Roles of mitogen-activated protein kinases and protein kinase C in alpha(1A)-adrenoceptor-mediated stimulation of the sarcolemmal Na(+)-H(+) exchanger

Activation of the sarcolemmal Na(+)-H(+) exchanger (NHE) has been implicated as a mechanism of inotropic, arrhythmogenic, antiacidotic, and hypertrophic effects of alpha(1)-adrenoceptor (AR) stimulation. Although such regulation of sarcolemmal NHE activity has been shown to be selectively mediated through the alpha(1A)-AR subtype, distal signaling mechanisms remain poorly defined. We investigated the roles of various kinase pathways in alpha(1A)-AR-mediated stimulation of sarcolemmal NHE activity in adult rat ventricular myocytes. As an index of NHE activity, trans-sarcolemmal acid efflux rate (J(H)) was determined through microepifluorescence in single cells, during recovery from intracellular acidosis in bicarbonate-free conditions. Extracellular signal-regulated kinase (ERK), p38-mitogen-activated protein kinase (MAPK), and p90(rsk) activities were indexed on the basis of analysis of their phosphorylation status. In control cells, there was no change in J(H) in response to vehicle. Phenylephrine and A61603, an alpha(1A)-AR subtype-selective agonist, increased J(H), as well as cellular ERK and p90(rsk) activities. Neither agonist affected p38 activity, which was increased with sorbitol. The MAPK kinase inhibitor PD98059 abolished phenylephrine- and A61603-induced increases in J(H) and cellular ERK and p90(rsk) activities. In contrast, the PKC inhibitor GF109203X abolished phenylephrine- and A61603-induced increases in J(H) but failed to prevent the increases in ERK and p90(rsk) activities. Our findings suggest that alpha(1A)-AR-mediated stimulation of sarcolemmal NHE activity in rat ventricular myocytes requires activation of the ERK (but not the p38) pathway of the MAPK cascade and that the ERK-mediated effect may occur via p90(rsk). Activation of PKC is also required for alpha(1A)-AR-mediated NHE stimulation, but such regulation occurs through an ERK-independent pathway.     

Ghrelin inhibits hydrogen peroxide-induced apoptotic cell death of oligodendrocytes via ERK and p38MAPK signaling

Here, we examined the protective effect of ghrelin on apoptotic cell death induced by hydrogen peroxide (H?O?) in primary oligodendrocyte cultures. Ghrelin receptor, growth hormone secretagogue receptor 1a, was expressed in mature oligodendrocytes. H?O? (1 mm) treatment induced apoptotic cell death of oligodendrocytes, which was significantly inhibited by ghrelin treatment. Ghrelin also reduced cytochrome c release, and caspase-3 activation increased by H?O? treatment. Furthermore, the protective effect of ghrelin against H?O?-induced oligodendrocyte cell death was mediated through growth hormone secretagogue receptor 1a. Both ERK and p38MAPK were activated (peaked at 8 h in ERK and 1 h in p38MAPK) by H?O? treatment, whereas c-Jun N-terminal kinase and Akt were not. Interestingly, ghrelin further increased ERK activation and decreased p38MAPK activation after H?O? treatment. Next, we tried to elucidate the role of ERK and p38MAPK activation in H?O?-induced apoptotic cell death of oligodendrocytes using pharmacological inhibitors. We found that the inhibition of apoptotic cell death of oligodendrocytes by ghrelin was abolished by ERK inhibitor, PD98059 (20 μM), whereas cell survival was increased by p38MAPK inhibitor, SB203580 (10 μM). These results thus indicate that ghrelin inhibits H?O? -induced oligodendrocytes cell death in part by increasing ERK activation and decreasing p38MAPK activation, and ghrelin may represent a potential therapeutic agent for protecting oligodendrocytes in central nervous system injuries.     

H(2)O(2) regulates cardiac myocyte phenotype via concentration-dependent activation of distinct kinase pathways

Reactive oxygen species (ROS) can act as signaling molecules to stimulate either hypertrophy or apoptosis in cardiac myocytes. We tested the hypothesis that the phenotypic effects of ROS are due to differential, concentration-dependent activation of specific kinase signaling pathways. Adult rat ventricular myocytes were exposed to H(2)O(2) over a broad concentration range (10-1000 microM). Low concentrations of H(2)O(2) (10-30 microM) increased protein synthesis without affecting survival. Higher concentrations of H(2)O(2) (100-200 microM) increased apoptosis (assessed by TUNEL). Still higher concentrations of H(2)O(2) (300-1000 microM) caused both apoptosis and necrosis. A hypertrophic concentration of H(2)O(2) (10 microM) increased the activity of ERK1/2, but not that of JNK, p38 kinase or Akt. An apoptotic concentration of H(2)O(2) (100 microM) activated JNK, p38 kinase and Akt, and further activated ERK1/2. The MEK1/2 inhibitor U0126 prevented the hypertrophic effect of 10 microM H(2)O(2). The apoptotic effect of 100 microM H(2)O(2) was inhibited bya dominant-negative JNK adenovirus, and was potentiated by U0126 or an Akt inhibitor. Thus, the concentration-dependent effects of ROS on myocyte hypertrophy and growth are due, at least in part, to the differential activation of specific kinase signaling pathways that regulate hypertrophy and apoptosis.     

Extracellular signal-regulated kinase and p38 mitogen-activated protein kinase mediate macrophage proliferation induced by oxidized low-density lipoprotein

We previously reported that oxidized low-density lipoprotein (Ox-LDL)-induced expression of granulocyte/macrophage colony-stimulating factor (GM-CSF) via PKC, leading to activation of phosphatidylinositol-3 kinase (PI-3K), was important for macrophage proliferation [J Biol Chem 275 (2000) 5810]. The aim of the present study was to elucidate the role of extracellular-signal regulated kinase 1/2 (ERK1/2) and of p38 MAPK in Ox-LDL-induced macrophage proliferation. Ox-LDL-induced proliferation of mouse peritoneal macrophages assessed by [3H]thymidine incorporation and cell counting assays was significantly inhibited by MEK1/2 inhibitors, PD98059 or U0126, and p38 MAPK inhibitors, SB203580 or SB202190, respectively. Ox-LDL-induced GM-CSF production was inhibited by MEK1/2 inhibitors but not by p38 MAPK inhibitors in mRNA and protein levels, whereas recombinant GM-CSF-induced macrophage proliferation was inhibited by p38 MAPK inhibitors but enhanced by MEK1/2 inhibitors. Recombinant GM-CSF-induced PI-3K activation and Akt phosphorylation were significantly inhibited by SB203580 but enhanced by PD98059. Our results suggest that ERK1/2 is involved in Ox-LDL-induced macrophage proliferation in the signaling pathway before GM-CSF production, whereas p38 MAPK is involved after GM-CSF release. Thus, the importance of MAPKs in Ox-LDL-induced macrophage proliferation was confirmed and the control of MAPK cascade could be targeted as a potential treatment of atherosclerosis.     

MEK1/2-ERK1/2 mediates alpha1-adrenergic receptor-stimulated hypertrophy in adult rat ventricular myocytes

We examined the relative roles of the mitogen-activated protein kinases (MAPK) in mediating the alpha1-adrenergic receptor (alpha1-AR) stimulated hypertrophic phenotype in adult rat ventricular myocytes (ARVM). Norepinephrine (NE; 1 microM) in the presence of the beta -AR antagonist propranolol (Pro; 2 microM) caused activation of Ras (>six-fold), MAPK/ERK kinase 1 and 2 (MEK1/2, >10-fold) and extracellular signal-regulated kinases 1 and 2 (ERK1/2, approximately 30-fold) within 5 min, as determined by kinase activity assays and Western blots using phospho-specific antibodies. Conversely, p38 and c-Jun amino-terminal kinases (JNK) were not activated by NE/Pro. Activated MEK1/2 signals remained detectable at 2 h, and activated ERK1/2 remained detectable at 48 h. The alpha1-AR selective inhibitor prazosin (100 nM) completely inhibited the NE/Pro-stimulated activation of Ras, MEK1/2 and ERK1/2. The MEK inhibitor PD98059 caused a concentration-dependent inhibition of NE/Pro-stimulated protein synthesis (as assessed by [3H]leucine incorporation and cellular protein accumulation) and ERK1/2 activation, with approximately 50% inhibition at a concentration between 10 and 50 microM, which is consistent with the known IC50 values of PD98059 for MEK1 (4 microM) and MEK2 (50 microM). Thus, these data show that alpha1-AR stimulated hypertrophy in ARVM is dependent on the MEK1/2-ERK1/2 signaling pathway.     

Mitogen-activated protein kinase activation by hydrogen peroxide is mediated through tyrosine kinase-dependent, protein kinase C-independent pathways in vascular smooth muscle cells: upregulation in spontaneously hypertensive rats

OBJECTIVE: To investigate the putative molecular mechanisms underlying mitogen-activated protein (MAP) kinase activation by hydrogen peroxide (H(2)O(2)) in vascular smooth muscle cells (VSMC) and to evaluate whether H(2)O(2)-induced actions are altered in VSMC from spontaneously hypertensive rats (SHR). METHOD: VSMC from mesenteric arteries of Wistar-Kyoto rats (WKY) and SHR were stimulated with H(2)O(2) (2-30 min). The phosphorylation of extracellular signal-regulated kinases (ERK)1/2 and p38MAP kinase was determined by immunoblotting. The involvement of tyrosine kinase and protein kinase C (PKC) was evaluated using pharmacological inhibitors, tyrphostin (A23 and A9) and GF109203X, respectively. The role of receptor tyrosine kinases (RTK) was assessed with AG1478, AG1296 and AG1024, selective inhibitors of epidermal growth factor receptor, platelet-derived growth factor receptor and insulin-like growth factor receptor, respectively. Non-receptor tyrosine kinases (NRTK) were studied using AG490 (JAK2 inhibitor) and PP2 (Src inhibitor). RESULTS: H(2)O(2) stimulated phosphorylation of ERK1/2 and p38MAP kinase in a time-dependent manner. This increase was significantly greater in SHR versus WKY (P < 0.01). The activation of MAP kinases was unaffected by GF109203X but was decreased by tyrphostins (P < 0.01). The inhibition of NRTK attenuated H(2)O(2)-mediated phosphorylation of ERK1/2 (P < 0.001) but not of p38MAP kinase, whereas Src and JAK2 inhibition significantly decreased phosphorylation of both MAP kinases (P < 0.01). CONCLUSION: These data indicate that H(2)O(2) increases ERK1/2 and p38MAP kinase activation through tyrosine kinase-dependent, PKC-independent mechanisms. Whereas ERK1/2 is regulated by both RTK and NRTK, p38MAP kinase is regulated by NRTK. Our findings identify an important role for tyrosine kinases, but not PKC, in H(2)O(2)-induced phosphorylation of ERK1/2 and p38MAP kinase in VSMC. The upregulation of these processes may contribute to enhanced redox-dependent MAP kinase signaling in SHR VSMC.     

Survival function of ERK1/2 as IL-3-activated, staurosporine-resistant Bcl2 kinases

Bcl2 phosphorylation at Ser-70 may be required for the full and potent suppression of apoptosis in IL-3-dependent myeloid cells and can result from agonist activation of mitochondrial protein kinase C (PKC). Paradoxically, expression of exogenous Bcl2 can protect parental cells from apoptosis induced by the potent PKC inhibitor, staurosporine (stauro). High concentrations of stauro of up to 1 microM only partially inhibit IL-3-stimulated Bcl2 phosphorylation but completely block PKC-mediated Bcl2 phosphorylation in vitro. These data indicate a role for a stauro-resistant Bcl2 kinase (SRK). We show that aurintricarboxylic acid (ATA), a nonpeptide activator of cellular MEK/mitogen-activated protein kinase (MAPK) kinase, can induce Ser-70 phosphorylation of Bcl2 and support survival of cells expressing wild-type but not the phosphorylation-incompetent S70A mutant Bcl2. A role for a MEK/MAPK as a responsible SRK was implicated because the highly specific MEK/MAPK inhibitor, PD98059, also can only partially inhibit IL-3-induced Bcl2 phosphorylation, whereas the combination of PD98059 and stauro completely blocks phosphorylation and synergistically enhances apoptosis. p44MAPK/extracellular signal-regulated kinase 1 (ERK1) and p42 MAPK/ERK2 are activated by IL-3, colocalize with mitochondrial Bcl2, and can directly phosphorylate Bcl2 on Ser-70 in a stauro-resistant manner both in vitro and in vivo. These findings suggest a role for the ERK1/2 kinases as SRKs. Thus, the SRKs can serve to functionally link the IL-3-stimulated proliferative and survival signaling pathways and, in a novel capacity, may explain how Bcl2 can suppress stauro-induced apoptosis. In addition, although the mechanism of regulation of Bcl2 by phosphorylation is not yet clear, our results indicate that phosphorylation may functionally stabilize the Bcl2-Bax heterodimerization.     

Noradrenaline-induced paxillin phosphorylation, ERK activation and MEK-regulated contraction in intact rat mesenteric arteries

In rat mesenteric arteries, noradrenaline (NA) induces a time-dependent increase in tyrosine phosphorylation of a number of proteins, one of which was identified as paxillin. NA-induced protein tyrosine phosphorylation was ablated by tyrosine kinase inhibition, virtually unaffected by protein kinase C (PKC) inhibition or PKC downregulation and was mimicked by KCl. NA also caused a time-dependent activation of the extracellular signal-regulated kinases (ERK)1 and ERK2. These responses were blocked by the ERK-activating kinase (MEK) inhibitor PD98059 and by tyrosine kinase inhibition but only modestly attenuated by PKC downregulation or inhibition. Pretreatment of cannulated mesenteric arteries (50 mm Hg internal pressure) with PD98059 significantly reduced the contractile responsiveness of the vessels to NA (1.56 +/- 0.14 microM, EC(50) control; 3.32 +/- 0.49 microM, EC(50) + PD98059, p < 0.01). Thus, NA induces time-dependent increases in protein-tyrosine phosphorylation and ERK activation in rat mesenteric arteries that could suggest a role for Ca(2+)-dependent non-receptor tyrosine kinases and ERKs in the response of small arteries to NA. In addition, the modulation of NA-induced mesenteric artery contraction by inhibition of the MEK/ERK pathway further implicates ERK in the regulation of, though perhaps not the mediation of NA-induced small artery contraction.     

Role of cyclooxygenase 2, p38 and p42/44 MAPK in the secretion of prostacyclin induced by epidermal growth factor,endothelin-1 and angiotensin II in rat ventricular cardiomyocytes

We studied the respective roles of cyclooxygenases (COX) isoforms as well as the p38 and p42/44 MAP kinase cascades in angiotensin II (AngII)-, endothelin-1 (ET-1)- and epidermal growth factor (EGF)-induced prostacyclin (PGI(2)) secretion in neonatal rat ventricular cardiomyocytes. Exposure of these cells for 1 h to 100 nM AngII, ET-1 or EGF resulted in an increase in prostacyclin formation which was abolished by the COX-2 specific inhibitor NS-398 (1 microM), while the COX-1 inhibitor valeryl salicylate (5 microM) had no effect. Agonist-induced prostacyclin secretion was also abolished in the presence of cycloheximide (10 microg/ml), indicating that newly synthesized proteins are necessary for this response. In this context, the COX-2 protein amount was significantly increased following 1 h incubation of cardiomyocytes, with AngII, ET-1 and EGF. These results indicate that in cardiomyocytes AngII, ET-1 and EGF induce both the synthesis and the activity of COX-2. Investigating the role of MAPK in the stimulation of prostacyclin induced by these three agonists, we found that both the p42/44 MAPK inhibitor PD 98059 (50 microM) and the p38 MAPK blocker SB 203580 (5 microM) prevented agonist-induced PGI(2) secretion without affecting COX-2 activity or synthesis. Our results show that p42/44 and p38 MAPK activation is at the basis of AngII-, ET-1- and EGF-induced prostacyclin secretion in cardiomyocytes. They further suggest that these MAPK act on a target(s) located upstream of COX-2.     

Inhibition of extracellular signal-regulated kinase enhances Ischemia/Reoxygenation-induced apoptosis in cultured cardiac myocytes and exaggerates reperfusion injury in isolated perfused heart

Three major mammalian mitogen-activated protein kinases, extracellular signal-regulated kinase (ERK), p38, and c-Jun NH(2)-terminal protein kinase (JNK), have been identified in the cardiomyocyte, but their respective roles in the heart are not well understood. The present study explored their functions and cross talk in ischemia/reoxygenation (I/R)-induced cardiac apoptosis. Exposing rat neonatal cardiomyocytes to ischemia resulted in a rapid and transient activation of ERK, p38, and JNK. On reoxygenation, further activation of all 3 mitogen-activated protein kinases was noted; peak activities increased (fold) by 5.5, 5.2, and 6.2, respectively. Visual inspection of myocytes exposed to I/R identified 18.6% of the cells as showing morphological features of apoptosis, which was further confirmed by DNA ladder and terminal deoxyribonucleotide transferase-mediated dUTP nick end labeling (TUNEL). Myocytes treated with PD98059, a MAPK/ERK kinase (MEK1/MEK2) inhibitor, displayed a suppression of I/R-induced ERK activation, whereas p38 and JNK activities were increased by 70.3% and 55.0%, respectively. In addition, the number of apoptotic cells was increased to 33.4%. With pretreatment of cells with SB242719, a selective p38 inhibitor, or SB203580, a p38 and JNK2 inhibitor, I/R+PD98059-induced apoptotic cells were reduced by 42.8% and 63.3%, respectively. Hearts isolated from rats treated with PD98059 and subjected to global ischemia (30 minutes)/reoxygenation (1 hour) showed a diminished functional recovery compared with the vehicle group. Coadministration of SB203580 attenuated the detrimental effects of PD98059 and significantly improved cardiac functional recovery. The data taken together suggest that ERK plays a protective role, whereas p38 and JNK mediate apoptosis in cardiomyocytes subjected to I/R, and the dynamic balance of their activities is critical in determining cardiomyocyte fate subsequent to reperfusional injury.     

Preptin对人成骨细胞增殖和分化的影响及机制研究

目的 探讨preptin对人成骨细胞增殖和分化的影响及其信号途径.方法 体外培养人成骨细胞,用10-10、10-9、10-8和10-7mol/L preptin干预24 h,以[3H]脱氧胸腺嘧啶苷掺入法分析细胞增殖,用分光光度计法测定细胞碱性磷酸酶(ALP)活性判断细胞分化程度.Western印迹法检测细胞外信号调节激酶(ERK)、p38丝裂原活化蛋白激酶(p38MAPK)和c-Jun氨基末端激酶(JNK)的磷酸化水平.并在preptin干预前以ERK抑制剂(PD98059)、p38 MAPK抑制剂(SB203580)和JNK抑制剂(SP600125)预处理,观察preptin诱导人成骨细胞增殖和分化的途径.结果 Preptin剂量依赖地增加人成骨细胞的增殖和ALP活性,10-9mol/L浓度时达最大效应(均P<0.01).Preptin刺激人成骨细胞ERK的磷酸化,对p38MAPK和JNK无作用.PD98059阻断preptin刺激的成骨细胞增殖及ALP活性增加(均P<0.05),而SP600125和SB203580无此效应.结论 Preptin通过ERK途径促进人成骨细胞的增殖和分化.     

Intermittent hypoxia-induced delayed cardioprotection is mediated by PKC and triggered by p38 MAP kinase and Erk1/2

We previously reported that acute intermittent hypoxia (IH) confers delayed cardioprotection against a prolonged ischemic insult in the rat, via the involvement of nitric oxide synthase and K(ATP) channels. In the present study, we investigated the role of protein kinase C (PKC), phosphatidylinositol-3-kinase (PI3K), stress activated p38 MAP kinase (MAPK) and extracellular signal-regulated kinase (ERK1/2) using selective inhibitors of these pathways. Adult male rats were exposed to 1-min cycles of IH (10% O(2), 40 s)/normoxia (21% O(2), 20 s) during 4 h or to normoxic cycles. 24 h later, isolated hearts were perfused in Langendorff mode and subjected to a 30-min global ischemia followed by 120 min of reperfusion. Compared to normoxic conditions, IH significantly reduced infarct size (22.2+/-2.4% vs. 33.8+/-2.6%, p<0.05), improved coronary flow and decreased the contracture at reperfusion. When administered before sustained ischemia, chelerythrine (a PKC inhibitor) abolished both the IH-induced reduction in infarct size (36.1+/-4.9%) and improvement in hemodynamic parameters. In contrast, chelerythrine administration 10 min before IH, did not modify the delayed cardioprotective response. Similarly, wortmannin (a PI3K inhibitor) administration 10 min before IH was unable to block the cardioprotective effects. However, administration of SB203580 (a p38 MAPK inhibitor) and PD98059 (an Erk1/2 inhibitor), 30 min before IH abolished its delayed infarct-sparing effect (32.2+/-3.4% and 33.9+/-2.9%, respectively). In addition, 24 h after IH, a significant increase in p38 MAPK and Erk1/2 phosphorylation was observed by Western blot. These results suggest that the delayed preconditioning induced by intermittent hypoxia does not involve the PI3K signalling pathway and that is mediated by PKC and triggered by p38 MAPK and Erk1/2.     

Extracellular signal-regulated protein kinase, but not c-Jun N-terminal kinase, is activated by type II gonadotropin-releasing hormone involved in the inhibition of ovarian cancer cell proliferation

Although a novel second form of GnRH (GnRH-II) has been reported to have an antiproliferative effect on gynecologic cancer cells, its biological mechanism remains to be elucidated. We have previously demonstrated that GnRH-II activates p38 MAPK. There is accumulating evidence that activation of MAPKs by GnRH-I and -II is important for cell proliferation, differentiation, and apoptosis. In the present study, we further investigated the involvement of GnRH-II in the inhibition of cell proliferation and activation of ERK1/2 and c-Jun N-terminal protein kinase/stress-activated protein kinase (JNK/SAPK) in ovarian cancer cells, OVCAR-3. The [(3)H]thymidine incorporation and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays revealed that treatment with GnRH-II suppresses cell proliferation of ovarian cancer cells. Western blot analysis demonstrated that ERK1/2 was activated by GnRH-II (100 nm). Moreover, PD98059 (10 mum), an inhibitor of a MAPK/ERK kinase, reversed the activation of ERK1/2 induced by GnRH-II. The activation of ERK1/2 by GnRH-II subsequently phosphorylated Elk-1 as a downstream pathway, which was blocked by PD98059. On the other hand, it is not likely that GnRH-II activates the JNK/SAPK pathway. Taken together, these results indicate that the ERK1/2 pathway is involved in the effect of GnRH-II on antiproliferation and may be an important target for ovarian cancer therapy.     

Preptin对成骨细胞结缔组织生长因子表达的影响及其机制研究

目的 探讨Preptin对成骨细胞结缔组织生长因子(CTGF)表达的影响及其机制.方法采用人重组preptin干预人原代成骨细胞,CTGF蛋白水平用Western印迹法检测.丝裂原活化蛋白激酶p38(p38MAPK)、细胞外信号调节激酶(ERK1/2)、c-Jun氨基端激酶(JNK)及其磷酸化水平用Western印迹法检测.在preptin干预前用细胞信号阻断剂(PD98059、SP600125或SB203580)预处理阻断人成骨细胞MAPK信号转导,以分析preptin诱导人成骨细胞CTGF表达的作用机制.结果 Preptin可呈时间和剂量依赖性地促进人成骨细胞CTGF的分泌,并且preptin可诱导人成骨细胞ERK的活化,对p38MAPK或JNK无激活作用;人成骨细胞用ERK抑制剂PD98059预处理可使preptin诱导的CTGF分泌降低.结论Preptin增加CTGF的表达,并通过ERK/MAPK信号途径来介导.     

Abrupt reoxygenation of microvascular endothelial cells after hypoxia activates ERK1/2 and JNK1, leading to NADPH oxidase-dependent oxidant production

OBJECTIVE: Mitogen-activated protein kinases (MAPK) in microvascular endothelial cells (EC) may participate in organ pathophysiology following hypoxia/reoxygenation (H/R). The authors aimed to determine the role of MAPK in H/R-induced reactive oxygen species (ROS) generation in mouse microvascular EC. METHODS: Cultured EC derived from skeletal muscle of male wild-type (WT), gp91phox-/- or p47phox-/- mice were subjected to hypoxia (0.1% O2, 1 h) followed by abrupt reoxygenation, H/RA (hypoxic medium quickly replaced by normoxic medium), or slow reoxygenation, H/RS (O2 diffused to cells through hypoxic medium). Cells were analyzed for ERK, JNK, and p38 MAPK phosphorylation, NADPH oxidase activation, and ROS generation. RESULTS: In WT cells, H/RA but not H/RS rapidly phosphorylated ERK1/2 and JNK1 and subsequently increased ROS production. H/RA did not affect p38. MAPK phosphorylation persisted despite inhibition of NADPH oxidase, mitochondrial respiration, protein tyrosine kinase, or PKC. ROS increase during H/RA was prevented by deletion of gp91phox or p47phox, or MAPK inhibition. CONCLUSIONS: Abrupt reoxygenation after hypoxia activates ERK1/2 and JNK1 in mouse microvascular endothelial cells via a tyrosine kinase-, PKC-, and NADPH oxidase-insensitive mechanism, leading to increased NADPH oxidase-dependent ROS production. The results suggest that MAPK activation in the microvascular endothelium is O2-sensitive, contributing critically to tissue pathophysiology after H/R.     

Obligate mitogen-activated protein kinase activation in parathyroid hormone stimulation of calcium transport but not calcium signaling

PTH regulates calcium homeostasis through direct actions on its cognate type I receptor in the kidney and bone. PTH inhibits phosphate transport in renal proximal (PCT) tubules and stimulates calcium absorption by distal convoluted tubules (DCT). We examined PTH activation of the mitogen-activated protein kinase (MAPK) cascade raf-MEK-ERK in PCT and DCT cells and its effects on calcium transport and signaling. In DCT cells, PTH stimulates phosphorylation of ERK2 and activation of ERK2 kinase and is blocked by the MEK inhibitor PD98059. In DCT cells, stimulation of calcium entry with ionomycin did not activate ERK2 or augment PTH-stimulated ERK2 activity, indicating that MAPK activation lies upstream of calcium entry. ERK2 activation by PTH was blocked by the protein kinase C inhibitor calphostin-C but was unaffected by the protein kinase A inhibitor Rp-cAMPs. PD98059 abolished the increase of intracellular calcium induced by PTH demonstrating that ERK2 activation is directly involved in the increase of intracellular calcium activated by PTH in the DCT. Thus, PTH- stimulated ERK2 activation is PKC dependent and calcium independent. PTH also induced ERK2 phosphorylation in PCT cells. However, this effect is not involved in the transient rise of intracellular calcium because PD98059 did not inhibit the PTH-stimulated rise of intracellular calcium but abolished ERK2 activation. In conclusion, PTH activates MAPK in both distal and proximal renal tubule cells. However, the rise of [Ca2+]i depends upon MAPK activation only in distal cells. Thus, a common PTH1R exhibits differential signaling along the nephron that contributes to the ability to regulate distinct physiological actions of PTH.     

p38 mitogen-activated protein kinase activation is required for thromboxane- induced contraction in perfused and pressurized rat mesenteric resistance arteries

Thromboxane A(2) (TxA2) is a potent proaggregating, vasoconstrictor agent produced in many physiological and pathological situations. Although mitogen-activated protein (MAP) kinases [MAPK (ERK1/2 and p38)] have been shown to be activated after endoperoxide/thromboxane receptor (TP) stimulation, no study has investigated their potential role in resistance arteries, especially in physiological conditions of pressure and flow in which the arteries can contract. Thus, responses to TP stimulation by the stable agonist U46619 were studied in isolated rat mesenteric resistance arteries (inner diameter 262 +/- 5 microm) mounted in an arteriograph. Changes in diameter were recorded under physiological levels of flow (90 microl/min) and pressure (50 mm Hg). TP stimulation induced a concentration-dependent contraction (EC(50) value of 1.94 +/- 0.22 x 10(-7) M), without desensitization. U46619-induced contraction was inhibited by calcium entry blockade (nifedipine) and protein kinase C inhibition (GF109203X), but it was not affected by tyrosine kinase inhibition (tyrphostin A25). MAPKK (MEK) inhibition (PD98059) did not alter U46619-dependent contraction, although ERK1/2 MAPK were activated. By contrast, p38 MAPK inhibition (SB203580) dose-dependently inhibited the contraction, and Western blot analysis showed activation of p38 MAPK in arteries contracted with U46619. Activation of p38 MAPK by U46619 was inhibited by nifedipine and in the absence of extracellular calcium. This study brings new insights in the transduction pathway involved in the contractile response of resistance arteries to TxA2/endoperoxide receptor stimulation. This contraction requires p38 MAPK activation, but did not involve ERK1/2 MAPK activation although both were activated.