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)

Myristoylated alanine-rich C kinase substrate (MARCKS) and MARCKS-related protein (MRP; MacMARCKS) are protein kinase C substrates in diverse cell types. Activation of murine macrophages by cytokines increases MRP expression, but infection with Leishmania promastigotes during activation results in MRP depletion. We therefore examined the effect of Leishmania major LV39 on recombinant MRP. Both live promastigotes and a soluble fraction of LV39 lysates degraded MRP to yield lower molecular weight fragments. Degradation was independent of MRP myristoylation and was inhibited by protein kinase C-dependent phosphorylation of MRP. MRP was similarly degraded by purified leishmanolysin (gp63), a Leishmania surface metalloprotease. Degradation was evident at low enzyme/substrate ratios, over a broad pH range, and was inhibited by 1,10-phenanthroline and by a hydroxamate dipeptide inhibitor of leishmanolysin. Using mass spectrometric analysis, cleavage was shown to occur within the effector domain of MRP between Ser(92) and Phe(93), in accordance with the substrate specificity of leishmanolysin. Moreover, an MRP construct in which the effector domain had been deleted was resistant to cleavage. Thus, Leishmania infection may result in leishmanolysin-dependent hydrolysis of MRP, a major protein kinase C substrate in macrophages.
 ...
PMID:MARCKS-related protein (MRP) is a substrate for the Leishmania major surface protease leishmanolysin (gp63). 1046 70

CD44 is a cell surface receptor for several extracellular matrix components and is implicated in tumor cell invasion and metastasis. Our previous studies have shown that CD44 expressed in cancer cells is proteolytically cleaved at the extracellular domain through membrane-associated metalloproteases and that CD44 cleavage plays a critical role in CD44-mediated tumor cell migration (Okamoto, I., Kawano, Y., Tsuiki, H., Sasaki, J., Nakao, M., Matsumoto, M., Suga, M., Ando, M., Nakajima, M., and Saya, H. (1999) Oncogene 18, 1435-1446). In the present study, we first demonstrate rapid degradation of the membrane-tethered CD44 cleavage product through intracellular proteolytic pathways, and it occurs only after CD44 extracellular cleavage. To address the mechanisms regulating CD44 cleavage at the extracellular domain, we show that 12-O-tetradecanoylphorbol 13-acetate (TPA) and the calcium ionophore ionomycin rapidly enhance metalloprotease-mediated CD44 cleavage in U251MG cells via protein kinase C-dependent and -independent pathways, respectively, suggesting the existence of multiple distinct pathways for regulation of CD44 cleavage. Concomitant with TPA-induced CD44 cleavage, TPA treatment induces redistribution of CD44 and ERM proteins (ezrin, radixin, and moesin) to newly generated membrane ruffling areas. Treatment with lysophosphatidic acid, which is known to activate the Rho-dependent pathway, inhibits TPA-induced CD44 redistribution and CD44 cleavage. Furthermore, overexpression of Rac dominant active mutants results in the redistribution of CD44 to the Rac-induced ruffling areas and the enhancement of CD44 cleavage. These results suggest that the Rho family proteins play a role in regulation of CD44 distribution and cleavage.
 ...
PMID:Regulated CD44 cleavage under the control of protein kinase C, calcium influx, and the Rho family of small G proteins. 1046 84

Ligands that bind to the epidermal growth factor (EGF) receptor are initially synthesized as integral membrane proteins that are released from the cell surface by regulated proteolysis. To study the role of the membrane-anchoring domain in ligand release, we made two artificial ligands. The first possessed the membrane-anchoring domain from EGF whereas the second had the corresponding domain from heparin binding EGF-like growth factor (HB-EGF). Both ligands lacked amino-terminal extensions, and were epitope-tagged at the carboxyl terminus. Following stable expression in human mammary epithelial cells, their cellular localization and rate of proteolytic release were examined. We found that constructs with the membrane-anchoring domain from EGF were found primarily at the cell surface and displayed a relatively high rate of constitutive release. Constructs with the HB-EGF membrane-anchoring domain displayed a higher internalized fraction and a very low rate of constitutive release. The two ligand constructs also displayed different patterns of stimulated release. Proteolysis of the chimera with the HB-EGF membrane-anchoring domain was stimulated by activation of protein kinase C, but release of EGF from constructs with the EGF membrane-anchoring domain was insensitive to this. Calcium ionophores, calmodulin antagonists, and tyrosine phosphatase inhibitors stimulated the release of both ligands. Furthermore, the release of the two constructs showed different sensitivity to metalloprotease inhibitors. Despite a large fold-increase in ligand proteolysis following cell stimulation, only a small fraction of total cell-associated ligand was released per hour. Our results show that the membrane-anchoring domain of EGF-like ligands can specify both their localization and proteolytic processing. The structures of the membrane-anchoring region of this class of ligands can thus regulate their activity.
 ...
PMID:Trafficking and proteolytic release of epidermal growth factor receptor ligands are modulated by their membrane-anchoring domains. 1061 51

The release of amyloidogenic amyloid-beta peptide (Abeta) from amyloid-beta precursor protein (APP) requires cleavage by beta- and gamma-secretases. In contrast, alpha-secretase cleaves APP within the Abeta sequence and precludes amyloidogenesis. Regulated and unregulated alpha-secretase activities have been reported, and the fraction of cellular alpha-secretase activity regulated by protein kinase C (PKC) has been attributed to the ADAM (a disintegrin and metalloprotease) family members TACE and ADAM-10. Although unregulated alpha-secretase cleavage of APP has been shown to occur at the cell surface, we sought to identify the intracellular site of PKC-regulated alpha-secretase APP cleavage. To accomplish this, we measured levels of secreted ectodomains and C-terminal fragments of APP generated by alpha-secretase (sAPPalpha) (C83) versus beta-secretase (sAPPbeta) (C99) and secreted Abeta in cultured cells treated with PKC and inhibitors of TACE/ADAM-10. We found that PKC stimulation increased sAPPalpha but decreased sAPPbeta levels by altering the competition between alpha- versus beta-secretase for APP within the same organelle rather than by perturbing APP trafficking. Moreover, data implicating the trans-Golgi network (TGN) as a major site for beta-secretase activity prompted us to hypothesize that PKC-regulated alpha-secretase(s) also reside in this organelle. To test this hypothesis, we performed studies demonstrating proteolytically mature TACE intracellularly, and we also showed that regulated alpha-secretase APP cleavage occurs in the TGN using an APP mutant construct targeted specifically to the TGN. By detecting regulated alpha-secretase APP cleavage in the TGN by TACE/ADAM-10, we reveal ADAM activity in a novel location. Finally, the competition between TACE/ADAM-10 and beta-secretase for intracellular APP cleavage may represent a novel target for the discovery of new therapeutic agents to treat Alzheimer's disease.
 ...
PMID:Protein kinase C-dependent alpha-secretase competes with beta-secretase for cleavage of amyloid-beta precursor protein in the trans-golgi network. 1064 15

The ectodomain of several membrane-bound proteins can be shed by proteolytic cleavage. The activity of the proteases involved in shedding is highly regulated by several intracellular second messenger pathways, such as protein kinase C (PKC) and intracellular Ca(2+). Recently, the shedding of the adhesion molecule L-selectin has been shown to be regulated by the interaction of calmodulin (CaM) with the cytosolic tail of L-selectin. Prevention of CaM-L-selectin interaction by CaM inhibitors or mutation of a CaM binding site in L-selectin induced L-selectin ectodomain shedding. Whether this action of CaM inhibitors also affects other membrane-bound proteins is not known. In the present paper we show that CaM inhibitors also stimulate the cleavage of several other transmembrane proteins, such as the membrane-bound growth factor precursors pro-transforming growth factor-alpha and pro-neuregulin-alpha2c, the receptor tyrosine kinase, TrkA, and the beta-amyloid precursor protein. Cleavage induced by CaM inhibitors was a rapid event, and resulted from the activation of a mechanism that was independent of PKC or intracellular Ca(2+) increases, but was highly sensitive to hydroxamic acid-based metalloprotease inhibitors. Mutational analysis of the intracellular domain of the TrkA receptor indicated that CaM inhibitors may stimulate membrane-protein ectodomain cleavage by mechanisms independent of CaM-substrate interaction.
 ...
PMID:Stimulation of cleavage of membrane proteins by calmodulin inhibitors. 1067 54

Previous observations raised the possibility that circulating GH-binding protein (GHBP) may serve as a useful index for tissue GH receptor (GHR) responsiveness in humans. Indeed, there are many examples to indicate that across a wide scope of comparative studies, ontogenic data, experimental systems, physiological conditions, nutritional states, and diseases there is a close relationship between the concentration of GHR and the level of serum GHBP. In the present review, we discuss various aspects that might affect differentially cellular GHR and circulating GHBP, based on species and tissue divergence, regulation of cell-surface GHR turnover, GHR cleavage mechanism, GHR mRNA splicing, and GH insensitivity (GHI) syndrome patients with normal or high serum GHBP levels. Most previous experimental data were collected through comparative analysis of human GHBP against GHR and GHBP determinations in animal models. Yet, GHBPs possess species-specific properties, and the mechanism for their generation and regulation display evolutionary divergence. Another important aspect is tissue divergence, in terms of GHR regulation and its cleavage to GHBP. Although GHBP is generated mainly from the liver GHR, many other tissues express GHRs and probably also contribute to the total GHBP level. Human GHBP is generated by proteolytic cleavage of GHR at the cell-surface and, thus, occupancy or modulation of GHR turnover/internalization would impact the level of cell-surface GHR that are available for proteolysis. An additional degree of complexity arises from recent reports, implicating a protein kinase C-regulated metalloprotease activity in GHBP generation. This suggests that the proteolytic system, which controls the specific cleavage mechanism and switch between GHR proteolysis and GHBP shedding, is a regulated process. Finally, differential splicing regulation to the full-length, active human GHR (hGHR) and the inactive truncated hGHRtr isoform messenger RNA transcripts might regulate both the production of GHBP and GHR bioactivity, as hGHRtr generates large amounts of GHBP but has a dominant negative effect on GH signaling. Several clinical GH-resistant conditions, such as liver cirrhosis, renal insufficiency, insulin-dependent diabetes mellitus, hypothyroidism, malnutrition, or critical illness are associated with reduced GHBP levels. However, this is not universally true, as in other conditions (e.g. early childhood, acromegaly) decreased GHBP levels are not associated with GHI. Divergence between serum GHBP and insulin-like growth factor I, such as which occur during puberty or obesity, also questions whether GHBP levels reflect GHR function. Even in patients with GHI syndrome, serum GHBP cannot be relied on to detect all GHR mutations. The correct assessment of GHR expression and GH functionality in an individual patient will require, in parallel to measurements of serum GHBP, additional detailed diagnostic screening of the entire GH-insulin-like growth factor I axis.
 ...
PMID:Clinical review 112: Does serum growth hormone (GH) binding protein reflect human GH receptor function? 1072 17

GH signals by interacting with GH receptor (GHR). A substantial fraction of circulating GH complexes with GH-binding protein (GHBP), which corresponds to the GHR extracellular domain. GHBP is generated by 1) alternative splicing of a common GHR precursor messenger RNA to encode secreted GHBP (the source of the vast majority of GHBP in rodents); and 2) proteolysis of the cell-associated GHR with shedding of GHBP (a mechanism operative in rabbits and humans). We previously observed that phorbol ester (PMA)-induced activation of protein kinase C (PKC) causes metalloprotease-mediated GHR proteolysis and GHBP shedding in human IM-9 lymphocytes. We now demonstrate that PMA-induced hydroxamate (IC3)-inhibitable GHR proteolysis and GHBP shedding were also detected in murine 3T3-F442A and 3T3-L1 preadipocytes and in Chinese hamster ovary (CHO) cells stably expressing rabbit GHR (rbGHR), although the degree of GHBP shedding was much smaller for murine GHR than for rabbit or human GHRs. PMA-induced GHR proteolysis in 3T3-F442A, 3T3-L1, and CHO-rbGHR cells was significantly reduced by pretreatment with mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1 inhibitors, suggesting involvement of the mitogen-activated protein kinase pathway in regulating this PKC-dependent effect. In contrast, GHR proteolysis promoted by N-ethylmaleimide, although inhibited by IC3, was unaffected by inhibition of either PKC or mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1. Thus, different pathways leading to metalloprotease-mediated receptor proteolysis are accessed by PMA vs. N-ethylmaleimide. To determine whether other, possibly more physiologically relevant, stimuli induce GHR proteolysis, we tested effects of platelet-derived growth factor (PDGF) and serum. Treatment of serum-deprived cells with PDGF (in 3T3-F442A cells) or serum (in 3T3-F442A and CHO-rbGHR cells) promoted GHR proteolysis, which was inhibited by IC3. Interestingly, PMA-, PDGF-, and serum-induced GHR proteolysis was associated with substantial decreases in GH-induced activation of Janus kinase-2, which were also prevented by IC3. These findings suggest that inducible metalloprotease-mediated GHR proteolysis constitutes an important mechanism of receptor down-regulation and modulation of GH signaling.
 ...
PMID:Phorbol ester- and growth factor-induced growth hormone (GH) receptor proteolysis and GH-binding protein shedding: relationship to GH receptor down-regulation. 1118 29

Plasma membrane-anchored proteases have key roles in cell signaling, migration and refashioning the cell surface and its surroundings. We report the first example of a plasma membrane-anchored protease on mature sperm, testase 1 (ADAM 24). Unlike other studied sperm ADAMs (fertilin alpha and beta, cyritestin) whose metalloprotease domains are removed during sperm development, we found testase 1 retains an active metalloprotease domain, suggesting it acts as a protease on mature sperm. Testase 1 is a glycoprotein (molecular mass 88 kDa), localized to the equatorial region of the plasma membrane of cauda epididymal sperm. Typically, proteolytic removal of the pro-domain is an initial activation step for ADAM proteases. The pro-domain of the testase 1 precursor (108 kDa) is proteolytically removed as sperm transit the caput epididymis to produce processed (mature) testase 1 (88 kDa). Testase 1 is unique among all studied ADAMs in that its proteolytic processing occurs on the sperm plasma membrane instead of at an intracellular site (the Golgi). Using GST-fusion proteins and a synthetic testase 1 C-terminal peptide, we found that the cytoplasmic tail of testase 1 could be phosphorylated in vitro by protein kinase C (PKC). Thus testase 1 apparently has a cytoplasmic PKC phosphorylation site(s). Protein kinase C is known to stimulate other ADAMs' protease activity. Because events of the acrosome reaction include PKC activation, we speculate that testase 1 protease function could be important in sperm penetration of the zona pellucida after sperm PKC is activated during the acrosome reaction.
 ...
PMID:Testase 1 (ADAM 24) a plasma membrane-anchored sperm protease implicated in sperm function during epididymal maturation or fertilization. 1130 8

The present study describes events postulated to be involved in the regulated mechanism of proteolytic shedding of growth hormone (GH)-binding protein (GHBP). Using Chinese hamster ovary (CHO) cell lines stably transfected either with the full-length human GH receptor (hGHR) or with the cytoplasmic domain-truncated hGHR (hGHR(tr)), we show that the phorbol ester, phorbol 12-myristate 13-acetate (PMA), caused a rapid time- and dose-dependent increase in GHBP secretion, which, as expected, was matched by a corresponding decrease in cell-surface GHR. Furthermore, PMA equally enhanced GHBP release from CHO/hGHR(tr) cells, suggesting that the cytoplasmic domain of hGHR is not essential for PMA-induced shedding. PMA is known to specifically activate protein kinase C and, indeed, the stimulatory effects of PMA in both cell lines were completely inhibited by the protein kinase inhibitor, staurosporine (100 nM), suggesting that activation of protein kinase C (PKC) may mediate PMA-induced GHBP shedding. Since proteolytic cleavage of several cell-surface proteins was shown to be stimulated by modulators of PKC activity and inhibited by metalloprotease inhibitors, we studied the effects of two hydroxamic acid-based inhibitors of zinc-dependent metalloproteases, BB-3103 and Ro31-9790, on GHBP proteolysis. Pretreatment of CHO/hGHR cells with both these inhibitors reduced PMA-enhanced shedding of GHBP, in a dose-dependent manner, with IC(50) values of approximately 0.41 microM for BB-3103 and approximately 0.97 microM for Ro31-9790. In addition, these inhibitors dose-dependently reduced the shedding enhanced by the sulfhydryl alkylator, N-ethylmaleimide (NEM), with IC(50) values of approximately 0.32 microM and approximately 0.58 microM for BB-3103 and Ro31-9790 respectively. It was of interest to find out that Ro31-9790 acted not only to modulate PMA- or NEM-induced shedding processes, but also markedly reduced the spontaneous, time-dependent accumulation of GHBP released from CHO/hGHR cells growing in serum-containing medium. Taken together, these results suggest that one or more zinc-dependent metalloprotease(s), acting at the cell surface, may be involved in GHBP secretase activity. A scheme is proposed whereby at least part of the regulated maturation and/or activation of the protease activity may involve a cysteine-switch mechanism and/or PKC-dependent phosphorylation. In the long run, specific inhibitors of these processes could be applied in the regulation of GHBP levels and, thus, of GH availability and/or activity.
 ...
PMID:Shedding of growth hormone-binding protein is inhibited by hydroxamic acid-based protease inhibitors: proposed mechanism of activation of growth hormone-binding protein secretase. 1131 56

Tumour necrosis factor-alpha (TNF-alpha) is a major immunomodulatory and proinflammatory cytokine which is shed in its soluble form by a membrane-anchored zinc protease, identified as a disintegrin and metalloproteinase (ADAM) called TNF-alpha convertase (TACE; ADAM17). The role of this protease in the adult nervous system remains poorly understood. During cerebral ischemia and subsequent reperfusion, expression and release of TNF-alpha have been shown. We have investigated the expression and activity of TACE in an in vitro model of brain ischemia consisting of rat forebrain slices exposed to oxygen-glucose deprivation (OGD). OGD caused the release of TNF-alpha, an effect which was inhibited by a hydroxamate-based metalloprotease inhibitor, BB-3103, with an IC(50) of 0.1 microM, suggesting that TNF-alpha release results selectively from TACE activity. Assay of TACE enzymatic activity on a fluorescein-labelled peptide spanning the cleavage site in pro-TNF-alpha, as well as Western blot and RT-PCR analyses showed that TACE is present in control forebrain and, more interestingly, that TACE expression is increased in OGD-exposed tissue. TACE enzymatic activity from OGD-exposed slices was significantly inhibited by cycloheximide, suggesting that de novo synthesis of TACE contributes to TNF-alpha release after ischaemia. Moreover, it was also inhibited by bisindolylmaleimide I, indicating that TACE activity is regulated by PKC. These findings posed the question of what was its function therein. Among other actions, TNF-alpha has been described to be involved in the expression of inducible nitric oxide synthase (iNOS), a high-output NOS isoform associated to cellular damage, but the link between TNF-alpha release after brain ischaemia and iNOS expression in this condition has not been shown. We have now found that iNOS expression in OGD-subjected brain slices is inhibited by BB-3103 at concentrations below 1 microM, indicating that shedding of TNF-alpha by TACE plays a necessary part in the induction of this NOS isoenzyme after OGD. Taken together, these data demonstrate that (1) TACE/ADAM17 activity accounts for the majority of TNF-alpha shedding after OGD in rat forebrain slices, (2) an increase in TACE expression contributes, at least in part, to the rise in TNF-alpha after OGD and (3) iNOS expression in OGD-subjected brain slices results from TACE activity and subsequent increase in TNF-alpha levels.
 ...
PMID:Up-regulation of TNF-alpha convertase (TACE/ADAM17) after oxygen-glucose deprivation in rat forebrain slices. 1140 1


<< Previous 1 2 3 4 5 6 7 8 9 Next >>