Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We demonstrate the mechanism by which Cordyceps sinensis (CS) mycelium regulates Leydig cell steroidogenesis. Mouse Leydig cells were treated with forskolin, H89, phorbol 12-myristate 13-acetate, staurosporine, or steroidogenic enzyme precursors with or without 3 mg/ml CS; then testosterone production was determined. H89, but not phorbol 12-myristate 13-acetate or staurosporine, decreased CS-treated Leydig cell steroidogenesis. CS inhibited Leydig cell steroidogenesis by suppressing the activity of P450scc enzyme, but not 3beta-hydroxysteroid dehydrogenase, 17alpha-hydroxylase, 20alpha-hydroxylase, or 17beta-hydroxysteroid dehydrogenase enzymes. Thus, CS activated the cAMP-protein kinase A signal pathway, but not protein kinase C, and attenuated P45scc enzyme activity to reduce human chorionic gonadotropin-stimulated steroidogenesis in purified mouse Leydig cells.
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PMID:Regulatory mechanism of Cordyceps sinensis mycelium on mouse Leydig cell steroidogenesis. 1275 21

Previous results showed that GnRH signaling is altered in cells from rat luteinized ovarian tumors (tumor group) because it did not activate the phospholipase C pathway, in contrast to control ovarian cells from superovulated prepubertal rats (SPO). In the present work, alternate GnRH-induced second messengers such as phospholipase A(2) and phospholipase D activation, cAMP production, ERK1/2 phosphorylation, and the presence of G proteins were evaluated to determine GnRH mechanism of action in tumor cells. G proteins examined were present in both cell types. Buserelin, a GnRH agonist, (1, 10, and 100 ng/ml) increased phosphatidylethanol in SPO, indicating phospholipase D activation. Only 100 ng/ml buserelin induced a significant response in the tumor group. Buserelin (100 ng/ml) increased (3)H-arachidonic acid in culture media in SPO, indicating phospholipase A(2) activation; no effect was observed in the tumor group. Buserelin (100 and 1000 ng/ml) induced pertussis toxin-insensitive cAMP increases in both cell types, with similar potencies. In the tumor group, buserelin (100 ng/ml) inhibited human chorionic gonadotropin-induced cAMP and progesterone; this effect was protein kinase C (PKC) dependent (inhibited by GF109203X, a PKC inhibitor). Buserelin (100 and 1000 ng/ml) induced ERK1/2 phosphorylation in both cell kinds. Buserelin-induced ERK1/2 activation was G(i/0) independent and PKC dependent. Only in the tumor group, buserelin-induced ERK1/2 activation was cAMP dependent (abolished by SQ 22536, the adenylyl cyclase inhibitor). Furthermore, dibutyryl cAMP-induced ERK1/2 activation in the tumor group was PKC dependent (inhibited by GF109203X). In conclusion, activation of phospholipases in tumor cells does not seem to mediate GnRH effects. GnRH signaling seems to involve adenylyl cyclase activation, PKC stimulation, and ERK1/2 phosphorylation.
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PMID:Gonadotropin-releasing hormone signaling pathways in an experimental ovarian tumor. 1281 May 51

We studied the involvement of the ERK cascade in human chorionic gonadotropin (hCG)-induced steroidogenesis by primary cultures of immature rat Leydig cells. Our findings indicate that protein kinase A and protein kinase C function as upstream kinases in connection with transduction of the signal from the gonadotropin receptor to the ERK cascade. These MAPKs enhance the stimulatory effects of hCG on the de novo synthesis of the steroidogenic acute regulatory protein and the activity of protein phosphatase 2A, which are associated with increased androgen production by the Leydig cell. Specific inhibition of ERK1/2 by Uo126 suppressed all of these cellular responses to hCG. In contrast, steroidogenesis from 22OHC (a cell-permeable form of cholesterol) is not inhibited by Uo126, suggesting that cholesterol delivery to mitochondria is being affected by this compound. We propose that the ERK cascade is an important part of the signal transduction pathway involved in the rapid hormonal responses of Leydig cells to trophic hormones. In hCG-activated Leydig cells, these MAPKs may play a role in controlling the biosynthesis of the steroidogenic acute regulatory protein as well as regulating protein phosphatase 2A activity, thereby governing cholesterol transport across the mitochondrial membrane.
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PMID:Extracellular signal-regulated kinases are involved in the acute activation of steroidogenesis in immature rat Leydig cells by human chorionic gonadotropin. 1524 88

We previously reported that lysozyme accounts for anti-HIV activity associated with the beta-core fraction of human chorionic gonadotropin [Lee-Huang, S., Huang, P. L., Sun, Y., Kung, H. F., Blithe, D. L. & Chen, H. C. (1999) Proc Natl Acad Sci U S A 96, 2678-81]. To define the structural and sequence requirements for anti-HIV activity, we carried out peptide fragmentation and activity mapping of human lysozyme. We identified two peptides that consist of 18 and 9 amino acids of human lysozyme (HL18 and HL9), corresponding to residues 98-115 and 107-115. HL18 and HL9 are potent inhibitors of HIV-1 infection and replication with EC(50)s of 50 to 55 nM, comparable to intact lysozyme. Scrambling the sequence or substitution of key arginine or tryptophan residues results in loss of antiviral activity. HL9, with the sequence RAWVAWRNR, is the smallest peptide we identified with full anti-HIV activity. It forms a pocket with its basic residues on the surface of the molecule. HL9 exists as an alpha-helix in native human lysozyme, in a region of the protein distinct from the muramidase catalytic site. Monte Carlo peptide folding energy minimizing simulation modeling and CD studies indicate that helical propensity does not correlate with antiviral activity. HL9 blocks HIV-1 viral entrance and replication, and modulates gene expression of HIV-infected cells, affecting pathways involved in survival, stress, TGFbeta, p53, NFkappaB, protein kinase C and hedgehog signaling.
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PMID:Structural and functional modeling of human lysozyme reveals a unique nonapeptide, HL9, with anti-HIV activity. 1577 91

This study investigated the roles of the protein kinase C (PKC) and protein kinase A (PKA) pathways in regulating constitutive steroidogenesis and steroidogenic acute regulatory (STAR; herein designated by its common name, StAR) protein in R2C Leydig tumor cells. Inhibition of PKC and phospholipase C resulted in significant decreases in steroid production, phosphorylation of cAMP-responsive element binding (CREB) protein, and Star gene transcription under basal conditions in R2C cells. These observations were corroborated in MA-10 and mLTC-1 Leydig tumor cell lines, in which activation of PKC by phorbol-12-myristate-13-acetate (PMA, 10 nM) increased CREB phosphorylation and total StAR (tot-StAR) protein expression. However, induction of StAR protein by PMA did not result in the expected concomitant increase in steroids because PKC failed to phosphorylate StAR, the biologically active form of the protein. However, in conjunction with PMA, minor increases in PKA activity using submaximal doses of (Bu)2cAMP (0.05-0.1 mM; a concentration range insufficient for induction of StAR), were able to stimulate dramatic increases in both phospho-StAR (P-StAR) and steroid production. Human chorionic gonadotropin stimulation also resulted in a further enhancement in P-StAR and progesterone production when added to PMA-treated MA-10 cells. Similar results for tot-StAR and P-StAR expression were observed in primary cultures of immature rat Leydig cells treated with PMA and submaximal doses of (Bu)2cAMP. In summary, the present study demonstrates that basal activities of both PKC and PKA play important roles in the constitutive steroidogenic characteristics of R2C cells. This study also demonstrates for the first time a role for PMA-induced PKC in StAR protein regulation and the requirement for submaximal doses of cAMP to produce steroids in Leydig cells.
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PMID:Involvement of protein kinase C and cyclic adenosine 3',5'-monophosphate-dependent kinase in steroidogenic acute regulatory protein expression and steroid biosynthesis in Leydig cells. 1581 1

Adlay (Coix lachryma-jobi L. var. ma-yuen Stapf.) has long been used as a traditional Chinese medicine for dysfunctions of the endocrine system and inflammation conditions. However, the effect of adlay seed on the endocrine system has not yet been reported. In the present study, the effects and the mechanisms of methanolic extract of adlay bran (ABM) on progesterone synthesis in rat granulosa cell were studied. ABM was further partitioned with different solvents including water, 1-butanol, ethyl acetate and n-hexane. Four subfractions named ABM-Wa (water fraction), ABM-Bu (1-butanol fraction), ABM-EA (ethyl acetate fraction) and ABM-Hex (n-hexane fraction) were obtained. ABM-Bu was further fractionated using Diaion HP-20 resin column chromatography with gradient elution. Granulosa cells were prepared from pregnant mare serum gonadotropin-primed immature female rats and challenged with different reagents including human chorionic gonadotropin (hCG 0.5 IU/ml), forskolin (10 microM), 8-bromo-adenosine-3',5'-cyclic monophosphate (8-Br-cAMP, 1 mM), A23187 (10 microM), phorbol 12-myristate 13-acetate (PMA, 0.01 microM), 25-OH-cholesterol (0.1-10 microM) and pregnenolone (0.1-10 microM) in the presence or absence of ABM-Bu (100 microg/ml). The functions of steroidogenic enzyme including protein expression of the steroidogenic acute regulatory protein (StAR) and cytochrome P450 side-chain cleavage enzyme (P450scc) protein were investigated. Expressions of both P450scc and StAR mRNA have also been explored. We found that ABM decreased progesterone production via an inhibition on (1) the cAMP-PKA and PKC signal transduction pathway, (2) P450scc and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) enzyme activity, (3) P450scc and StAR protein and mRNA expressions and (4) the phosphorylation of ERK1/2 in rat granulosa cells.
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PMID:Downregulation of progesterone biosynthesis in rat granulosa cells by adlay (Coix lachryma-jobi L. var. ma-yuen Stapf.) bran extracts. 1625 70

In the regulation of steroid biosynthesis, a process mediated by the steroidogenic acute regulatory (StAR) protein, both cAMP-dependent and -independent pathways are involved. While the cAMP-dependent regulatory events represent, by far, the most robust increase in steroid synthesis and are well established, the knowledge regarding cAMP-independent mechanisms is lacking. The present investigation was designed to elucidate the potential involvement of the latter in regulating StAR expression and steroidogenesis in mouse Leydig tumor cells (mLTC-1 cells). Treatment of mLTC-1 cells with a number of factors including insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF), fibroblast growth factor, transforming growth factor (TGF)alpha, interleukin-1 (IL-1), and colony-stimulating factor-1, increased the levels of StAR mRNA, StAR protein, and progesterone to varying degrees and utilized signaling pathways that are not associated with elevations in intracellular cAMP levels. Importantly, phosphorylation of StAR in response to these stimuli was undetectable, which is in marked contrast to observations with human chorionic gonadotropin (hCG), indicating factors that do not alter intracellular cAMP, regulate the steroid biosynthesis in a StAR phosphorylation-independent manner. In addition, the roles for factors involved in cross-talk between the protein kinase pathways, PKA and PKC, were demonstrated. Further characterization of signaling by one such cAMP-independent factor, TGFalpha, demonstrated that the mechanism, whereby it increased StAR expression and steroid synthesis, was dependent on de novo protein synthesis and mediated via activation of the EGF receptor. TGFalpha was also able to augment hCG-stimulated cAMP synthesis, StAR protein and StAR phosphorylation, and influence hCG binding and LH receptor mRNA expression. Furthermore, TGFalpha increased phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2) and cAMP-response element-binding protein (CREB), processes inhibited by the mitogen-activated protein kinase/ERK inhibitor U0126 and by expression of non-phosphorylatable CREB-M1 respectively. Inhibition of ERK activity enhanced TGFalpha-mediated StAR protein expression (but not its phosphorylation) and decreased progesterone synthesis, events correlated with the expression of dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 (DAX-1) and scavenger receptor class B type 1 (SR-B1). Collectively, these findings demonstrate that, in mouse Leydig cells, cAMP-independent signaling events regulate steroidogenesis in a StAR phosphorylation-independent manner.
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PMID:cAMP-independent signaling regulates steroidogenesis in mouse Leydig cells in the absence of StAR phosphorylation. 1690 26

Human chorionic gonadotropin and human FSH (hFSH) elicit a transient increase in ERK1/2 phosphorylation lasting less than 60 min in immature granulosa cells expressing a low density of gonadotropin receptors. In cells expressing a high density of receptors, human chorionic gonadotropin and human FSH elicit this fast transient increase in ERK1/2 phosphorylation and also a delayed and more sustained increase that is detectable after 6-9 h. Both the early and delayed increases in ERK1/2 phosphorylation can be blocked with inhibitors of protein kinase A, the epidermal growth factor receptor kinase, metalloproteases, and MAPK kinase. The delayed effect, but not the early effect, can also be blocked with an inhibitor of protein kinase C. Because the delayed increase in ERK1/2 phosphorylation correlates with low aromatase expression in response to gonadotropins, we tested the effects of these inhibitors on aromatase expression. These inhibitors had little or no effect on gonadotropin-induced aromatase expression in cells expressing a low density of receptors, but they enhanced gonadotropin-induced aromatase expression in cells expressing a high density of receptors. Phorbol esters also induced a prolonged increase in ERK1/2 phosphorylation and, when added together with hFSH, blocked the induction of aromatase expression by hFSH in cells expressing a low density of hFSH receptor. A MAPK kinase inhibitor reversed the inhibitory effect of the phorbol ester on aromatase induction. We conclude that the effects of gonadotropins on ERK1/2 phosphorylation are mediated by epidermal growth factor-like growth factors and that the delayed effect is partially mediated by protein kinase C and acts as a negative regulator of aromatase expression.
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PMID:A delayed gonadotropin-dependent and growth factor-mediated activation of the extracellular signal-regulated kinase 1/2 cascade negatively regulates aromatase expression in granulosa cells. 1697 59

The steroidogenic acute regulatory (StAR) protein plays a central role in the regulation of steroid biosynthesis. While steroidogenesis is influenced by many processes, their modes of actions, in a few cases, remain obscure. In this study, we explored the mechanism of action of one such signaling pathway, the extracellular signal-regulated kinase 1/2 (ERK1/2), in regulating StAR expression and steroidogenesis in conjunction with the protein kinase A (PKA) and protein kinase C (PKC) pathways. Using MA-10 mouse Leydig tumor cells, we demonstrate that the activation of PKC and PKA signaling, by phorbol-12-myristate-13-acetate (PMA) and dibutyryl cAMP (dbcAMP)/human chorionic gonadotropin (hCG) respectively, was able to phosphorylate ERK1/2, an event markedly decreased by an upstream kinase inhibitor, U0126. Treatment with PMA enhanced StAR protein expression (associated with a slight increase in progesterone synthesis) but not its phosphorylation (P-StAR), which, in contrast, coordinately increased in response to dbcAMP/hCG. Inhibition of ERK1/2 activity by U0126 decreased PMA-treated StAR expression but increased dbcAMP/hCG-mediated StAR and P-StAR; however, progesterone levels were attenuated. U0126 was found to affect StAR expression and steroidogenesis both at the transcriptional and translational levels. Further studies demonstrated that the effect of U0126 on PMA- and dbcAMP/hCG-mediated StAR expression and steroid synthesis was tightly correlated with the expression of dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 (DAX-1) and scavenger receptor class B type 1 (SR-B1). In fact, both DAX-1 and SR-B1 appear to play important roles in hormone-regulated steroidogenesis. These findings clearly demonstrate that the ERK1/2 signaling cascade involved in regulating StAR expression and steroid synthesis is mediated by multiple factors and pathways and is stimulus specific in mouse Leydig cells.
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PMID:Regulation of Leydig cell steroidogenesis by extracellular signal-regulated kinase 1/2: role of protein kinase A and protein kinase C signaling. 1740 Aug 3

The effects of salmon calcitonin (sCT) on the secretion of 17beta-estradiol (E(2)) were examined in female common carp, Cyprinus carpio. Vitellogenic stage fish adapted to high-Ca water were i.p. injected with vehicle, sCT, human chorionic gonadotropin (hCG), or hCG plus sCT. To determine whether ovarian follicles are equipped with CT receptors, a CT binding assay was conducted. In the in vitro experiments, vitellogenic follicles were incubated with stimulators and inhibitors. Administration of sCT increased the basal and hCG-stimulated E(2) release in vivo and in vitro. Binding characteristics of [(125)I]sCT to plasma membrane preparation of carp ovarian follicles showed saturability with high-affinity (K(d)=48.48 pmol/l and B(max)=1.2 pmol/mg protein). To clarify the mechanism of E(2) production by sCT, in vitro effect of sCT and hCG on aromatase activity (conversion of testosterone to E(2)) and cytochrome P450 aromatase (P450arom) gene expression in carp ovarian follicles were investigated. Salmon CT-stimulated both aromatase activity and P450arom gene expression in ovarian follicles of carp. sCT-stimulated E(2) release by the ovarian follicles in vitro was augmented in the presence of dibutyryl cAMP. Inhibitor of protein kinase A (PKA), SQ 22536 inhibited sCT-stimulated steroid production in a dose-dependent manner. Specific inhibitor of protein kinase C (PKC), NPC-15437 dihydrochloride had no inhibitory effects on sCT-induced E(2) release. The present study indicates that sCT binds specifically to carp ovary and stimulates E(2) production by increasing the activity of cytochrome P450 aromatase and P450arom gene expression. The results further suggest that stimulatory action of sCT on E(2) production is mediated through cAMP pathway.
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PMID:Stimulation of salmon calcitonin on secretion of 17beta-estradiol by the ovarian follicles of common carp, Cyprinus carpio. 1825 64


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