Different Protein Tyrosine Kinases Are Required for B Cell Antigen Receptor–mediated Activation of Extracellular Signal–Regulated kinase,c-Jun NH2-terminal Kinase 1, and p38 Mitogen-activated Protein Kinase

B cell antigen receptor (BCR) cross-linking activates three distinct families of nonreceptor protein tyrosine kinases (PTKs): src-family kinases, Syk, and Btk; these PTKs are responsible for initiating downstream events. BCR cross-linking in the chicken DT40 B cell line also activates three distinct mitogen-activated protein kinases (MAPKs): extracellular signal–regulated kinase (ERK)2, c-jun NH₂-terminal kinase (JNK)1, and p38 MAPK. To dissect the functional roles of these PTKs in MAPK signaling, activation of MAPKs was examined in various PTK-deficient DT40 cells. BCR-mediated activation of ERK2, although maintained in Lyn-deficient cells, was abolished in Syk-deficient cells and partially inhibited in Btk-deficient cells, indicating that BCR-mediated ERK2 activation requires Syk and that sustained ERK2 activation requires Btk. BCR-mediated JNK1 activation was maintained in Lyn-deficient cells but abolished in both Syk- and Btk-deficient cells, suggesting that JNK1 is activated via a Syk- and Btk-dependent pathway. Consistent with this, BCR-mediated JNK1 activation was dependent on intracellular calcium and phorbol myristate acetate–sensitive protein kinase Cs. In contrast, BCR-mediated p38 MAPK activation was detected in all three PTK-deficient cells, suggesting that no single PTK is essential. However, BCR-mediated p38 MAPK activation was abolished in Lyn/Syk double deficient cells, demonstrating that either Lyn or Syk alone may be sufficient to activate p38 MAPK. Our data show that BCR-mediated MAPK activation is regulated at the level of the PTKs.     

Integrin-mediated Ras–Extracellular Regulated Kinase (ERK) Signaling Regulates Interferon γ Production in Human Natural Killer Cells

Recent evidence indicates that integrin engagement results in the activation of biochemical signaling events important for regulating different cell functions, such as migration, adhesion, proliferation, differentiation, apoptosis, and specific gene expression. Here, we report that β1 integrin ligation on human natural killer (NK) cells results in the activation of Ras/mitogen-activated protein kinase pathways. Formation of Shc–growth factor receptor–bound protein 2 (Grb2) and Shc–proline-rich tyrosine kinase 2–Grb2 complexes are the receptor-proximal events accompanying the β1 integrin–mediated Ras activation. In addition, we demonstrate that ligation of β1 integrins results in the stimulation of interferon γ (IFN-γ) production, which is under the control of extracellular signal–regulated kinase 2 activation. Overall, our data indicate that β1 integrins, by delivering signals capable of triggering IFN-γ production, may function as NK-activating receptors.     

Selective activation of the mitogen-activated protein kinase subgroups c-Jun NH2 terminal kinase and p38 by IL-1 and TNF in human articular chondrocytes.

Previous studies suggested that tyrosine kinase activation is an important signal transduction event in the IL-1 response of chondrocytes. The present study identifies the mitogen-activated protein (MAP) kinases extracellular signal-regulated kinase (ERK)-1 and ERK-2 as major tyrosine phosphorylated proteins in IL-1 stimulated chondrocytes. Kinase assays on immunoprecipitates with myelin basic protein as substrate showed that ERK-1 and ERK-2 activation was detectable within 5 min after IL-1 stimulation and decreased to baseline within 60 min. Analysis of other members of the MAP kinase family showed that chondrocytes also express c-Jun NH2 terminal kinase (JNK)-1, JNK-2, and p38 proteins. These kinases were time-dependently activated by IL-1. Among other chondrocyte activators tested, only TNF activated all three of the MAP kinase subgroups. JNK and p38 were not activated by any of the other cytokines and growth factors tested. However, ERK was also activated by PDGF, IGF-1, and IL-6. Phorbol 12-myristate 13-acetate, calcium ionophore, and cAMP analogues only increased ERK activity but had no significant effects on JNK or p38. These results suggest differential activation of MAP kinase subgroups by extracellular stimuli. ERK is activated in response to qualitatively diverse extracellular stimuli and various second messenger agonists. In contrast, JNK and p38 are only activated by IL-1 or TNF, suggesting that these kinases participate in the induction of the catabolic program in cartilage.     

Glucose or diabetes activates p38 mitogen-activated protein kinase via different pathways

Hyperglycemia can cause vascular dysfunctions by multiple factors including hyperosmolarity, oxidant formation, and protein kinase C (PKC) activation. We have characterized the effect of hyperglycemia on p38 mitogen-activated protein (p38) kinase activation, which can be induced by oxidants, hyperosmolarity, and proinflammatory cytokines, leading to apoptosis, cell growth, and gene regulation. Glucose at 16.5 mM increased p38 kinase activity in a time-dependent manner compared with 5.5 mM in rat aortic smooth muscle cells (SMC). Mannitol activated p38 kinase only at or greater than 22 mM. High glucose levels and a PKC agonist activated p38 kinase, and a PKC inhibitor, GF109203X, prevented its activation. However, p38 kinase activation by mannitol or tumor necrosis factor-α was not inhibited by GF109203X. Changes in PKC isoform distribution after exposure to 16.5 mM glucose in SMC suggested that both PKC-β2 and PKC-δ isoforms were increased. Activities of p38 kinase in PKC-δ– but not PKC-β1–overexpressed SMC were increased compared with control cells. Activation of p38 kinase was also observed and characterized in various vascular cells in culture and aorta from diabetic rats. Thus, moderate hyperglycemia can activate p38 kinase by a PKC-δ isoform–dependent pathway, but glucose at extremely elevated levels can also activate p38 kinase by hyperosmolarity via a PKC-independent pathway.     

Impaired Plasma Membrane Targeting of Grb2–Murine Son of Sevenless (mSOS) Complex and Differential Activation of the Fyn–T Cell Receptor (TCR)-ζ–Cbl Pathway Mediate T Cell Hyporesponsiveness in Autoimmune Nonobese Diabetic Mice

Nonobese diabetic (NOD) mouse thymocytes are hyporesponsive to T cell antigen receptor (TCR)-mediated stimulation of proliferation, and this T cell hyporesponsiveness may be causal to the onset of autoimmune diabetes in NOD mice. We previously showed that TCR-induced NOD T cell hyporesponsiveness is associated with a block in Ras activation and defective signaling along the PKC/Ras/MAPK pathway. Here, we report that several sequential changes in TCR-proximal signaling events may mediate this block in Ras activation. We demonstrate that NOD T cell hyporesponsiveness is associated with the (a) enhanced TCR-β–associated Fyn kinase activity and the differential activation of the Fyn–TCR-ζ–Cbl pathway, which may account for the impaired recruitment of ZAP70 to membrane-bound TCR-ζ; (b) relative inability of the murine son of sevenless (mSOS) Ras GDP releasing factor activity to translocate from the cytoplasm to the plasma membrane; and (c) exclusion of mSOS and PLC-γ1 from the TCR-ζ–associated Grb2/pp36–38/ZAP70 signaling complex. Our data suggest that altered tyrosine phosphorylation and targeting of the Grb2/pp36–38/ZAP70 complex to the plasma membrane and cytoskeleton and the deficient association of mSOS with this Grb2-containing complex may block the downstream activation of Ras and Ras-mediated amplification of TCR/CD3-mediated signals in hyporesponsive NOD T cells. These findings implicate mSOS as an important mediator of downregulation of Ras signaling in hyporesponsive NOD T cells.     

Amelioration of hyperglycemic and hyperosmotic induced vascular dysfunction by in vivo inhibition of protein kinase C and p38 MAP kinase pathway in the rat mesenteric microcirculation

BACKGROUND: Recently, we demonstrated in vivo effects of acutely induced hyperglycemia, diabetes and mannitol infusions on rat mesenteric microcirculation concerning leukocyte-endothelial-cell interaction (Sch?ffler et al. EJCI 28: 886-893, 1998). DESIGN: In this study we have investigated the possible involvement of the protein kinase C (PKC) and p38 MAP kinase cascade as signal transducing elements during hyperglycemic and osmotic stress in an in vivo rat model. RESULTS: Acutely induced hyperglycemia resulted in a significant increase in leukocyte adhesion. This effect could be mimicked by mannitol. Both PKC and p38 MAP kinase were involved in the effects mediated by glucose and mannitol. Acutely induced hyperglycemia resulted in a significant increase in leukocyte emigration. This effect could be imitated by mannitol. However, PKC and p38 MAP kinase were only involved under osmotic stimulation. The hyperglycemia-induced reduction in leukocyte rolling velocity seemed to be a glucose-specific effect, since mannitol did not influence leukocyte rolling velocity. This glucose effect on leukocyte rolling velocity was mediated by an activation of the PKC/p38 MAP kinase cascade. Both hyperglycemia and osmotic stimuli alone were able to reduce venular shear rate without recruitment of the p38 MAP kinase cascade. The observed reduction of shear rate seems to be mediated only by the osmotic effects of glucose via activation of the PKC system. CONCLUSION: The observed effects of glucose on adhesion, emigration and shear rate are due to osmotic effects. The PKC/MAP kinase cascade is involved as a signal transducing component. The reduction of leukocyte rolling velocity is a glucose-specific effect, mediated by the activation of both the PKC and the p38 MAP kinase cascade. Venular shear rate and leukocyte emigration can be influenced by glucose and mannitol due to different regulation mechanisms. It is concluded, that isoform-specific inhibitors of PKC and specific MAP kinase inhibitors represent a potential drug target for preventing microvascular dysfunction in diabetes.     

丝裂素活化蛋白激酶途径在缺氧复合烧伤血清致心肌细胞损伤中的作用

目的　观察缺氧复合烧伤血清对心肌细胞丝裂素活化蛋白激酶 (MAPKs)活化的影响 ,探讨MAPKs信号途径在缺氧复合烧伤血清致心肌细胞损伤中的作用。方法　乳鼠心肌细胞原代培养 ,缺氧复合烧伤血清作用心肌细胞后不同时间点用免疫印迹化学发光法检测 p38激酶、细胞外信号调节激酶 (ERK)和c Jun氨基末端蛋白激酶 (JNK)磷酸化程度 ;分别用 p38激酶特异抑制剂 SB2 0 35 80和 ERK特异抑制剂PD980 5 9抑制 p38激酶和 ERK途径 ,观察其对缺氧复合烧伤血清培养条件下心肌细胞活性和培养上清中乳酸脱氢酶 (L DH)含量的影响。结果　心肌细胞 p38激酶和 ERK在缺氧复合烧伤血清作用后迅速、持续活化 ,而 JNK活化不明显。用 SB2 0 35 80抑制 p38激酶可显著减少细胞 L DH漏出 (各时间点 P<0 .0 5或 P<0 .0 1)和改善细胞活性 (双因素作用 12 h后 ,两者间比较 ,P均 <0 .0 1) ;相反 ,抑制 ERK途径在一定程度上增加了细胞 L DH漏出和降低细胞活性 (双因素作用 6 h和 12 h,两者间比较 ,P均 <0 .0 1)。结论　心肌细胞 MAPKs的 3条信号转导途径中 ,p38激酶途径和 ERK途径介导了缺氧复合烧伤血清刺激信号的胞内转导。其中 p38激酶途径激活介导了心肌细胞的损伤效应 ,而 ERK途径激活则有一定的细胞保护作用。     

Anti-invasive activity of α-tocopherol against hepatoma cells in culture via protein kinase C inhibition

Effects of α-, β-, γ- and δ-tocopherols on the proliferation and invasion of AH109A hepatoma cells and their modes of action were investigated. Four tocopherols inhibited the invasion as well as the proliferation of AH109A cells. Their inhibitory effects were more prominent on the invasion than on the proliferation. At 1 µM, α-tocopherol showed most potent anti-invasive activity without any influence on the proliferation. We have previously demonstrated that reactive oxygen species increase the invasion of AH109A cells. α-Tocopherol suppressed the reactive oxygen species-induced invasion but failed to suppress the reactive oxygen species-induced rises in intracellular peroxide level. GF 109203X, a protein kinase C inhibitor, decreased the invasive activity of AH109A cells. In contrast, phorbol-12-myristate-13-acetate, a protein kinase C activator, increased the invasive capacity of AH109A cells. α-Tocopherol suppressed the phorbol-12-myristate-13-acetate-induced increase in the invasion, and canceled the phorbol-12-myristate-13-acetate-induced rises in protein kinase C activity and phosphorylation of extracellular signal-regulated kinase. These results suggest that tocopherols, especially α-tocopherol, possess inhibitory effect more strongly on the invasion of AH109A cells than on the proliferation. They also suggest that the anti-invasive activity of α-tocopherol is raised through suppression of PKC/ERK signaling.     

The JNK Pathway Regulates the In Vivo Deletion of Immature CD4+CD8+ Thymocytes

The extracellular signal-regulated kinase (ERK), the c-Jun NH₂-terminal kinase (JNK), and p38 MAP kinase pathways are triggered upon ligation of the antigen-specific T cell receptor (TCR). During the development of T cells in the thymus, the ERK pathway is required for differentiation of CD4⁻CD8⁻ into CD4⁺CD8⁺ double positive (DP) thymocytes, positive selection of DP cells, and their maturation into CD4⁺ cells. However, the ERK pathway is not required for negative selection. Here, we show that JNK is activated in DP thymocytes in vivo in response to signals that initiate negative selection. The activation of JNK in these cells appears to be mediated by the MAP kinase kinase MKK7 since high levels of MKK7 and low levels of Sek-1/MKK4 gene expression were detected in thymocytes. Using dominant negative JNK transgenic mice, we show that inhibition of the JNK pathway reduces the in vivo deletion of DP thymocytes. In addition, the increased resistance of DP thymocytes to cell death in these mice produces an accelerated reconstitution of normal thymic populations upon in vivo DP elimination. Together, these data indicate that the JNK pathway contributes to the deletion of DP thymocytes by apoptosis in response to TCR-derived and other thymic environment– mediated signals.     

MAP Kinase cross talks in oxidative stress‐induced impairment of insulin secretion. Involvement in the protective activity of quercetin

Insulin secretion preservation is a major issue for the prevention or treatment of type 2 diabetes. We previously showed on β‐cells that quercetin (Q), but not resveratrol (R) or N‐acetyl cysteine (NAC), amplified glucose‐induced insulin secretion in a calcium‐ and ERK1/2‐dependent manner. Quercetin, but not resveratrol or NAC, also protected β‐cell function and hyperamplified ERK1/2 phosphorylation in oxidative stress conditions. As quercetin may interfere with other stress‐activated protein kinases (JNK and p38 MAPK), we further explored MAPK cross talks and their relationships with the mechanism of the protective effect of quercetin against oxidative stress. In INS‐1 insulin‐secreting β‐cells, using pharmacological inhibitors of MAPK pathways, we found that under oxidative stress (50 μm H₂O₂) and glucose‐stimulating insulin secretion conditions: (i) p38 MAPK phosphorylation was increased and regulated by ERK1/2 (positively) and JNK (negatively), although p38 MAPK activation did not seem to play any significant role in oxidative stress‐induced insulin secretion impairment; (ii) the JNK pathway appeared to inhibit both ERK1/2 activation and insulin secretion, although JNK phosphorylation was not significantly changed in our experimental conditions; (iii) the functionality of β‐cell in the presence of oxidative stress was closely linked to the level of ERK1/2 activation, (iv) quercetin, resveratrol, or NAC inhibited H₂O₂‐induced p38 MAPK phosphorylation. The preservation of β‐cell function against oxidative stress appears dependent on the balance between ERK1/2 and JNK activation. The protecting effect of quercetin appears due to ERK1/2 hyperactivation, possibly induced by L‐type calcium channel opening as we recently showed (Br. J. Pharmacol. 2013, 169, 1102–1113).     

Protein kinase C and extracellular signal regulated kinase are involved in cardiac hypertrophy of rats with progressive renal injury

Increased cardiovascular mortality is an unresolved problem in patients with chronic renal failure. Cardiac hypertrophy is observed in the majority of patients with chronic renal failure undergoing haemodialysis. However, the mechanisms, including signal transduction pathways, responsible for cardiac hypertrophy in renal failure remain unknown. We examined the subcellular localization of protein kinase C (PKC) isoforms and phosphorylation activities of 3 mitogen-activated protein (MAP) kinase families in hypertrophied hearts of progressive renal injury rat model by subtotal nephrectomy (SNx). We also examined the effects of a novel angiotensin II type-1 receptor antagonist, CS-866, on the PKC translocation, MAP kinase activity and cardiac hypertrophy in SNx rats. The left ventricle/body weight ratios were significantly larger in SNx rats than in sham rats at 1, 2, and 4 weeks after surgery. The translocation of PKCalpha and epsilon isoforms to membranous fraction was observed in SNx rat hearts at 1, 2, and 4 weeks after surgery. Activation of extracellular signal regulated kinase (ERK) 1/2, but not p38 MAP kinase and c-Jun N-terminal kinase (JNK), was observed at 1 and 2 weeks after surgery. Angiotensin II receptor blockade with CS-866 (1 mg kg-1 day-1) prevented cardiac hypertrophy, PKC translocation and ERK1/2 activation in SNx rats without significant changes in blood pressure. These data suggest that PKC and ERK1/2 are activated by an angiotensin II receptor-mediated pathway and might play an important role in the progression of cardiac hypertrophy in renal failure.     

Up-regulation of vascular and renal mitogen-activated protein kinases in hypertensive rats is normalized by inhibitors of the Na+/Mg2+ exchanger

In the present in vivo study, we have investigated whether inhibitors of the Na(+)/Mg(2+) exchanger quinidine and imipramine influence the development of hypertension and whether this is associated with modulation of mitogen-activated protein (MAP) kinase activation in arteries and kidneys of hypertensive rats. Sprague-Dawley rats were divided into four groups (n =6/group): control (vehicle), angiotensin II (Ang II; 150 ng/kg of body weight per min subcutaneously), quinidine [Ang II (150 ng/kg of body weight per min)+quinidine (5 mg/kg of body weight per day in food)] and imipramine groups [Ang II (150 ng/kg of body weight per min)+imipramine (5 mg/kg/day in food)]. Rats were studied for 3 weeks. Phosphorylation of vascular and renal extracellular-signal-regulated protein kinase 1/2 (ERK1/2), p38MAP kinase and c-Jun N-terminal kinase (JNK) were assessed using phospho-specific antibodies. Ang II increased systolic blood pressure from 112+/-5 mmHg to 215+/-9 mmHg ( P <0.01). Development of hypertension was attenuated in Ang II-infused rats treated with quinidine (173+/-6 mmHg) and imipramine (152+/-6 mmHg) (P <0.01). Phosphorylation of ERK1/2, p38MAP kinase and JNK, which were increased 2-3-fold in arteries of the Ang II group, were reduced by quinidine and imipramine (P <0.05). Activation of renal MAP kinases was also increased in the Ang II group (P <0.05). Quinidine and imipramine reduced the phosphorylation of renal ERK1/2, but did not modify renal p38MAP kinase or JNK. Our data demonstrate that Ang II induces severe hypertension in Sprague-Dawley rats and this is associated with increased phosphorylation of vascular and renal MAP kinases. Quinidine and imipramine attenuated the development of hypertension and normalized MAP kinase activity. The findings from this study suggest a possible role for the Na(+)/Mg(2+) exchanger in vascular signalling events associated with blood pressure elevation in Ang II-dependent hypertension.     

Hydrogen peroxide-induced extracellular signal-regulated kinase activation in cultured feline ileal smooth muscle cells

H(2)O(2) has been shown to act as a signaling molecule involved in many cellular functions such as apoptosis and proliferation. In the present study, we characterized the effects of H(2)O(2) on the activation of mitogen-activated protein (MAP) kinases and examined the factors involved in the process of extracellular signal-regulated kinase (ERK) activation by H(2)O(2) in ileal smooth muscle cells (ISMC). ISMC were cultured and exposed to H(2)O(2). Western blot analysis was performed with phosphospecific MAP kinase antibodies. Potent activation of ERK and moderate activation of stress-activated protein kinase/c-Jun NH(2)-terminal kinase occurred within 30 min of 1 mM H(2)O(2) treatment. However, p38 MAP kinase was not activated by H(2)O(2). The activation of ERK by H(2)O(2) was reduced by the mitogen-activated/ERK-activating kinase inhibitor PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one], Ras inhibitor S-farnesylthiosalicylic acid, removal of extracellular Ca(2+), depletion of the intracellular Ca(2+) pool by thapsigargin, or pretreatment of ISMC with the calmodulin antagonist W-7. Also, H(2)O(2)-induced ERK activation was attenuated by a receptor tyrosine kinase inhibitor, tyrphostin 51, but not by down-regulation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate or by a PKC inhibitor, GF109203X [3-[1-(dimethylaminopropyl)indol-3-yl]-4-(indol-3-yl)maleimide hydrochloride]. Growth factor receptor antagonist suramin pretreatment inhibited H(2)O(2)-induced ERK activation, highlighting a role for growth factor receptors in this activation. Furthermore, the ERK activation by H(2)O(2) was blocked by pretreatment with either N-acetyl-cysteine, o-phenanthroline, or mannitol indicating that metal-catalyzed free radical formation may mediate the initiation of signal transduction by H(2)O(2). These data suggest that short-term stimulation with H(2)O(2) activates the signaling pathways of cell mitogenic effects which are thought to be a protective response against intestinal oxidative stress.