luteal cells, increasing delivery of substrate to mitochondria for progesterone production. Mitochondria maintain a highly regulated equilibrium between fusion and fission in order to sustain biological function. Dynamin-related protein 1 (DRP1), is a key mediator of mitochondrial fission. The mechanism by which DRP1 is regulated in the ovary is largely unknown. We hypothesize that LH via PKA differentially regulates the phosphorylation of DRP1 on Ser616 and Ser637 in bovine luteal cells. In primary cultures of steroidogenic small luteal cells (SLCs), LH, and forskolin stimulated phosphorylation of DRP1 (Ser 637), and inhibited phosphorylation of DRP1 (Ser 616). Overexpression of a PKA inhibitor blocked the effects of LH and forskolin on DRP1 phosphorylation. In addition, LH decreased the association of DRP1 with the mitochondria. Genetic knockdown of the DRP1 mitochondria receptor, and a small molecule inhibitor of DRP1 increased basal and LH-induced progesterone production. Studies with a general Dynamin inhibitor and siRNA knockdown of DRP1 showed that DRP1 is required for optimal LH-induced progesterone biosynthesis. Taken together, the findings place DRP1 as an important target downstream of PKA in steroidogenic luteal cells.

Analysis of Vascular Hydrogen Sulfide Biosynthesis

With potent vasodilatory and pro-angiogenic properties, hydrogen sulfide (H₂S) is now accepted as the third gasotransmitter after nitric oxide (NO) and carbon monoxide. Endogenous H₂S is mainly synthesized by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). Akin to previous studies showing hormonal regulation of NO biosynthesis, we first reported that uterine and systemic artery H₂S biosynthesis is regulated by exogenous estrogens in an ovariectomized sheep model of estrogen replacement therapy, specifically stimulating CBS, but not CSE, expression, in uterine (UA) and mesenteric (MA), but not carotid (CA), arteries in ovariectomized nonpregnant sheep. We have found significantly elevated H₂S biosynthesis due to CBS upregulation under estrogen-dominant physiological states, the proliferative phase of menstrual cycle and pregnancy in primary human UAs. Our studies have pioneered the role of H₂S biology in uterine hemodynamics regulation although there is still much that needs to be learned before a thorough elucidation of a role that H₂S plays in normal physiology of uterine hemodynamics and its dysregulation under pregnancy complications can be determined. In this chapter we describe a series of methods that we have optimized for analyzing vascular H₂S biosynthesis, including (1) real-time quantitative PCR (qPCR) for assessing tissue and cellular levels of CBS and CSE mRNAs, (2) immunoblotting for assessing CBS and CSE proteins, (3) semiquantitative immunofluorescence microscopy to specifically localize CBS and CSE proteins on vascular wall and to quantify their cellular expression levels, and (4) methylene blue assay for assessing H₂S production in the presence of selective CBS and CSE inhibitors.

Temporal regulation of extracellular signal-regulated kinase 1/2 phosphorylation, heat shock protein 70 and activating transcription factor 3 during prostaglandin F-induced luteal regression in pseudopregnant rats following heat stress

The aim of the present study was to investigate the effects of heat stress on heat shock protein (HSP) 70 expression and mitogen-activated protein kinase (MAPK) and protein kinase (PK) B signalling during prostaglandin F (PGF)-induced luteal regression. During pseudopregnancy, rats were exposed to heat stress (HS, 40°C, 2h) for 7 days and treated with PGF or physiological saline on Day 7; serum and ovaries were collected 0, 1, 2, 8 or 24h after PGF treatment. The early inhibitory effect of PGF on progesterone was reduced in HS rats. HSP70 expression in response to PGF was significantly enhanced in HS rats. PGF-induced phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 was significantly greater in the HS group; however, HS rats exhibited elevated basal levels of phosphorylation of p38 MAPK, but not ERK1/2. PGF treatment increased expression of activating transcription factor (ATF) 3 at 2h, which was inhibited by heat stress. Evaluating PKB signalling revealed that phosphorylation of p-Akt (Thr³⁰⁸ and Ser⁴⁷³) was reduced at 8 and 24h after PGF treatment in both non-heat stress (NHS) and HS groups, but there were no significant differences between the HS and NHS groups at any of the time points. In conclusion, the present study provides further evidence that heat stress may enhance HSP70 and affect ERK1/2 and ATF3 expression, but not Akt activation, during PGF-induced luteal regression in pseudopregnant rats.

Influence of omega-3 fatty acids on bovine luteal cell plasma membrane dynamics

Fish oil is a rich source of omega-3 fatty acids which disrupt lipid microdomain structure and affect mobility of the prostaglandin F_2α (FP) receptor in bovine luteal cells. The objectives of this study were to determine the effects of individual omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on 1) membrane fatty acid composition, 2) lipid microdomain structure, and 3) lateral mobility of the FP receptor in bovine luteal cells. Ovaries were collected from a local abattoir (n=5/experiment). The corpus luteum was resected and enzymatically digested using collagenase to generate a mixed luteal cell population. In all experiments, luteal cells were treated with 0, 1, 10 or 100μM EPA or DHA for 72h to allow incorporation of fatty acids into membrane lipids. Results from experiment 1 show that culturing luteal cells in the presence of EPA or DHA increased these luteal fatty acids. In experiment 2, both EPA and DHA increased spatial distribution of lipid microdomains in a dose-dependent manner. Single particle tracking results from experiment 3 show that increasing both EPA and DHA concentrations increased micro- and macro-diffusion coefficients, increased domain size, and decreased residence time of FP receptors. Collectively, results from this study demonstrate similar effects of EPA and DHA on lipid microdomain structure and lateral mobility of FP receptors in cultured bovine luteal cells. Moreover, only 10μM of either fatty acid was needed to mimic the effects of fish oil.

Early transcriptome responses of the bovine midcycle corpus luteum to prostaglandin F2α includes cytokine signaling

In ruminants, prostaglandin F2alpha (PGF2α)-mediated luteolysis is essential prior to estrous cycle resumption, and is a target for improving fertility. To deduce early PGF2α-provoked changes in the corpus luteum a short time-course (0.5-4 h) was performed on cows at midcycle. A microarray-determined transcriptome was established and examined by bioinformatic pathway analysis. Classic PGF2α effects were evident by changes in early response genes (FOS, JUN, ATF3) and prediction of active pathways (PKC, MAPK). Several cytokine transcripts were elevated and NF-κB and STAT activation were predicted by pathway analysis. Self-organizing map analysis grouped differentially expressed transcripts into ten mRNA expression patterns indicative of temporal signaling cascades. Comparison with two analogous datasets revealed a conserved group of 124 transcripts similarly altered by PGF2α treatment, which both, directly and indirectly, indicated cytokine activation. Elevated levels of cytokine transcripts after PGF2α and predicted activation of cytokine pathways implicate inflammatory reactions early in PGF2α-mediated luteolysis.

Induction of chemokines and prostaglandin synthesis pathways in luteinized human granulosa cells: potential role of luteotropin withdrawal and prostaglandin F2α in regression of the human corpus luteum

Our objective was to determine the effects of prostaglandin F2α (PGF2α) and withdrawal of luteotropic stimulants (forskolin or hCG) on expression of chemokines and prostaglandin-endoperoxide synthase 2 (PTGS2) in luteinized human granulosa cells. Human granulosa cells were collected from 12 women undergoing oocyte retrieval and were luteinized in vitro with forskolin or hCG. In first experiment, granulosa-lutein cells were treated with PGF2α, the primary luteolytic hormone in most species. In second experiment, granulosa cells that had been luteinized for 8 d had luteotropins withdrawn for 1, 2, or 3 d. Treatment with PGF2α induced mRNA for chemokine (c-x-c motif) ligand 2 (CXCL2) and CXC ligand 8 (CXCL8; also known as interleukin-8) in granulosa cells luteinized for 8 d but not in cells that were only luteinized for 2 d. Similarly, luteinization of human granulosa cells for 8 d with forskolin or hCG followed by withdrawal of luteotropic stimulants, not only decreased P4 production, but also increased mRNA concentrations for CXCL8, CXCL-2 (after forskolin withdrawal), and PTGS2. These results provide evidence for two key steps in differentiation of luteolytic capability in human granulosa cells. During 8 d of luteinization, granulosa cells acquire the ability to respond to luteolytic factors, such as PGF2α, with induction of genes involved in immune function and PG synthesis. Finally, a decline in luteotropic stimuli triggers similar pathways leading to induction of PTGS2 and possibly intraluteal PGF2α production, chemokine expression, leukocyte infiltration and activation, and ultimately luteal regression.

Prostaglandin F2α induces expression of activating transcription factor 3 (ATF3) and activates MAPK signaling in the rat corpus luteum

The current study was conducted to evaluate the expression of ATF3, in association with the activation of mitogen-activated protein kinases (MAPK) during prostaglandin F2α analog (PGF)-induced luteal regression in rats. A sequential PMSG/hCG treatment paradigm was used to obtain a single, well-defined generation of corpora lutea (CL) in rats. Rats were treated with PGF for 0-4h on day 7 of pseudopregnancy. Results showed that serum progesterone (P4) concentrations declined in a time dependent manner. Western blot results revealed that ATF3 increased within 2h post-PGF injection. Phosphorylated ERK1/2 (p-ERK) and JNK (p-JNK) increased within 30min and then were gradually reduced in response to PGF. In contrast, the levels of phosphorylated p38 MAPK (p-p38) were not significantly altered. The immunostaining density for p-ERK decreased from the periphery to the center of the corpus luteum following treatment with PGF, while ATF3 was expressed uniformly in the nuclei of luteal steroidogenic cells. These results indicated that treatment with PGF in vivo could induce increases in MAPK phosphorylation, especially in p-ERK, which might be correlated with the increases in ATF3 expression and the decline in P4 concentrations. To our knowledge, this is the first study to provide evidence for temporal relationships between MAPK activation and ATF3 expression during PGF-induced luteal regression in the rat.

Estrogen promotes luteolysis by redistributing prostaglandin F2α receptors within primate luteal cells

Prostaglandin F2α (PGF2α) has been proposed as a functional luteolysin in primates. However, administration of PGF2α or prostaglandin synthesis inhibitors in vivo both initiate luteolysis. These contradictory findings may reflect changes in PGF2α receptors (PTGFRs) or responsiveness to PGF2α at a critical point during the life span of the corpus luteum. The current study addressed this question using ovarian cells and tissues from female cynomolgus monkeys and luteinizing granulosa cells from healthy women undergoing follicle aspiration. PTGFRs were present in the cytoplasm of monkey granulosa cells, while PTGFRs were localized in the perinuclear region of large, granulosa-derived monkey luteal cells by mid-late luteal phase. A PTGFR agonist decreased progesterone production in luteal cells obtained at mid-late and late luteal phases, but did not decrease progesterone production by granulosa cells or luteal cells from younger corpora lutea. These findings are consistent with a role for perinuclear PTGFRs in functional luteolysis. This concept was explored using human luteinizing granulosa cells maintained in vitro as a model for luteal cell differentiation. In these cells, PTGFRs relocated from the cytoplasm to the perinuclear area in an estrogen- and estrogen receptor-dependent manner. Similar to our findings with monkey luteal cells, human luteinizing granulosa cells with perinuclear PTGFRs responded to a PTGFR agonist with decreased progesterone production. These data support the concept that PTGFR stimulation promotes functional luteolysis only when PTGFRs are located in the perinuclear region. Estrogen receptor-mediated relocation of PTGFRs within luteal cells may be a necessary step in the initiation of luteolysis in primates.

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.

Prostaglandin E2 regulation of amnion cell vascular endothelial growth factor expression: relationship with intramembranous absorption rate in fetal sheep

We hypothesized that prostaglandin E2 (PGE2) stimulates amniotic fluid transport across the amnion by upregulating vascular endothelial growth factor (VEGF) expression in amnion cells and that amniotic PGE2 concentration correlates positively with intramembranous (IM) absorption rate in fetal sheep. The effects of PGE2 at a range of concentrations on VEGF 164 and caveolin-1 gene expressions were analyzed in cultured ovine amnion cells. IM absorption rate, amniotic fluid (AF) volume, and PGE2 concentration in AF were determined in late-gestation fetal sheep during control conditions, isovolumic fetal urine replacement (low IM absorption rate), or intra-amniotic fluid infusion (high IM absorption rate). In ovine amnion cells, PGE2 induced dose- and time-dependent increases in VEGF 164 mRNA levels and reduced caveolin-1 mRNA and protein levels. VEGF receptor blockade abolished the caveolin-1 response, while minimally affecting the VEGF response to PGE2. In sheep fetuses, urine replacement reduced amniotic PGE2 concentration by 58%, decreased IM absorption rate by half, and doubled AF volume (P < 0.01). Intra-amniotic fluid infusion increased IM absorption rate and AF volume (P < 0.01), while amniotic PGE2 concentration was unchanged. Neither IM absorption rate nor AF volume correlated with amniotic PGE2 concentration under each experimental condition. Although PGE2 at micromolar concentrations induced dose-dependent responses in VEGF and caveolin-1 gene expression in cultured amnion cells consistent with a role of PGE2 in activating VEGF to mediate AF transport across the amnion, amniotic PGE2 at physiological nanomolar concentrations does not appear to regulate IM absorption rate or AF volume.

Effects of IL8 and immune cells on the regulation of luteal progesterone secretion

Recent studies have suggested that chemokines may mediate the luteolytic action of prostaglandin F2α (PGF). Our objective was to identify chemokines induced by PGF in vivo and to determine the effects of interleukin 8 (IL8) on specific luteal cell types in vitro. Mid-cycle cows were injected with saline or PGF, ovaries were removed after 0.5-4 h, and expression of chemokine was analyzed by qPCR. In vitro expression of IL8 was analyzed after PGF administration and with cell signaling inhibitors to determine the mechanism of PGF-induced chemokine expression. Purified neutrophils were analyzed for migration and activation in response to IL8 and PGF. Purified luteal cell types (steroidogenic, endothelial, and fibroblast cells) were used to identify which cells respond to chemokines. Neutrophils and peripheral blood mononuclear cells (PBMCs) were cocultured with steroidogenic cells to determine their effect on progesterone production. IL8, CXCL2, CCL2, and CCL8 transcripts were rapidly increased following PGF treatment in vivo. The stimulatory action of PGF on IL8 mRNA expression in vitro was prevented by inhibition of p38 and JNK signaling. IL8, but not PGF, TNF, or TGFB1, stimulated neutrophil migration. IL8 had no apparent action in purified luteal steroidogenic, endothelial, or fibroblast cells, but stimulated ERK phosphorylation in neutrophils. In coculture experiments neither IL8 nor activated neutrophils altered basal or LH-stimulated luteal cell progesterone synthesis. In contrast, activated PBMCs inhibited LH-stimulated progesterone synthesis from cultured luteal cells. These data implicate a complex cascade of events during luteolysis, involving chemokine signaling, neutrophil recruitment, and immune cell action within the corpus luteum.

ATF3 expression in the corpus luteum: possible role in luteal regression

The present study investigated the induction and possible role of activating transcription factor 3 (ATF3) in the corpus luteum. Postpubertal cattle were treated at midcycle with prostaglandin F2α(PGF) for 0-4 hours. Luteal tissue was processed for immunohistochemistry, in situ hybridization, and isolation of protein and RNA. Ovaries were also collected from midluteal phase and first-trimester pregnant cows. Luteal cells were prepared and sorted by centrifugal elutriation to obtain purified small (SLCs) and large luteal cells (LLCs). Real-time PCR and in situ hybridization showed that ATF3 mRNA increased within 1 hour of PGF treatment in vivo. Western blot and immunohistochemistry demonstrated that ATF3 protein was expressed in the nuclei of LLC within 1 hour and was maintained for at least 4 hours. PGF treatment in vitro increased ATF3 expression only in LLC, whereas TNF induced ATF3 in both SLCs and LLCs. PGF stimulated concentration- and time-dependent increases in ATF3 and phosphorylation of MAPKs in LLCs. Combinations of MAPK inhibitors suppressed ATF3 expression in LLCs. Adenoviral-mediated expression of ATF3 inhibited LH-stimulated cAMP response element reporter luciferase activity and progesterone production in LLCs and SLCs but did not alter cell viability or change the expression or activity of key regulators of progesterone synthesis. In conclusion, the action of PGF in LLCs is associated with the rapid activation of stress-activated protein kinases and the induction of ATF3, which may contribute to the reduction in steroid synthesis during luteal regression. ATF3 appears to affect gonadotropin-stimulated progesterone secretion at a step or steps downstream of PKA signaling and before cholesterol conversion to progesterone.

AKR1C3 as a target in castrate resistant prostate cancer

Aberrant androgen receptor (AR) activation is the major driver of castrate resistant prostate cancer (CRPC). CRPC is ultimately fatal and more therapeutic agents are needed to treat this disease. Compounds that target the androgen axis by inhibiting androgen biosynthesis and or AR signaling are potential candidates for use in CRPC treatment and are currently being pursued aggressively. Aldo-keto reductase 1C3 (AKR1C3) plays a pivotal role in androgen biosynthesis within the prostate. It catalyzes the 17-ketoreduction of weak androgen precursors to give testosterone and 5α-dihydrotestosterone. AKR1C3 expression and activity has been implicated in the development of CRPC, making it a rational target. Selective inhibition of AKR1C3 will be important, however, due to the presence of closely related isoforms, AKR1C1 and AKR1C2 that are also involved in androgen inactivation. We examine the evidence that supports the vital role of AKR1C3 in CRPC and recent developments in the discovery of potent and selective AKR1C3 inhibitors. This article is part of a Special Issue entitled 'CSR 2013'.

Biasing the prostaglandin F2α receptor responses toward EGFR-dependent transactivation of MAPK

The G protein-coupled prostaglandin F2α (PGF2α) receptor [F prostanoid (FP) receptor] has been implicated in many physiological events including cardiovascular, respiratory, immune, reproductive, and endocrine responses. Binding of PGF2α to FP receptor elicits inositol production and protein kinase C-dependent MAPK activation through Gα(q) coupling. Here we report that AL-8810, previously characterized as an orthosteric antagonist of PGF2α-dependent, Gα(q)-mediated signaling, potently activates ERK1/2 in a protein kinase C-independent manner. Rather, AL-8810 promoted ERK1/2 activation via an epidermal growth factor receptor transactivation mechanism in both human embryonic kidney 293 cells and in the MG-63 osteoblast-like cells, which express endogenous FP receptors. Neither AL-8810- nor PGF2α-mediated stimulation of FP receptor promoted association with β-arrestins, suggesting that MAPK activation induced by these ligands is independent of β-arrestin's signaling scaffold functions. Interestingly, the spatiotemporal activation of ERK1/2 promoted by AL-8810 and PGF2α showed almost completely opposite responses in the nucleus and the cytosol. Finally, using [(3)H]thymidine incorporation, we noted differential regulation of PGF2α- and AL-8810-induced cell proliferation in MG-63 cells. This study reveals, for the first time, the signaling biased nature of FP receptor orthosteric ligands toward MAPK signaling. Our findings on the specific patterns of ERK1/2 activation promoted by FP receptor ligands may help dissect the distinct roles of MAPK in FP receptor-dependent physiological responses.

Patterns of gene expression in the bovine corpus luteum following repeated intrauterine infusions of low doses of prostaglandin F2alpha

Natural luteolysis involves multiple pulses of prostaglandin F2alpha (PGF) released by the nonpregnant uterus. This study investigated expression of 18 genes from five distinct pathways, following multiple low-dose pulses of PGF. Cows on Day 9 of the estrous cycle received four intrauterine infusions of 0.25 ml of phosphate-buffered saline (PBS) or PGF (0.5 mg of PGF in 0.25 ml of PBS) at 6-h intervals. A luteal biopsy sample was collected 30 min after each PBS or PGF infusion. There were four treatment groups: Control (n = 5; 4 PBS infusions), 4XPGF (4 PGF infusions; n = 5), 2XPGF-non-regressed (2 PGF infusions; n = 5; PGF-PBS-PGF-PBS; no regression after treatments), and 2XPGF-regressed (PGF-PBS-PGF-PBS; regression after treatments; n = 5). As expected, the first PGF pulse increased mRNA for the immediate early genes JUN, FOS, NR4A1, and EGR1 but unexpectedly also increased mRNA for steroidogenic (STAR) and angiogenic (VEGFA) pathways. The second PGF pulse induced immediate early genes and genes related to immune system activation (IL1B, FAS, FASLG, IL8). However, mRNA for VEGFA and STAR were decreased by the second PGF infusion. After the third and fourth PGF pulses, a distinctly luteolytic pattern of gene expression was evident, with inhibition of steroidogenic and angiogenic pathways, whereas, there was induction of pathways for immune system activation and production of PGF. The pattern of PGF-induced gene expression was similar in corpus luteum not destined for luteolysis (2X-non-regressed) after the first PGF pulse but was very distinct after the second PGF pulse. Thus, although the initial PGF pulse induced mRNA for many pathways, the second and later pulses of PGF appear to have set the distinct pattern of gene expression that result in luteolysis.

Discovery of substituted 3-(phenylamino)benzoic acids as potent and selective inhibitors of type 5 17β-hydroxysteroid dehydrogenase (AKR1C3)

Aldo-keto reductase 1C3 (AKR1C3) also known as type 5 17β-hydroxysteroid dehydrogenase has been implicated as one of the key enzymes driving the elevated intratumoral androgen levels observed in castrate resistant prostate cancer (CRPC). AKR1C3 inhibition therefore presents a rational approach to managing CRPC. Inhibitors should be selective for AKR1C3 over other AKR1C enzymes involved in androgen metabolism. We have synthesized 2-, 3-, and 4-(phenylamino)benzoic acids and identified 3-(phenylamino)benzoic acids that have nanomolar affinity and exhibit over 200-fold selectivity for AKR1C3 versus other AKR1C isoforms. The AKR1C3 inhibitory potency of the 4'-substituted 3-(phenylamino)benzoic acids shows a linear correlation with both electronic effects of substituents and the pK(a) of the carboxylic acid and secondary amine groups, which are interdependent. These compounds may be useful in treatment and/or prevention of CRPC as well as understanding the role of AKR1C3 in endocrinology.

Effect of decreasing intraluteal progesterone on sensitivity of the early porcine corpus luteum to the luteolytic actions of prostaglandin F2alpha

Prostaglandin F2alpha (PGF) causes luteolysis of the pig corpus luteum (CL) only after Day 12 of the estrous cycle. Recent evidence indicates that progesterone (P4) may protect the CL from cell death. The present study tested the hypothesis that acute inhibition of P4 by treatment with epostane (EPO; 3betaHSD inhibitor) in CL lacking luteolytic capacity (Day 9 CL) will allow PGF to induce responses associated with luteolysis. Multiple PGF-induced responses were evaluated, including genes involved in production of PGF and estradiol-17beta, apoptosis (caspase 3), and transcription (FOSB). These responses are associated with PGF-induced luteolysis and do not normally occur in CL lacking luteolytic capacity. Animals on Day 7 after estrus were divided into four groups: 1) control (C), 2) PGF, 3) EPO, and 4) PGF plus EPO (PGF+EPO). Treatment with EPO (10 mg/kg) or vehicle was given every 12 h for 36 h. Treatment with PGF (25 mg) or vehicle was given at 38 h, and CL were collected from all animals at 48 h. Some CL from each animal were frozen in liquid nitrogen for mRNA and protein analysis. Remaining CL were incubated in media for 2 h for determination of P4 and PGF production. EPO dramatically decreased production of P4 by luteal tissue (ng/mg tissue) by 90% and 95% in EPO and PGF+EPO groups, respectively, compared to C (P < 0.01). Low production of PGF by luteal tissue was found in C, PGF, and EPO groups; however, treatment with PGF+EPO dramatically increased (782%) luteal PGF production. Similar to intraluteal PGF production, increased mRNA for cyclooxygenase 2 (PTGS2) and phospholipase A2 (group IB; PLA2G1B) was found in the PGF+EPO, but not in the EPO or PGF, group. Aromatase (CYP19A1) mRNA was not induced by PGF or EPO; however, PGF+EPO caused a more than 40-fold increase in CYP19A1 mRNA (P < 0.01). CASP3 mRNA was increased (P < 0.01) by EPO (3.4-fold) and by PGF (2.7-fold) but was most dramatically increased by PGF+EPO (5.3-fold), whereas caspase activity was only increased by PGF (1.5-fold) or PGF+EPO (2.2-fold). Thus, these data support the hypothesis that elimination of the protective effect of intraluteal P4 does not directly cause luteolysis of the early CL but allows PGF to induce luteolytic responses in CL lacking luteolytic capacity.

Regulation of caveolin-1 expression and phosphorylation by VEGF in ovine amnion cells

Vascular endothelial growth factor (VEGF) has been implicated in the regulation of vesicular transport of amniotic fluid via caveolae across the amnion. This study tested the hypothesis that VEGF regulates caveolar function by stimulating caveolin-1 expression and phosphorylation in ovine amniotic epithelial cells (oAECs). Using primary cultures of oAECs, caveolin-1 was identified by immunofluorescent staining. Caveolin-1 messenger RNA (mRNA) abundance was determined by Reverse Transcription-Polymerase Chain Reaction (RT-PCR) and protein by Western blotting. The effects of VEGF( 165) on caveolin-1 expression and phosphorylation were determined. Caveolin-1 immunoreactivity was detected in oAECs. In response to 10 ng/mL VEGF( 165), caveolin-1 mRNA levels increased whereas the protein levels were unaffected. Furthermore, VEGF stimulated caveolin-1 phosphorylation, an effect abrogated by the inhibition of c-Src protein kinase. These data suggest that VEGF upregulates caveolin-1 activity through c-Src signaling pathways. Our observations support the hypothesis that VEGF regulates amniotic fluid transport across the amnion by stimulating caveolin-1 activity to mediate caveolar function in amnion 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.

Compartmentalizing VEGF-induced ERK2/1 signaling in placental artery endothelial cell caveolae: a paradoxical role of caveolin-1 in placental angiogenesis in vitro

On vascular endothelial growth factor (VEGF) stimulation, both VEGF R1 and R2 receptors were phosphorylated in ovine fetoplacental artery endothelial (oFPAE) cells. Treatment with VEGF stimulated both time- and dose-dependent activation of ERK2/1 in oFPAE cells. VEGF-induced ERK2/1 activation was mediated by VEGFR2, but not VEGFR1, and was linked to intracellular calcium, protein kinase C, and Raf-1. VEGF stimulated oFPAE cell proliferation, migration, and tube formation in vitro. Blockade of ERK2/1 pathway attenuated VEGF-induced cell proliferation and tube formation but failed to inhibit migration in oFPAE cells. Disruption of caveolae by cholesterol depletion with methyl-beta-cyclodextrin or by down-regulation of its structural protein caveolin-1 blunted VEGF-induced ERK2/1 activation, proliferation, and tube formation in oFPAE cells, indicating an essential role of integral caveolae in these VEGF-induced responses. Adenoviral overexpression of caveolin-1 and addition of a caveolin scaffolding domain peptide also inhibited VEGF-stimulated ERK2/1 activation, cell proliferation, and tube formation in oFPAE cells. Furthermore, molecules comprising the ERK2/1 signaling module, including VEGFR2, protein kinase Calpha, Raf-1, MAPK kinase 1/2, and ERK2/1, resided with caveolin-1 in caveolae. VEGF transiently stimulated ERK2/1 activation in the caveolae similarly as in intact cells. Caveolae disruption greatly diminished ERK2/1 activation by VEGF in oFPAE cell caveolae. We conclude that caveolae function as a platform for compartmentalizing the VEGF-induced ERK2/1 signaling module. Caveolin-1 and caveolae play a paradoxical role in regulating VEGF-induced ERK2/1 activation and in vitro angiogenesis as evidenced by the similar inhibitory effects of down-regulation and overexpression of caveolin-1 and disruption of caveolae in oFPAE cells.

Hypoxia modulation of caveolin-1 and vascular endothelial growth factor in ovine fetal membranes

During normal pregnancy, amniotic fluid is absorbed from the amniotic compartment into fetal blood through the intramembranous blood vessels in the fetal membranes. It has been hypothesized that this transport process is mediated by transcytosis of caveolae-like vesicles. Because fetal hypoxia increases intramembranous absorption, the authors explore the effects of hypoxia on the gene expression of caveolin-1, a structural protein of caveolae, in ovine fetal membranes and cultured amnion cells. Near-term ovine fetuses were rendered hypoxic for 4 days. Caveolin-1 mRNA and protein levels were significantly reduced in the amnion and chorion but not in the placenta. In cultured ovine amnion cells incubated in 2% oxygen for 24 hours, hypoxia did not significantly alter caveolin-1 mRNA or protein expression. Vascular endothelial growth factor mRNA levels were increased in response to hypoxia in the fetal membranes as well as in cultured amnion cells. The results indicate that hypoxia does not augment but instead down-regulates or has no effect on caveolin-1 gene expression in the amnion and chorion, suggesting that caveolin-1 may play a role as a negative regulator of amnion transport function under hypoxic conditions.

Factors released from cholestatic rat livers possibly involved in inducing bone marrow hepatic stem cell priming

Previous studies have shown that bone marrow beta 2m(-)/Thy-1+ hepatic stem cells (BMHSCs) were able to engraft in vivo and differentiate into functioning hepatocytes in vitro. Our transcriptomic profiling on BMHSCs derived from rats subjected to common bile duct ligation (CBDL) demonstrated CBDL-derived beta 2m(-)/Thy-1+ BMHSCs expressed hepatocyte-like genes and shared more commonly expressed genes with hepatocytes, suggesting that an "on-site" priming of BMHSCs into hepatocyte lineage was initiated under the condition of CBDL. In this paper, transcriptomic profiling was carried out on livers from rats with CBDL to identify candidate factors released from cholestatic livers possibly involved in the priming of BMHSCs using Affymetrix Rat Genome U34A arrays. In CBDL rat livers, 1,091 probe sets were differentially expressed, of which 188 up-regulated probe sets were annotated as "extracellular" components. Gene ontology analysis showed many up-regulated genes belonged to cytokines, chemokines and growth factors, including Il1b, Il18, Ptn, Spp1, Grn, Ccl2, Cxcl1, Pf4, Tgfb, and Tgfb3. Cell differentiation and proliferation regulation factors such as Dmbt1, Efna1, Lgals1, Lep, Pmp2, and Gas6 were also induced in CBDL livers. Furthermore, many proteolysis and peptidolysis genes such as Mmp2, Mmp12, Mmp14, and Mmp23 were up-regulated in CBDL livers. Gene expression profiling showed that many cytokine-, chemokine-, growth factor- as well as certain extracellular protein-related genes were induced in CBDL livers, suggesting that these genes may be involved in hepatic BMHSCs priming.

The aldo-keto reductase superfamily and its role in drug metabolism and detoxification

The aldo-keto reductase (AKR) superfamily comprises enzymes that catalyze redox transformations involved in biosynthesis, intermediary metabolism, and detoxification. Substrates of AKRs include glucose, steroids, glycosylation end-products, lipid peroxidation products, and environmental pollutants. These proteins adopt a (beta/alpha)(8) barrel structural motif interrupted by a number of extraneous loops and helixes that vary between proteins and bring structural identity to individual families. The human AKR family differs from the rodent families. Due to their broad substrate specificity, AKRs play an important role in the phase II detoxification of a large number of pharmaceuticals, drugs, and xenobiotics.

Prostaglandin F2alpha stimulates the expression and secretion of transforming growth factor B1 via induction of the early growth response 1 gene (EGR1) in the bovine corpus luteum

In most mammals, prostaglandin F2alpha (PGF2alpha) is believed to be a trigger that induces the regression of the corpus luteum (CL), whereby progesterone synthesis is inhibited, the luteal structure involutes, and the reproductive cycle resumes. Studies have shown that the early growth response 1 (EGR1) protein can induce the expression of proapoptotic proteins, suggesting that EGR1 may play a role in luteal regression. Our hypothesis is that EGR1 mediates the actions of PGF2alpha by inducing the expression of TGF beta1 (TGFB1), a key tissue remodeling protein. The levels of EGR1 mRNA and protein were up-regulated in the bovine CL during PGF2alpha-induced luteolysis in vivo and in PGF2alpha-treated luteal cells in vitro. Using chemical and genetic approaches, the RAF/MAPK kinase (MEK) 1/ERK pathway was identified as a proximal signaling event required for the induction of EGR1 in PGF2alpha-treated cells. Treatment with PGF2alpha increased the expression of TGFB1 mRNA and protein as well as the binding of EGR1 protein to TGFB1 promoter in bovine luteal cells. The effect of PGF2alpha on TGFB1 expression was mimicked by a protein kinase C (PKC)/RAF/MEK1/ERK activator or adenoviral-mediated expression of EGR1. The stimulatory effect of PGF2alpha on TGFB1 mRNA and TGFB1 protein secretion was inhibited by blockade of MEK1/ERK signaling and by adenoviral-mediated expression of NAB2, an EGR1 binding protein that inhibits EGR1 transcriptional activity. Treatment of luteal cells with TGFB1 reduced progesterone secretion, implicating TGFB1 in luteal regression. These studies demonstrate that PGF2alpha stimulates the expression of EGR1 and TGFB1 in the CL. We suggest that EGR1 plays a role in the expression of genes whose cognate proteins coordinate luteal regression.

An indomethacin analogue, N-(4-chlorobenzoyl)-melatonin, is a selective inhibitor of aldo-keto reductase 1C3 (type 2 3alpha-HSD, type 5 17beta-HSD, and prostaglandin F synthase), a potential target for the treatment of hormone dependent and hormone independent malignancies

Aldo-keto reductase (AKR) 1C3 (type 2 3alpha-HSD, type 5 17beta-HSD, and prostaglandin F synthase) regulates ligand access to steroid hormone and prostaglandin receptors and may stimulate proliferation of prostate and breast cancer cells. NSAIDs are known inhibitors of AKR1C enzymes. An NSAID analogue that inhibits AKR1C3 but is inactive against the cyclooxygenases and the other AKR1C family members would provide an important tool to examine the role of AKR1C3 in proliferative signaling. We tested NSAIDs and NSAID analogues for inhibition of the reduction of 9,10-phenanthrenequinone (PQ) catalyzed by AKR1C3 and the closely related isoforms AKR1C1 and AKR1C2. Two of the compounds initially screened, indomethacin and its methyl ester, were specific for AKR1C3 versus the other AKR1C isoforms. Based on these results and the crystal structure of AKR1C3, we predicted that N-(4-chlorobenzoyl)-melatonin (CBM), an indomethacin analogue that does not inhibit the cyclooxygenases, would selectively inhibit AKR1C3. CBM inhibited the reduction of PQ by AKR1C3, but did not significantly inhibit AKR1C1 or AKR1C2. Indomethacin and CBM also inhibited the AKR1C3-catalyzed reduction of Delta(4)-androstene-3,17-dione but did not significantly inhibit the reduction of steroid hormones catalyzed by AKR1C1 or AKR1C2. The pattern of inhibition of AKR1C3 by indomethacin and CBM was uncompetitive versus PQ, but competitive versus Delta(4)-androstene-3,17-dione, indicating that two different inhibitory complexes form during the ordered bi bi reactions. The identification of CBM as a specific inhibitor of AKR1C3 will aid the investigation of its roles in steroid hormone and prostaglandin signaling and the resultant effects on cancer development.

AKT-independent phosphorylation of TSC2 and activation of mTOR and ribosomal protein S6 kinase signaling by prostaglandin F2alpha

Prostaglandin F2alpha (PGF2alpha) is an important mediator of corpus luteum (CL) regression, although the cellular signaling events that mediate this process have not been clearly identified. It is established that PGF2alpha binds to a G-proteincoupled receptor (GPCR) to stimulate protein kinase C (PKC) and Raf-MEK-Erk signaling in luteal cells. The present experiments were performed to determine whether PGF2alpha stimulates the mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase 1 (S6K1) signaling pathway in steroidogenic luteal cells. We demonstrate that PGF2alpha treatment results in a timeand concentration-dependent stimulation of the phosphorylation and activation of S6K1. The stimulation of S6K1 in response to PGF2alpha treatment was abolished by the mTOR inhibitor rapamycin. Treatment with PGF2alpha did not increase AKT phosphorylation but increased the phosphorylation of Erk and the tumor suppressor protein tuberous sclerosis complex 2 (TSC2), an upstream regulator of mTOR. The effects of PGF2alpha were mimicked by the PKC activator PMA and inhibited by U0126, a MEK1 inhibitor. The activation of mTOR/S6K1 and putative down stream processes involving the translational apparatus (i.e. 4EBP1 phosphorylation, release of 4EBP1 binding in m(7)G cap binding assays, and the phosphorylation and synthesis of S6) were completely sensitive to treatment with rapamycin, implicating mTOR in the actions of PGF2alpha. Taken together, our data suggest that GPCR activation in response to PGF2alpha stimulates the mTOR pathway which increases the translational machinery in luteal cells. The translation of proteins under the control of mTOR may have implications for luteal development and regression and offer new strategies for therapeutic intervention in PGF2alpha-target tissues.

Activation of the human FP prostanoid receptor disrupts mitosis progression and generates aneuploidy and polyploidy

Studies have shown prostaglandin F(2alpha) (PGF(2alpha)) to be an endogenous tumor promoter in mouse models of skin carcinogenesis; however, the mechanisms by which PGF(2alpha) affects cell cycle events remain unknown. Here we performed cell cycle analyses on HEK cells stably expressing the human FP receptor and found that treatment with PGF(2alpha) delays mitosis and is associated with an increased expression of cyclin B1 and Cdc2 kinase activity. In addition, multipolar spindles and misaligned chromosomes were observed in a significant proportion of cells treated with PGF(2alpha). Defective cytokinesis was also observed which resulted in gross aneuploidy and polyploidy. Expression of dominant negative Rho attenuated the cell cycle delay and prevented the generation of micronuclei following treatment with PGF(2alpha). This suggests that FP receptor activation of Rho signaling by PGF(2alpha) can interfere with nuclear division. Aneuploidy is associated with genomic instability and may underlie the tumor-promoting properties of PGF(2alpha).

Tyrosine Phosphorylation of Caveolin 1 by Oxidative Stress Is Reversible and Dependent on the c-src Tyrosine Kinase but Not Mitogen-Activated Protein Kinase Pathways in Placental Artery Endothelial Cells1

Acute H(2)O(2) exposure to placental artery endothelial cells induced an array of tyrosine-phosphorylated proteins, including caveolin 1 (CAV1) rapid and transient tyr(14) phosphorylated in a time- and concentration-dependent manner. Basal tyr(14) phosphorylated CAV1 was primarily located at the edges of cells and associated with actin filaments. Phosphorylated CAV1 was markedly increased and diffused with the disorganization of actin filaments at 20 min, disappeared at 120 min treatment with 0.2 mM H(2)O(2). Treatment with H(2)O(2) also disorganized actin filaments and changed cell shape in a time-dependent manner. Pretreatment with antioxidants catalase completely, whereas the other tested superoxide dismutase, N-acetyl-l-cysteine and sodium formate partially attenuated H(2)O(2)-induced CAV1 phosphorylation in a concentration-dependent manner. Acute treatment with H(2)O(2) activated multiple signaling pathways, including the mitogen-activated protein kinases (MAPK) members (MAPK3/1-ERK2/1, MAPK8/9-JNK1/2, and MAPK11-p38(mapk)) and the c-src tyrosine kinase (CSK). Pharmacological studies demonstrated that, among these pathways, only the blockade of CSK activation abolished H(2)O(2)-induced CAV1 phosphorylation. Additionally, H(2)O(2)-induced CAV1 phosphorylation was reversible rapidly (<10 min) upon H(2)O(2) withdrawal. Because maternal and fetal endothelia must make dynamic adaptations to oxidative stress resulting from enhanced pregnancy-specific oxygen metabolism favoring prooxidant production, which is emerging as one of the leading causes of the dysfunctional activated endothelium during pregnancy, these unique features of CAV1 phosphorylation on oxidative stress observed implicate an important role of CAV1 in placental endothelial cell biology during pregnancy.

Expression of prostaglandin G/H synthase (PGHS) and heat shock protein-70 (HSP-70) in the corpus luteum (CL) of prostaglandin F2 alpha-treated immature superovulated rats

In this study we examined the mechanism of corpus luteum (CL) regression by measuring changes in expression of prostaglandin G/H synthase-1 (PGHS-1) and -2 (PGHS-2) in day 4 CL and inducible heat shock protein 70 (HSP-70) in day 4 and day 9 CL of immature superovulated rats. The rats were superovulated and treated with 500 microg of prostaglandin F2alpha (PGF2alpha) on day 4 or day 9 after CL formation. Ovaries and serial blood samples were removed during the 24-hour period following treatment. Plasma progesterone was determined by radioimmunoassay while mRNA abundance and protein expression were assessed by semiquantitative RT-PCR and immunoblot analysis, respectively. One hour after PGF2alpha, both day 4 and day 9 rats exhibited a significant decrease in progesterone secretion; however, there was a greater decrease in day 9 rats. In ovarian samples removed on day 4, there was a significant increase in mRNA for PGHS-2 at 1 hour after PGF2alpha. PGHS-1 mRNA content remained unchanged. Immunoblot analyses showed an increase in PGHS-2 protein expression only at 8 h. There were no changes in PGHS-1 protein expression. In day 9 rats, ovarian HSP-70 protein levels increased by 50% after PGF2alpha injection; however, on day 4 there was no change in expression of this protein over the sampling period. These results suggest that expression of PGHS-2 may be involved in inhibiting progesterone production and that expression of HSP-70 may be required for complete CL regression in the rat.

Membrane estrogen receptor-dependent extracellular signal-regulated kinase pathway mediates acute activation of endothelial nitric oxide synthase by estrogen in uterine artery endothelial cells

Rapid uterine vasodilatation after estrogen administration is believed to be mediated by endothelial production of nitric oxide (NO) via endothelial NO synthase (eNOS). However, the mechanism(s) by which estrogen activates eNOS in uterine artery endothelial cells (UAEC) is unknown. In this study, we observed that estradiol-17beta (E2) and E2-BSA rapidly (<2 min) increased total NOx production in UAEC in vitro. This was associated with rapid eNOS phosphorylation and activation but was unaltered by pretreatment with actinomycin-D. Estrogen receptor-alpha protein was detectable in isolated plasma membrane proteins by immunoblotting, and E2-BSA-fluorescein isothiocyanate binding was evident on the plasma membrane of UAEC. E2 did not mobilize intracellular Ca2+, but E2 and ionomycin in combination induced greater eNOS phosphorylation than either E2 or ionomycin alone. E2 did not stimulate rapid Akt phosphorylation. E2 stimulated rapid ERK2/1 activation in a time- and dose-dependent manner, with maximal responses observed at 5-10 min with E2 (10 nm to 1 microm) treatment. Acute activation of eNOS and NOx production by E2 could be inhibited by PD98059 but not by LY294002. When E2-BSA was applied, similar responses in NOx production, eNOS, and ERK2/1 activation to those of E2 were achieved. In addition, E2 and E2-BSA-induced ERK2/1 activation and ICI 182,780 could inhibit NOx production by E2. Thus, acute activation of eNOS to produce NO in UAEC by estrogen is at least partially through an ERK pathway, possibly via estrogen receptor localized on the plasma membrane. This pathway may provide a novel mechanism for NO-mediated rapid uterine vasodilatation by estrogen.

Biochemical and endocrine aspects of oxytocin production by the mammalian corpus luteum

A review of the current state of knowledge of oxytocin production by the preovulatory follicle and corpus luteum is presented. Corpora lutea of a number of mammalian species have been found to synthesize oxytocin. However, the synthesis and secretion of this nanopeptide by the corpus luteum of the ruminant has been most extensively studied because of the potential role of this peptide in facilitating luteal regression. While much information exists relative to various biochemical and endocrine factors that impact on oxytocin gene expression, this aspect about luteal synthesis of this peptide hormone remains enigmatic. Prostaglandin F-2alpha (PGF-2alpha) has been shown to be a primary endogenous hormone responsible for triggering luteal secretion of oxytocin. Details are provided regarding the PGF-2alpha-induced intracellular signal transduction pathway that ultimately results in exocytosis of luteal oxytocin. Evidence is also presented for potential autocrine/paracrine actions of oxytocin in regulating progesterone production by luteal and granulosa cells. Concluding remarks highlight aspects about luteal oxytocin production that require further research.

Regulation of intraluteal production of prostaglandins

There is clear evidence for intraluteal production of prostaglandins (PGs) in numerous species and under a variety of experimental conditions. In general, secretion of PGs appears to be elevated in the early corpus luteum (CL) and during the period of luteolysis. Regulation of intraluteal PG production is regulated by a variety of factors. An autoamplification pathway in which PGF-2alpha stimulates intraluteal production of PGF-2alpha has been identified in a number of species. The mechanisms underlying this autoamplification pathway appear to differ by species with expression of Cyclooxygenase-2 (Cox-2) and activity of phospholipase A2 acting as important physiological control points. In addition, a number of other responses that are induced by PGF-2alpha (decreased luteal progesterone, increased endothelin-1, increased cytokines) also have been found to increase intraluteal PGF-2alpha production. Thus, regulation of intraluteal PG production may serve to initiate or amplify physiological signals to the CL and may be important in specific aspects of luteal physiology particularly during luteal regression.

Signaling mechanisms in tumor necrosis factor alpha-induced death of microvascular endothelial cells of the corpus luteum

The microvasculature of the corpus luteum (CL), which comprises greater than 50% of the total number of cells in the CL, is thought to be the first structure to undergo degeneration via apoptosis during luteolysis. These studies compared the apoptotic potential of various cytokines (tumor necrosis factor alpha, TNFalpha; interferon gamma, IFNgamma; soluble Fas ligand, sFasL), a FAS activating antibody (FasAb), and the luteolytic hormone prostaglandin F2alpha (PGF2alpha) on CL-derived endothelial (CLENDO) cells. Neither sFasL, FasAb nor PGF2alpha had any effect on CLENDO cell viability. Utilizing morphological and biochemical parameters it was evident that TNFalpha and IFNgamma initiated apoptosis in long-term cultures. However, TNFalpha was the most potent stimulus for CLENDO cell apoptosis at early time points. Unlike many other studies described in non-reproductive cell types, TNFalpha induced apoptosis of CLENDO cells occurs in the absence of inhibitors of protein synthesis. TNFalpha-induced death is typically associated with acute activation of distinct intracellular signaling pathways (e.g. MAPK and sphingomyelin pathways). Treatment with TNFalpha for 5-30 min activated MAPKs (ERK, p38, and JNK), and increased ceramide accumulation. Ceramide, a product of sphingomyelin hydrolysis, can serve as an upstream activator of members of the MAPK family independently in numerous cell types, and is a well-established pro-apoptotic second messenger. Like TNFalpha, treatment of CLENDO cells with exogenous ceramide significantly induced endothelial apoptosis. Ceramide also activated the JNK pathway, but had no effect on ERK and p38 MAPKs. Pretreatment of CLENDO cells with glutathione (GSH), an intracellular reducing agent and known inhibitor of reactive oxygen species (ROS) or TNFalpha-induced apoptosis, significantly attenuated TNFalpha-induced apoptosis. It is hypothesized that TNFalpha kills CLENDO cells through elevation of reactive oxygen species, and intracellular signals that promote apoptosis.

Modulation of JB6 mouse epidermal cell transformation response by the prostaglandin F2alpha receptor

Prostaglandin F(2alpha) (PGF(2alpha)) modulates clonal selection processes in the mouse skin model of carcinogenesis. In this study we investigated whether JB6 mouse epidermal cells expressed a functional PGF(2alpha) receptor (FP) coupled with a cell-transformation response. Treatment of JB6 cells with an FP agonist (fluprostenol) potently (pM-nM) increased anchorage-dependent and anchorage-independent growth. Inositol phospholipid accumulation and extracellular signal-regulated kinase (Erk) activity were increased in cells treated with FP agonists, consistent with established FP-related signal transduction. FP mRNA was detected by reverse transcription-polymerase chain reaction, and the average specific [(3)H]PGF(2alpha) binding was 8.25 +/- 0.95 fmol/mg protein. Erk activity and colony size were increased by cotreatment of JB6 cells with epidermal growth factor (EGF) and fluprostenol to a greater extent than with either treatment alone, whereas the cotreatment effect on colony number appeared to be simply additive. Collectively, our data indicated that JB6 cells expressed a functional FP coupled with transformation-related signal transduction and the regulation of clonal selection processes. Erk activity appears to be a convergence point in the EGF and FP pathways. The data raise the possibility that the FP contributes to clonal selection processes but probably plays a more important role as a response modifier.

Prostaglandin F2alpha-induced nest-building behaviour is associated with increased hypothalamic c-fos and c-jun mRNA expression

Intramuscular injection of the naturally occurring prostaglandin F2alpha (PGF2alpha) to sexually mature female pigs induces luteolysis and rapidly elicits a behavioural response consistent with pre-partum nest-building. Intramuscular injection of the synthetic prostaglandin F2alpha (cloprostenol) also induces luteolysis but no nest-building behaviour is observed. The effects of PGF2alpha, but not cloprostenol, on nest-building behaviour may be mediated via peripheral PGF2alpha receptors (FP) or via direct action on central FP receptors. We have previously shown FP receptor mRNA to be localized in porcine paraventricular nucleus (PVN), supraoptic nucleus (SON) and pars dorso-medialis of the suproptic nucleus (SOD), suprachiasmatic nucleus, choroid plexus and anterior and intermediate pituitary lobes. In this experiment, we examined hypothalamic expression of the immediate early genes c-fos and c-jun mRNA after treatment with PGF2alpha or cloprostenol. Twenty-one 8-month-old nulliparous female pigs (gilts) were injected intramuscularly with a luteolytic dose of PGF2alpha (15 mg), cloprostenol (175 microg) or saline control, their behaviour was recorded and they were killed 60 min later. Coronal hypothalamic sections and control ovarian tissues were incubated with 45-mer oligonucleotide probes complementary to porcine c-fos and c-jun genes using standard in situ hybridization histochemistry techniques. Significantly higher c-fos and c-jun mRNA expression was found in PGF2alpha-treated compared to saline or cloprostenol-treated pigs in the PVN, SON and SOD. Significantly higher c-fos and c-jun mRNA expression was found in corpus lutea of PGF2alphaand cloprostenol-treated pigs compared to saline controls. Treatment with PGF2alpha induced nest-building behaviour whereas treatment with cloprostenol and saline did not. This suggests that PGF2alpha, or one of its metabolites, and not cloprostenol, crosses the blood-brain barrier and acts directly on hypothalamic receptors to mediate its effect on nest-building behaviour.

Secretion of monocyte chemoattractant protein-1 by endothelial cells of the bovine corpus luteum: regulation by cytokines but not prostaglandin F2alpha

Information regarding the regulation of monocyte chemoattractant protein-1 (MCP-1) in regression of the corpus luteum (CL) is limited. This study tested the hypothesis that endothelial cells derived from bovine CL are a source of MCP-1, and that proinflammatory cytokines, prostaglandin F2alpha (PGF2alpha), and progesterone regulate MCP-1 expression. Endothelial cells were treated without (Control) or with PGF2alpha (1 micro M), TNFalpha (100 ng/ml), interferon-gamma (IFNgamma, 200 IU/ml), and TNFalpha + IFNgamma for 24 and 48 h in the absence or presence of progesterone (P4, 250 ng/ml). Increases in MCP-1 mRNA and protein were observed in response to TNFalpha within 24 and 48 h of culture, respectively (P < 0.05). Interferon-gamma stimulated (P < 0.05) both MCP-1 mRNA and protein after 24 h of culture, and this effect was also sustained through 48 h of culture (P < 0.05). Cotreatment of cultures with TNFalpha + IFNgamma lead to further increases (P < 0.05) in MCP-1 in both 24- and 48-h cultures. Surprisingly, neither PGF2alpha nor P4 affected MCP-1 production. Subsequent experiments revealed that the endothelial cells lacked prostaglandin F2alpha receptor mRNA, and the MAPK pathway, although present and responsive to growth factor stimulation, was unresponsive to PGF2alpha stimulation. In summary, endothelial cells derived from bovine CL respond to TNFalpha and IFNgamma stimulation with an increase in MCP-1 secretion. In contrast, neither PGF2alpha nor P4 directly influenced endothelial expression of MCP-1. These results suggest that cytokines stimulate the synthesis of MCP-1 observed during PGF2alpha-induced luteal regression.

Apoptosis during spontaneous and prostaglandin F(2alpha)-induced luteal regression in the buffalo cow (Bubalus bubalis): involvement of mitogen-activated protein kinases

The present study was conducted to evaluate whether the corpus luteum (CL) of the water buffalo (Bubalus bubalis) cow undergoes luteal regression by the process of apoptosis and to examine the involvement of mitogen-activated protein (MAP) kinases during prostaglandin (PG) F(2alpha)-induced luteolysis. Sections of CL from late in the estrous cycle, i.e., during spontaneous luteolysis, stained for 4',6'-diamidino-2-phenylindole revealed increased numbers of condensed nuclei, indicating cell death by apoptosis, which was confirmed further by the occurrence of pronounced oligonucleosome formation. For morphological and biochemical characterization during PGF(2alpha)-induced apoptosis, CL were collected at 0, 4, 12, and 18 h after injection of 750 micro g of Tiaprost, a synthetic analogue of PGF(2alpha), to midestrous buffalo cows. Serum progesterone concentrations fell within 4 h and decreased (P < 0.05) maximally by 18 h. Concomitant decreases (P < 0.05) in the levels of steroidogenic acute regulatory mRNA and protein were observed in CL during 12-18 h, with the more profound effect on mRNA levels. Quantitative analysis of the genomic DNA showed a >5-fold increase (P < 0.05) in the low molecular weight DNA fragments by 18 h postinjection. Immunoblot analysis of CL tissue lysates showed increased (P < 0.05) levels of phospho-Jun N-terminal kinase (JNK) 1 (4- to 14-fold during 4-18 h) and phospho-p38 (2- to 4-fold at 18 h). Immunohistochemical evaluation of CL sections revealed an increased nuclear localization of phospho-JNK after treatment. These findings demonstrate that the CL of the buffalo cow undergoes cell death by the process of apoptosis both during spontaneous and PGF(2alpha)-induced luteolysis and that MAP kinases are involved during PGF(2alpha)-mediated apoptosis in the CL.

Treatment with prostaglandin F2alpha increases expression of prostaglandin synthase-2 in the rat corpus luteum

Recent studies indicate that the corpus luteum (CL) may be a source of prostaglandin F2alpha (PGF2alpha) for regression. We investigated expression of mRNA and protein for prostaglandin G/H synthase (PGHS) in the CL of immature superovulated rats following administration of PGF2alpha. We observed an increase in mRNA for PGHS-2, the induced isoform, at 1 h and protein at 8 and 24 h after treatment. One hour after PGF2alpha, there was also a progressive decrease in plasma progesterone concentration. There were no changes, however, in expression of PGHS-1, the constitutive isoform, over the 24 h sampling period. These results indicate that PGHS-2 increases following PGF2alpha treatment and that expression of this enzyme in the rat CL may contribute to the luteolytic mechanism.

Follicle-stimulating hormone activates mitogen-activated protein kinase in preneoplastic and neoplastic ovarian surface epithelial cells

To investigate the role of FSH in ovarian cancer development, the present study examined the expression of FSH receptor (FSH-R) and the effect of FSH on proliferation of normal, preneoplastic, and neoplastic ovarian surface epithelium (OSE) cells. Recently, immortalized OSE (IOSE) cell lines, including IOSE-29 (preneoplastic) and IOSE-29EC (neoplastic), were used. Our results indicated that FSH-R mRNA was expressed and that FSH exerted a growth stimulatory effect in normal, preneoplastic, and neoplastic OSE cells. To investigate the mechanism of the growth stimulatory effect, the activation of MAPKs by FSH was examined in preneoplastic and neoplastic OSE cells. Treatment with FSH resulted in MAPK activation of IOSE-29 and IOSE-29EC cells, whereas the stimulatory effect of FSH on cellular proliferation and MAPK activation was completely abolished in the presence of PD98059, a MAPK kinase inhibitor, suggesting that the growth stimulatory effect of FSH is mediated through MAPK activation in these OSE cells. In a time-dependent study, FSH significantly increased MAPK activity at 5-10 min in IOSE-29 cells. The activated MAPK declined to the control level after 20 min in these cells. Similarly, treatment with FSH significantly induced MAPK activation after 5 min and sustained it for 60 min in IOSE-29EC cells. In addition, treatment with FSH resulted in substantial phosphorylation of Elk-1, confirming that FSH action is mediated via activation of MAPK. In conclusion, we have demonstrated that FSH-R was expressed, and FSH induced growth stimulation in normal, preneoplastic, and neoplastic OSE cells. Furthermore, treatment with FSH stimulated activation of the MAPK cascade and phosphorylated Elk-1 in neoplastic OSE cells. These results suggest that the MAPK cascade may be involved in cellular functions such as growth stimulation in response to FSH in preneoplastic and neoplastic OSE cells.

A calcium/calmodulin-dependent activation of ERK1/2 mediates JunD phosphorylation and induction of nur77 and 20alpha-hsd genes by prostaglandin F2alpha in ovarian cells

We have previously demonstrated that prostaglandin F(2alpha) (PGF(2alpha)) induces a rapid and transient expression of Nur77 in luteal cells. We have shown that Nur77 plays an important role in ovarian physiology by mediating the PGF(2alpha) induction of 20alpha-HSD, a steroidogenic enzyme involved in the catabolism of progesterone. In this report we established, using luteinized granulosa cells, that PGF(2alpha) stimulates in vitro nur77 expression in a time- and dose-dependent manner. Serial 5'-deletion of the nur77 promoter revealed that the necessary and sufficient elements for PGF(2alpha) induction of Nur77 promoter activity are located between the nucleotides -86 and -33 upstream of the transcription start site, this region containing two AP1 elements. JunD binds to these AP1 sites, but its binding is not stimulated by PGF(2alpha). However, mutation of the AP1 sites as well as a dominant-negative JunD abolished nur77 induction by PGF(2alpha). PGF(2alpha) induces phosphorylation of JunD bound to the nur77 promoter. Stimulation of nur77 expression and JunD phosphorylation were prevented by inhibitors of calcium, calmodulin, or ERK1/2 kinase. PGF(2alpha)-induced ERK1/2 phosphorylation was prevented by calcium/calmodulin inhibitors. We conclude that activation of JunD through a calmodulim-dependent activation of ERK1/2 mediates nur77 induction by PGF(2alpha). Finally, we demonstrated that this molecular mechanism also mediates 20alpha-hsd induction.

Transcriptional regulation of cyclooxygenase-2 gene in ovine large luteal cells

There is positive feedback pathway in the ovine large luteal cell, such that prostaglandin (PG) F(2 alpha) stimulation induces intraluteal PGF(2 alpha) production as the result of induction of one of the rate-limiting enzymes in PG production, cyclooxygenase-2 (Cox-2). The objective of the present study was to evaluate the intracellular effector systems and important DNA transcriptional element(s) involved in regulating the Cox-2 gene in ovine large luteal cells. In transient transfection assays, Cox-2 promoter was rapidly induced (4 h) by phorbol didecanoate (a protein kinase [PK] C activator), ionomycin, and cloprostenol (PGF(2 alpha) analogue), with a peak induction at 12 h. Cloprostenol-mediated promoter activation was not blocked by inhibition of various second messenger systems, including PKA, calcium calmodulin kinase II, or mitogen-activated protein kinases. However, myristoylated PKC pseudosubstrate peptide inhibited cloprostenol stimulation of Cox-2 promoter, indicating the critical role of PKC in this stimulation. The Cox-2 promoter could be reduced to 282 base pairs (bp) of the 5' flanking sequence with retention of full inducibility by cloprostenol. Mutation of three critical cis-responsive elements within this 282-bp region (C/EBP, cAMP responsive element [CRE], and E-box) indicated that E-box was critical in both basal and cloprostenol-induced promoter activity. However, there was also significant but less dramatic inhibition of cloprostenol stimulation by mutation of C/EBP and CRE in the Cox-2 promoter, and mutation of all three elements eliminated cloprostenol induction of this promoter. Electrophoretic mobility shift assays of nuclear extracts from large luteal cells revealed that upstream stimulatory factor (USF)-1 and USF-2 bound to the E-box in Cox-2. Thus, PKC directly regulates transcription of the Cox-2 gene in large luteal cells by acting through DNA elements close to the putative transcriptional start point, particularly an E-box region at -50 bp.

Suppression of protein kinase C signaling by the novel isoform for bovine PGF(2alpha) receptor

A cDNA clone for a novel isoform of prostaglandin (PG) F(2alpha) receptor (FP) was isolated from the cDNA pool of the bovine corpus luteum. The sequence analysis revealed that the new FP isoform (FP(a)) encodes a 295-amino acid protein carrying a specific 28-amino acid sequence from the middle of transmembrane segment VI to the carboxyl terminus. Because only one copy gene has been identified for FP, FP(a) was generated by alternative mRNA splicing at the middle of the VI transmembrane region, resulting in the lack of a VII transmembrane segment and an intracellular carboxyl tail. The RT-PCR analysis for FP and FP(a) indicated that both mRNAs are expressed similarly during the estrous cycle and pregnancy. The PGF(2alpha) stimulation drastically enhanced protein kinase C (PKC) activity in the COS-7 cell transfected with FP, whereas no PKC activation was detected in FP(a)-transfected cells. Cotransfection of an excess amount of FP(a) markedly reduced FP-mediated PKC activity, suggesting that the novel FP isoform might play a role as a negative regulator to attenuate normal FP function.

Developmental regulation of mitogen-activated protein kinase-activated kinases-2 and -3 (MAPKAPK-2/-3) in vivo during corpus luteum formation in the rat

The current study investigates the activation in vivo and regulation of the expression of components of the p38 mitogen-activated protein kinase (MAPK) pathway during gonadotropin-induced formation and development of the rat corpus luteum, employing a sequential PMSG/human CG (hCG) treatment paradigm. We postulated that the p38 MAPK pathway could serve to promote phosphorylation of key substrates during luteal maturation, since maturing luteal cells, thought to be cAMP-nonresponsive, nevertheless maintain critical phosphoproteins. Both p38 MAPK and its upstream activator MAPK kinase-6 (MKK6) were found to be chronically activated during the luteal maturation phase, with activation detected by 24 h post hCG and maintained through 4 days post hCG. The p38 MAPK downstream protein kinase target termed MAPK-activated protein kinase-3 (MAPKAPK-3) was newly induced at both mRNA and protein levels during luteal formation and maturation, while mRNA and protein expression of the closely related MAPKAPK-2 diminished. Two potential substrates for MAPKAPKs, the small heat shock protein HSP-27 and the cAMP regulatory element binding protein CREB, were monitored in vivo for phosphorylation. HSP-27 phosphorylation was not modulated during luteal maturation. In contrast, we observed sustained luteal-phase CREB phosphorylation in vivo, consistent with upstream MKK6/p38 MAPK activation and MAPKAPK-3 induction. MAPKAPK-3-specific immune complex kinase assays provided direct evidence that MAPKAPK-3 was in an activated state during luteal maturation in vivo. Cellular inhibitor studies indicated that an intact p38 MAPK path was required for CREB phosphorylation in a cellular model of luteinization, as treatment of luteinized granulosa cells with the p38 MAPK inhibitor SB 203580 strongly inhibited CREB phosphorylation. Transient transfection studies provided direct evidence that MAPKAPK-3 was capable of signaling to activate CREB transcriptional activity, as assessed by means of GAL4-CREB fusion protein construct coexpressed with GAL4-luciferase reporter construct. Introduction of wild-type, but not kinase-dead mutant, MAPKAPK-3 cDNA, into a mouse ovarian cell line stimulated GAL4-CREB- dependent transcriptional activity approximately 3-fold. Thus MAPKAPK-3 is indeed uniquely poised to support luteal maturation through the phosphorylation and activation of the nuclear transcription factor CREB.

Prostaglandin F(2alpha) receptor in the corpus luteum: recent information on the gene, messenger ribonucleic acid, and protein

The prostaglandin (PG) F(2alpha) receptor (FPr) in the corpus luteum is essential for maintaining normal reproductive cyclicity in many species. Activation of this seven-transmembrane spanning receptor at the end of the cycle leads to a decrease in progesterone and the demise of the corpus luteum (luteolysis). Recently, the gene structure of the FPr in three mammalian species has been elucidated; however, promoter regulation of the gene is still poorly understood. The FPr mRNA is extremely low in steroidogenic follicular cells (theca or granulosa) but is expressed at high levels in the corpus luteum, particularly in the large luteal cells. Treatment with PGF(2alpha) decreased FPr mRNA expression in luteal cells in most species that have been studied. Key amino acids have been suggested to be critical for binding of FPr to PGF(2alpha) based on three-dimensional modeling and comparisons with other G-protein-coupled receptors. Moieties of the PGF(2alpha) molecule that are essential for binding or specificity of binding to the FPr have been identified by radioreceptor binding studies. In this article, recent information is reviewed on the structure of the FPr gene, regulation of luteal FPr mRNA, and receptor/ligand interaction requirements for the FPr protein.

Stimulation of mitogen-activated protein kinase by gonadotropin-releasing hormone in human granulosa-luteal cells

The present study investigated the activation of mitogen-activated protein kinases (MAPKs) by a GnRH agonist (GnRHa) in human granulosa-luteal cells (hGLCs). The phosphorylation state of p44 and p42 MAPK was examined using antibodies that distinguish phospho-p44/42 MAPK (Thr(202)/Tyr(204)) from total p44/42 MAPK (activated plus inactivated). Activation of MAPK by GnRHa was observed within 5 min and was sustained for 60 min after treatment. GnRHa stimulated MAPK activation in a dose-dependent manner, with maximum stimulation (6.7-fold over basal levels) at 10(-7) M. Pretreatment with a protein kinase C (PKC) inhibitor, GF109203X, completely blocked GnRHa-induced MAPK activation. In addition, pretreatment with a PKC activator, phorbol-12-myristate 13-acetate, potentiated GnRH-induced MAPK activation. These results indicate that GnRHa stimulates MAPK activation through a PKC-dependent pathway in hGLCs, possibly coupled to G(q)alpha protein. MAPK activation was also observed in response to 8-bromo-cAMP or cholera toxin, but not pertussis toxin. Forskolin (50 microM) substantially stimulated a rapid cAMP accumulation, whereas GnRHa (10(-7) M) or pertussis toxin (100 mg/ml) did not affect basal intracellular cAMP levels. Cotreatment of GnRHa (10(-7) M) did not attenuate forskolin- or hCG-stimulated cAMP accumulation. These results suggest that the GnRH receptor is probably not coupled to G(s)alpha or G(i)alpha in hGLCs. Finally, GnRHa (10(-7) M) stimulated a significant increase in Elk-1 phosphorylation and c-fos messenger RNA expression, as revealed by an in vitro kinase assay and Northern blot analysis, respectively. These results clearly demonstrate that GnRH activates the MAPK cascade through a PKC-dependent pathway in the human ovary.

Induction of c-fos and c-jun messenger ribonucleic acid expression by prostaglandin F2alpha is mediated by a protein kinase C-dependent extracellular signal-regulated kinase mitogen-activated protein kinase pathway in bovine luteal cells

PGF2alpha triggers the demise of the corpus luteum whereby progesterone synthesis is inhibited, the luteal structure regresses, and the estrus cycle resumes. Upon binding to its heterotrimeric G-protein-coupled receptors, PGF2alpha initiates the phospholipase C/diacylglycerol and inositol-1,4,5-trisphosphate/Ca(2+)-protein kinase C (PKC) signaling pathway. More recently, we have demonstrated that PGF2alpha activates extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase signaling through a Raf-dependent mechanism in bovine luteal cells. However, the relationship between PKC and ERK activation in PGF2alpha signaling has not been clearly defined. Moreover, the signaling pathway that PGF2alpha uses to regulate gene expression is unknown. In this report, primary cultures of bovine luteal cells were used to address the role of PKC in ERK activation and the signaling pathway for induction of c-fos and c-jun messenger RNA (mRNA) expression in response to PGF2alpha. By using a PKC inhibitor and a PKC-deficient luteal cell model, we observed that phorbol ester-responsive isoforms of PKC were required for ERK phosphorylation and activation by PGF2alpha (1 microM) or phorbol 12-myristate 13-acetate (PMA) (20 nM). In PGF2alpha- and PMA-treated cells, active ERK MAP kinase was localized in the nucleus. PGF2alpha-induced ERK phosphorylation was dose-dependently inhibited by the MEK1 inhibitor PD098059 (1-50 microM). The expression of c-fos and c-jun mRNA in luteal cells was markedly increased by treatment with PGF2alpha (1 microM) or PMA (20 nM) for 30 min. We also observed that activation of ERK MAP kinase was required for the expression of c-fos and c-jun mRNA in response to PGF2alpha and PMA because it was abrogated by blocking the ERK pathway with PD098059. In addition, PGF2alpha and PMA-induced c-fos and c-jun mRNA expression was abolished in the PKC-deficient cells. Taken together, our data demonstrate that a PKC-dependent ERK MAP kinase pathway mediates the expression of c-fos and c-jun mRNA in PGF2alpha-treated bovine luteal cells.

Tumor necrosis factor-alpha stimulates prostaglandin F2alpha secretion by bovine luteal cells via activation of mitogen-activated protein kinase and phospholipase A2 pathways

It has been well demonstrated that tumor necrosis factor-alpha (TNFalpha) stimulates prostaglandin (PG) F2alpha secretion by bovine corpus luteum (CL) in vitro. The objective of the present study was to clarify the intracellular signaling pathway of TNFalpha to stimulate PGF2alpha production in cultured bovine luteal cells. Bovine luteal cells that were obtained from mid- (days 8-12 after ovulation) CL were incubated with TNFalpha (0.6 nM) and/or various compounds as follows: U-73122 (an inhibitor of phospholipase [PL] C), ACA (an inhibitor of PL-A2), H-89 (an inhibitor of protein kinase [PK] A), calphostin C (an inhibitor of PK-C), L-NAME/L-NORG (inhibitors of nitric oxide synthase), and PD98059 (an inhibitor of mitogen-activated protein kinase [MAPK] kinase). Although U-73122 (0. 1-10 microM), H-89 (0.1-10 microM), calphostin C (0.01-1 microM) and L-NAME/L-NORG (1-100 microM) did not affect TNFalpha-induced PGF2alpha secretion by the cultured cells, ACA (1-100 microM) and PD98059 (0.1-100 microM) inhibited TNFalpha-stimulated PGF2alpha secretion by the cells in a dose-dependent fashion (P < 0.05 or lower). These findings suggest that TNFalpha activates the MAPK and PL-A2 pathways in bovine luteal cells to stimulate PGF2alpha secretion.