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)

The receptor for hepatocyte growth factor, also known as scatter factor (HGF/SF), has recently been identified as the 190-kDa heterodimeric tyrosine kinase encoded by the MET proto-oncogene (p190MET). The signaling pathway(s) triggered by HGF/SF are unknown. In A549 cells, a lung epithelial cell line, nanomolar concentrations of HGF/SF induced tyrosine phosphorylation of the p190MET receptor. The autophosphorylated receptor coprecipitated with phosphatidylinositol 3-kinase (PI 3-kinase) activity. In GTL16 cells, a cell line derived from a gastric carcinoma, the p190MET receptor, overexpressed and constitutively phosphorylated on tyrosine, coprecipitated with PI 3-kinase activity and with the 85-kDa PI 3-kinase subunit. In these cells activation of protein kinase C or the increase of intracellular [Ca2+] inhibits tyrosine phosphorylation of the p190MET receptor as well as the association with both PI 3-kinase activity and the 85-kDa subunit of the enzyme. In an in vitro assay, tyrosine phosphorylation of the immobilized p190MET receptor was required for binding of PI 3-kinase from cell lysates. These data strongly suggest that the signaling pathway activated by the HGF/SF receptor includes generation of D-3-phosphorylated inositol phospholipids.
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PMID:The tyrosine-phosphorylated hepatocyte growth factor/scatter factor receptor associates with phosphatidylinositol 3-kinase. 171 89

We have detected a novel type of structural variant of the tyrosine kinase receptor for c-met, also known as the hepatocyte growth factor receptor, in mouse tissues. The cDNA of the variant transcript of c-met lacks 141 base pairs, which predicts an in-frame deletion of 47 amino acids in the juxtamembrane region of the cytoplasmic domain. Sequence analysis of genomic DNA containing the c-met locus revealed that the absence of a discrete exon is responsible for this 141-base pair deletion and that alternative splicing leads to production of two forms of transcript. These two forms of transcript are designated as c-metsm (for small) and c-metlg (for large) to distinguish the absence or presence of the 141-base pair segment, respectively. The c-metsm variant is present in adult mouse tissues including kidney, liver, and brain as well as in 9-10-day-old embryos. In all cases, expression of c-metsm was lower than that of the normal transcript, c-metlg. An antiserum against mouse c-Met protein immunoprecipitated corresponding protein forms of approximately 152 and approximately 145 kDa from whole kidney lysate under reducing conditions. The size difference of approximately 7 kDa between these isoforms corresponds to the predicted difference of 47 amino acids. The presence of this shorter variant transcript and its corresponding protein isoform in a variety of normal tissues suggests a physiological role. The deleted region in the cytoplasmic domain of c-metsm contains a sequence motif (S985ARS) for protein kinase C phosphorylation that has recently been shown to play a key role in the down-regulation of hepatocyte growth factor receptor kinase activity. The identification of this novel isoform, c-metsm, demonstrates that a tyrosine kinase receptor can achieve additional diversity by alternative splicing at a key regulatory site in its cytoplasmic domain.
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PMID:Identification of a novel type of alternative splicing of a tyrosine kinase receptor. Juxtamembrane deletion of the c-met protein kinase C serine phosphorylation regulatory site. 751 57

The receptor for the growth and motility factor, hepatocyte growth factor/scatter factor (HGF/SF), is a transmembrane tyrosine kinase encoded by the MET oncogene. Previous work has shown that receptor phosphorylation on tyrosine is critical for both kinase activation and association with intracellular signal transducers. In this paper, we report that a protein tyrosine phosphatase activity (PTP) coprecipitates with the HGF/SF receptor. The associated PTP activity correlates with the kinase activation of the receptor, increasing up to 5-fold over the basal level after HGF/SF stimulation. The increase is reversible and time- and dose-dependent. A comparable level of activity is associated with constitutively tyrosine-phosphorylated receptors immunoprecipitated from cells where the MET oncogene is amplified and overexpressed. In these cells, a parallel decrease in PTP activity is observed after inhibition of receptor tyrosine phosphorylation following protein kinase C activation. The associated PTP activity is effective in dephosphorylating the HGF/SF receptor. These data show that a protein tyrosine phosphatase is functionally coupled to the HGF/SF receptor.
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PMID:A protein tyrosine phosphatase activity associated with the hepatocyte growth factor/scatter factor receptor. 768 41

Hepatocyte growth factor/scatter factor (HGF/SF) is a heparin-binding polypeptide which shares structural domains with enzymes of the blood clotting cascade. HGF/SF is secreted by cells of mesodermal origin and has powerful mitogenic, motogenic and morphogenic activity on epithelial and endothelial cells. HGF/SF is produced as a biologically inactive single-chain precursor (pro-HGF/SF) most of which is sequestered on the cell surface or bound to the extracellular matrix. Maturation into the active alpha beta heterodimer results from proteolytic cleavage by a urokinase-type protease, which acts as a pro-HGF/SF convertase. The primary determinant for receptor binding appears to be located within the alpha-chain. The interaction of the alpha-chain with the receptor is sufficient for the activation of the signal cascade involved in the motility response. However, the complete HGF/SF protein seems to be required to elicit a mitogenic response. HGF/SF binds with high affinity to a transmembrane receptor, p190MET, encoded by the MET proto-oncogene. p190MET is the prototype of a distinct subfamily of heterodimeric tyrosine kinases, including the putative receptors Ron and Sea. The mature form of p190MET is a heterodimer of two disulfide-linked subunits (alpha and beta). The alpha-subunit is extracellular and heavily glycosylated. The beta-subunit consists of an extracellular portion involved in ligand binding, a membrane spanning segment, and a cytoplasmic tyrosine kinase domain. Both subunits derive from glycosylation and proteolytic cleavage of a common precursor of 170 kDa. In polarized epithelial cells the HGF/SF receptor is selectively exposed in the basolateral plasmalemma, where it is associated with detergent-insoluble components. Two Met isoforms, carrying an intact ligand binding domain but lacking the kinase domain due to truncation of the beta-subunit, arise from alternative post-transcriptional processing of the mature form. One truncated form is soluble and released from the cells. HGF/SF binding triggers tyrosine autophosphorylation of the receptor beta-subunit. Autophosphorylation on the major phosphorylation site Y1235 upregulates the kinase activity of the receptor, increasing the Vmax of the phosphotransfer reaction. Negative regulation of the kinase activity occurs through phosphorylation of a unique serine residue (S985) located in the juxtamembrane domain of the receptor. This phosphorylation is triggered by two distinct pathways involving either protein kinase C activation or increase in intracellular Ca2+ concentration. Upon ligand binding, the HGF/SF receptor recruits and activates several cytoplasmic effectors, including phosphatidylinositol 3-kinase (PI 3-K), phospholipase C-gamma (PLC-gamma), pp60c-Src, a tyrosine phosphatase, and a Ras-guanine nucleotide exchanger.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Identification of functional domains in the hepatocyte growth factor and its receptor by molecular engineering. 776 52

The c-MET proto-oncogene encodes the tyrosine kinase receptor for hepatocyte growth factor (HGF), also known as scatter factor, a potent mitogen and motogen for epithelial cells. The level of the HGF receptor expressed by epithelial cells varies in different growth conditions, being lower in growth arrested confluent monolayers and higher in growing sparse cells. The amount of HGF receptor mRNA increases from 3- to 5-fold after stimulation of confluent monolayers by serum and up to 10-fold after stimulation of protein kinase C by 12-O-tetradecanoylphorbol-13-acetate (TPA). An increased level of the receptor mRNA was also observed after cell stimulation with nanomolar concentration of HGF itself. The effect was transient, dose, and time-dependent. Transcription of a reporter gene under control of the cloned 297 base pair c-MET promoter was also stimulated by serum, TPA, or HGF. The accumulation of specific mRNA is followed by appearance of the HGF receptor precursor protein, which is further processed to the receptor mature form. After HGF stimulation, HGF receptor expression follows c-FOS and c-JUN induction with a peak approximately 4 h. Pretreatment with the protein synthesis inhibitor puromycin strongly reduced the response to HGF, while cycloheximide alone increased the level of the receptor mRNA. These data show that c-MET behaves as a delayed early-response gene and suggest that the HGF response is autoamplified by inducing the specific receptor.
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PMID:Hepatocyte growth factor (HGF) receptor expression is inducible and is part of the delayed-early response to HGF. 817 99

The receptor for hepatocyte growth factor/scatter factor (HGF/SF) is an alpha beta tyrosine kinase of 190 kDa which mediates growth and motility in several cell types. We have previously shown that tyrosine autophosphorylation enhances the receptor kinase activity, while serine phosphorylation by protein kinase C or other Ca(2+)-dependent kinase(s) is inhibitory. We now identify Ser985 as the major phosphorylation site for the protein kinases responsible for such inhibition. Both phorbol esters or Ca2+ ionophore treatment induces phosphorylation of the same tryptic phosphopeptide corresponding to the sequence Leu983-Arg987 located in the juxta-membrane domain of the receptor beta chain. Purified protein kinase C phosphorylates in vitro a synthetic peptide (V14S) including Ser985. Trypsin digestion of the phosphorylated V14S generates a single phosphopeptide comigrating in reverse-phase high performance liquid chromatography with the tryptic peptide phosphorylated in vivo. Phorbol ester treatment of cultured cells inhibits the ligand-induced tyrosine autophosphorylation of the receptor. In vitro, Ser985 phosphorylation inhibits the receptor tyrosine kinase activity on exogenous substrates. Substitution of Ser985 by site-directed mutagenesis results in increased tyrosine phosphorylation of the receptor and abolishes down-modulation by protein kinase C. These data show that phosphorylation of Ser985 is a key mechanism for the negative regulation of HGF/SF receptor.
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PMID:Phosphorylation of serine 985 negatively regulates the hepatocyte growth factor receptor kinase. 829 30

Hepatocyte Growth Factor (HGF) and Scatter Factor (SF) are identical glycoproteins secreted by cells of mesodermal origin. The factor has several activities on epithelial cells, including mitogenesis, dissociation of epithelial sheets, stimulation of cell motility, and promotion of matrix invasion. HGF is the ligand for p190MET, the receptor tyrosine kinase encoded by the MET proto-oncogene. This was proved by HGF binding to immunopurified p190MET, chemical cross-linking of radiolabelled ligand, HGF-induced tyrosine phosphorylation of p190MET, and reconstitution of high-affinity binding sites for HGF into insect cells infected with a recombinant baculovirus carrying the human MET cDNA. p190MET is a 190 kDa heterodimer of two (alpha beta) disulfide-linked protein subunits. The alpha subunit is heavily glycosylated and extracellular. The beta subunit bears an extracellular portion involved in ligand binding, a membrane spanning segment and a cytoplasmic tyrosine kinase domain with phosphorylation sites regulating its activity. Both subunits originate from glycosylation and proteolytic cleavage of a common precursor of 170 kDa. Alternative post-transcriptional processing originates two truncated Met proteins, endowed with ligand binding activity, lacking the cytoplasmic kinase domain of the beta subunit. One form is soluble and released from the cells. HGF binding triggers tyrosine autophosphorylation of the receptor beta subunit in intact cells. Autophosphorylation upregulates the kinase activity of the receptor, increasing the Vmax of the phosphotransfer reaction. The major phosphorylation site has been mapped to Tyr1235. Negative regulation of the receptor kinase activity occurs through distinguishable pathways involving protein kinase C activation or increase in the intracellular Ca2+ concentration. Both lead to the serine phosphorylation of a unique phosphopeptide of the receptor and to a decrease in its kinase activity. Receptor autophosphorylation also triggers the signal transduction pathways inside the target cells. The phosphorylated receptor associates ras GAP, phospholipase C-gamma, and src-related tyrosine kinase in vitro; Phosphatidylinositol 3-kinase, in vitro and in vivo, indicating that the generation of the D-3 phosphorylated inositol lipids is involved in effecting the motility and/or the growth response to HGF. The p190MET HGF receptor is expressed in several epithelial tissues and it is often overexpressed in neoplastic cells. In some tumors of the gastrointestinal tract the Met tyrosine kinase is constitutively activated, either by overexpression of the amplified MET oncogene or by lack of cleavage of the receptor precursor, due to defective post-translational processing.
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PMID:Structure, biosynthesis and biochemical properties of the HGF receptor in normal and malignant cells. 838 Jul 35

To understand the signalling mechanisms involved in the dual stimulatory effects of endothelin-1 (ET-1) on DNA synthesis and melanization in cultured human melanocytes, we analysed the biological profile of ET-1 receptor and determined the effects of ET-1 on the protein kinase C, cyclic AMP system and mitogen-activated protein kinase (MAP kinase) in comparison with their relevant stimulants. The photoaffinity labelling of ET-1 receptors with Denny-Jaff reagents revealed an ET-1 receptor with a molecular mass of 51 kDa in human melanocytes. The ET(A) receptor subtype-sensitive antagonist BQ123(50 nM) or pertussis toxin (100 ng/ml) significantly suppressed the ET-1-induced intracellular calcium mobilization, indicating the presence of pertussis toxin-sensitive G-protein-coupled ET(A) receptors. An assay of protein kinase C activity revealed that 10nM ET-1 translocated cytosolic protein kinase C to membrane-bound protein kinase C within 5 min of the start of incubation. In contrast, receptor-mediated melanocyte activation by ET-1 was accompanied by an elevated level of cyclic AMP (4-fold over control) after 10-60 min of incubation, whereas 60 min of incubation of human melanocytes with c-Kit or c-Met ligands such as stem cell factor (10 nM) or basic fibroblast growth factor (10 nM) did not elevate the cyclic AMP level. We have also demonstrated that a specific tyrosine kinase inhibitor, tyrphostin B-42 (10 microM), inhibited the ET-1-induced growth stimulation, suggesting the involvement of the tyrosine kinase pathway in growth stimulation. Consistently, an assay of MAP kinase revealed that ET-1 caused a 10-fold activation of MAP kinase after 5 min of incubation with human melanocytes in a similar way to tyrosine kinase ligands such as stem cell factor and hepatocyte growth factor. Further, the DNA synthesis stimulated by the c-Kit ligand stem cell factor at a concentration of 1 nM was synergistically enhanced by 5 nM ET-1. These results suggest that ET-induced dual cellular events in human melanocytes are closely associated with cross-talk between the protein kinase C and A and tyrosine kinase pathways.
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PMID:Signalling mechanisms of endothelin-induced mitogenesis and melanogenesis in human melanocytes. 866 Feb 99

Matrix metalloproteinases participate in normal physiologic processes; however, their overproduction has been associated with connective tissue destruction in a variety of pathological states. Migrating basal keratinocytes transiently express collagenase-1 during normal cutaneous reepithelialization. However, the overexpression of both collagenase-1 and stromelysin-1 has been associated with the pathogenesis of chronic nonhealing ulcers. Aberrant expression of metalloproteinases in inflammation is mediated, at least in part, by soluble factors. Since hepatocyte growth factor/scatter factor (HGF/SF) has been reported to promote keratinocyte migration and proliferation, key events in wound repair, and since HGF/SF is produced by dermal fibroblasts and its c-Met receptor is expressed by basal keratinocytes in wounded skin, we have studied the effects of HGF/SF upon keratinocyte metalloproteinase expression. We have found that HGF/SF can stimulate keratinocyte collagenase-1 and stromelysin-1 production in a dose-dependent and matrix-dependent manner. Expression of 92-kDa gelatinase was not affected by HGF/SF. We determined that HGF/SF regulation of collagenase-1 expression is transcriptionally mediated and requires tyrosine kinase and protein kinase C activaties. HGF/NK1, a naturally occurring, truncated form of HGF/SF, also stimulates collagenase-1 production, but much less efficiently than does the parent molecule. However, HGF/NK2, another HGF/SF splice variant, as well as heparin, potently inhibit HGF/SF-induced collagenase-1 synthesis. These results indicate that HGF/SF and its naturally occurring splice variants have diverse biological effects on keratinocytes and suggest an additional mechanism whereby HGF/SF may regulate keratinocyte function during wound repair.
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PMID:Mechanisms of hepatocyte growth factor stimulation of keratinocyte metalloproteinase production. 879 21

Hepatocyte growth factor (HGF) has been implicated as a paracrine regulator of organogenesis and repair in many tissues. Here we have studied the expression and actions of HGF in intact rachitic rat growth plate and derived cultures of proliferative zone chondrocytes. In vivo and in vitro chondrocytes express HGF mRNA; 1,25(OH)2 has a three-fold maximal stimulatory effect, which can be blocked by H-7, an inhibitor of protein kinase C. Although HGF elaboration and action generally follow a paracrine model, chondrocytes appear capable of both expressing and responding to HGF. mRNA encoding the HGF receptor (c-met) was detected in both growth cartilage and derived chondrocyte cultures. HGF addition to chondrocyte cultures increased collagen II mRNA and alkaline phosphatase enzymatic activity to degrees comparable to that observed for active vitamin D metabolites. Combining HGF and 1,25-D evoked a synergistic response (ninefold) of alkaline phosphatase activity. To assess whether a similar stimulatory effect might be seen with bioactive peptides and HGF, we investigated the effect of HGF pretreatment on acute responses of chondrocytes to synthetic human calcitonin, an anabolic chondrocyte regulator whose skeletal action are mediated principally by cAMP elevation and subsequent protein kinase A activation. CT's maximal activation of protein kinase A was increased by prior HGF treatment from 56% to 78%. In concert, our findings indicate that in addition to HGF's classical paracrine role during skeletal growth, this growth factor may modulate hormonal sensitivity of the chondrocyte during proliferation, differentiation, and/or apoptosis.
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PMID:Hepatocyte growth factor and its actions in growth plate chondrocytes. 887 66


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