Role of the JNK pathway in thrombin-induced ICAM-1 expression in endothelial cells

OBJECTIVE: Thrombin induces leukocyte adherence to endothelial cells via increased expression of intercellular adhesion molecule-1 (ICAM-1). Although ICAM-1 expression is regulated by NF-kappaB, recent studies have suggested that additional signaling mechanisms may also be involved. The goal of this study was to determine whether mitogen-activated protein (MAP) kinases, including extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 MAP kinase (p38), mediate thrombin-induced ICAM-1 expression in endothelial cells. METHODS: Western blot analysis using anti-ICAM-1 antibody and luciferase assays were performed in cultured endothelial cells after addition of signal transduction inhibitors or transfection of various gene constructs. JNK kinase activity was determined by a kinase assay using c-Jun as a substrate or by Western blot analysis with anti-phospho-JNK antibody. RESULTS: Treatment of endothelial cells with the JNK-specific inhibitors, SP600125 or JNK inhibitory peptide 1 (JNKI1), resulted in a significant decrease in thrombin-induced ICAM-1 expression as demonstrated by Western blot analysis (67 +/- 3% and 72 +/- 7%, respectively). In contrast, inhibitors of MEK and p38 had only minimal effect. The combination of SP600125 and the NF-kappaB inhibitor, BAY11-7082, resulted in complete inhibition of thrombin-induced ICAM-1 expression. The Galpha(q) inhibitor, YM-254890, inhibited thrombin-induced JNK activation and ICAM-1 expression. Dominant-negative Ras and Rac1, but not Rho, inhibited thrombin-induced JNK activation and ICAM-1 promoter activity. Finally, thrombin-induced JNK activation and ICAM-1 promoter activity were inhibited by betaARK1ct (a Gbetagamma subunit scavenger) and Csk. CONCLUSIONS: These data suggest that, in concert with NF-kappaB, JNK regulates thrombin-induced ICAM-1 expression by a mechanism that is dependent on Galpha(q), Gbetagamma, Ras, Rac1 and the Src kinase family.     

Paclitaxel induces thrombomodulin downregulation in human aortic endothelial cells

Patients with paclitaxel-eluting stents are at risk of developing stent thrombosis upon premature discontinuation of dual antiplatelet therapy. In this study, we set out to clarify whether paclitaxel can modulate thrombomodulin expression in human aortic endothelial cells. Human aortic endothelial cells were stimulated with paclitaxel. Methoxyphenyl tetrazolium inner salt cell viability assay, Western blot analysis, real-time polymerase chain reaction, and immunohistochemical assay were performed. In human aortic endothelial cells, paclitaxel (10(-5) to 10(-9) mol/L) treatment for 13 hours caused significant cytotoxicity at drug concentrations greater than 10(-7) mol/L. Paclitaxel (10(-5) to 10(-9) mol/L) treatment for 5 hours downregulated thrombomodulin expression dose-dependently, persisting even at 13 hours. Cotreatment with thrombin and paclitaxel did not alter the effect of paclitaxel on thrombomodulin downregulation. Paclitaxel caused a 0.63-fold decrease in thrombomodulin messenger RNA expression, and thrombin cotreatment did not alter this decrease. In vivo studies confirmed that paclitaxel (10 mg/kg) caused endothelial thrombomodulin downregulation in mice. In summary, paclitaxel downregulates thrombomodulin expression regardless of thrombin stimulation, which is an important factor for patients receiving paclitaxel-eluting stents. Therefore, further designs of drug-eluting stents should consider the influence of the eluted drugs on endothelial thrombogenicity.     

PDGF-CC induces tissue factor expression: role of PDGF receptor α/β

Tissue factor (TF) is the principal trigger of the coagulation cascade and involved in arterial thrombus formation. Platelet-derived growth factor CC (PDGF-CC) is a recently discovered member of the PDGF family released upon platelet activation. This study assesses the impact of PDGF-CC on TF expression in human cells. PDGF-CC concentration-dependently induced TF expression by 2.5-fold in THP-1 cells, by 2.0-fold in human peripheral blood monocytes, by 1.4-fold in vascular smooth muscle cells, and by 2.6-fold in microvascular endothelial cells, but did not affect TF expression in aortic endothelial cells. A similar pattern was observed with PDGF-BB. In contrast, PDGF-AA did not alter TF expression in THP-1 cells. TF whole cell activity was induced following stimulation with PDGF-BB and PDGF-CC in THP-1 cells. Real-time polymerase chain reaction revealed that PDGF-CC induced TF mRNA. PDGF-CC transiently activated p42/44 MAP kinase [extracellular signal-regulated kinase (ERK)], while phosphorylation of the MAP kinases c-Jun NH₂-terminal kinase (JNK) and p38 remained unaffected. PD98059, a specific inhibitor of ERK phosphorylation, but not the p38 inhibitor SB203580 or the JNK inhibitor SP600125 prevented PDGF-CC induced TF expression in a concentration-dependent manner. The effect of PDGF-CC was antagonized by both PDGF receptor α and PDGF receptor β neutralizing antibodies; in contrast, PDGF-BB was only inhibited by PDGF receptor β blocking antibody. PDGF receptor α and PDGF receptor β inhibition prevented PDGF-CC-induced ERK phosphorylation. PDGF-CC induces TF expression via activation of α/β receptor heterodimers and an ERK-dependent signal transduction pathway.     

JNK信号通路在热化疗抑制人小细胞肺癌细胞生长中的作用

目的研究热化疗对肺部肿瘤细胞生长的影响及其可能的机制。方法采用43℃加热联合120μg/L紫杉醇（热化联合组）、43℃加热联合120μg/L紫杉醇及20μmol/L JNK特异抑制剂SP600125（SP600125组）、单纯使用120μg/L紫杉醇（单纯化疗组）处理H446细胞,以未处理的H446细胞作对照;采用噻唑兰比色法检测各组细胞增殖率,RT-PCR检测有丝分裂素激活蛋白激酶激酶4（MKK4）表达,Western blotting法检测JNK磷酸化水平。结果热化联合组细胞增殖率低于其余各组（P〈0.05）;热化联合组MKK4表达高于对照组和单纯化疗组（P〈0.05）,JNK磷酸化水平在热化联合组中表达明显增高（P〈0.05）,SP600125可抑制其磷酸化（P〈0.05）。结论热化疗联合应用可以明显抑制H446细胞的生长,这种抑制作用可能是通过激活JNK信号转导通路实现的。     

SP600125, an anthrapyrazolone inhibitor of Jun N-terminal kinase

Jun N-terminal kinase (JNK) is a stress-activated protein kinase that can be induced by inflammatory cytokines, bacterial endotoxin, osmotic shock, UV radiation, and hypoxia. We report the identification of an anthrapyrazolone series with significant inhibition of JNK1, -2, and -3 (K(i) = 0.19 microM). SP600125 is a reversible ATP-competitive inhibitor with >20-fold selectivity vs. a range of kinases and enzymes tested. In cells, SP600125 dose dependently inhibited the phosphorylation of c-Jun, the expression of inflammatory genes COX-2, IL-2, IFN-gamma, TNF-alpha, and prevented the activation and differentiation of primary human CD4 cell cultures. In animal studies, SP600125 blocked (bacterial) lipopolysaccharide-induced expression of tumor necrosis factor-alpha and inhibited anti-CD3-induced apoptosis of CD4(+) CD8(+) thymocytes. Our study supports targeting JNK as an important strategy in inflammatory disease, apoptotic cell death, and cancer.     

Reconstituted high-density lipoprotein inhibits thrombin-induced endothelial tissue factor expression through inhibition of RhoA and stimulation of phosphatidylinositol 3-kinase but not Akt/endothelial nitric oxide synthase

Endothelial cells express negligible amounts of tissue factor (TF) that can be induced by thrombin, which is important for acute coronary syndromes. Recent research suggests that endothelial TF expression is positively regulated by RhoA and p38mapk, but negatively by Akt/endothelial nitric oxide synthase (eNOS) pathway. High-density lipoprotein (HDL) is atheroprotective and exerts antiatherothrombotic effect. This study investigated the effect of a reconstituted HDL (rHDL) on endothelial TF expression induced by thrombin and the underlying mechanisms. In cultured human umbilical vein and aortic endothelial cells, thrombin (4 U/mL, 4 hours) increased TF protein level, which was reduced by rHDL (0.1 mg/mL, 43% inhibition, n=3 to 7, P<0.01). Activation of RhoA but not p38mapk by thrombin was prevented by rHDL. rHDL stimulated Akt/eNOS pathway. The phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 abolished the activation of Akt/eNOS and reversed the inhibitory effect of rHDL on TF expression. Adenoviral expression of the active PI3K mutant (p110) reduced TF expression stimulated by thrombin without inhibiting RhoA activation, whereas expression of the active Akt mutant (m/p) further facilitated TF upregulation by thrombin. Moreover, a dominant-negative Akt mutant (KA) reduced thrombin's effect and did not reverse the rHDL's inhibitory effect on TF expression. Inhibition of eNOS by N(omega)-nitro-L-arginine methyl ester (100 micromol/L) did not affect the rHDL's effect. In conclusion, rHDL inhibits thrombin-induced human endothelial TF expression through inhibition of RhoA and activation of PI3K but not Akt/eNOS. These findings implicate a novel mechanism of antiatherothrombotic effects of HDL.     

神经生长因子对人脐静脉内皮细胞在体外形成管腔样结构的影响

目的探讨神经生长因子(NGF)对人脐静脉内皮细胞(HUVECs)在体外形成管腔样结构(LLSs)的影响及其信号机制。方法将接种在基质胶上的HUVECs分为空白对照组、NGF组、NGF中和抗体组、对照IgG组、NGF中和抗体+NGF组、对照IgG+NGF组,以相差显微镜直接观察LLSs形态,并通过二脒基苯基吲哚/鬼笔环肽免疫荧光染色观察LLSs的细胞组成。为证实NGF促LLSs形成的信号通路,向培养液中分别预先加入丝裂原活化蛋白激酶3个主要信号通路的特异性抑制剂(PD98059、SB203580及SP600125),观察上述3个信号通路对NGF促LLSs形成的影响,并应用Western blot检测NGF及c-Jun N末端激酶(JNK)特异性抑制剂SP600125对HUVECs JNK表达及活性的影响。结果 NGF组LLSs的平均面积较空白对照组明显增加(P<0.01)。NGF中和抗体+NGF组LLSs的平均面积较对照IgG+NGF组明显减少(P<0.01);NGF中和抗体组LLSs的平均面积较对照IgG组亦明显减少(P<0.01)。NGF可激活HUVECs的JNK信号通路,SP600125可显著减少NGF诱导的LLSs形成(P<0.01)。PD98059及SB203580对NGF诱导的LLSs形成均无明显影响(P>0.05)。结论NGF能促进HUVECs在体外形成LLSs,可能与激活JNK信号通路有关。     

Jun N-terminal kinase promotes proliferation of immature erythroid cells and erythropoietin-dependent cell lines

Erythropoietin (EPO) is the hormone necessary for development of erythrocytes from immature erythroid cells. EPO activates Jun N-terminal kinase (JNK), a member of the mitogen-activated protein kinase (MAPK) family in the EPO-dependent murine erythroid HCD57 cells. Therefore, we tested if JNK activity supported proliferation and/or survival of these cells. Treatment with the JNK inhibitor SP600125 inhibited JNK activity and EPO-dependent proliferation of HCD57 cells and the human EPO-dependent cell lines TF-1 and UT7-EPO. SP600125 also increased the fraction of cells in G2/M. Introduction of a dominant-negative form of JNK1 inhibited EPO-dependent proliferation in HCD57 cells but did not increase the fraction of cells in G2/M. Constitutive JNK activity was observed in primary murine erythroid progenitors. Treatment of primary mouse bone marrow cells with the SP600125 inhibitor reduced the number of erythroid burst-forming units (BFU-e's) but not the more differentiated erythroid colony-forming units (CFU-e's), and SP600125 protected the BFU-e's from apoptosis induced by cytosine arabinoside, demonstrating that the SP600125 inhibited proliferation of the BFU-e's. Therefore, JNK activity appears to be an important regulator of proliferation in immature, primary erythroid cells and 3 erythroid cell lines but may not be required for the survival or proliferation of CFU-e's or proerythroblasts.     

The c-Jun-N-terminal-Kinase inhibitor SP600125 enhances the butyrate derivative D1-induced apoptosis via caspase 8 activation in Kasumi 1 t(8;21) acute myeloid leukaemia cells

We recently showed that the histone deacetylase inhibitor D1 induced apoptosis in the t(8;21) Kasumi 1 acute myeloid leukaemia (AML) cell line and activated caspase 9. The present study characterised the effects of the combined administration of D1 with PD98059, SB203580 or SP600125, specific inhibitors of mitogen-activated protein kinase, extracellular signal-regulated kinases 1 and 2 (ERK1/2), p38 or Jun N-terminal kinase (JNK), respectively. Among these inhibitors, SP600125 was the only one to markedly induce apoptosis and decrease cell proliferation. These experiments showed that SP600125 activated caspase 8 and confirmed that D1 activated the intrinsic pathway of apoptosis, as caspase 8 was not affected while Bcl-2 was down-regulated following D1 administration. The combination of the two drugs enhanced caspase-8 activation and induced apoptosis in an additive fashion. JNK was constitutively activated in the Kasumi 1, NB4, HL60 and THP-1 human AML cell lines, as well as in primary blasts from a t(8;21) AML patient. In all these cells, the pro-apoptotic effect of the two drugs alone was increased when they were combined. On this basis, the combined administration of D1 with SP600125 seems to be very promising as a potential anti-leukaemic tool in AML.     

Cross-talk between phosphatidylinositol 3-kinase/AKT and c-jun NH2-terminal kinase mediates survival of isolated human islets

Therapeutic strategies aimed at the inhibition of specific cell death mechanisms may increase islet yield and improve cell viability and function after routine isolation. The aim of the current study was to explore the possibility of AKT-JNK cross-talk in islets after isolation and the relevance of c-jun NH2-terminal kinases (JNK) suppression on islet survival. After routine isolation, increased AKT activity correlated with suppression of JNK activation, suggesting that they may be related events. Indeed, the increase in AKT activation after isolation correlated with suppression of apoptosis signal-regulating kinase 1 (ASK1), a kinase acting upstream of JNK, by phosphorylation at Ser83. We therefore examined whether modulators of phosphatidylinositol 3-kinase (PI3K)/AKT signaling affected JNK activation. PI3K inhibition led to increased JNK phosphorylation and islet cell death, which could be reversed by the specific JNK inhibitor SP600125. In addition, IGF-I suppressed cytokine-mediated JNK activation in a PI3K-dependent manner. We also demonstrate that inhibition of PI3K rendered islets more susceptible to cytokine-mediated cell death. SP600125 transiently protected islets from cytokine-mediated cell death, suggesting that JNK may not be necessary for cytokine-induced cell death. When administered immediately after isolation, SP600125 improved islet survival and function, even 48 h after removal of SP600125, suggesting that JNK inhibition by SP600125 may be a viable strategy for improving isolated islet survival. Taken together, these results demonstrate that PI3K/AKT suppresses the JNK pathway in islets, and this cross-talk represents an important antiapoptotic consequence of PI3K/AKT activation.     

Stress-activated signaling pathways mediate the stimulation of pregnancy-associated plasma protein-A expression in cultured human fibroblasts

Pregnancy-associated plasma protein-A (PAPP-A) is an IGF binding protein protease that appears to function as a posttranslational modulator of IGF bioavailability in response to injury. A previous study indicated that the proinflammatory cytokines, TNFalpha and IL-1beta, were potent stimulators of PAPP-A expression in cultured human fibroblasts. In this study, we investigated the intracellular signaling pathways mediating cytokine-stimulated PAPP-A expression. Treatment of human fibroblasts with TNFalpha and IL-1beta (1 nm) had little or no effect on phosphatidylinositol 3-kinase and Erk1/2 activation, pathways commonly associated with proliferation. On the other hand, TNFalpha and IL-1beta induced p38, c-Jun N-terminal kinase (JNK), and nuclear factor (NF)kappaB activation, pathways more closely related to stress response. An inhibitor of p38 activation (SB203580) had no effect on TNFalpha- or IL-1beta-stimulated PAPP-A expression. The JNK inhibitor, SP600125, had no effect on IL-1beta- or TNFalpha-stimulated PAPP-A mRNA expression. However, SP600125 effectively inhibited IL-1beta-induced PAPP-A protein expression. MG-132, a proteasome inhibitor that blocked degradation of the intrinsic NFkappaB inhibitor, IkappaB, and thereby prevented NFkappaB activation, was a potent inhibitor of both TNFalpha- and IL-1beta-stimulated PAPP-A mRNA and protein expression and IGF binding protein-4 protease activity. MG-132 had no effect on JNK phosphorylation or p38 activation, and SB203580 and SP600125 had no effect on IkappaB degradation, documenting inhibitor specificity. BAY11-7082, another inhibitor of NFkappaB activation, also inhibited TNFalpha- and IL-1beta-stimulated PAPP-A expression and IGF binding protein-4 protease activity. These data indicate that NFkappaB activation is the primary mediator of cytokine-stimulated PAPP-A expression in human fibroblasts.     

S-adenosyl-methionine decreases ethanol-induced apoptosis in primary hepatocyte cultures by a c-Jun N-terminal kinase activity-independent mechanism

AIM:To determine the role of c-Jun N-terminal kinase(JNK)activity in ethanol-induced apoptosis and themodulation of this signaling cascade by S-Adenosyl-methionine(AdoMet).METHODS:Primary hepatocyte cultures werepretreated with 100 μmol/L SP600125,a selective JNKinhibitor,1 mL/L DMSO or 4 mmol/L AdoMet and thenexposed to 100 mmo/L ethanol.Hepatocyte apoptosiswas determined by the TUNEL and DNA ladder assays.JNK activity and its inhibition by SP600125 and AdoMetwere determined by Western blot analysis of c-junphosphorylation and Bid fragmentation.SP600125 andAdoMet effects on the apoptotic signaling pathway weredetermined by Western blot analysis of cytochrome crelease and pro-caspase 3 fragmentation.The AdoMeteffect on glutathione levels was measured by Ellman'smethod and reactive oxygen species(ROS)generationby cell cytometry.RESULTS:The exposure of hepatocytes to ethanolinduced JNK activation,c-jun phosphorylation,Bidfragmentation,cytochrome c release and pro-caspase 3cleavage;these effects were diminished by SP600125,and caused a significant decrease in ethanol-inducedapoptosis(P<0.05).AdoMet exerted an antioxidanteffect maintaining glutathione levels and decreasing ROSgeneration,without a significant effect on JNK activity,and prevented cytochrome c release and pro-caspase 3cleavage. CONCLUSION:The JNK signaling cascade is a keycomponent of the proapoptotic signaling pathwayinduced by ethanol.JNK activation may be independentfrom ROS generation,since AdoMet which exertedantioxidant properties did not have a significant effect onJNK activity.JNK pathway modulator agents and AdoMetmay be components of promising therapies for alcoholicliver disease(ALD)treatment.     

Berberine, a natural lipid-lowering drug, exerts prothrombotic effects on vascular cells

Berberine (BBR) is a novel natural hypolipidemic agent. This study investigates whether BBR, similar to statins, exerts pleiotropic effects on endothelial tissue factor (TF) expression. BBR enhanced tumor necrosis factor-α (TNF-α) and thrombin induced TF expression in human endothelial cells by 3.5-fold. These effects were paralleled by an enhanced TF surface activity. In contrast, expression of TF pathway inhibitor was impaired. BBR enhanced TNF-α induced TF mRNA expression; however, TF promoter activity was inhibited. Activation of ERK and p38 remained unaffected, while c-Jun terminal NH₂ kinase was inhibited. BBR reduced TF mRNA degradation rates, prolonging its half-life from 1.1 to 4.3 h. The HMG-CoA reductase inhibitor simvastatin impaired thrombin induced TF expression, and BBR blunted this inhibition. Simvastatin did not affect TNF-α induced TF expression, and BBR enhanced TF under these conditions. Administration of BBR (100 mg/kg/d) increased TF activity and impaired TFPI expression in carotid artery of ApoE^−/− mice. BBR enhances TF via mRNA stabilization at clinically relevant concentrations. Clinical application of BBR, either as an alternative to or in combination with statins, should be considered with caution.     

Involvement of SAPK/JNK in prostaglandin E(1)-induced VEGF synthesis in osteoblast-like cells

We previously reported that prostaglandin E₁ (PGE₁) activates both p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase via cAMP-dependent protein kinase in osteoblast-like MC3T3-E1 cells, and that p38 MAP kinase but not p42/p44 MAP kinase is involved in PGE₁-induced synthesis of vascular endothelial growth factor (VEGF). In the present study, we investigated the involvement of stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in the PGE₁-induced VEGF synthesis in MC3T3-E1 cells. PGE₁ induced the phosphorylation of SAPK/JNK. SP600125, a specific inhibitor of SAPK/JNK, markedly reduced the PGE₁-induced VEGF synthesis. Forskolin, a direct activator of adenylyl cyclase, elicited the phosphorylation of SAPK/JNK, and 8bromo-cAMP, a plasma membrane-permeable cAMP analogue-stimulated VEGF synthesis was significantly reduced by SP600125. SP600125 suppressed the PGE₁-induced phosphorylation of SAPK/JNK without affecting the phosphorylation of p38 MAP kinase induced by PGE₁. The phosphorylation of c-Jun induced by PGE₁ was also inhibited by SP600125. SB203580, a p38 MAP kinase inhibitor, failed to reduce the PGE₁ induced phosphorylation of SAPK/JNK. A combination of SP600125 and SB203580 suppressed the PGE₁-stimulated VEGF synthesis in an additive manner. These results strongly suggest that PGE₁ activates SAPK/JNK in osteoblasts, and that SAPK/JNK plays a part in PGE₁-induced VEGF synthesis.     

Activation of endothelial cells to pathological status by down-regulation of connexin43

AIMS: We investigated the effects of connexin43 (Cx43) down-regulation on endothelial function. METHODS AND RESULTS: We used two different sequences of Cx43-specific small interference RNA (siRNA) to reduce de novo synthesis of Cx43 in human aortic endothelial cells and then examined the expression profiles, proliferation activity and viability, and angiogenic potential. The involvement of mitogen-activated protein kinase signalling pathways was analysed. In parallel, the effect of inhibition of gap-junctional communication by connexin-mimetic peptides was evaluated. During the down-regulation of Cx43 by the siRNA, the cells exhibited impaired gap-junctional communication, proliferation, viability, and angiogenic potential. In addition, plasminogen activator inhibitor-1 (PAI-1) and von Willebrand factor were up-regulated. Furthermore, c-jun N-terminal kinase (JNK) and its downstream target c-jun were activated, while caspase-3, p38, and extracellular signal-regulated kinase remained unchanged. Inhibition of JNK by SP600125 blocked the siRNA-induced increased expression of PAI-1 and partially recovered the impaired angiogenic potential. Short-term inhibition of Cx43 channels by connexin-mimetic peptides did not activate JNK. CONCLUSION: Down-regulation of Cx43 inhibits gap-junctional communication and activates endothelial cells to pathological status, as characterized by up-regulation of coagulatory molecules and impairment of proliferation, viability, and angiogenesis. The processes are associated with activation of JNK signalling pathways and rectified by inhibition of the activation. These results suggest that inadequate expression of Cx43 per se impairs endothelial function by the activation of stress-activated protein kinase.     

Involvement of stress-activated protein kinase/c-Jun N-terminal kinase in endothelin-1-induced heat shock protein 27 in osteoblasts

OBJECTIVE: We have reported that endothelin-1 (ET-1) activates p38 mitogen-activated protein (MAP) kinase through protein kinase C in osteoblast-like MC3T3-E1 cells, and that p38 MAP kinase plays a role in the ET-1-induced heat shock protein 27 (HSP27). Recently, we found that stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) is activated by ET-1 in these cells. In the present study, we have investigated the involvement of SAPK/JNK in ET-1-induced HSP27 in MC3T3-E1 cells. METHODS: The concentration of HSP27 in soluble extracts of the cells, the expression of mRNA for HSP27, and the phosphorylation of SAPK/JNK were determined by an enzyme immunoassay, Northern blot analysis, and Western blot analysis respectively. RESULTS: SP600125, a specific inhibitor of SAPK/JNK, markedly reduced ET-1-stimulated HSP27 accumulation. The inhibitory effect of SP600125 was dose dependent in the range between 1 and 50 microM. SP600125 reduced the ET-1-increased level of HSP27 mRNA. Calphostin C and Go 6976, inhibitors of protein kinase C, reduced the ET-1-induced phosphorylation of SAPK/JNK. 12-O-Tetradecanoylphorbol-13-acetate, a direct activator of protein kinase C, induced SAPK/JNK phosphorylation, which was suppressed by SP600125. A combination of SP600125 and p38 MAP kinase inhibitor such as SB203580 and PD169316 additively reduced the ET-1-stimulated accumulation of HSP27. CONCLUSIONS: These results strongly suggest that JNK plays a part in ET-1-induced HSP27 in addition to p38 MAP kinase in osteoblasts.