Expression of progesterone receptor membrane component-1 in bovine reproductive system during estrous cycle.

Several reports suggest the participation of progesterone receptor membrane component 1 (PGRMC1) in progesterone signaling in the reproductive system. This study aimed at investigating the presence and localization of PGRMC1 in bovine ovary, oviduct and uterus, during the follicular and luteal phases of the estrous cycle. In the ovary, PGRMC1 has been detected in surface germinal epithelium, granulosa cells, theca cells and in the germinal vesicle of the oocytes at all stages of folliculogenesis. In the corpus luteum the expression of PGRMC1 was influenced by the stage of the estrous cycle. In the oviducts and in the uterus horns, PGRMC1 was immunolocalized in the luminal epithelium, in the muscle layer cells and in the endothelial cells. In the uterus, PGRMC1 was intensely localized also in the glandular endometrium. However, in the oviducts and in the uterus horns, the localization of PGRMC1 was independent on the stage of the estrous cycle and on whether evaluating the ipsilateral or the contralateral organ. In conclusion, the present immunohistochemical study showed that PGRMC1 is located in various compartments of the bovine female reproductive organs. With the exception of the corpora lutea, PGRMC1 localization showed similar pattern during different stages of the estrous cycle.

Progesterone inhibits apoptosis in part by PGRMC1-regulated gene expression.

Progesterone receptor membrane component-1 (PGRMC1) is present in both the cytoplasm and nucleus of spontaneously immortalized granulosa cells (SIGCs). PGRMC1 is detected as a monomer in the cytoplasm and a DTT-resistant PGRMC1 dimer in the nucleus. Transfected PGRMC1-GFP localizes mainly to the cytoplasm and does not form a DTT-resistant dimer. Moreover, forced expression of PGRMC1-GFP increases the sensitivity of the SIGCs to progesterone (P4)'s anti-apoptotic action, indicating that the PGRMC1 monomer is functional. However, when endogenous PGRMC1 is depleted by siRNA treatment and replaced with PGRMC1-GFP, P4 responsiveness is not enhanced, although overall levels of PGRMC1 are increased. P4's anti-apoptotic action is also attenuated by actinomycin D, an inhibitor of RNA synthesis, and P4 activation of PGRMC1 suppresses Bad and increases Bcl2a1d expression. Taken together, the present studies suggest a genomic component to PGRMC1's anti-apoptotic mechanism of action, which requires the presence of the PGRMC1 dimer.

N-cadherin mediated cell contact inhibits germinal vesicle breakdown in mouse oocytes maintained in vitro.

The effect of granulosa cell contact on the ability of zona-free oocytes to undergo germinal vesicle breakdown (GVBD) was assessed using a granulosa cell co-culture system. Oocytes contacted granulosa cells in a site-specific manner such that their GV was away from the granulosa cells. Also contact with granulosa cells reduced the percentage of oocytes undergoing GVBD from about 40% to 15%. GVBD was inhibited by contact with granulosa cells but not a granulosa cell-secreted product, since oocytes cultured in the same culture, that were adjacent to the granulosa cell monolayer underwent GVBD at the same rate as controls. Similarly, media collected from granulosa cell cultures did not attenuate the rate of GVBD. The ability of granulosa cell contact to inhibit GVBD was equal to that of db-cAMP. Moreover, the ability of granulosa cells to inhibit GVBD was not mimicked by spontaneously immortalized granulosa cells. This cell specificity appeared to be related to N-cadherin, since granulosa cells and oocytes express N-cadherin and a N-cadherin antibody attenuates the effect of granulosa cell contact. The mechanism through which N-cadherin mediated cell contact maintains meiotic arrest is unknown. It is possible that homophilic N-cadherin binding between the granulosa cells and oocyte acts through a junxtacrine mechanism, which in part may lead in the activation fibroblast growth factor (FGF) receptors that are expressed by the oocyte. The involvement of FGF receptors is supported by the observations that FGF and a N-cadherin peptide known to activate FGF receptors inhibit GVBD.

Progesterone membrane receptor component 1 expression in the immature rat ovary and its role in mediating progesterone's antiapoptotic action.

Progesterone receptor membrane component-1 (PGRMC1) interacts with plasminogen activator inhibitor RNA binding protein-1 (PAIRBP1), a membrane-associated protein involved in the antiapoptotic action of progesterone (P4). In this paper, the first studies were designed to assess the ovarian expression pattern of PGRMC1 and PAIRBP1. Western blot analysis revealed that spontaneously immortalized granulosa cells (SIGCs) as well as granulosa and luteal cells express both proteins. Luteal cells were shown to express more PGRMC1 than granulosa cells. Immunohistochemical studies confirmed this and demonstrated that PGRMC1 was present in thecal/stromal cells, ovarian surface epithelial cells, and oocytes. PAIRBP1 was also expressed in thecal/stromal cells and ovarian surface epithelial cells but not oocytes. Furthermore, PAIRBP1 and PGRMC1 were detected among the biotinylated surface proteins that were isolated by avidin affinity purification, indicating that they localized to the extracellular surface of the plasma membrane. Confocal microscopy revealed that both of these proteins colocalize to the plasma membrane as well as the cytoplasm. The second studies were designed to assess PGRMC1's role in P4's antiapoptotic actions. These studies showed that overexpression of PGRMC1 increased 3H-P4 binding and P4 responsiveness. Conversely, treatment with a PGRMC1 antibody blocked P4's antiapoptotic action. Taken together, the present findings indicate that both PAIRBP1 and PGRMC1 show a similar expression pattern within the ovary and colocalize to the extracellular surface of the plasma membrane. At the plasma membrane, these two proteins interact to form a complex that is required for P4 to transduce its antiapoptotic action.

Progesterone regulates granulosa cell viability through a protein kinase G-dependent mechanism that may involve 14-3-3sigma.

Progesterone (P4) inhibits granulosa cell and spontaneously immortalized granulosa cell (SIGC) apoptosis by regulating membrane-initiated events. However, the nature of the signal transduction pathway that is induced by these membrane-initiated events has not been defined. To gain insights into the P4-regulated signal transduction pathway, mouse granulosa cells and SIGCs were cultured with 8-br-cGMP and P4. In culture, 8-br-cGMP mimicked P4's antiapoptotic actions. Because cGMP activates protein kinase G (PKG), the effect of PKG antagonists on P4-regulated SIGC viability was assessed. P4's antiapoptotic action was attenuated by the PKG inhibitors, Rp-8-pCPT-cGMP, KT5823, the PKG-1alpha-specific inhibitor, DT-3, and a dominant negative PKG-1alpha. Further, the type I isoform of PKG was shown to be expressed by SIGCs and activated by P4. P4's antiapoptotic action was not affected by the PKA inhibitor, KT5720. Collectively, these findings indicate that P4 maintains SIGC viability by activating PKG-1alpha. PKG-1alpha-GFP was shown to localize predominantly to the cytoplasm of SIGCs. To identify potential cytoplasmic targets of PKG-1alpha, SIGCs were cultured for 5 h with P4 in the presence or absence of DT-3. Cell lysates were prepared and subjected to two-dimensional electrophoresis. The resulting gels were sequentially stained with ProQ-Diamond Gel Stain and Coomassie Blue to reveal phosphorylated proteins. The two-dimensional gels revealed one major protein, the phosphorylation status of which was abrogated by DT-3. Mass spectrometric analysis identified this protein as 14-3-3sigma, with 14-3-3sigma being phosphorylated on tyrosine 19, serine 28, serine 69, serine 74, threonine 90, threonine 98, and serine 116. Finally, difopein, a specific 14-3-3 inhibitor, was shown to induce apoptosis even in the presence of serum. These data suggest that 1) P4 regulates the phosphorylation status of 14-3-3sigma through a PKG-dependent pathway and 2) 14-3-3sigma plays a central and essential role in maintaining the viability of SIGCs.

Involvement of an unnamed protein, RDA288, in the mechanism through which progesterone mediates its antiapoptotic action in spontaneously immortalized granulosa cells.

Progesterone (P4) inhibits apoptosis of rat granulosa cells and spontaneously immortalized granulosa cells (SIGCs), which were derived from rat granulosa cells. Defining the mechanism through which P4 mediates its action has been difficult because these cells do not express the classic nuclear P4 receptor. Previous studies have shown that a P4 receptor antibody, C-262, detects a 60-kDa protein that is involved in regulating P4's antiapoptotic action. Using a C-262 affinity column, this 60-kDa protein was isolated and sequenced by mass spectrometry. This analysis revealed that the C-262-detectable protein is an unnamed protein referred to as RDA288. This protein has several putative hyaluronic acid binding sites. Further hyaluronic acid antagonizes (3)H-P4 binding to SIGCs and mimics P4's action, whereas exogenous hyaluronic acid binding protein attenuates P4's actions. RT-PCR demonstrated that RDA288 mRNA was present in SIGCs, immature rat ovary, lung, and skeletal muscle but was not present in several other organs. Forced expression of RDA288 increased the capacity of SIGCs to bind and respond to P4. An antibody was also developed against RDA288. Using this antibody in a Western blot protocol, RDA288 expression was confirmed in both SIGCs and granulosa cells. An immunohistochemical study detected RDA288 in the cytoplasm and plasma membrane components of granulosa cells of antral follicles. Immunocytochemical studies on living nonpermeabilized SIGCs revealed that RDA288 was present on the extracellular surface of the plasma membrane. Finally, pretreatment with the RDA288 antibody blocked P4's antiapoptotic actions. Taken together, these data suggest that RDA288 plays a significant role in mediating P4's antiapoptotic action in granulosa cells.

Progesterone as a regulator of granulosa cell viability.

Progesterone (P4) prevents numerous cells, including uterine, mammary and ovarian cells, from undergoing apoptosis. Interestingly, P4 prevents apoptosis of ovarian granulosa cells (GCs), which do not express the classic nuclear P4 receptor. This review presents data that support a non-genomic action of P4 in granulosa cells. These studies were conducted using both primary rat granulosa cells and rat spontaneously immortalized granulosa cells (SIGCs). Specifically, these studies reveal that (1) 3H-P4 specifically binds to SIGCs; (2) an antibody directed against the ligand binding domain of the nuclear P4 receptor (C-262) detects a 60kDa protein, which localizes to the plasma membrane and binds P4; and (3) treatment with C-262 blocks P4's ability to maintain granulosa cell viability. Additional studies demonstrate that a protein kinase G (PKG) activator, 8-br-cGMP, mimics and PKG antagonists, Rp-8-pcCPT-GMP and KT5823, attenuate P4's action. These studies support the concept that the 60kDa P4 binding protein functions as membrane receptor for P4 which activates a PKG-dependent mechanism to regulate granulosa cell survival.

Expression pattern and role of a 60-kilodalton progesterone binding protein in regulating granulosa cell apoptosis: involvement of the mitogen-activated protein kinase cascade.

Progesterone (P4) inhibits both granulosa cells and spontaneously immortalized granulosa cells (SIGCs) from undergoing apoptosis. P4 does so through a plasma membrane-initiated event. It appears that P4's membrane-initiated actions are mediated by a 60-kDa P4 binding protein (P4BP), which is detected by an antibody directed against the ligand binding domain of the nuclear P4 receptor (i.e., C-262). Immunohistochemical analysis revealed that a C-262-detectable protein was first observed in the periphery of a few granulosa cells within early antral-stage follicles. In nonatretic antral follicles, this protein was detected at the periphery of virtually all granulosa cells. In contrast, granulosa cells of atretic follicles lost the distinct peripheral localization of this C-262-detectable protein. This reduction in the membrane localization was also observed by Western blot analysis. To assess the temporal changes in this 60-kDa P4BP during apoptosis, studies were conducted using SIGCs. That this 60-kDa protein is important in mediating P4's action was confirmed by the observation that C-262 but not IgG attenuated P4's antiapoptotic action. Interestingly, the membrane localization of this 60-kDa P4BP was maintained but the ability of P4 to prevent apoptosis was lost within 20 min of initiating the apoptotic cascade. In addition, Erk-1 and -2 phosphorylation (i.e., activity) increased within 20 min of P4 withdrawal. Further, P4 suppressed the increase in the Erk-1 phosphorylation if administered within 5 but not 20 min of initiating the apoptotic cascade. Moreover, the mitogen-activated protein kinase kinase (MEK) inhibitor, PD98059, reduced the percentage of SIGCs undergoing apoptosis in the absence of P4. Because MEK phosphorylates Erk, these observations suggests that 1) the increase in Erk-1 activity is an important part of the apoptotic cascade, 2) P4 promotes granulosa cell viability by modulating the activity of Erk-1, and 3) P4 becomes "uncoupled" from its antiapoptotic signal transduction mechanism within 20 min of initiating apoptosis, even though the membrane localization of the 60-kDa P4BP is maintained.

Basic fibroblast growth factor maintains calcium homeostasis and granulosa cell viability by stimulating calcium efflux via a PKC delta-dependent pathway.

Previous studies have demonstrated that basic fibroblast growth factor prevents granulosa cell apoptosis. The following six observations provide insight into the mechanism by which basic fibroblast growth factor mediates its antiapoptotic action. First, loading granulosa cells with 1,2 bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, an intracellular calcium chelator, prevented apoptosis when granulosa cells were deprived of basic fibroblast growth factor. Second, treatment with thapsigargin, an agent known to increase intracellular free calcium, induced granulosa cell apoptosis even in the presence of basic fibroblast growth factor. Third, an activator of PKC mimicked, whereas PKC inhibitors blocked, basic fibroblast growth factor's antiapoptotic action. Fourth, continuous basic fibroblast growth factor exposure maintained relatively constant levels of intracellular free calcium, and a PKC inhibitor induced a sustained 2- to 3-fold increase in intracellular free calcium. Fifth, granulosa cells, as well as spontaneously immortalized granulosa cells, were shown to express PKC delta, -lambda, and -zeta. Finally, the PKC delta-specific inhibitor, rottlerin, blocked basic fibroblast growth factor's antiapoptotic action in granulosa cells and spontaneously immortalized granulosa cells. These studies suggest that basic fibroblast growth factor regulates intracellular free calcium through a PKC delta-dependent mechanism and that a sustained increase in intracellular free calcium is sufficient to induce and is required for granulosa cell apoptosis. Additional studies demonstrated that in spontaneously immortalized granulosa cells, basic fibroblast growth factor increased PKC delta activity by 60% within 2.5 min compared with serum-free control levels. Rottlerin attenuated basic fibroblast growth factor's ability to stimulate PKC delta activity and to maintain intracellular free calcium. Further, intracellular free calcium levels in spontaneously immortalized granulosa cells transfected with a PKC delta antibody in the presence of basic fibroblast growth factor were 2-fold higher than those spontaneously immortalized granulosa cells transfected with IgG. Similarly, transfecting spontaneously immortalized granulosa cells with a specific PKC delta-substrate increased intracellular free calcium compared with spontaneously immortalized granulosa cells transfected with a specific substrate for PKC epsilon. Moreover, basic fibroblast growth factor increased and rottlerin attenuated (45)Ca efflux by 50% compared with that in basic fibroblast growth factor-treated cells. Finally, an inhibitor of the plasma membrane calciumadenosine triphosphatase pump suppressed (45)Ca efflux, elevated intracellular free calcium, and induced apoptosis. Collectively, these studies demonstrate that basic fibroblast growth factor activates PKC delta, which, in turn, stimulates calcium efflux, accounting in part for basic fibroblast growth factor's ability to maintain calcium homeostasis and, ultimately, granulosa cell viability.

Characterization of a putative membrane receptor for progesterone in rat granulosa cells.

Progesterone (P(4)) inhibits granulosa cell apoptosis in a steroid-specific, dose-dependent manner, but these cells do not express the classic nuclear P(4) receptor. It has been proposed that P(4) mediates its action through a 60-kDa protein that functions as a membrane receptor. The present studies were designed to determine the P(4) binding characteristics of this protein. Western blot analysis using an antibody that recognizes the P(4) binding site of the nuclear P(4) receptor (C-262) confirmed that the 60-kDa protein was localized to the plasma membrane of both granulosa cells and spontaneously immortalized granulosa cells (SIGCs). To determine whether this protein binds P(4), proteins were immunoprecipitated with the C-262 antibody, electrophoresed, transferred to nitrocellulose, and probed with a horseradish peroxidase-labeled P(4) in the presence or absence of nonlabeled P(4). This study demonstrated that the 60-kDa protein specifically binds P(4). Scatchard plot analysis revealed that (3)H-P(4) binds to a single site (i.e., single protein), which is relatively abundant (200 pmol/mg) with a K(d) of 360 nM. (3)H-P(4) binding was not reduced by dexamethasone, mifepristone (RU 486), or onapristone (ZK98299). Further studies with SIGCs showed that P(4) inhibited apoptosis and mitogen-activated protein kinase kinase (MEK) activity, and maintained calcium homeostasis. These studies taken together support the concept that the 60-kDa P(4) binding protein functions as a low-affinity, high-capacity membrane receptor for P(4).

E-cadherin-mediated cell contact prevents apoptosis of spontaneously immortalized granulosa cells by regulating Akt kinase activity.

The present studies were designed to determine the role that homophilic E-cadherin binding plays in preventing apoptosis of spontaneously immortalized granulosa cells (SIGCs). Although the levels of E-cadherin were similar to serum control levels, the amount of E-cadherin at the plasma membrane was dramatically reduced by 5 h after serum withdrawal. To determine whether disrupting homophilic E-cadherin binding leads to apoptosis, SIGCs were cultured in serum in the presence of either EGTA or an E-cadherin antibody. Treatment with either EGTA, which disrupts all calcium-dependent contacts, or E-cadherin antibody, induced apoptosis. Exposure to EGTA reduced MEK and Akt kinase activity, whereas E-cadherin antibody only attenuated Akt kinase activity. Because Akt kinase controls caspase-3 activity, an important activator of apoptosis, caspase-3 activity was monitored. Caspase-3 activity increased after serum depletion, or EGTA or E-cadherin antibody treatment. Time-series analysis of caspase-3 activity within single cells revealed that during apoptosis cell contact was disrupted then caspase-3 activity was detected. Finally, the caspase inhibitor, Z-VAD-FMK, blocked apoptosis. These data taken together are consistent with the concept that E-cadherin-mediated cell contact, either directly or indirectly, promotes Akt kinase activity, which in turn, inhibits caspase-3 activation and thereby maintains SIGC viability.

Basic fibroblast growth factor inhibits apoptosis of spontaneously immortalized granulosa cells by regulating intracellular free calcium levels through a protein kinase Cdelta-dependent pathway.

Previous studies have shown that basic fibroblast growth factor (bFGF) inhibits primary granulosa cells from undergoing apoptosis. The present studies were designed to determine whether spontaneously immortalized granulosa cells (SIGCs) undergo apoptosis when deprived of growth factors and whether bFGF prevents apoptosis. In the absence of serum, the SIGCs lost cell contact and underwent apoptosis as indicated by the presence of annexin V binding, DNA ladders, and nuclear fragmentation. Basic FGF maintained cell contact and reduced the percentage of apoptotic cells. This antiapoptotic action was not observed ifbFGF was added 30 min after serum withdrawal. Further, intracellular free calcium ([Ca2+]i) levels gradually increased 3- to 4-fold within 10 min of serum withdrawal. This increase was inhibited by bFGF. The intracellular calcium chelator, BAPTA, completely prevented the SIGCs from undergoing apoptosis in the absence of serum. These observations suggest that bFGF's ability to regulate [Ca2+]i is an essential component of its antiapoptotic action. The phorbol ester TPA, an activator of protein kinase C (PKC), blocked apoptosis due to serum deprivation. Conversely, bisindolylmaleimide II, an inhibitor of PKC, completely attenuated, whereas bisindolylmaleimide V, an inactive bisindolylmaleimide analog, did not influence bFGF's antiapoptotic action. Also, treatment with the PKC inhibitor, chelerythrine chloride, interfered with bFGF's ability to maintain calcium homeostasis. Western blot analysis revealed that SIGCs expressed PKCdelta, tau, lambda, and zeta. Of these PKC isoforms, only PKCdelta has been shown to be activated by TPA. In apoptotic SIGCs, PKCdelta levels were depleted. When PKCdelta levels were reduced by pretreatment with 500 nM TPA, neither bFGF nor 10 nM TPA suppressed apoptosis. Collectively, these observations suggest that bFGF maintains [Ca2+]i and thereby SIGC viability through a PKCdelta-dependent pathway.

Effect of disrupting cell contact on the nuclear accumulation of beta-catenin and subsequent apoptosis of rat ovarian surface epithelial cells in vitro.

The present studies were designed to determine how disrupting cell contact induces rat ovarian surface epithelial cells (i.e., ROSE-179 cells) to undergo apoptosis. In the first series of studies, the effect of depleting serum and calcium on the levels of the adhesion proteins N-cadherin and beta-catenin was examined. These studies revealed that the depletion of serum and calcium results in the degradation of N-cadherin but not beta-catenin. However, the localization of beta-catenin changed from principally the plasma membrane to the nucleus. The nuclear localization of beta-catenin was demonstrated by Western blot and confocal microscopy. A second series of studies demonstrated that cells that lost contact in response to the depletion of serum and calcium showed enhanced beta-catenin-dependent transcription. Finally, forced expression of a stable form of beta-catenin resulted in an increase in beta-catenin within the cytoplasm of transfected ROSE-179 cells. When these beta-catenin transfected ROSE-179 cells were deprived of serum and calcium, beta-catenin accumulated within the nucleus and accelerated the rate at which these cells became apoptotic. These data indicate that in viable cells, beta-catenin is part of the adhesion complex that maintains cell contact. If calcium-dependent cell contacts are broken, beta-catenin accumulates within the nucleus, where it promotes transcription and ultimately the apoptotic death of ROSE-179 cells.

Hepatocyte growth factor disrupts cell contact and stimulates an increase in type 3 inositol triphosphate receptor expression, intracellular calcium levels, and apoptosis of rat ovarian surface epithelial cells.

The present studies revealed that hepatocyte growth factor (HGF) disrupts cell contact, increases both type 3 IP3 receptor and intracellular calcium ([Ca2+]i) levels and induces apoptosis of rat ovarian surface epithelial cells (ROSE-179 cells). Type 3 IP3 receptor was only increased in cells that lost cell contact. Disrupting cell contact by depleting extracellular calcium (Ca2+) also resulted in an increase in [Ca2+]i levels and an increase in apoptosis. These responses were prevented by the addition of 0.7 mM Ca2+. Actinomycin D and cycloheximide prevented apoptosis that resulted from Ca2+ removal. In situ hybridization studies revealed that type 3 IP3 receptor was expressed at relatively low levels by ROSE-179 cells cultured with Ca2+ but at high levels in the absence of Ca2+. ROSE-179 cells cultured in Ca2+-free medium with type 3 IP3 receptor antisense oligonucleotide lost cell contact but did not show an increase in either type 3 IP3 receptor protein, [Ca2+]i, or apoptosis. The nonsense oligonucleotide did not alter these responses to Ca2+ removal. Thus, the disruption of cell contact by either HGF or Ca2+ depletion increases the expression of type 3 IP3 receptor, which causes an increase in [Ca2+]i and the apoptotic death of ROSE-179 cells.

N-cadherin-mediated cell contact regulates ovarian surface epithelial cell survival.

The present study shows that in cells derived from the rat ovarian surface epithelium (i.e. ROSE-179 cells) the adhesion protein, N-cadherin, binds to the receptor for fibroblast growth factor (FGF). This interaction likely accounts for the ability of the N-cadherin antibody to decrease the activation (i.e. tyrosine phosphorylation) of the FGF receptor and induce apoptosis. The loss of N-cadherin-mediated cell contact also results in the accumulation of beta-catenin within the nucleus. Since beta-catenin also functions as a transcription factor, nuclear beta-catenin may promote mRNA synthesis that is required for ROSE-179 cells to undergo apoptosis in response to serum/calcium withdrawal. This hypothesis requires further testing and validation.

Negative regulation of N-cadherin-mediated cell-cell adhesion by the estrogen receptor signaling pathway in rat pituitary GH3 cells.

The ability of the estrogen receptor signaling pathway to regulate cell-cell adhesion, and N-cadherin and beta-catenin expression was examined in rat somatolactotropic GH3 cells cultured in serum-free, phenol red-free medium (SFM). Estradiol-17beta (E2) promoted a nonadherent phenotype, whereas the steroidal antiestrogen, ICI 182,780, induced the formation of tightly adherent aggregates of cells. The antiestrogen-induced cell-cell adhesion was associated with the presence of adherens junctions, and was Ca2+-dependent. E2 reduced surface N-cadherin protein to barely detectable levels, whereas ICI 182,780-treated cells displayed abundant punctate immunoreactive N-cadherin. Antiestrogen failed to induce adhesion in the presence of a blocking antibody to N-cadherin. ICI 182,780 increased the protein levels for N-cadherin and the cadherin-binding protein, beta-catenin, by twofold over SFM controls or E2-treated samples. ICI 182,780 also increased the mRNA levels for N-cadherin and beta-catenin by two- to fivefold. In GH3 cells cultured in growth medium, ICI 182,780 increased N-cadherin and beta-catenin levels by twofold over untreated controls, and inhibited cell proliferation by 53%. These results provide the first demonstration of the regulation of N-cadherin-mediated cell-cell adhesion by the estrogen receptor (ER) signaling pathway in pituitary somatolactotrophs through the coordinate regulation of N-cadherin and beta-catenin expression. The inverse relationship between ICI 182,780-induced adhesion and proliferation raises the possibility that these two processes are functionally related.

Hepatocyte growth factor induces rat ovarian surface epithelial cell mitosis or apoptosis depending on the presence or absence of an extracellular matrix.

The present studies showed that sequential treatment with equine CG (eCG) and hCG not only induced an increase in ovarian weight, but also caused an estimated 4.6-fold increase in the number of ovarian surface epithelial cells. In addition, eCG-hCG treatment increased ovarian hepatocyte growth factor (HGF) messenger RNA levels. These studies also demonstrated that rat primary ovarian surface epithelial cells as well as a cell line derived from rat ovarian surface epithelium (i.e. ROSE-179 cells) do not express the LH (hCG) receptor. Both of these cells express c-Met, the receptor for HGF. To assess the effects of hCG and HGF on ovarian surface epithelial cell mitosis, ROSE-179 cells were cultured for 24 h in serum-supplemented medium on either glass or the synthetic fibronectin-like extracellular matrix protein, pronectin (RGD). The cells were then cultured for 24 h in serum-free medium in the presence or absence of hCG or HGF. The numbers of cells at 2, 24, and 48 h of culture were determined. The percentage of apoptotic cells was assessed by in situ DNA staining at 48 h of culture. In the serum-supplemented medium in the presence or absence of RGD, the number of ROSE-179 cells doubled. In serum-free medium, cell proliferation was reduced, and the percentage of apoptotic nuclei ranged between 10-15% regardless of the substrate. Neither mitosis nor apoptosis was influenced by hCG in the presence or absence of RGD. For ROSE-179 cells cultured in serum-free medium on RGD, HGF induced mitosis, resulting in a 2.8 +/- 0.2-fold increase in cell number compared with the 24 h control values. On a glass substrate in serum-free medium, HGF did not induce mitosis, but increased the percentage of apoptotic nuclei. Time-lapse photographic analysis revealed that on RGD, cells undergoing HGF-induced mitosis showed a transient reduction in cell contact. On glass, HGF caused many cells to completely lose contact and separate from each other. Collectively, these data suggest that in vivo gonadotropins stimulate HGF expression and ovarian surface epithelial cell proliferation. Based on in vitro studies, it is likely that the mitogenic action of hCG is mediated by HGF. However, HGF only induces mitosis in the presence of an extracellular matrix.

Progesterone maintains large rat granulosa cell viability indirectly by stimulating small granulosa cells to synthesize basic fibroblast growth factor.

Ovarian follicles are composed of small and large granulosa cells (GCs). Since progesterone (P4) inhibits large GCs from undergoing apoptosis, studies were designed to determine whether both sizes of GCs bind P4. These studies revealed that fluorescein isothiocyanate-BSA-P4 bound only to the surface membranes of small GCs. This binding was steroid-specific and inhibited by an antibody directed against the ligand-binding domain of the nuclear P4 receptor (PR). In addition, a cell-impermeable derivative of P4, BSA-conjugated P4, was as effective as P4 in preventing apoptosis. Quantitative in situ hybridization studies showed that P4 increased the relative amount of basic fibroblast growth factor (bFGF) mRNA expressed per cell as well as the percentage of small GCs that expressed bFGF. To determine whether the anti-apoptotic action of P4 was mediated by bFGF, GCs were cultured in control medium supplemented with either P4, a neutralizing antibody to bFGF, or both P4 and the bFGF antibody. The results from this study demonstrated that P4 suppressed apoptosis and that this effect was attenuated in presence of the bFGF antibody. Basic FGF also prevented GC apoptosis, and its action was not influenced by either the PR antagonist (RU-486), an inhibitor of P4 synthesis (aminoglutethimide), or a PR antibody. Finally, FGF receptors were detected on both small and large GCs. Collectively, these data support the hypothesis that P4 acts through a putative membrane receptor on small GCs to stimulate the synthesis of bFGF. Basic FGF then activates its receptors within large GCs, and this initiates a signal transduction pathway that maintains large GC viability.

Steroidogenic factor-1 regulates the rate of proliferation of normal and neoplastic rat ovarian surface epithelial cells in vitro.

Steroidogenic factor-1 (SF-1) is a transcription factor that is expressed by many cell types within the ovary and has been shown to inhibit granulosa cell proliferation. The present studies were designed to determine whether: 1) SF-1 is expressed by primary and transformed rat ovarian surface epithelial cells (i.e. ROSE cells); and 2) SF-1 expression effects the proliferation of both normal and neoplastic ROSE cells. These studies used immature, gonadotropin-primed and mature rat ovaries, as well as ROSE-179 cells from early passages (EP) and late passages (LP), T-sv-40 transformed ROSE cells, and T-ras transformed ROSE cells. In situ hybridization studies demonstrated that SF-1 was detected in the surface epithelium of rat ovaries, independent of age or gonadotropin treatment. Further, Northern blot and quantitative in situ hybridization studies revealed that significant amounts of SF-1 messenger RNA (mRNA) were present in EP-ROSE-179 cells but not in the other cell lines. Interestingly, EP-ROSE-179 cells proliferated at a significantly slower rate than the other cell lines. Further, SF-1 mRNA levels were higher in EP-ROSE-179 cells in the G0/G1 stage than in the S-, G2/M stage of the cell cycle. These observations suggest that a cause and effect relationship exists between the level of SF-1 expression and cell proliferation. To test this hypothesis, LP, T-sv-40, and T-ras ROSE cells were transfected with either control vector or SF-1 expression vector. Forty-eight hours after transfection, SF-1 expression was assessed by in situ hybridization, and the fold increase in cell number/24 h was determined. For each cell line, about 30% of the cells were successfully transfected. The fold increase in the number of cells observed after transfection with the SF-1 expression vector was significantly less than the increase in cell number after transfection with the control vector (P < 0.05). To confirm that the forced expression of SF-1 prevented proliferation, LP cells were cotransfected with a green fluorescent protein (GFP) expression vector and either control vector or SF-1 expression vector. This study demonstrated that virtually none of the GFP/SF-1-transfected cells proliferated over a 24-h period, whereas GFP/Control vector-transfected cells proliferated. Further, approximately 40% of the GFP/SF-1-transfected cells underwent apoptosis after 24 h of culture in serum-supplemented medium. These data demonstrate that: 1) normal ovarian surface epithelial cells express SF-1; 2) SF-1 is also expressed by EP-ROSE-179 cells, but its expression seems to be suppressed when the cells enter the cell cycle; 3) LP-, T-sv, and T-ras ROSE cells do not express SF-1 mRNA; and 4) the inability to express SF-1 is associated with an increase in cell proliferation. Finally, forced SF-1 expression interferes with serum-induced proliferation and leads to apoptosis.

A role for hepatocyte growth factor/scatter factor in regulating normal and neoplastic cells of reproductive tissues.

OBJECTIVE: To review data regarding the expression, function, and signal transduction pathways associated with hepatocyte growth factor/scatter factor (HGF/SF) as related to normal and neoplastic cells of reproductive tissues. METHODS: Studies involving HGF/SF were reviewed and the data were summarized. RESULTS: Hepatocyte growth factor/scatter factor is generally expressed within the stromal components of the testis, prostate, placenta, mammary gland, uterine endometrium, and ovary. The receptor for HGF/SF, c-met, is expressed in the epithelial cells of these tissues. Ligand activation of c-met results in its autotyrosine phosphorylation and the subsequent stimulation of numerous signal transduction pathways. Which pathways are activated determine in part the effect that HGF/SF has on a specific tissue. Hepatocyte growth factor/scatter factor can promote a variety of biologic responses including mitosis, motogenesis (i.e., cell movement), differentiation, and apoptosis. In addition, both HGF/SF and c-met continue to be expressed during the neoplastic transformation of cells from these reproductive tissues. CONCLUSION: Hepatocyte growth factor/scatter factor plays an important role in regulating the physiologic function of several reproductive tissues and may also be involved in the oncogenesis of cells within these tissues.