Identification and H2O2 sensitivity of the major constitutive MAPK phosphatase from rat brain

The present study examined in subcellular fractions from rat brain the nature and sensitivity to hydrogen peroxide of constitutively expressed mitogen-activated protein kinase (MAPK) phosphatase activity. MAPK phosphatase activity was defined as the activity directed towards a dual-phosphorylated (pT/pY) peptide corresponding to the activation domain of the extracellular-regulated kinase (ERK) subtype of the MAPKs. The use of phosphatase inhibitors and biochemical analyses demonstrate that the MAPK phosphatase activity, which was highest in the microsomal membrane and soluble fractions, was attributable mainly, if not entirely, to protein phosphatase 2A (PP2A). Moreover, hydrogen peroxide (in the absence and presence of reduced glutathione) and glutathione disulfide inhibited the MAPK phosphatase activity by a dithiothreitol-reversible mechanism. These results provide direct support for mounting evidence that PP2A is a major regulator of MAPK phosphorylation in brain and suggest that inhibition of PP2A activity via reversible oxidation of a cysteine thiol(s) may underlie at least in part the activation of MAPKs occurring in response to hydrogen peroxide and oxidative stress.     

MAPK signaling in H9c2 cardiomyoblasts exposed to cholesterol secoaldehyde – Role of hydrogen peroxide

3β-Hydroxy-5,6-secocholestan-6-al (cholesterol secoaldehyde or ChSeco), an oxysterol known to be formed in ozone- and singlet oxygen-mediated oxidations of cholesterol, has been detected in the atherosclerotic plaque and in the brain of patients suffering from Alzheimer’s disease and Lewy body dementia. Previously, we have shown that, in H9c2 cardiomyoblasts, ChSeco induces oxidative stress followed by apoptosis involving both intrinsic and extrinsic signaling pathways. In the present study, we investigated the nature of reactive oxygen species (ROS) and its associated redox signaling in H9c2 cells upon treatment with ChSeco. Both catalase and deferoxamine, which lowered intracellular ROS, were found to alleviate the ChSeco-induced cytotoxicity. ChSeco-treated H9c2 cells showed a significant decrease in the intracellular catalase activity, suggesting the involvement of H₂O₂ in the associated cytotoxicity. Additionally, in ChSeco-exposed cells, there was a marked increase in lipid peroxidation and pre-treatment with SB 203580 (p38 MAPK inhibitor) and MEK1/2 inhibitor (ERK1/2 and JNK inhibitor) rendered protection against the cytotoxicity. An early increase in the expression of p-SAPK/JNK or delayed p38 MAPK did not alter ATF-2 but decreased c-Jun expression in these cells. Overall, these findings are consistent with MAPK signaling resulting from increased cellular H₂O₂ in ChSeco-induced cytotoxicity in cardiomyoblasts.     

p21(Cip-1/SDI-1/WAF-1) expression via the mitogen-activated protein kinase signaling pathway in insulin-induced chondrogenic differentiation of ATDC5 cells

The embryonal carcinoma-derived cell line, ATDC5, differentiates into chondrocytes in response to insulin or insulin-like growth factor-I stimulation. In this study, we investigated the roles of mitogen-activated protein (MAP) kinases in insulin-induced chondrogenic differentiation of ATDC5 cells. Insulin-induced accumulation of glycosaminoglycan and expression of chondrogenic differentiation markers, type II collagen, type X collagen, and aggrecan mRNA were inhibited by the MEK1/2 inhibitor (U0126) and the p38 MAP kinase inhibitor (SB203580). Conversely, the JNK inhibitor (SP600125) enhanced the synthesis of glycosaminoglycan and expression of chondrogenic differentiation markers. Insulin-induced phosphorylation of ERK1/2 and JNK but not that of p38 MAP kinase. We have previously clarified that the induction of the cyclin-dependent kinase inhibitor, p21(Cip-1/SDI-1/WAF-1), is essential for chondrogenic differentiation of ATDC5 cells. To assess the relationship between the induction of p21 and MAP kinase activity, we investigated the effect of these inhibitors on insulin-induced p21 expression in ATDC5 cells. Insulin-induced accumulation of p21 mRNA and protein was inhibited by the addition of U0126 and SB203580. In contrast, SP600125 enhanced it. Inhibitory effects of U0126 or stimulatory effects of SP600125 on insulin-induced chondrogenic differentiation were observed when these inhibitors exist in the early phase of differentiation, suggesting that MEK/ERK and JNK act on early phase differentiation. SB202580, however, is necessary not only for early phase but also for late phase differentiation, indicating that p38 MAP kinase stimulates differentiation by acting during the entire period of cultivation. These results for the first time demonstrate that up-regulation of p21 expression by ERK1/2 and p38 MAP kinase is required for chondrogenesis, and that JNK acts as a suppressor of chondrogenesis by down-regulating p21 expression.     

LmxMPK4, an essential mitogen-activated protein kinase of Leishmania mexicana is phosphorylated and activated by the STE7-like protein kinase LmxMKK5

The essential mitogen-activated protein kinase (MAP kinase), LmxMPK4, of Leishmania mexicana is minimally active when purified following recombinant expression in Escherichia coli and was therefore unsuitable for drug screening until now. Using an E. coli protein co-expression system we identified LmxMKK5, a STE7-like protein kinase from L. mexicana, which phosphorylates and activates recombinant LmxMPK4 in vitro. LmxMKK5 is comprised of 525 amino acids and has a calculated molecular mass of 55.9 kDa. The co-expressed, purified LmxMPK4 showed strong phosphotransferase activity in radiometric kinase assays and was confirmed by immunoblot and tandem mass spectrometry analyses to be phosphorylated on threonine 190 and tyrosine 192 of the typical TXY MAP kinase activation motif. The universal protein kinase inhibitor staurosporine reduced the phosphotransferase activity of co-expressed and activated LmxMPK4 in a dose-dependent manner. To our knowledge this is the first time that an in vitro activator of an essential Leishmania MAP kinase was identified and our findings form the basis for the development of drug screening assays to identify small molecule inhibitors of LmxMPK4 in the search for new therapeutic drugs against leishmaniasis.     

MKP1基因对小鼠造血干细胞功能的影响

目的通过构建MKP1转基因小鼠模型,研究MKP1基因对造血干细胞自我更新能力的影响。方法运用显微注射法建立MKP1转基因小鼠;PCR和RT-PCR检测MKP1基因在转基因小鼠的表达水平;流式细胞术测定小鼠骨髓干细胞和外周血单个核细胞的比例;通过竞争性骨髓移植实验检测MKP1转基因小鼠骨髓干细胞的功能。结果建立了MKP1转基因小鼠;MKP1转基因小鼠骨髓干细胞数量减少;竞争性骨髓移植实验显示MKP1转基因骨髓干细胞来源的外周血细胞总数、B细胞、粒细胞显著减少（P〈0.001）,提示MKP1转基因小鼠骨髓干细胞的功能下降。结论在MKP1转基因小鼠模型中,MKP1基因的过表达影响了小鼠的骨髓干细胞的功能。     

水稻促分裂原活化蛋白激酶家族的研究进展

促分裂原活化蛋白激酶(mitogen-activated protein kinase,MAPK)是生物体内信号转导途径MAPK级联反应的重要组分,通过传递胞内外信号,介导生物及非生物胁迫反应、激素反应、调控细胞分化和发育过程.对水稻(Oryza sativa L.)MAPK家族的结构、作用机制、分类以及在抗逆应答、生长发育中的作用进行了综述,为水稻MAPK的深入研究和应用提供参考.     

柴胡提取物诱导人类白血病细胞HL-60的细胞凋亡及其机理研究

柴胡提取物诱导人类白血病细胞HL-60的细胞凋亡从而抑制其细胞生长.为了研究该过程的作用机理,我们研究了丝裂原活化蛋白激酶(MAPKs),包括胞外信号调节激酶(ERK1/2),c-jun氨基末端蛋白激酶(JNK)和p38丝裂原活化蛋白激酶(MAPK),在该过程中的磷酸化特征与动态变化.结果表明,柴胡提取物显著的增加了p38丝裂原活化蛋白激酶和胞外信号调节激酶(ERK1/2)的磷酸化作用,其增加值在测试范围内与测试剂量和作用时间成正相关,但在柴胡提取物诱导人类白血病细胞HL-60的细胞凋亡过程中,没有发现对氨基末端蛋白激酶(JNK)表现出磷酸化活性.柴胡提取物诱导白血病HL-60的细胞凋亡部分归结于对p38丝裂原活化蛋白激酶的上调节作用,这种上调节作用能够受到p38 MAPK特异性的抑制剂SB203580的部分逆转,而MEK的抑制剂U0126则对柴胡提取物诱导HL-60细胞凋亡过程中的胞外信号调节激酶(ERK1/2)的磷酸化具有显著的协同效应.这是首次报道柴胡提取物在诱导人白血病细胞HL-60细胞凋亡过程中参与p38丝裂原活化蛋白激酶的磷酸化,同时柴胡提取物作为胞外信号调节激酶(ERK1/2)抑制剂的协同作用物具有相应的药物学功能.     

P38 MAPK 信号传导通路与卵巢癌关系的研究进展

丝裂原活化蛋白激酶(mitogen-activated proteinkinases,MAPKs)级联反应是细胞内重要的信号传导系统之一,参与细胞生长、发育、分化和凋亡等一系列生理、病理过程.P38 MAPK信号传导通路是MAPK通路的分支之一,介导了应激、炎性细胞因子、细菌产物等多种刺激引起的细胞反应,对细胞周期调控具有重要作用.但对不同的卵巢癌细胞系,或者不同的刺激,P38通路的作用不完全相同,甚至可能相反,提示对P38通路的功能仍需进一步的研究,他可能是肿瘤治疗的新靶点.本文就P38 MAPK信号传导通路与卵巢癌关系作一综述。     

Phylogenetic and Functional Classification of Mitogen- and Stress-Activated Protein Kinases

All currently sequenced stress-activated protein kinases (SAPKs), extracellular signal-regulated kinases (ERKs), and other mitogen-activated protein kinases (MAPKs) were analyzed by sequence alignment, phylogenetic tree construction, and three-dimensional structure modeling in order to classify members of the MAPK family. Based on this analysis the MAPK family was divided into three subgroups (SAPKs, ERKs, and MAPK3) that consist of at least nine subfamilies. Members of a given subfamily were exclusively from animals, plants, or yeast/fungi. A single signature sequence, [LIVM][TS]XX[LIVM]XT[RK][WY]YRXPX[LIVM] [LIVM], was identified that is characteristic for all MAPKs and sufficient to distinguish MAPKs from other members of the protein kinase superfamily. This signature sequence contains the phosphorylation site and is located on loop 12 of the three-dimensional structure of MAPKs. I also identified signature sequences that are characteristic for each of the nine subfamilies of MAPKs. By modeling the three-dimensional structure of three proteins for each MAPK subfamily based on the resolved atomic structures of rat ERK2 and murine p38, it is demonstrated that amino acids conserved in all MAPKs are located primarily in the center of the protein around the catalytic cleft. I conclude that these residues are important for maintaining proper folding into the gross structure common to all MAPKs. On the other hand, amino acids conserved in a given subfamily are located mainly in the periphery of MAPKs, indicating their possible importance for defining interactions with substrates, activators, and inhibitors. Within these subfamily-specific regions, amino acids were identified that represent unique residues occurring in only a single subfamily and their location was mapped in three-dimensional structure models. These unique residues are likely to be crucial for subfamily-specific interactions of MAPKs with substrates, inhibitors, or activators and, therefore, represent excellent targets for site-directed mutagenesis experiments. Received: 13 August 1997 / Accepted: 21 November 1997