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

Recent evidence has suggested that prolactin (PRL), internalized by lactogen-dependent Nb2 lymphoma cells, is actively translocated to the nucleus where it binds to PRL receptors. Moreover, the mitogenic action of PRL in these cells has been separately linked to protein tyrosyl phosphorylation and activation of protein kinase C (PKC). Therefore, the coupling of PRL internalization and nuclear translocation to the activation of these signal transduction pathways was investigated. Results from control experiments indicated that 30% of internalized and 5% total cell-associated 125I-rat PRL could be recovered within nuclei obtained from Nb2 cells previously incubated with the radiolabel for 3 h at 37 degrees C. Furthermore, internalized PRL was found to be intact and not associated with any carrier proteins. Addition of tyrosine kinase (TK) antagonists, genistein or tyrphostin, significantly reduced cell surface binding, internalization, and nuclear translocation of 125I-rat PRL. In contrast, neither the level of cell-associated nor internalized hormone differed between cells treated with the PKC antagonists, staurosporine or calphostin C, and control cultures. Instead, PKC inhibition significantly reduced nuclear PRL translocation. The inhibitory effects of the TK and PKC antagonists on PRL internalization and nuclear translocation in intact Nb2 cells were verified by immunofluorescence microscopy in parallel experiments. In other experiments, each of the kinase inhibitors blocked PRL-stimulated Nb2 cell proliferation in a concentration-dependent manner. It is concluded that activated TK and PKC collaborate in the process of PRL internalization and translocation to the nucleus. TK activation may participate in PRL receptor binding or hormone internalization while activation of PKC appears to be required for its nuclear targeting. Since TK and PKC activation are required for lactogen-stimulated Nb2 cell proliferation, we suggest that a component of the mitogenic pathway in these cells is a direct nuclear interaction of PRL.
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PMID:Nuclear translocation of prolactin: collaboration of tyrosine kinase and protein kinase C activation in rat Nb2 node lymphoma cells. 770 71

Studies were undertaken to identify intracellular mediators of prolactin inhibition of glucocorticoid-induced apoptosis in Nb2 lymphoma cells. A short-term assay was implemented that quantitates fragmented DNA released from the genome by reaction with diphenylamine. Induction and inhibition of internucleosomal DNA cleavage (indicative of apoptosis) was verified by agarose gel electrophoresis of extracted cellular DNA. Synchronized Nb2 cells (G0/G1) exhibited increased DNA fragmentation after 4-hr incubation with dexamethasone (DEX) (25-100 nM) which was inhibited by ovine prolactin (oPRL) (0.1-1 ng/ml), the glucocorticoid receptor antagonist, RU486 (500 nM), and the nuclease inhibitor, aurintricarboxylic acid (100 microM). Signals previously implicated in prolactin induction of mitogenesis in Nb2 cells were investigated for their role in prolactin inhibition of apoptosis including: protein kinase C activation, arachidonic acid metabolism, polyamine production, tyrosine phosphorylation, and extracellular calcium. Protein kinase C agonists, phorbol-12-myristate-13-acetate, and 1,2-dioctanoyl-sn-glycerol, +/- the calcium ionophore, A23187 (200 nM), did not mimic oPRL inhibition of DEX-induced DNA fragmentation. Protein kinase C inhibitors, gossypol and quercetin, did not block prolactin action. Arachidonic acid did not mimic prolactin protection against DEX-induced DNA fragmentation. Inhibitors of arachidonic acid metabolism, 5,8,11,14-eicosatetraynoic acid, nordihydroguaiaretic acid, and indomethacin did not block prolactin action. The polyamine, spermine, inhibited DEX-induced DNA fragmentation at 1.5 to 2.5 mM. However, inhibition of polyamine synthesis with alpha-difluoromethyl ornithine or methylglyoxal bis(guanylhydrazone) did not inhibit prolactin action. Prolactin action was not blocked by inhibitors of tyrosine kinase activation, genistein and tyrphostin-47. On the other hand, pervanadate, a potent tyrosine phosphatase inhibitor, consistently inhibited DEX-induced DNA fragmentation. Prolactin action and DEX-induced apoptosis both occurred in calcium-free PBS. In summary, protein kinase C activation and eicosanoid production do not appear to mediate this prolactin action. Although spermine could block DNA fragmentation, blockade of the polyamine cascade did not inhibit prolactin action, suggesting that polyamines do not mediate this prolactin effect. While inhibitors of tyrosine kinase activation did not block prolactin action, tyrosine phosphatase inhibition in the presence of basal tyrosine kinase activity mimicked prolactin action, suggesting tyrosine phosphorylation participation in the anti-apoptotic effect. Extra-cellular calcium was not required for prolactin or DEX action.
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PMID:Investigation of intracellular signals mediating the anti-apoptotic action of prolactin in Nb2 lymphoma cells. 777 88

In mammosomatotropes GH3B6 cells, one of the primary responses to thyrotropin-releasing hormone (TRH) is the parallel induction of two proto-oncogenes, c-fos and jun B, which code for constituents of AP1 transcription factor. To better understand the mode of action of TRH and to look for possible functions of c-fos and jun B in these cells, we have investigated the role of different intracellular signals in the induction of each proto-oncogene on the one hand, and on prolactin (PRL) release and PRL gene expression on the other hand. Northern and dot-blot analyses revealed that the activation of protein kinase C (PKC)-, Ca(2+)- or adenylyl cyclase-dependent pathways acutely increased both c-fos and jun B transcripts. However, a gene specific responsiveness was revealed using phorbol 12-myristate 13-acetate (TPA) and several combined treatments. The simultaneous activation of PKC and Ca(2+)-dependent pathways resulted in synergistic stimulations of c-fos mRNA levels only. Consistently, ionomycin plus low doses of TPA solely reproduced the potent effect of TRH on c-fos transcripts. Data collected from TRH and TPA down-regulated cells indicated that TRH probably recruits TPA-dependent PKC isoforms for stimulating c-fos but not jun B transcripts. On the contrary, the TRH-induced stimulation of either proto-oncogene likely involves Ca(2+)-dependent mechanisms because calcium agonists and the peptide exert non-additive effects. Finally, the synergistic stimulations observed in response to TRH combined with forskolin, indicate that adenylyl cyclase-dependent mechanisms are interconnected with TRH-induced proto-oncogene expression. The overall study also reveals that among the agonists tested, the dihydropyridine Bay K 8644 and forskolin only were capable to induce a long-lasting stimulation of c-fos and jun B mRNA levels, concomitant to increased levels of PRL transcripts, as does TRH. Considering that AP1 is assumed to be involved in signal transmission from the cell surface to the nucleus, it might be thus proposed that a common stimulation of c-fos and jun B gene expression is possibly involved in the activation of the PRL gene. On the other hand, the systematic coincidence between acute PRL release and proto-oncogenes expression suggest a role for c-fos and jun B in the control of genes involved in the secretory process.
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PMID:Multiple intracellular signallings are involved in thyrotropin-releasing hormone (TRH)-induced c-fos and jun B mRNA levels in clonal prolactin cells. 779 33

We have recently shown that FSH, LH, and prolactin (PRL)--alone or combined--act as luteotropins when incubated with luteal cells from pregnant hamsters (Yuan and Greenwald, Biol Reprod 1994; 51:43-49). The purpose of the present study was to determine which second messenger systems are affected by these hormones with progesterone (P4) synthesis as the principal endpoint after 4 h of incubation with 100,000 luteal cells. Luteal cells on Days 4, 10, or 12 of pregnancy were incubated with the following reagents: 10 ng of recombinant human FSH (r-hFSH), ovine (o) FSH, oLH, oPRL, forskolin, db-cAMP, protein kinase A inhibitor (PKI), protein kinase C activator (phorbol 12-myristate 13-acetate; PMA), or various combinations of the reagents. Forskolin and db-cAMP each stimulated P4 in a dose-dependent manner, while PKI significantly inhibited forskolin-, r-hFSH-, oFSH-, and oLH-stimulated P4 on Day 4 of pregnancy. PMA (0.001-1.0 microM) did not affect basal P4 on Day 4, 10, or 12 of pregnancy; however, 100 nM PMA inhibited db-cAMP-, forskolin-, oFSH-, and oLH-stimulated P4 synthesis on Days 4 and 12. The antagonistic effects of PMA were reversed in all cases by concurrent incubation with a PKC inhibitor, H-7. On Day 4 of pregnancy, P4 was stimulated by oFSH and oLH with the highest levels observed in medium stimulated by the luteotropic complex of oFSH, oLH, and oPRL. Recombinant hFSH enhanced P4 production in a dose-dependent manner; doses of 10 ng and above resulted in statistically significant differences from the control values (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Luteotropic effects of follicle-stimulating hormone (FSH): II. FSH luteinizing hormone, and prolactin effects on second messenger systems in the corpus luteum of the pregnant hamster. 780 18

Endothelin (ET)-1 stimulates the synthesis and release of renin and inhibits the expression of prolactin (PRL) from term human decidual cells. To examine the mechanisms by which ET-1 exerts its differential effects on renin and PRL expression, we have studied total renin and PRL release from term human decidual cells in response to pharmacological agents that affect calcium- and protein kinase C-dependent mechanisms. Calcium ionophore A-23187 stimulated basal renin release and potentiated ET-1-stimulated renin release but had no effect on basal or ET-inhibited PRL release. The calcium channel blocker nifedipine inhibited ET-1-stimulated renin release but had no effect on PRL release. The protein kinase C agonist phorbol 12-myristate 13-acetate (PMA) stimulated basal renin release and potentiated the effect of ET-1 on renin release. However, PMA inhibited basal PRL release and also enhanced the inhibitory effect of ET-1. The PKC inhibitor staurosporine increased basal PRL release and completely reversed the inhibitory effect of ET on PRL release. These results indicate that the effects of ET-1 on both decidual renin and PRL release are dependent on the activation of protein kinase C. However, the effect of ET-1 on renin release appears to be dependent on extracellular calcium, whereas the effect on PRL is not influenced by extracellular calcium.
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PMID:Endothelin-1 modulates renin and prolactin release from human decidua by different mechanisms. 781 Jun 25

Lactogens [prolactin (Prl) and growth hormone] stimulate phosphorylation of the 40S ribosomal protein, S6, in Nb2 cells by mechanisms that do not involve participation of cAMP or protein kinase A, protein kinase C, or cGMP-dependent protein kinase. However, inhibition of tyrosine kinase (TK) abrogates Prl-mediated macromolecular biosynthesis. Inasmuch as lactogen signaling may involve sequential activation of protein kinases, the effect of Prl on the well-characterized mitogen-activated protein kinase (MAPK) and S6 kinase (S6K), the enzyme responsible for S6 phosphorylation in vivo, and their relationship to Nb2 macromolecular biosynthesis and mitogenesis were investigated. The results show that MAPK stimulation is transient (peak activity, 30 min) and precedes that of S6K, which reaches a maximum at 1.5-2 h, and slowly returns towards control levels at 6 h. Both staurosporine which inhibits GH receptor-associated kinase (JAK2) and genistein (GEN), an inhibitor of membrane-associated and cytoplasmic TKs, abrogate Prl-stimulated TK, MAPK, and S6K. Rapamycin (RAP), a specific inhibitor of p70S6K, completely blocks S6K but does not affect TK and MAPK. TK and MAPK activity correlates with Prl-stimulated anabolism, i.e., protein and DNA synthesis and mitogenesis. Thus, concentrations of STR and GEN which abrogate TK and MAPK inhibit anabolism virtually 100%. However, RAP, which inhibits S6K (ca. 100%) but not TK or MAPK, only delays Prl-mediated anabolism. These results indicate that Prl signaling in Nb2 cells involves a protein kinase cascade and that regulation of receptor-associated kinase, TK, and MAPK correlates with anabolism. The role of S6K (and S6 phosphorylation) appears to be ancillary.
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PMID:Stimulation of receptor-associated kinase, tyrosine kinase, and MAP kinase is required for prolactin-mediated macromolecular biosynthesis and mitogenesis in Nb2 lymphoma. 784 Jun 14

The mechanism of the short-term activation by prolactin (PRL) of tyrosine hydroxylase (TH) in tuberoinfundibular dopaminergic neurons was examined in vitro on hypothalamic slices from ovariectomized rats. TH activity (determined by 3,4-dihydroxyphenylalanine accumulation in the median eminence after blockade of decarboxylase with NSD 1055) showed a dose-dependent increase within 2 h of incubation of the hypothalamic slices with PRL. To determine whether a phosphorylation process was involved in this increase in TH activity, we studied the sensitivity of the enzyme to dopamine (DA) feedback inhibition. In control median eminences, two kinetically different forms of TH coexisted, one exhibiting a Ki(DA) value of 29.92 +/- 0.49 microM, the other being approximately 15-fold more sensitive to DA inhibition with a Ki(DA) of 1.96 +/- 0.09 microM, likely corresponding to a phosphorylated and active form and to a nonphosphorylated and less active form, respectively. After PRL treatment, the TH form of low Ki(DA) remained unaffected, whereas the Ki(DA) of the purported active form of TH increased to 62.6 +/- 0.8 microM, suggesting an increase in the enzyme phosphorylation. This increase in the Ki(DA) of TH was selectively prevented by GF 109203X, a potent and selective inhibitor of protein kinase C, but not by a specific inhibitor of protein kinase A or calmodulin. Finally, this action of PRL could be mimicked by 12-O-tetradecanoylphorbol 13-acetate (a direct activator of protein kinase C). These results suggest that PRL, at the median eminence level, activates TH by increasing the enzyme phosphorylation and that this action may involve an activation of protein kinase C.
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PMID:Evidence for protein kinase C involvement in the short-term activation by prolactin of tyrosine hydroxylase in tuberoinfundibular dopaminergic neurons. 790 22

Previously we have shown that partial hepatectomy (PH) or exposure of the liver to the mitogen prolactin induces activation of hepatic protein kinase C (PKC). Here, we used suramin, an antitrypanosomal and chemotherapeutic drug which inhibits that enzyme, as a probe of PKC signal transduction in the regenerative response after PH in the rat. Suramin was administered i.p. in nonhepatotoxic doses of 20 to 160 mg/kg 14 days prior to PH. Three measures of hepatic DNA synthesis or cell division, thymidine kinase activity, [3H]thymidine incorporation, and mitotic index were inhibited in a dose-dependent fashion. Baseline PKC activity, in both the cytosolic and particulate fractions, was unchanged by suramin. After PH, PKC activation, signalled by an increase in activity in the particulate fraction, was observed in control rats at 30 and 60 min. However, rats which had previously received suramin demonstrated dose-dependent inhibition of PKC activation. Suramin is known to also disrupt the binding of certain growth factors to their receptors. But if inhibition of PKC activation were conferred by interference with growth factor-receptor binding by suramin, then the generation of diacylglycerol, the second messenger for PKC activation, should likewise be impaired. However, we observed that the diacylglycerol mass generated at 15, 30, and 45 min after PH was not altered by suramin pretreatment. We conclude that the diminution in DNA synthesis after PH by suramin is likely the consequence of direct inhibition of PKC, suggesting that PKC activation is an important, perhaps obligatory, signal transduction event in liver regeneration.
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PMID:Suramin, a protein kinase C inhibitor, impairs hepatic regeneration. 794 91

The hypothalamic hormone, thyrotropin releasing hormone (TRH), stimulates prolactin (PRL) secretion and gene transcription in the GH3 pituitary cell line. Several studies have provided indirect evidence that phosphorylation of the pituitary-specific transcription factor Pit-1 may mediate TRH effects on PRL transcription. In the present study we have investigated the ability of TRH to alter the phosphorylation of Pit-1. In vivo 32P labeling experiments demonstrated that TRH stimulated a transient phosphorylation of Pit-1, reaching a maximum in 5 min and returning to basal levels within 30 min. Phosphopeptide mapping experiments demonstrated that TRH induced the transient phosphorylation of specific sites in Pit-1. TRH-stimulated phosphorylation of Pit-1 was blocked by treatments that deplete the cellular content of protein kinase C. Metabolic labeling and Western blot analysis demonstrate that TRH does not alter the total cellular content or nuclear concentration of Pit-1. TRH-mediated stimulation of a PRL promoter-luciferase fusion gene occurred under conditions that blocked the transient phosphorylation of Pit-1. These studies suggest that phosphorylation of Pit-1 may not be necessary for TRH mediated enhancement of PRL gene transcription.
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PMID:Thyrotropin releasing hormone stimulates transient phosphorylation of the tissue-specific transcription factor, Pit-1. 796 16

Studies have shown that mastoparan and other amphiphilic peptides induce exocytosis of hormones from anterior pituitary cells. We have studied the effect of mastoparan on the secretion of prolactin from cultured rat anterior pituitary cells and on the concomitant functional status of signal-transducing pathways in lactotroph-enriched cell cultures. Mastoparan stimulation of prolactin secretion was dose-dependent, time-dependent, reversible and required the presence of calcium. Pretreatment of pituitary cell cultures with cholera and pertussis toxin had no effect on the secretory response, whereas encapsulation of guanosine 5-[beta-thio]diphosphate (GDP-beta-S) by reversible electropermeabilization inhibited mastoparan-stimulated secretion. Incubation of mastoparan with myo-[3H]inositol-labelled lactotroph-enriched anterior pituitary cell cultures resulted in increased formation of inositol phosphates compared with control cells, and encapsulation of GDP-beta-S blocked mastoparan-induced inositol lipid hydrolysis. Mastoparan caused translocation of protein kinase C activity from a soluble to a membrane-attached form. Mastoparan was able to increase the intracellular Ca2+ concentration in Fura-2-loaded individual lactotrophs. Omission of Ca2+ from the extracellular medium did not change the Ca2+ response in lactotrophs when stimulated with mastoparan. On the basis of these results it is concluded that mastoparan-induced release of prolactin is preceded by activation of the inositol(1,4,5)trisphosphate/diacylglycerol pathway with resulting translocation of protein kinase activity and increment in intracellular Ca2+. However, other signal-transducing pathways may be involved in the secretory process.
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PMID:Mastoparan, a wasp venom peptide, stimulates release of prolactin from cultured rat anterior pituitary cells. 796 88


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