Kallikrein-mediated cell signalling: targeting proteinase-activated receptors (PARs)

We tested the hypothesis that human tissue kallikreins (hKs) may regulate signal transduction by cleaving and activating proteinase-activated receptors (PARs). We found that hK5, 6 and 14 cleaved PAR N-terminal peptide sequences representing the cleavage/activation motifs of human PAR1 and PAR2 to yield receptor-activating peptides. hK5, 6 and 14 activated calcium signalling in rat PAR2-expressing (but not background) KNRK cells. Calcium signalling in HEK cells co-expressing human PAR1 and PAR2 was also triggered by hK14 (via PAR1 and PAR2) and hK6 (via PAR2). In isolated rat platelets that do not express PAR1, but signal via PAR4, hK14 also activated PAR-dependent calcium signalling responses and triggered aggregation. The aggregation response elicited by hK14 was in contrast to the lack of aggregation triggered by hK5 and 6. hK14 also caused vasorelaxation in a phenylephrine-preconstricted rat aorta ring assay and triggered oedema in an in vivo model of murine paw inflammation. We propose that, like thrombin and trypsin, the kallikreins must now be considered as important 'hormonal' regulators of tissue function, very likely acting in part via PARs.     

Kallikrein-related peptidase 4 (KLK4) initiates intracellular signaling via protease-activated receptors (PARs). KLK4 and PAR-2 are co-expressed during prostate cancer progression

Kallikrein-related peptidase 4 (KLK4) is one of the 15 members of the human KLK family and a trypsin-like, prostate cancer-associated serine protease. Signaling initiated by trypsin-like serine proteases are transduced across the plasma membrane primarily by members of the protease-activated receptor (PAR) family of G protein-coupled receptors. Here we show, using Ca(2+) flux assays, that KLK4 signals via both PAR-1 and PAR-2 but not via PAR-4. Dose-response analysis over the enzyme concentration range 0.1-1000 nM indicated that KLK4-induced Ca(2+) mobilization via PAR-1 is more potent than via PAR-2, whereas KLK4 displayed greater efficacy via the latter PAR. We confirmed the specificity of KLK4 signaling via PAR-2 using in vitro protease cleavage assays and anti-phospho-ERK1/2/total ERK1/2 Western blot analysis of PAR-2-overexpressing and small interfering RNA-mediated receptor knockdown cell lines. Consistently, confocal microscopy analyses indicated that KLK4 initiates loss of PAR-2 from the cell surface and receptor internalization. Immunohistochemical analysis indicated the co-expression of agonist and PAR-2 in primary prostate cancer and bone metastases, suggesting that KLK4 signaling via this receptor will have pathological relevance. These data provide insight into KLK4-mediated cell signaling and suggest that signals induced by this enzyme via PARs may be important in prostate cancer.     

Proteinase-activated receptor 4 (PAR4): action of PAR4-activating peptides in vascular and gastric tissue and lack of cross-reactivity with PAR1 and PAR2.

We studied the actions of the human and murine proteinase-activated receptor 4 (PAR4) derived receptor-activating peptides (APs), GYPGQV-NH2 (GQV-NH2) and GYPGKF-NH2 (GKF-NH2), (i) to activate-desensitize either PAR1 or PAR2 in cultured cell systems (calcium signalling in PAR1/PAR2-bearing human HEK cells and in rat KNRK cells expressing either rat or human PAR2) and (ii) to affect contractility in rat aorta (RA) and rat gastric longitudinal muscle (LM) preparations in vitro. We found that neither PAR1 nor PAR2 was affected by concentrations of the PAR4-APs (800 microM) that caused both an endothelium-dependent nitric oxide mediated relaxation of preconstricted RA tissue and a contractile response in the LM preparation. The potencies (EC50 values 300 to 400 microM) of GQV-NH2 and GKF-NH2 for causing a relaxant effect were identical and comparable with the potency of GQV-NH2 for causing a contractile effect in the LM. However, the potencies of the PAR4-APs in the RA and LM preparations were 20- to 150-fold lower than the potency of the receptor-selective PAR1-AP, TFLLR-NH2. We conclude that the PAR4-APs do not activate either PAR1 or PAR2, and we suggest that along with PAR1 and PAR2, PAR4 may also be present in rat vascular and gastric smooth muscle.     

激肽释放酶转基因大鼠模型的建立

目的建立KLK1转基因大鼠模型。方法腹腔注射PMSG-HCG（150-150IU/kg）超排不同周龄（4-8周）SD大鼠比较超排效果的差异,以可用于注射胚胎数作为评判标准确定最佳超排周龄。构建pBC-klk1转基因构件,经酶切、纯化后通过显微注射方法导入SD大鼠受精卵原核并移植到同期受孕的SD受体母鼠输卵管内。出生后仔鼠用PCR和Southern方法检测鼠尾DNA鉴定基因型,通过RT-PCR和免疫组化方法检测klk1基因表达。结果4-8周SD大鼠超排后分别获得受精卵14±14.8、30±15.2、13.3±13.7、13±14.7、8±5.7,5周龄大鼠超排效果最好,与其他周龄大鼠相比有显差异,P〈0.05;显微注射1538枚卵,移植685（44.53%）枚卵于31只受体输卵管中,12（12/31,38.7%）只怀孕,共产仔62只,经PCR检测获得6只阳性鼠,Southern检测3只阳性。对Southern检测阳性转基因大鼠子代进行RT-PCR检测和免疫组化分析证明klk1基因在肾脏、胰腺和乳腺内表达。结论成功建立klk1基因表达的转基因大鼠模型,该模型是高血压病研究的理想动物模型。     

Major role of human KLK14 in seminal clot liquefaction

Liquefaction of human semen involves proteolytic degradation of the seminal coagulum and release of motile spermatozoa. Several members of human kallikrein-related peptidases (KLKs) have been implicated in semen liquefaction, functioning through highly regulated proteolytic cascades. Among these, KLK3 (also known as prostate-specific antigen) is the main executor enzyme responsible for processing of the primary components of semen coagulum, semenogelins I and II. We have recently identified KLK14 as a potential activator of KLK3 and other KLKs. This study aims to elucidate the cascade-mediated role of KLK14 ex vivo. KLK14 expression was significantly lower (p = 0.0252) in individuals with clinically delayed liquefaction. Concordantly, KLK14 expression was significantly (p = 0.0478) lower in asthenospermic cases. Specific inhibition of KLK14 activity by the synthetic inhibitor ACT(G9) resulted in a significant delay in semen liquefaction, a drop in the "early" (30 min postejaculation) "chymotrypsin-like" and KLK1 activity, and an increase in the "late" (90 min postejaculation) chymotrypsin-like activity. Conversely, the addition of recombinant active KLK14 facilitated the liquefaction process, augmented the early chymotrypsin-like activity, and lowered late chymotrypsin-like activity. Given that the observed chymotrypsin-like activity was almost completely attributed to KLK3 activity, KLK3 seems to be regulated bidirectionally. Accordingly, a higher level of KLK3 fragmentation was observed in KLK14-induced coagula, suggesting an inactivation mechanism via internal cleavage. Finally, semenogelins I and II were directly cleaved by KLK14. Semenogelins were also able to reverse KLK14 inhibition by Zn2+, providing a novel regulatory mechanism for KLK14 activity. Our results show that KLK14 exerts a significant and dose-dependent effect in the process of semen liquefaction.     

Proteinase-activated receptors, targets for kallikrein signaling

Serine proteinases like thrombin can signal to cells by the cleavage/activation of proteinase-activated receptors (PARs). Although thrombin is a recognized physiological activator of PAR(1) and PAR(4), the endogenous enzymes responsible for activating PAR(2) in settings other than the gastrointestinal system, where trypsin can activate PAR(2), are unknown. We tested the hypothesis that the human tissue kallikrein (hK) family of proteinases regulates PAR signaling by using the following: 1) a high pressure liquid chromatography (HPLC)-mass spectral analysis of the cleavage products yielded upon incubation of hK5, -6, and -14 with synthetic PAR N-terminal peptide sequences representing the cleavage/activation motifs of PAR(1), PAR(2), and PAR(4); 2) PAR-dependent calcium signaling responses in cells expressing PAR(1), PAR(2), and PAR(4) and in human platelets; 3) a vascular ring vasorelaxation assay; and 4) a PAR(4)-dependent rat and human platelet aggregation assay. We found that hK5, -6, and -14 all yielded PAR peptide cleavage sequences consistent with either receptor activation or inactivation/disarming. Furthermore, hK14 was able to activate PAR(1), PAR(2), and PAR(4) and to disarm/inhibit PAR(1). Although hK5 and -6 were also able to activate PAR(2), they failed to cause PAR(4)-dependent aggregation of rat and human platelets, although hK14 did. Furthermore, the relative potencies and maximum effects of hK14 and -6 to activate PAR(2)-mediated calcium signaling differed. Our data indicate that in physiological settings, hKs may represent important endogenous regulators of the PARs and that different hKs can have differential actions on PAR(1), PAR(2), and PAR(4).     

Kallikrein-related peptidase signaling in colon carcinoma cells: targeting proteinase-activated receptors

We hypothesized that kallikrein-related peptidase 14 (KLK14) is produced by colonic tumors and can promote tumorigenesis by activating proteinase-activated receptors (PARs). We found that KLK14 is expressed in human colon adenocarcinoma cells but not in adjacent cancer-free tissue; KLK14 mRNA, present in colon cancer, leads to KLK14 protein expression and secretion; and KLK14 signals viaPAR-2 in HT-29 cells to cause (1) receptor activation/internalization, (2) increases in intracellular calcium, (3) stimulation of ERK1/2/MAP kinase phosphorylation, and (4) cell proliferation. We suggest that KLK14, acting via PAR-2, represents an autocrine/paracrine regulator of colon tumorigenesis.     

Nonfunctional epidermal growth factor receptor in cells transformed by Kirsten sarcoma virus

The cell membrane receptor for epidermal growth factor (EGF) appears to be a glycoprotein of Mr 170,000 and mediates the mitogenic and metabolic responses of cells with EGF receptors (EGF-R). Normal rat kidney (NRK) have about 3 X 10(5) EGF-R per cell. Upon transformation of NRK cells by Kirsten sarcoma virus, the transformed derivative (KNRK) loses the ability to bind 125I-EGF. Membranes from NRK and KNRK cells were included in EGF-dependent phosphorylation reactions to search for evidence of the EGF-R. A phosphorylated protein of Mr 170,000 was detected in both NRK and KNRK membranes. The Mr 170,000 protein was identified to be EGF-R by immunoprecipitation with monoclonal antibody to the receptor. Furthermore, two-dimensional peptide mapping using trypsin and chymotrypsin digestions of the iodinated receptors from both NRK and KNRK cells showed essentially identical patterns. These data indicate that the EGF-R is present in KNRK cells with apparently the same protein structure as the NRK counterpart.     

Galangal Pungent Component, 1′-Acetoxychavicol Acetate,Activates TRPA1

We investigated the activation of transient receptor potential cation channel (TRP) subfamily V, member 1 (TRPV1) and TRP subfamily A, member 1 (TRPA1) by 1′-acetoxychavicol acetate (ACA), the main pungent component in galangal. ACA did not activate TRPV1-expressing human embryonic kidney (HEK) cells, but strongly activated TRPA1-expressing HEK cells. ACA was more potent than allyl isothiocyanate, the typical TRPA1 agonist.     

The organic cation transporters rOCT1 and hOCT2 are inhibited by cGMP

The electrogenic cation transporters OCT1 and OCT2 in the basolateral membrane of renal proximal tubules mediate the first step during secretion of organic cations. Previously we demonstrated stimulation and change of selectivity for rat OCT1 (rOCT1) by protein kinase C. Here we investigated the effect of cGMP on cation transport by rOCT1 or human OCT2 (hOCT2) after expression in human embryonic kidney cells (HEK293) or oocytes of Xenopus laevis. In HEK293 cells, uptake was measured by microfluorimetry using the fluorescent cation 4-(4-(dimethyl-amino)styryl)-N-methylpyridinium iodide (ASP + ) as substrate, whereas uptake into Xenopus laevis oocytes was measured with radioactively labelled cations. In addition, ASP +-induced depolarizations of membrane voltages (Vm) were measured in HEK293 cells using the slow whole-cell patch-clamp method. Incubation of rOCT1-expressing HEK293 cells for 10 min with 100 mM 8-Br-cGMP reduced initial ASP + uptake by maximally 78% with an IC50 value of 24 +/- 16 mM. This effect was not abolished by the specific PKG inhibitor KT5823, indicating that a cGMP-dependent kinase is not involved. An inhibition of ASP + uptake by rOCT1 in HEK293 cells was also obtained when the cells were incubated for 10 min with 100 mM cGMP, whereas no effect was obtained when cGMP was given together with ASP +. ASP + (100 mM)-induced depolarizations of Vm were reduced in the presence of 8-Br-cGMP (100 mM) by 44 +/- 11% (n = 6). Since it could be demonstrated that [3H]cGMP is taken up by an endogeneous cyanine863-inhibitable transporter, the effect of cGMP is probably mediated from inside the cell. Uptake measurements with [14C]tetraethylammonium and [3H]2-methyl-4-phenylpyridinium in Xenopus laevis oocytes expressing rOCT1 performed in the absence and presence of 8-Br-cGMP showed that cGMP does not interact directly with the transporter. The data suggest that the inhibition mediated by cGMP observed in HEK293 cells occurs most likely via a mammalian cGMP-binding protein that interacts with OCT1-2 transporters.     

Proteinase-mediated cell signalling: targeting proteinase-activated receptors (PARs) by kallikreins and more

Serine proteinases, like trypsin, can play a hormone-like role by triggering signal transduction pathways in target cells. In many respects these hormone-like actions of proteinases can now be understood in terms of the pharmacodynamics of the G protein-coupled 'receptor' responsible for the cellular actions of thrombin (proteinase-activated receptor-1, or PAR1). PAR1, like the other three members of this receptor family (PAR2, PAR3 and PAR4), has a unique mechanism of activation involving the proteolytic unmasking of an N-terminally tethered sequence that can activate the receptor. The selective activation of each PAR by short synthetic peptides representing these sequences has demonstrated that PAR1, PAR2 and PAR4 play important roles in regulating physiological responses ranging from vasoregulation and cell growth to inflammation and nociception. We hypothesise that the tissue kallikreins may regulate signal transduction via the PARs. Although PARs can account for many of their biological actions, kallikreins may also cause effects by mechanisms not involving the PARs. For instance, trypsin activates the insulin receptor and thrombin can act via a mechanism involving its non-catalytic domains. Based on the data we summarise, we propose that the kallikreins, like thrombin and trypsin, must now be considered as important 'hormonal' regulators of tissue function.     

Protease-activated receptor dependent and independent signaling by kallikreins 1 and 6 in CNS neuron and astroglial cell lines

While protease-activated receptors (PARs) are known to mediate signaling events in CNS, contributing both to normal function and pathogenesis, the endogenous activators of CNS PARs are poorly characterized. In this study, we test the hypothesis that kallikreins (KLKs) represent an important pool of endogenous activators of CNS PARs. Specifically, KLK1 and KLK6 were examined for their ability to evoke intracellular Ca(2+) flux in a PAR-dependent fashion in NSC34 neurons and Neu7 astrocytes. Both KLKs were also examined for their ability to activate mitogen-activated protein kinases (extracellular signal-regulated kinases, C-Jun N-terminal kinases, and p38) and protein kinase B (AKT) intracellular signaling cascades. Cumulatively, these studies show that KLK6, but not KLK1, signals through PARs. KLK6 evoked intracellular Ca(2+) flux was mediated by PAR1 in neurons and both PAR1 and PAR2 in astrocytes. Importantly, both KLK1 and KLK6 altered the activation state of mitogen-activated protein kinases and AKT, suggestive of important roles for each in CNS neuron and glial differentiation, and survival. The cellular specificity of CNS-KLK activity was underscored by observations that both proteases promoted AKT activation in astrocytes, but inhibited such signaling in neurons. PAR1 and bradykinin receptor inhibitors were used to demonstrate that KLK1-mediated activation of extracellular signal-regulated kinases in neurons occurred in a non-PAR, bradykinin 2 (B2) receptor-dependent fashion, while similar signaling by KLK6 was mediated by the combined activation of PAR1 and B2. Cumulatively results indicate KLK6, but not KLK1 is an activator of CNS PARs, and that both KLKs are poised to signal in a B2 receptor-dependent fashion to regulate multiple signal transduction pathways relevant to CNS physiologic function and dysfunction.     

KLK8 promotes the proliferation and metastasis of colorectal cancer via the activation of EMT associated with PAR1

Kallikrein-related peptidase 8 (KLK8) acts as an oncogene or anti-oncogene in various tumours, and the abnormal expression of KLK8 is involved in the carcinogenesis of several tumours. However, the role of KLK8 in colorectal cancer (CRC) and the underlying mechanism remain largely unclear. In this study, the carcinogenic effect of KLK8 was determined via CCK-8 and colony formation assays in vitro and a xenograft model in nude mice in vivo. The metastasis-promoting effect of KLK8 was investigated with transwell migration and invasion assays and wound-healing assay in vitro and a metastasis model in nude mice in vivo. Bioinformatics analyses and mechanistic experiments were conducted to elucidate the molecular mechanism. Herein, we reported that KLK8 had a promotive effect on the proliferation, migration and invasion of RKO and SW480 cells. Epithelial−mesenchymal transition (EMT) played an important role in the promotive effects of KLK8 on CRC. In addition, protease-activated receptor-1 (PAR-1) antagonist {"type":"entrez-protein","attrs":{"text":"SCH79797","term_id":"1052762130","term_text":"SCH79797"}}SCH79797 but not protease-activated receptor-2 (PAR-2) antagonist FSLLRY-NH2 attenuated the proliferation, migration and invasion of KLK8-upregulated RKO and SW480 cells. PAR-1 antagonist {"type":"entrez-protein","attrs":{"text":"SCH79797","term_id":"1052762130","term_text":"SCH79797"}}SCH79797 reduced the tumour volume of xenograft model and decreased the metastatic nodules in the livers of metastasis model. Furthermore, {"type":"entrez-protein","attrs":{"text":"SCH79797","term_id":"1052762130","term_text":"SCH79797"}}SCH79797 could reverse the positive impact of KLK8 on the EMT process in CRC both in vitro and in vivo. Taken together, these findings demonstrated for the first time that KLK8 promoted EMT and CRC progression, and this effect might be, at least partly mediated by PAR1-dependent pathway.Subject terms: Colorectal cancer, Oncogenes, Tumour biomarkers     

Opposing effects of beta-arrestin1 and beta-arrestin2 on activation and degradation of Src induced by protease-activated receptor 1

Protease-activated receptor 1 (PAR1), a G protein-coupled receptor for thrombin, is irreversibly proteolytically activated. beta-Arrestin1 and beta-arrestin2 have been reported to have different effects on signal desensitization and transduction of PAR1. In this study, we investigated whether beta-arrestin1 and beta-arrestin2 regulate Src-dependent activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) induced by PAR1 in HEK 293 cells. Our results show that PAR1-mediated activation of Src and ERK1/2 in HEK 293 cells was increased with overexpression of beta-arrestin1 or depletion of beta-arrestin2. PAR1-mediated activation of Src and ERK1/2 in HEK 293 cells was decreased or eliminated with depletion of beta-arrestin1 or overexpression of beta-arrestin2. Furthermore, depletion of beta-arrestin2 blocked PAR1-induced degradation of Src. Thus, beta-arrestin1 and beta-arrestin2 have opposing roles in regulating the activation of Src induced by PAR1. beta-Arrestin2 also appears to promote PAR1-induced degradation of Src. This degradation of Src provides a possible mechanism for terminating PAR1 signaling.     

LEKTI fragments specifically inhibit KLK5, KLK7, and KLK14 and control desquamation through a pH-dependent interaction

LEKTI is a 15-domain serine proteinase inhibitor whose defective expression underlies the severe autosomal recessive ichthyosiform skin disease, Netherton syndrome. Here, we show that LEKTI is produced as a precursor rapidly cleaved by furin, generating a variety of single or multidomain LEKTI fragments secreted in cultured keratinocytes and in the epidermis. The identity of these biological fragments (D1, D5, D6, D8-D11, and D9-D15) was inferred from biochemical analysis, using a panel of LEKTI antibodies. The functional inhibitory capacity of each fragment was tested on a panel of serine proteases. All LEKTI fragments, except D1, showed specific and differential inhibition of human kallikreins 5, 7, and 14. The strongest inhibition was observed with D8-D11, toward KLK5. Kinetics analysis revealed that this interaction is rapid and irreversible, reflecting an extremely tight binding complex. We demonstrated that pH variations govern this interaction, leading to the release of active KLK5 from the complex at acidic pH. These results identify KLK5, a key actor of the desquamation process, as the major target of LEKTI. They disclose a new mechanism of skin homeostasis by which the epidermal pH gradient allows precisely regulated KLK5 activity and corneodesmosomal cleavage in the most superficial layers of the stratum corneum.