SEARCH · PubMed Health

Results for “Receptor, PAR-2”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources

PubMed1996

Genomic cloning and characterization of the human thrombin receptor gene. Structural similarity to the proteinase activated receptor-2 gene.

The seven-transmembrane segment thrombin receptor (TR) represents the prototype of a putative family of proteolytically cleaved receptors that may include the proteinase activated receptor-2. A panel of somatic cell hybrids retaining distinct portions of human chromosome 5 were used to establish that the human TR gene is present as a single-copy locus within the region 5q11.2 -->q13.3, confirming our previous localization using fluorescent in situ hybridization analysis. To further characterize the TR gene, overlapping clones from a human genomic library were isolated. Genomic analysis confirmed that the TR gene is of limited complexity, spanning approximately 27 kilobases and containing two exons separated by a large approximately 22-kilobase intron. The larger second exon contains the majority of the coding sequence and the thrombin cleavage site, remarkably similar to the organization of the proteinase activated receptor-2 gene in which the putative cleavage site is also contained within the large second exon. Primer extension analysis using two 30-mer oligonucleotide primers known to be contained within the first exon identified the predominant transcription initiation site 351 base pairs upstream from the initiator methionine in both human umbilical vein endothelial and human erythroleukemia cells. Sequence analysis of the 5'-flanking region revealed the TR promoter to be TATA-less, although nucleic acid motifspotentially involved in transcriptional gene regulation were evident and include a GATA motif, octamer enhancer sequences, AP-2-like sites, and Sp1 sites. These data provide evidence for remarkable similarity at the gene level between both proteolytically cleaved receptors described to date.

Base Sequence↗

PubMed1996

Agonist recognition by proteinase-activated receptor 2 and thrombin receptor. Importance of extracellular loop interactions for receptor function.

Thrombin receptor and proteinase-activated receptor 2 (PAR2) define a family of G protein-coupled receptors that are activated by a novel proteolytic mechanism. Specific cleavage of their amino-terminal exodomains unmasks a new amino terminus which then serves as a tethered ligand, docking intramolecularly to the body of the receptor to effect signaling. Identification of the docking interactions between tethered ligand domain and receptor is critical for understanding transmembrane signaling by these receptors. Synthetic "agonist peptides" that mimic the tethered ligand domains of thrombin receptor and PAR2 act as agonists at their respective receptors. Toward defining the docking interactions which mediate receptor activation, we determined the specificity of the thrombin receptor and PAR2 for their respective agonist peptides and used receptor chimeras to identify the receptor domains responsible for such specificity. PAR2 responded to both thrombin receptor and PAR2 agonist peptides. In contrast, thrombin receptor was selective for its own agonist peptide. Substitution of the extracellular face of PAR2, its amino-terminal exodomain and three extracellular loops, for the cognate thrombin receptor structures yielded a chimeric receptor with PAR2-like agonist specificity. Substitution of individual extracellular domains revealed that the primary determinant of agonist specificity was extracellular loop 2. Strikingly, substitution of either the amino-terminal exodomain or third extracellular loop alone caused marked loss of receptor function, but the double substitution yielded a functional receptor. Thus, the extracellular domains of these G protein-coupled receptors are more than simply passive links between transmembrane domains. They participate in agonist recognition and must interact, directly or indirectly, for proper receptor function.

Amino Acid Sequence↗

PubMed1996

Conserved structure and adjacent location of the thrombin receptor and protease-activated receptor 2 genes define a protease-activated receptor gene cluster.

BACKGROUND: Thrombin is a serine protease that elicits a variety of cellular responses. Molecular cloning of a thrombin receptor revealed a G protein-coupled receptor that is activated by a novel proteolytic mechanism. Recently, a second protease-activated receptor was discovered and dubbed PAR2. PAR2 is highly related to the thrombin receptor by sequence and, like the thrombin receptor, is activated by cleavage of its amino terminal exodomain. Also like the thrombin receptor, PAR2 can be activated by the hexapeptide corresponding to its tethered ligand sequence independent of receptor cleavage. Thus, functionally, the thrombin receptor and PAR2 constitute a fledgling receptor family that shares a novel proteolytic activation mechanism. To further explore the relatedness of the two known protease-activated receptors and to examine the possibility that a protease-activated gene cluster might exist, we have compared the structure and chromosomal locations of the thrombin receptor and PAR2 genes. MATERIALS AND METHODS: The genomic structures of the two protease-activated receptor genes were determined by analysis of lambda phage, P1 bacteriophage, and bacterial artificial chromosome (BAC) genomic clones. Chromosomal location was determined with fluorescent in situ hybridization (FISH) on metaphase chromosomes, and the relative distance separating the two genes was evaluated both by means of two-color FISH and analysis of YACs and BACs containing both genes. RESULTS: Analysis of genomic clones revealed that the two protease-activated receptor genes share a two-exon genomic structure in which the first exon encodes 5'-untranslated sequence and signal peptide, and the second exon encodes the mature receptor protein and 3'-untranslated sequence. The two receptor genes also share a common locus with the two human genes located at 5q13 and the two mouse genes at 13D2, a syntenic region of the mouse genome. These techniques also suggest that the physical distance separating these two genes is less than 100 kb. CONCLUSIONS: The fact that the thrombin receptor and PAR2 genes share an identical structure and are located within approximately 100 kb of each other in the genome demonstrates that these genes arose from a gene duplication event. These results define a new protease-activated receptor gene cluster in which new family members may be found.

Amino Acid Sequence↗

PubMed1996

Rat proteinase-activated receptor-2 (PAR-2): cDNA sequence and activity of receptor-derived peptides in gastric and vascular tissue.

1. The biological activities of the proteinase-activated receptor number 2 (PAR-2)-derived peptides, SLIGRL (PP6) SLIGRL-NH2 (PP6-NH2) and SLIGR-NH2 (PP5-NH2) were measured in mouse and rat gastric longitudinal muscle (LM) tissue and in a rat aortic ring preparation and the actions of the PAR-2-derived peptides were compared with trypsin and with the actions of the thrombin receptor activating peptide, SFLLR-NH2 (TP5-NH2). 2. From a neonatal rat intestinal cDNA library, and from intestinal and kidney-derived cDNA, the coding region of the rat PAR-2 receptor was cloned and sequenced, thereby establishing its close sequence identity with the previously described mouse PAR-2 receptor; and this information, along with a reverse-transcriptase (RT) polymerase chain reaction (PCR) analysis of cDNA derived from gastric and aortic tissue was used to establish the concurrent presence of PAR-2 and thrombin receptor mRNA in both tissues. 3. In the mouse and rat gastric preparations, the PAR-2-derived polypeptides, PP6, PP6-HN2 and PP5-NH2 caused contractile responses that mimicked the contractile actions of low concentrations of trypsin (5 u/ml-1; 10 nM) and that were equivalent to contractions caused by TP5-NH2. 4. The cumulative exposure of the rat LM tissue to PP6-NH2 led to a desensitization of the contractile response to this polypeptide, but not to TP5-NH2 and vice versa, so as to indicate a lack of cross-desensitization between the receptors responsive to the PAR-2 and thrombin receptor-derived peptides. 5. In the rat gastric preparation, the potencies of the PAR-2-activating peptides were lower than the potency of TP5-NH2 (potency order: TP5-NH2 > > PP6-NH2 > or = PP6 > PP5-NH2); PP6 was a partial agonist in this preparation. 6. The contractile actions of PP6 and PP6-NH2 in the rat gastric preparation required the presence of extracellular calcium, were inhibited by nifedipine and were blocked by the cyclo-oxygenase inhibitor, indomethacin and by the tyrosine kinase inhibitor, genistein, but not by the kinase C inhibitor, GF109203X. The contractile responses were not blocked by atropine, chlorpheniramine, phenoxybenzamine, propranolol, ritanserin or tetrodotoxin. 7. In a precontracted rat aortic ring preparation, with an intact endothelium, all of the PAR-2-derived peptides caused a prompt relaxation response that was blocked by the nitric oxide synthase inhibitor, N omega-nitro-L-arginine-methyl ester (L-NAME) but not by D-NAME; in an endothelium-free preparation, which possessed mRNA for both the PAR-2 and thrombin receptors, the PAR-2-activating peptides caused neither a relaxation nor a contraction, in contrast with the contractile action of TP5-NH2. The relaxation response to PP6-NH2 was not blocked by atropine, chlorpheniramine, genistein, indomethacin, propranolol or ritanserin. 8. In the rat aortic preparation, the potencies of PP6, PP6-NH2 and PP5-NH2 were greater than those of the thrombin receptor activating peptide, TP5-NH2 (potency order: PP6-NH2 > or = PP6 > PP5-NH2 > TP5-NH2). 9. In the rat aortic preparation, the relaxant actions of the PAR-2-derived peptides were mimicked by trypsin, at concentrations (0.5-1 u ml-1; 1-2 nM) lower than those that can activate the thrombin receptor. 10. The bioassay data obtained with the PAR-2 peptides and with trypsin, along with the molecular cloning/RT-PCR analysis, point to the presence of functional PAR-2 receptors that can activate distinct responses in the gastric and vascular smooth muscle preparations. These responses were comparable to those resulting from thrombin receptor activation in the same tissues, so as to suggest that the receptor for the PAR-2-activating peptides may play a physiological role as far reaching as the one proposed for the thrombin receptor.

Animals↗

PubMed1996

The proteinase activated receptor-2 (PAR-2) mediates mitogenic responses in human vascular endothelial cells.

Proteolytically cleaved receptors, typified by the functional thrombin receptor (TR), represent a novel class of receptors that mediate signaling events by functional coupling to G proteins. Northern blot analysis completed with a human proteinase activated receptor-2 (PAR-2) cDNA as probe demonstrated the approximately 3.5kb PAR-2 transcript in total cellular RNA from human umbilical vein endothelial cells (HUVEC). Microspectrofluorimetry using Fura2-loaded HUVEC demonstrated a dose-dependent elevation in intracellular calcium transients ([Ca2+]i) to murine PAR39-44 (SLIGRL, putative neoligand after cleavage), with an approximate EC50 of 30 microM, and evidence for homologous desensitization with complete recovery at 45 min. Xenopus oocytes microinjected with TR cRNA failed to respond to 200 microM PAR39-44, and TR-targeted antisense oligonucleotides specifically abrogated thrombin-induced but not PAR39-44-mediated [Ca2+]i, excluding the possibility that TR/PAR-2 cell-surface coexpression was structurally linked. HUVEC incubated with PAR39-44 demonstrated a dose- and time-dependent mitogenic response similar to that seen with thrombin or TR42-47 (TR-activating peptide, SFLLRN). Preactivation of HUVEC with either PAR39-44 or thrombin resulted in heterologous desensitization to the corresponding agonist, an effect that was mediated primarily by TR internalization as evaluated by immunofluorescence and quantitative ELISA. These results ascribe a previously unrecognized function to the PAR-2 receptor, imply that a natural enzyme agonist may circulate in plasma, and suggest the presence of an additional regulatory mechanism controlling receptor activation events in vascular endothelial cells.

Animals↗

PubMed1997

Thrombin receptor antagonists: a work in progress.

The thrombin receptor and protease-activated receptor 2 (PAR-2) are the two currently known members of the large family of G protein-coupled receptors that are activated by proteases. Both receptors are located on cells in and around the vascular space, including platelets, endothelial cells, vascular smooth muscle cells, fibroblasts and some lymphocytes. This brief review summarizes current information on thrombin receptors and focuses on some of the issues that are relevant for ongoing efforts to develop thrombin receptor antagonists.

Amino Acid Sequence↗

PubMed1995

The mouse proteinase-activated receptor-2 cDNA and gene. Molecular cloning and functional expression.

We have reported the cloning from mouse genomic DNA of a fragment encoding a G-protein-coupled receptor related to the receptor for the blood clotting enzyme thrombin. Like the thrombin receptor this receptor is activated by proteolytic cleavage of its extracellular amino terminus. Because the physiological agonist at the receptor was unknown, we provisionally named it proteinase-activated receptor 2 (PAR-2). Here we present a PAR-2 cDNA of 2729 nucleotides that differs from the published genomic sequence at the 5' end, including a part of the protein coding region. The differences do not affect the peptide sequence of the activating proteinase cleavage site proper, but may include amino acid residues important for enzyme-substrate recognition. Analysis of the PAR-2 gene structure showed that the cDNA 5' end is derived from a separate exon located about 10 kilobases away from the 3' exon. Results from a primer extension experiment indicate that transcription starts at a unique site around nucleotide -203 respective to the translation initiation ATG. Chinese hamster ovary cells transfected with either the PAR-2 cDNA or a construct made from the published PAR-2 genomic sequence responded with intracellular calcium mobilization to stimulation with 1 nM trypsin, 10 microM PAR-2-activating peptide (SLIGRL), or 1 microM thrombin receptor-activating peptide (SFLLRN). Untransfected cells responded only to stimulation with thrombin receptor activating peptide. Only transcripts corresponding to the PAR-2 cDNA could be detected in three mouse tissues examined.

Amino Acid Sequence↗

PubMed1996

The proteinase-activated receptor 2 is induced by inflammatory mediators in human endothelial cells. Comparison with the thrombin receptor.

The proteinase-activated receptor 2 (PAR-2) belongs to the family of seven transmembrane region receptors, and, like the related thrombin receptor, it is activated by specific proteolytic cleavage of its extracellular amino terminus. It is not known which proteinase is the physiological activator of the PAR-2, but candidates can be found among the enzymes involved in the inflammatory cascade systems. Here, we have studied the effects of various mediators on the expression of the PAR-2 and the thrombin receptor in cultured human umbilical vein endothelial cells. Stimulation with the cytokines tumor necrosis factor alpha or interleukin-1 alpha as well as bacterial lipopolysaccharide elevated the expression of PAR-2 in a dose-dependent manner. The time course of induction after cytokine stimulation was similar to those published for the adhesion molecules intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. After 20 h of stimulation, PAR-2 mRNA and protein levels were increased to 5-10-fold basal values, and, in the continued presence of tumor necrosis factor alpha, PAR-2 mRNA expression was found to remain elevated for up to 4 days. In contrast, the thrombin receptor gene was not induced by any of these inflammatory mediators. The responses to phorbol ester treatment also differed between the two genes. Thrombin receptor mRNA levels decreased steadily up to 20 h, whereas PAR-2 mRNA levels first rose to about 3-fold basal values at 4 h before decreasing again. Cell surface protein levels of both receptors were decreased after 20 h of phorbol ester stimulation. Elevating intracellular cAMP levels by treatment with forskolin resulted in decreased expression of both receptors, and inhibition of cAMP degradation appeared to blunt the cytokine-induced increase in PAR-2 expression. The induction of the PAR-2 by cytokine treatment supports the concept of PAR-2 involvement in the acute inflammatory response.

1-Methyl-3-isobutylxanthine↗

PubMed1997

Luminal trypsin may regulate enterocytes through proteinase-activated receptor 2.

Proteinase-activated receptor 2 (PAR-2) is a recently characterized G-protein coupled receptor that is cleaved and activated by pancreatic trypsin. Trypsin is usually considered a digestive enzyme in the intestinal lumen. We examined the hypothesis that trypsin, at concentrations normally present in the lumen of the small intestine, is also a signaling molecule that specifically regulates enterocytes by activating PAR-2. PAR-2 mRNA was highly expressed in the mucosa of the small intestine and in an enterocyte cell line. Immunoreactive PAR-2 was detected at the apical membrane of enterocytes, where it could be cleaved by luminal trypsin. Physiological concentrations of pancreatic trypsin and a peptide corresponding to the tethered ligand of PAR-2, which is exposed by trypsin cleavage, stimulated generation of inositol 1,4,5-trisphosphate, arachidonic acid release, and secretion of prostaglandin E2 and F1alpha from enterocytes and a transfected cell line. Application of trypsin to the apical membrane of enterocytes and to the mucosal surface of everted sacs of jejunum also stimulated prostaglandin E2 secretion. Thus, luminal trypsin activates PAR-2 at the apical membrane of enterocytes to stimulate secretion of eicosanoids, which regulate multiple cell types in a paracrine and autocrine manner. We conclude that trypsin is a signaling molecule that specifically regulates enterocytes by triggering PAR-2.

Animals↗

PubMed1997

Thrombin and trypsin induce granulocyte-macrophage colony-stimulating factor and interleukin-6 gene expression in cultured normal human keratinocytes.

We studied the effects of serine proteases on cytokine gene expression by cultured normal human keratinocytes. In resting keratinocytes, steady-state mRNA levels for interleukins IL-1 alpha, IL-1 beta, IL-7, and IL-8, transforming growth factors alpha and beta, and tumor necrosis alpha were sufficient to be detected by our reverse transcriptase-polymerase clozin reaction method. Incubation of keratinocytes with 25 nM trypsin or 1 unit/ml thrombin for 24 hr selectively upregulated mRNA levels for granulocyte-macrophage colony-stimulating factor (GM-CSF) and Il-6 to detectable levels. Keratinocytes secreted GM-CSF and IL-6 protein in response to these proteases. Monensin did not inhibit the gene expression for the cytokines, thereby excluding the possibility of intervention by secreted molecules. Aprotinin and argatroban inhibited the effects of the proteases. SFLLRN and SLIGRL, tethered ligand receptor peptides for thrombin receptor and for proteinase-activated receptor 2 (PAR-2), respectively, duplicated the effects of the proteases on keratinocytes, which expressed mRNA for both receptors. Trypsin increased tyrosine phosphorylated proteins and intracellular free calcium concentrations. Tyrphostin, pertussis toxin, or H-7 suppressed trypsin- and thrombin-induced GM-CSF gene expression. Our results demonstrate that the serine proteases activate thrombin receptors and PAR-2 on keratinocytes, triggering intracellular signaling and then inducing the synthesis of GM-CSF. We speculate that serine proteases modulate the course of physiological and pathological processes in the skin by stimulating keratinocytes to produce the cytokines.

Aprotinin↗

PubMed1996

Trypsin stimulates proteinase-activated receptor-2-dependent and -independent activation of mitogen-activated protein kinases.

We have examined protease-mediated activation of the mitogen-activated protein (MAP) kinase cascade in rat aortic smooth-muscle cells and bovine pulmonary arterial fibroblasts. Exposure of smooth-muscle cells to trypsin evoked rapid and transient activation of c-Raf-1, MAP kinase kinase 1 and 2 and MAP kinase that was sensitive to inhibition by soybean trypsin inhibitor. The actions of trypsin were closely mimicked by the proteinase-activated receptor 2 (PAR-2)-activating peptide sequence SLIGRL but not LSIGRL. Peak MAP kinase activation in response to both trypsin and SLIGRL was also dependent on concentration, with EC50 values of 12.1 +/- 3.4 nM and 62.5 +/- 4.5 microM respectively. Under conditions where MAP kinase activation by SLIGRL was completely desensitized by prior exposure of smooth-muscle cells to the peptide, trypsin-stimulated MAP kinase activity was markedly attenuated (78.9 +/- 15.1% desensitization), whereas the response to thrombin was only marginally affected (16.6 +/- 12.1% desensitization). Trypsin and SLIGRL also weakly stimulated the activation of the MAP kinase homologue p38 in smooth-muscle cells without any detectable activation of c-Jun N-terminal kinase. Strong activation of the MAP kinase cascade and modest activation of p38 by trypsin were also observed in fibroblasts, although in this cell type these effects were not mimicked by SLIGRL nor by the thrombin receptor-activating peptide SFLLRNPNDKYEPF. Reverse transcriptase-PCR analysis confirmed the presence of PAR-2 mRNA in smooth-muscle cells but not fibroblasts. Our results suggest that in vascular smooth-muscle cells, trypsin stimulates the activation of the MAP kinase cascade relatively selectively, in a manner consistent with an interaction with the recently described PAR-2. Activation of MAP kinase by trypsin in vascular fibroblasts, however, seems to be independent of PAR-2 and occurs by an undefined mechanism possibly involving novel receptor species.

Animals↗

PubMed1996

Molecular cloning, expression and potential functions of the human proteinase-activated receptor-2.

We used PCR to amplify proteinase activated receptor-2 (PAR-2) from human kidney cDNA. The open reading frame comprised 1191 bp and encoded a protein of 397 residues with 83% identity with mouse PAR-2. In KNRK cells (a line of kirsten murine sarcoma virus-transformed rat kidney epithelial cells) transfected with this cDNA, trypsin and activating peptide (AP) corresponding to the tethered ligand exposed by trypsin cleavage (SLIGKV-NH2) induced a prompt increase in cytosolic calcium ion concentration ([Ca2+]i). Human PAR-2 (hPAR-2) resided both on the plasma membrane and in the Golgi apparatus. hPAR-2 mRNA was highly expressed in human pancreas, kidney, colon, liver and small intestine, and by A549 lung and SW480 colon adenocarcinoma cells. Hybridization in situ revealed high expression in intestinal epithelial cells throughout the gut. Trypsin and AP stimulated an increase in [Ca2+]i in a rat intestinal epithelial cell line (hBRIE 380) and stimulated amylase secretion in isolated pancreatic acini. In A549 cells, which also responded to trypsin and AP with mobilization of cytosolic Ca2+, AP inhibited colony formation. Thus PAR-2 may serve as a trypsin sensor in the gut. Its expression by cells and tissues not normally exposed to pancreatic trypsin suggests that other proteases could serve as physiological activators.

Adenocarcinoma↗

PubMed1996

Proteinase-activated receptor-2 in rat aorta: structural requirements for agonist activity of receptor-activating peptides.

We measured in rat aorta rings the relaxant activity of a number of peptides derived from the activating sequence (SLIGRL, or PP6) of the proteinase-activated receptor-2 (PAR-2). The relaxant action of PP6-NH2 mimicked the action of low concentrations of trypsin (0.5-1 unit/ml; 1-2 nM), was dependent on an intact endothelium, and was blocked by N-omega-nitro-L-arginine methyl ester but not by N-omega-nitro-D-arginine methyl ester. The relaxant actions of PP6, SLIGRL-NH2 (PP6-NH2), SLIGR (PP5), and SLIGR-NH2 (PP5-NH2) were comparable in magnitude, with relative potencies of PP6-NH2 > or = PP6 > PP5-NH2 > PP5. Peptides lacking either a leucine at position 2 (SAIGRL) or an arginine at position 5 (SLIGAL) exhibited markedly reduced or no relaxant activity; nevertheless, the tetrapeptide LIGR-NH2 exhibited low but detectable intrinsic activity. With the use of reverse-transcriptase/polymerase chain reaction, we documented the presence of PAR-2 mRNA in aorta tissue and determined that the rat aorta amino-terminal receptor-activating sequence was the same as that reported for the murine PAR-2 receptor. We concluded that the rat aorta tissue has a PAR-2 receptor that can be activated by peptides as short as four amino acids; the leucine and arginine at positions 2 and 5, respectively, of the proteolytically revealed PAR-2 receptor-activating sequence play key roles in regulating receptor function.

Amino Acid Sequence↗

PubMed1997

Proteinase-activated receptor-2: expression by human neutrophils.

Neutrophils were shown to express the proteinase-activated receptor-2 (PAR-2), a seven transmembrane domain receptor, which is activated by cleavage by trypsin. Granulocytes from 14 donors stained positively for PAR-2 with affinity-purified rabbit antibodies raised against a peptide corresponding to the trypsin cleavage site of human PAR-2. Neutrophil activation in response to a receptor activating peptide (RAP) varied between donors. RAP (Ser-Leu-Ile-Gly-Lys-Val-NH2) alone induced an increase in the forward and side light scatter after 5-10 minutes and a small increase in the expression of the activation molecule CD11b. The increased expression of CD11b induced by RAP was markedly enhanced by priming the neutrophils with a low concentration (1 nM) of formyl-Leu-Met-Phe. Trypsin and RAP also induced an increase in intracellular calcium, but there were large variations in the magnitude of responses between donors also in this assay. The effects of RAP in the different assays were specific; acetylated RAP was completely without activity.

Adult↗

PubMed1996

Mechanisms of desensitization and resensitization of proteinase-activated receptor-2.

Proteinase-activated receptor-2 (PAR-2) is a G-protein-coupled receptor that is expressed by intestinal epithelial cells, which are episodically exposed to pancreatic trypsin in the intestinal lumen. Trypsin cleaves PAR-2 to expose a tethered ligand, which irreversibly activates the receptor. Thus, PAR-2 may desensitize and resensitize by novel mechanisms. We examined these mechanisms in kidney epithelial cells, stably expressing human PAR-2, and intestinal epithelial cells, which naturally express PAR-2. Trypsin stimulated a prompt increase in [Ca2+]i, due to mobilization of intracellular Ca2+, followed by a sustained plateau, due to influx of extracellular Ca2+. Repeated application of trypsin caused marked desensitization of this response, which is due in part to (a) irreversible cleavage of the receptor by trypsin and (b) protein kinase C-mediated termination of signaling. Trypsin exposure resulted in internalization of PAR-2 into early endosomes and then lysosomes; but endocytosis was not the mechanism of rapid desensitization. Thus, activated PAR-2 is endocytosed and degraded. The Ca2+ response to trypsin resensitized by 60-90 min. Brefeldin A, which disrupted Golgi stores of PAR-2, and cycloheximide, which inhibited protein synthesis, markedly attenuated resensitization. Thus, PAR-2-mediated Ca2+ mobilization desensitizes by irreversible receptor cleavage, protein kinase C-mediated termination of signaling, and PAR-2 targeting to lysosomes. It resensitizes by mobilization of large Golgi stores and synthesis of new receptors.

Arsenicals↗

PubMed1997

The human thrombin receptor and proteinase activated receptor-2 genes are tightly linked on chromosome 5q13.

The thrombin receptor (TR) and proteinase activated receptor-2 (PAR-2) may represent the prototypes of an emerging family of cell-surface receptors that effect cell activation events mediated by serine proteases generated during inflammatory, fibrinolytic or haemostatic-regulated pathways. To further characterize the molecular genetics of these receptors, we have refined the genetic and physical mapping of both PAR-2 and TR. Utilization of two distinct radiation hybrid mapping panels with different levels of resolution demonstrated that both genes are tightly linked to the microsatellite markers D5S424, D5S1977, D5S2529 and D5S2596 (in order of decreasing LOD scores, from 13.7 for D5S424 to 7.7 for D5S2596). Physical mapping using yeast artificial chromosomes (YACs) and inversion field gel electrophoresis demonstrated that they are maximally separate by 90 kb. If the association of TR and PAR-2 genes resulted from a relatively recent gene duplication event from a common ancestral gene, these observations provide a general framework for the identification of gene transcripts representing alternative proteolytically activated receptors which may be clustered within this region of the human genome. These observations are especially relevant given recent evidence that murine and human platelets express alternative signalling mechanisms or receptors for thrombin.

Animals↗

PubMed1997

Differential regulation of human keratinocyte growth and differentiation by a novel family of protease-activated receptors.

Thrombin receptor (ThrR) and protease-activated receptor-2 (PAR-2) are members of a unique G protein-coupled receptor family, which are characterized by the unveiling of a tethered peptide ligand upon proteolysis of their NH2 terminus. We have previously shown that cultured human basal keratinocytes express both receptors (R.J. Santulli et al., Proc. Natl. Acad. Sci. USA, 92: 9151-9155, 1995); however, their functional role in epidermal physiology has yet to be described. In the present study, we determined the effects of receptor activation on keratinocyte cell growth and differentiation using thrombin (selective for ThrR), SLIGRL (selective for PAR-2), and SFLLRN (stimulates ThrR and PAR-2), as agonists. ThrR stimulation enhanced cell growth in a dose-dependent manner in the absence of growth factors (epidermal growth factor and bovine pituitary extract). In contrast, under the same conditions, activation of PAR-2 led to the inhibition of cell growth. This inhibitory activity by PAR-2 activation was also observed in the presence of growth factors. Activation of both receptors diminished protein expression of the differentiation marker transglutaminase type 1 induced by either calcium or IFN-gamma. Calcium-induced involucrin expression was also decreased. These results indicate that PAR-2 and ThrR differentially modulate keratinocyte function and may provide an important regulatory function in the epidermis by altering the functional state of keratinocytes.

Animals↗

PubMed1996

Coagulation factors VII and X induce Ca2+ oscillations in Madin-Darby canine kidney cells only when proteolytically active.

We have recently reported that the activated serine protease and blood coagulation Factor VII (FVIIa) can induce Ca2+ oscillations in Madin-Darby canine kidney cells. We now demonstrate a similar response by Madin-Darby canine kidney cells to the active coagulation Factor X (FXa), which is also a serine protease and a substrate of the tissue factor (TF).FVIIa complex in the initiation of the coagulation cascade. The phosphatidyl inositol-specific phospholipase C inhibitor U73122 inhibited the signals elicited by both FVIIa and FXa. Lack of sensibility to the tyrosine kinase inhibitors herbimycin A, genistein, and the tyrphostin AG18 and discordance between TF expression and FVIIa responsiveness argued against TF acting as a cytokine-like receptor, with tyrosine kinase-mediated activation by FVIIa. As demonstrated using the protease inhibitor benzamidine and by specific active site inhibition with 1,5-dansyl-Glu-Gly-Arg chloromethyl ketone, both FVIIa and FXa lost their ability to elicit a calcium response when devoid of their proteolytic activity. Consistent with this, the native (zymogen) form of Factor X did not induce Ca2+ transients. Homologous but not heterologous inhibition of FVIIa- and FXa-evoked Ca2+ signals by 1,5-dansyl-Glu-Gly-Arg chloromethyl ketone-inactivated FVIIa and FXa suggested that each factor had its own specific cell surface anchoring receptor. The two coagulation factors did not show homologous desensitization as seen for thrombin stimulation. Studies with hirudin excluded involvement of the established activation pathway through thrombin itself. Lack of desensitization of the response to FVIIa or FXa by thrombin ruled out any involvement of proteinase activated receptor-1 (PAR-1), the thrombin receptor. We speculate that FXa and FVIIa may work via a receptor (possibly common) analogous to PAR-1 or its functional homologue PAR-2. Although TF is essential for the FVIIa-induced signaling event, its role in the phosphatidyl inositol-specific phospholipase C-mediated Ca2+ signal may be in anchoring FVIIa to the cell surface rather than in transmembrane signal mediation.

Animals↗