Akt/PKB信号转导通路与脑缺血

Akt被生长因子介导的受体酪氨酸激酶磷酸化激活后可激活一系列底物分子,包括Forkhead转录因子等,对细胞生存和死亡进行调控.随着脑缺血后Akt磷酸化水平(Ser473)的改变,其上游、下游蛋白磷酸化水平也发生变化.预处理可能通过改变Akt蛋白磷酸化水平而产生缺血耐受.Akt/PKB信号转导通路功能障碍可能介导了脑缺血后神经元死亡.     

阿托伐他汀对晚期糖基化终末产物诱导的人内皮细胞单核细胞趋化蛋白-1mRNA表达影响及其机制的实验研究

目的 观察阿托伐他汀对晚期糖基化终末产物(advanced glycation end products,AGE)诱导的人脐静脉内皮细胞表达单核细胞趋化蛋白-1(MCP-1)的影响,并探讨其作用机制.方法 实验分组:(1)空白对照组.(2)牛血清白蛋白(BSA)对照组.(3)AGE诱导组:不同作用浓度的AGE(10-4、10-3、10-2及10-1g/L)与细胞共同培养24 h.(4) AGE+阿托伐他汀组:用不同作用浓度的阿托伐他汀(0.1、1、10 μmol/L)分别与细胞培养1 h,而后加入10-1 g/L AGE[根据(3)实验结果选取最佳浓度]与细胞共孵育24 h.(5)PPAR-γ激动剂(15 d-PGJ2)组:15 d-PGJ2( 10 μmol/L)与细胞孵育1 h后加入10-1 g/L AGE再与细胞共孵育24 h.(6)PPAR-γ抑制剂(GW9662)组:GW9662(5000 g/L)与细胞孵育1 h后加入AGE(10-1 g/L)和阿托伐他汀(1 μmol/L)[根据(4)实验结果选取最佳浓度]再与细胞共孵育24 h.胶原酶消化法获取人脐静脉内皮细胞.逆转录聚合酶链反应法分析细胞MCP-1和过氧化物酶增殖物活化受体γ(PPAR-γ)基因的表达.蛋白免疫印迹法测定细胞核因子-κB(NF-κB )p65表达水平.结果 (1)AGE(10-4、10-3、10-2及10-1 g/L)呈浓度依赖性提高人脐静脉内皮细胞MCP-1 mRNA表达水平,分别是空白对照组的1.53倍、2.12倍、2.56倍及4.71倍;AGE浓度为10-4 g/L时,细胞MCP-1 mRNA表达明显高于空白对照组(0.26±0.02比0.17±0.04,P<0.01).(2)与AGE组比,阿托伐他汀(0.1、1、10 μmol/L)呈浓度依赖性抑制AGE诱导的人内皮细胞MCP-1 mRNA的表达;阿托伐他汀浓度为1 μmol/L时,细胞MCP-1 mRNA表达水平显著低于AGE(10-1g/L)组(0.63±0.11比1.03±0.07,P<0.01).(3)AGE(10-1 g/L)组人脐静脉内皮细胞PPAR-γ mRNA的表达水平显著低于空白对照组(0.22±0.08比0.69±0.09,P<0.01),磷酸化和非磷酸化NF-κB p65蛋白表达水平显著高于空白对照组(0.78±0.06比0.31±0.01和1.61±0.16 比0.59±0.14,P均<0.01).(4)阿托伐他汀(1、10 μmol/L)组人脐静脉内皮细胞PPAR-γ mRNA表达水平显著高于AGE(10-1 g/L)组(0.59±0.02和0.61±0.06比0.22±0.08,P均<0.01);阿托伐他汀(1 μmol/L)组磷酸化和非磷酸化NF-κB p65蛋白表达水平显著低于AGE(10-1g/L)组(0.40±0.03比0.78±0.06和0.65±0.12比1.61±0.16,P均<0.01).(5)PPAR-γ激动剂(15 d-PGJ2)组细胞磷酸化和非磷酸化NF-κB p65蛋白表达水平显著低于AGE(10-1g/L)组 (0.21±0.01比0.78±0.06和0.67±0.14比1.61±0.16,P均<0.01),MCP-1 mRNA表达水平显著低于AGE(10-1g/L)组(0.17±0.02比0.93±0.12,P<0.01).(6)PPAR-γ抑制剂(GW9662)组细胞磷酸化和非磷酸化NF-κB p65蛋白表达水平显著高于AGE(10-1g/L)+阿托伐他汀(1 μmol/L)组(0.53±0.02比0.40±0.03和1.38±0.18比0.65±0.12,P均<0.01),MCP-1 mRNA表达水平显著高于AGE(10-1g/L)+阿托伐他汀(1 μmol/L)组(0.62±0.05比0.30±0.07,P<0.01).结论 阿托伐他汀可通过提高AGE诱导的人脐静脉内皮细胞对PPAR-γ表达抑制细胞NF-κB信号途径,进而抑制AGE诱导的人脐静脉内皮细胞的炎性反应.

Abstract：

Objective To investigate the effects of atorvastatin on advanced glycation end products (AGE) induced monocyte chemoattractant protein-1(MCP-1) expression in human umbilical vein endothelial cells(HUVECs)and whether this effect could be linked to peroxisome proliferator-activated receptor-γ (PPAR-γ) and nuclear factor-κB(NF-κB).Methods Grouping: (1)Blank control group;(2)BSA group;(3)AGE group:cells were incubated with different concentrations of AGE(10-4,10-3, 10-2 and 10-1g/L)for 24 hours; (4)AGE+Atorvastatin group: cells were incubated with different concentrations of atorvastatin(0.1,1,10 μmol/L)for 1 hour,then incubated with AGE (10-1 g/L) for 24 hours; (5)PPAR-γ agonist(15 d-PGJ2)group: cells were incubated with 15 d-PGJ2(10 μmol/L)for 1 hour,then incubated with AGE (10-1g/L) for 24 hours;(6)PPAR-γ inhibitor(GW9662)group:cells were incubated with GW9662(5000 nmol/L)for 1 hour,then incubated with atorvastatin (1 μmol/L)and AGE (10-1g/L) for 24 hours. Collagenase was used to isolate the endothelial cell from human umbilical vein;RT-PCR was performed to examine the mRNA expression of MCP-1 and PPAR-γ;Western blot was performed to detect NF-κB p65 protein.Results (1) The expression of MCP-1 mRNA was increased in proportion with increasing concentrations of AGEs which could be blocked by atorvastatin in a dose-dependent manner. (2) AGE(10-1g/L)significantly downregulated the expression of PPAR-γ mRNA(0.22±0.08 vs. 0.69±0.09, P<0.01) while upregulated the expression of phospho-NF-κB p65 protein (0.78±0.06 vs. 0.31±0.01,P<0.01) and nonphospho-NF-κB p65 protein (1.61±0.16 vs. 0.59±0.14,P<0.01) comparaed with the control group which could be significantly attenuated by atorvastatin. (3) PPAR-γ agonist decreased the expression of phospho-NF-κB p65 protein (0.21±0.01 vs. 0.78±0.06, P<0.01),nonphospho-NF-κB p65 protein (0.67±0.14 vs. 1.61±0.16,P<0.01)and MCP-1 mRNA (0.17±0.02 vs. 0.93±0.12, P<0.01)compared with AGE(10-1g/L)group. (4) PPAR-γ inhibitor antagonized the effect of atorvastatin on the expression of phospho-NF-κB p65 protein, nonphospho-NF-κB p65 protein and MCP-1 mRNA stimulated by AGE in HUVECs(P<0.01).Conclusion The anti-inflammatory properties of atorvastatin in AGE stimulated HUVECs may partly be attributed to the effect on upregulation of PPAR-γ and downregulation of NF-κB signaling pathway.     

MCI-186减轻Aβ1-40诱导PC12细胞tau蛋白磷酸化的研究

目的 探讨依达拉奉(MCI-186)对β样淀粉蛋白(Aβ1-40)引起的PC12细胞tau蛋白磷酸化的保护作用及其机制.方法 采用 Western 印迹等检测Ser396,Ser199/202,Tau-5及GSK-3β,GSK-3βSer9磷酸化水平,观察MCI-186对Aβ25-35致PC12细胞的损伤保护作用.结果 模型组 tau蛋白在Ser396、Ser199/202位点的磷酸化水平及总tau蛋白水平在Aβ1-40作用3 h后开始升高,同时GSK-3β的表达增多,磷酸化GSK-3βSer9的表达减少,MCI-186保护组tau蛋白在Ser396,Ser199/202位点的磷酸化水平和总tau蛋白水平均明显低于Aβ模型组(P＜0.05),GSK-3β的表达减少,磷酸化GSK-3βSer9的表达增多(P＜0.05).结论 在Aβ1-40诱导PC12细胞损伤过程中,出现了tau蛋白的过度磷酸化,可以使Ser396,Ser199/202位点及Tau-5蛋白升高.激活GSK-3β是产生tau蛋白过度磷酸化的主要途径.MCI-186可通过抑制GSK-3β的活性,从而减轻Aβ1-40诱导的tau蛋白过度磷酸化,而达到保护神经细胞的目的 .     

Smad7对终末期糖基化产物介导大鼠肾小管上皮细胞转分化及Ⅰ型胶原合成的影响

目的 探讨Smad7对终末期糖基化产物(AGE)介导肾小管上皮细胞转分化及Ⅰ型胶原合成的影响.方法 Tet-on质粒系统构建表达Smad7的正常大鼠近端肾小管上皮细胞(NRK52E)株,通过强力霉素(Dox)上调Smad7的表达,以细胞免疫化学、RT-PCR或Western印迹技术观察Smad7对AGE介导NRK52E细胞磷酸化(P)Smad2/3核转位、及α-平滑肌肌动蛋白(SMA)、E-钙黏着糖蛋白(cadherin)和Ⅰ型胶原mRNA和蛋白表达的影响.结果 Smad7转染的NRK52E细胞以剂量依赖方式受Dox调控.Smad7的高表达可抑制AGE介导的30 min(68.3%vs31.2%,P＜0.01)和24h(69.8%vs28.7%,P＜0.01)P-Smad2/3的核转位水平;明显下调α-SMA、Ⅰ型胶原mRNA和蛋白的表达,上调E-钙黏着糖蛋白mRNA和蛋白的表达.结论 Smad7通过抑制Smad信号通路活化,阻抑AGE介导的肾小管上皮细胞向肌成纤维母细胞转分化和Ⅰ型胶原的合成.     

葡萄糖和晚期糖基化终产物联合刺激对人单核细胞血红素加氧酶1表达的影响

目的 探讨葡萄糖和晚期糖基化终产物(AGE)联合刺激对人单核细胞THP-1血红素加氧酶1(HO-1)表达的影响. 方法 分别以15mmol/L葡萄糖、100μg/ml AGE和二者联合刺激THP-1,比较各组活性氧(ROS)产量,培养液丙二醛(MDA)、肿瘤坏死因子α(TNFα)水平和细胞HO-1mRNA及蛋白的表达量. 结果葡萄糖和AGE联合刺激的ROS产量、MDA、TNFα水平及HO-1mRNA和蛋白表达均明显高于单独刺激组. 结论 葡萄糖和AGE联合刺激可导致THP-1细胞氧化应激和HO-1表达增加.     

AGEs刺激对小鼠肝脏moesin表达及其磷酸化水平的影响

目的探讨糖基化蛋白终产物（AGEs）刺激对小鼠肝脏膜突蛋白（moesin）表达及其磷酸化水平的影响。方法 24只C57 BL/6雌性小鼠,随机分为对照组、AGE组、SB203580＋AGE组和Y27632＋AGE组,各6只。制备模型后,取小鼠肝脏组织进行石蜡包埋、切片,通过免疫组化法对各组肝脏moesin及其磷酸化moesin进行观察并行半定量分析。结果四组moesin均主要表达在肝窦和微血管的内皮细胞,肝细胞或胆管上皮细胞无表达;对照组磷酸化moesin几乎观察不到;AGE组肝窦和微血管内皮细胞中558位苏氨酸磷酸化moesin的表达明显增加;SB203580＋AGE组和Y27632＋AGE组肝脏内皮细胞磷酸化moesin染色深度明显低于AGE组并高于对照组。对照组、AGE组、SB203580＋AGE组、Y27632＋AGE组moesin灰度值分别为84.7±0.35、86.2±0.57、85.5±0.69、84.9±0.67,各组moesin相比,P均〉0.05;其磷酸化moesin灰度值分别为34.6±0.36、82.2±0.92、35.7±0.51、35.9±1.67;AGE组的磷酸化moesin与其余三组相比,P均〈0.05。结论 moesin在肝脏主要表达在肝窦和微血管的内皮细胞,AGEs处理或抑制p38 MAPK、ROCK活性后再给予AGEs均不影响肝脏moesin蛋白的表达;AGEs可导致肝脏内皮细胞moesin磷酸化,p38 MAPK和ROCK两条信号途径参与了moesin磷酸化的过程。     

糖原合酶激酶3β信号通路在脑缺血中的作用

糖原合酶激酶3β( glycogen synthase kinase 3β,GSK3β)是一种丝氨酸/苏氨酸蛋白激酶.生长因子、Wnt等多条信号通路可抑制GSK3β活性,从而促进细胞存活.脑缺血时,随着GSK3β磷酸化水平发生改变,其上游和下游蛋白磷酸化水平也发生改变.缺血预处理和后处理可能通过调节GSK3β信号通路诱导脑缺血耐受.     

p38MAPK-eNOS-N0信号通路在人脐静脉内皮细胞凋亡中的保护作用

目的探讨p38MAPK信号通路在胰高血糖素样肽1(GLP-1)拮抗人脐静脉内皮细胞凋亡中的作用。方法实验分为对照组、糖基化终末产物(AGE)组、GLP-1组、AGE+GLP-1组、AGE+SB203580组、AGE+GLP-1+SB203580组及AGE+GLP-1+L-NAME组,Western blot检测p-p38MAPK/p38MAPK、磷酸化内皮型一氧化氮合酶/内皮型一氧化氮合酶(p-eNOS/eNOS)蛋白表达情况,NO检测试剂盒(一步法)检测NO含量,DCFH-DA荧光探针检测细胞活性氧(ROS)含量,Annexin V/PI流式检测细胞凋亡率。结果与AGE组相比,GLP-1预处理可诱导p-p38MAPK蛋白表达下降(P=0.000);与对照组比较,GLP-1或p38 MAPK抑制剂(SB203580)预处理后,受AGE抑制的eNOS蛋白表达或诱导的ROS水平分别显著升高(P=0.004)或下降(P=0.000);GLP-1预处理后,因AGE诱导的细胞凋亡率显著降低(P=0.000),而加入L-NAME后,GLP-1的抗凋亡作用显著减弱(P=0.002);GLP-1预处理后,细胞NO含量较单纯AGE组明显升高(P=0.000),而予以L-NAME后,细胞NO含量显著降低(P=0.011)。结论GLP-1可抑制p38 MAPK信号通路的活化,拮抗AGE对血管内皮细胞的氧化损伤;上调eNOS蛋白的表达,拮抗AGE诱导的内皮细胞NO生成障碍及细胞凋亡,从而延缓糖尿病合并动脉粥样硬化的发生发展。     

粘着斑激酶及磷酸化粘着斑激酶在结肠癌中的表达及其临床意义

目的研究粘着斑激酶(FAK)和磷酸化粘着斑激酶(phospho-FAK,Tyr397)在结肠癌中的表达水平及其与侵袭和转移的关系.方法用免疫组织化学S-P法检测45例结肠癌和对应癌旁组织的FAK和磷酸化FAK(Tyr397)的表达.结果癌与癌旁组织FAK表达率分别为82.22%(37/45)和28.89%(13/45),磷酸化FAK(Tyr397)表达率分别为66.78%(30/45)和26.78%(12/45),两者比较差异有显著性(P值均＜0.01).癌组织中FAK表达率在分化程度(P＜0.05)、浸润深度(P＜0.01)和淋巴结转移(P＜0.05)中有显著性差异,磷酸化FAK(Tyr397)在分化程度(P＜0.01)、浸润深度(P＜0.05)和淋巴结转移(P＜0.01)中也有显著性差异,FAK和磷酸化FAK(Tyr397)在年龄(P>0.05)、性别(P>0.05)及远处转移(P>0.05)中差异无显著性.结论结肠癌中FAK和磷酸化FAK(Tyr397)的表达水平明显升高,与分化程度、浸润、淋巴结转移相关.     

血红素加氧酶1在高糖和晚期糖基化终末产物诱导的THP-1细胞氧化应激中的作用

目的 探讨血红素加氧酶1(heme oxygenase-1,HO-1)在高糖和晚期糖基化终末产物(AGE)诱导的人单核细胞氧化应激中的作用.方法 根据是否加用15 mmoL/L葡萄糖(高糖)+100μg/ml AGE或HO-1抑制剂锌原卟啉(zinc protoporphyrin,ZnPP),将人单核细胞白m病细胞株THP-1细胞分为正常糖组(5 mmoL/L)、高糖+AGE组、高糖+AGE+ZnPP组、正常糖+ZnPP组,孵育24 h后收集细胞及培养液上清,榆测各组细胞的活性氧簇(ROS)、培养液上清丙二醛和肿瘤坏死因子α(TNF-α)水平以及HO-1 mRNA和蛋白的表达.结果 高糖+AGE组和正常糖+ZnPP组的ROS、丙二醛和TNF-α水平均显著高于正常糖组(均P<0.05).高糖+AGE+ZnPP组的ROS、TNF-α水平显著高于高糖+AGE组(均P<0.05).高糖+AGE+ZnPP组的HO-1 mRNA和蛋白表达水平显著低于高糖+AGE组(0.39+0.02±0.89 vs 0.09±0.384±0.00 vs 0.81±0.02,均P<0.05).结论 ZnPP通过抑制HO-1表达加重高糖和AGE导致的单核细胞氧化应激,HO-1可能在糖尿病氧化应激中起重要作用.     

Advanced glycation endproduct (AGE) receptor 1 is a negative regulator of the inflammatory response to AGE in mesangial cells

Advanced glycation endproducts (AGE) contribute to kidney disease due to diabetes or aging by means of mesangial cell (MC) receptors, such as the receptor for AGE (RAGE), which promote oxidant-stress-dependent NF-kappaB activation and inflammatory gene expression. MC also express scavenger receptors SR-I and SR-II and AGE receptors 1, 2, and 3 (AGE-R1, -R2, and -R3), some of which are linked to AGE turnover. Because AGE-R1 expression is found suppressed in severe diabetic kidney disease, as other receptors increase, we investigated whether his molecule has a protective role against AGE-induced MC injury. A stable murine MC line overexpressing AGE-R1 (R1-MC) was generated, exhibiting a 1.8- to 2.7-fold increase in (125)I-AGE-specific binding, uptake, and degradation, compared with mock-MC. However, AGE-stimulated NF-kappaB activity and mitogen-activated protein kinase (MAPK) (p44/42) phosphorylation were found markedly suppressed in R1-MC. Additionally, AGE-stimulated macrophage chemotaxis protein 1 and RAGE overexpression were abolished in R1-MC. The effect of R1 on RAGE signaling was investigated after overexpressing RAGE in Chinese hamster ovary cells, which lack RAGE. AGE stimulation elicited NF-kappaB and MAPK activities in RAGE-Chinese hamster ovary cells; however, after cotransfection with R1, these responses were suppressed. Also, after silencing endogenous R1 in wild-type MC by R1 small interfering RNA, AGE-mediated MAPK/p44/42 activation exceeded by >2-fold that of mock-MC, consistent with loss of the activation-inhibitory properties of native AGE-R1. AGE-R1, although enhancing AGE removal, is also a distinct receptor in that it suppresses AGE-mediated MC inflammatory injury through negative regulation of RAGE, a previously uncharacterized pathway that may protect renal and other tissue injury due to diabetes and aging.     

Gonadotropin regulation of testosterone production by primary cultured theca and granulosa cells of Atlantic croaker: II. Involvement of a mitogen-activated protein kinase pathway

Previous investigations in Atlantic croaker ovaries and primary co-cultured theca and granulosa cells have identified multiple signal transduction pathways involved in the control of gonadotropin-induced steroidogenesis, including adenylyl cyclase- and calcium-dependent signaling pathways. In the present study, evidence was obtained for an involvement of a third signal transduction pathway, a mitogen-activated protein kinase (MAP kinase) signaling cascade, in the regulation of gonadal steroidogenesis in this lower vertebrate teleost model. Gonadotropin-stimulated testosterone synthesis was markedly attenuated by two antagonists of mitogen-activated protein kinase kinases 1/2 (MEK1/2, also known as Map2k1/Map2k2). Moreover, treatment with gonadotropin-induced MEK1/2-dependent phosphorylation of extracellular signal-regulated protein kinases 1/2 (ERK1/2, also known as Mapk3/Mapk1) in a concentration- and time-dependent manner in co-cultured croaker theca and granulosa cells. Active MEK1/2 was required for a complete steroidogenic response to activators of the adenylyl cyclase pathway, including forskolin and dbcAMP, suggesting that the target(s) of MAP kinase signaling are distal to cAMP generation and activation of cAMP-dependent protein kinase (PKA). Interestingly, dbcAMP caused a similar increase of ERK1/2 phosphorylation as was observed with gonadotropin treatment, although an inhibitor of PKA did not attenuate this response. Finally, there was no evidence of cross-talk between calcium-dependent signaling pathways and this MAP kinase cascade. While drugs that block calcium-dependent signal transduction, including inhibitors of voltage-sensitive calcium channels, calmodulin, and calcium/calmodulin-dependent kinases, significantly reduced gonadotropin-induced testosterone accumulation, these drugs had no apparent effect on hCG-induced ERK1/2 phosphorylation.     

Visfatin inhibits pancreatic β-cell line MIN6 apoptosis via PI3K-Akt and MAPK-ERK1/2 signaling pathways

探讨内脂素对胰岛β细胞株MIN6细胞信号通路和棕榈酸诱导细胞凋亡的影响,并探讨其分子机制.人重组内脂素呈剂量和时间依赖性促进MIN6细胞细胞外信号调节激酶(ERK)1/2和蛋白激酶B(Akt)的磷酸化,抑制棕榈酸诱导的MIN6细胞凋亡(P<0.05或P<0.01).激活磷脂酰肌醇3激酶(PBK)-Akt和丝裂原活化蛋白激酶(MAPK)-ERK1/2信号通路是内脂素抑制MIN6细胞凋亡的分子机制之一.     

Visfatin inhibits pancreatic β-cell line MIN6 apoptosis via PI3K-Akt and MAPK-ERK1/2 signaling pathways

探讨内脂素对胰岛β细胞株MIN6细胞信号通路和棕榈酸诱导细胞凋亡的影响,并探讨其分子机制.人重组内脂素呈剂量和时间依赖性促进MIN6细胞细胞外信号调节激酶(ERK)1/2和蛋白激酶B(Akt)的磷酸化,抑制棕榈酸诱导的MIN6细胞凋亡(P<0.05或P<0.01).激活磷脂酰肌醇3激酶(PBK)-Akt和丝裂原活化蛋白激酶(MAPK)-ERK1/2信号通路是内脂素抑制MIN6细胞凋亡的分子机制之一.     

C-peptide stimulates ERK1/2 and JNK MAP kinases via activation of protein kinase C in human renal tubular cells

Aims/hypothesis Accumulating evidence indicates that replacement of C-peptide in type 1 diabetes ameliorates nerve and kidney dysfunction, but the molecular mechanisms involved are incompletely understood. C-peptide shows specific binding to a G-protein-coupled membrane binding site, resulting in Ca²⁺ influx, activation of mitogen-activated protein kinase signalling pathways, and stimulation of Na⁺, K⁺-ATPase and endothelial nitric oxide synthase. This study examines the intracellular signalling pathways activated by C-peptide in human renal tubular cells.Methods Human renal tubular cells were cultured from the outer cortex of renal tissue obtained from patients undergoing elective nephrectomy. Extracellular-signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK) and Akt/protein kinase B (PKB) activation was determined using phospho-specific antibodies. Protein kinase C (PKC) and RhoA activation was determined by measuring their translocation to the cell membrane fraction using isoform-specific antibodies.Results Human C-peptide increases phosphorylation of ERK1/2 and Akt/PKB in a concentration- and time-dependent manner in renal tubular cells. The C-terminal pentapeptide of C-peptide is equipotent with the full-length C-peptide, whereas scrambled C-peptide has no effect. C-peptide stimulation also results in phosphorylation of JNK, but not of p38 mitogen-activated protein kinase. MEK1/2 inhibitor PD98059 blocks the C-peptide effect on ERK1/2 phosphorylation. C-peptide causes specific translocation of PKC isoforms and to the membrane fraction in tubular cells. All stimulatory effects of C-peptide were abolished by pertussis toxin. The isoform-specific PKC- inhibitor rottlerin and the broad-spectrum PKC inhibitor GF109203X both abolish the C-peptide effect on ERK1/2 phosphorylation. C-peptide stimulation also causes translocation of the small GTPase RhoA from the cytosol to the cell membrane. Inhibition of phospholipase C abolished the stimulatory effect of C-peptide on phosphorylation of ERK1/2, JNK and PKC-.Conclusions/interpretation C-peptide signal transduction in human renal tubular cells involves the activation of phospholipase C and PKC- and PKC-, as well as RhoA, followed by phosphorylation of ERK1/2 and JNK, and a parallel activation of Akt.     

Polyamine-enhanced casein kinase 11 in mouse pancreatic islets

Summary The occurrence of polyamine-stimulated protein kinase (casein kinase II) in cytosol of mouse pancreatic islets was investigated. Islet protein phosphorylation was enhanced by spermidine, spermine, lysine-rich histone and polylysine; the major endogenous substrates in the cytosol were three proteins of Mr 50000, 55000 and 100000. Cadaverine and putrescine were without effects. A Mr 100 000 protein is a major substrate for Ca²⁺-calmodulin-dependent protein kinase, and Mr 50 000 and 55 000 proteins are substrates for cyclic adenosine 3,5-cyclic monophosphate (AMP) dependent protein kinase in mouse islets. However, neither cyclic-AMP-dependent protein kinase inhibitor nor trifluoperazine inhibited polyamine-enhanced protein phosphorylation. Both basal and polyamine-enhanced protein phosphorylation patterns were identical when either [-³²P] adenosine 5-triphosphate (ATP) or [-³²P] guanosine 5-triphosphate (GTP) was used as phosphate donors, indicative of the presence of a polyaminestimulated casein kinase 11 in pancreatic islets. It is suggested that polyamines and polyamine-enhanced casein kinase II activity may have an important role in regulation of protein phosphorylation in pancreatic islets.     

Phosphorylation of myosin light chain kinase from vascular smooth muscle by cAMP- and cGMP-dependent protein kinases

The enzyme, myosin light chain kinase, has been purified to homogeneity from bovine aortic vascular smooth muscle. Approximately 10 mg of enzyme could be obtained from 1 kg of fresh aortas with an overall yield of 26% of the original activity. The vascular myosin light chain kinase has a molecular weight of 160 000 by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Antiserum raised to the aortic myosin light chain kinase in rabbits strongly inhibited phosphotransferase activity. In addition, the antiserum was used to identify myosin kinase in a crude homogenate of vascular smooth muscle by radioimmunoblotting. A single species of the enzyme (Mr = 160 000) was identified. The bovine aortic myosin kinase could be phosphorylated by both cyclic AMP- and GMP-dependent protein kinases. Approximately 2 mols PO4/mole of enzyme could be incorporated by the cyclic AMP-dependent protein kinase in the absence of calmodulin. If Ca2+ and calmodulin were included in the reaction mixture, phosphate incorporation by the cyclic AMP-dependent protein kinase was reduced to 1 mol and phosphorylation by cyclic GMP-dependent protein kinase was completely inhibited. These results were confirmed by tryptic peptide mapping. Two distinct phosphopeptides were identified: site-1 and site-2. Both could be phosphorylated by the cyclic AMP-dependent protein kinase but only site-1 was phosphorylated by the cyclic GMP-dependent enzyme. In the presence of Ca2+ and calmodulin, phosphorylation by cAMP-dependent protein kinase was restricted to site-1. The effect of phosphorylation on myosin light chain kinase activity was determined. Only phosphorylation by cyclic AMP-dependent protein kinase was found to alter the requirement of myosin kinase for calmodulin. The K0.5 (i.e. the concentration of calmodulin required for half-maximal enzyme activation) for calmodulin was 5 nM for the unphosphorylated myosin kinase. With 2 mol PO4/mol myosin kinase incorporated, the K0.5 for calmodulin was increased to 82 nM. When only 1 mol PO4/mol myosin kinase was incorporated, no effect on calmodulin requirement was observed. Moreover, single site phosphorylation had no effect on other activity parameters, including Km for ATP and for light chains. Our studies suggest that cyclic AMP-dependent protein kinase may play an important role in the regulation of vascular myosin kinase activity. Moreover, our results indicate that cyclic GMP-dependent protein kinase does not affect calmodulin-activation of myosin kinase or several other activity parameters.     

Aberrant p38 mitogen-activated protein kinase signalling in skeletal muscle from Type 2 diabetic patients

Aims/hypothesis p38 mitogen activated protein kinase (MAPK) is generally thought to facilitate signal transduction to genomic, rather than metabolic responses. However, recent evidence implicates a role for p38 MAPK in the regulation of glucose transport; a site of insulin resistance in Type 2 diabetes. Thus we determined p38 MAPK protein expression and phosphorylation in skeletal muscle from Type 2 diabetic patients and non-diabetic subjects.Methods In vitro effects of insulin (120 nmol/l) or AICAR (1 mmol/l) on p38 MAPK expression and phosphorylation were determined in skeletal muscle from non-diabetic (n=6) and Type 2 diabetic (n=9) subjects.Results p38 MAPK protein expression was similar between Type 2 diabetic patients and non-diabetic subjects. Insulin exposure increased p38 MAPK phosphorylation in non-diabetic, but not in Type 2 diabetic patients. In contrast, basal phosphorylation of p38 MAPK was increased in skeletal muscle from Type 2 diabetic patients.Conclusion/interpretation Insulin increases p38 MAPK phosphorylation in skeletal muscle from non-diabetic subjects, but not in Type 2 diabetic patients. However, basal p38 MAPK phosphorylation is increased in skeletal muscle from Type 2 diabetic patients. Thus, aberrant p38 MAPK signalling might contribute to the pathogenesis of insulin resistance.Abbreviations AICAR 5-aminoimidazole-4-carboxamide ribonucleoside - AMPK 5-AMP activated protein kinase - ERK 1/2 extracellular regulated kinase - GIR glucose infusion rate - IRS-1 insulin receptor substrate 1 - MAPK mitogen-activated protein kinase - PI phosphatidylinositol - VO_2max maximal oxygen uptake     

内脂素激活PI3K-Akt和MAPK-ERK1/2信号通路抑制MIN6细胞凋亡

探讨内脂素对胰岛β细胞株MIN6细胞信号通路和棕榈酸诱导细胞凋亡的影响,并探讨其分子机制.人重组内脂素呈剂量和时间依赖性促进MIN6细胞细胞外信号调节激酶(ERK)1/2和蛋白激酶B(Akt)的磷酸化,抑制棕榈酸诱导的MIN6细胞凋亡(P<0.05或P<0.01).激活磷脂酰肌醇3激酶(PBK)-Akt和丝裂原活化蛋白激酶(MAPK)-ERK1/2信号通路是内脂素抑制MIN6细胞凋亡的分子机制之一.     

IkappaB kinase epsilon and TANK-binding kinase 1 activate AKT by direct phosphorylation

AKT activation requires phosphorylation of the activation loop (T308) by 3-phosphoinositide-dependent protein kinase 1 (PDK1) and the hydrophobic motif (S473) by the mammalian target of rapamycin complex 2 (mTORC2). We recently observed that phosphorylation of the AKT hydrophobic motif was dramatically elevated, rather than decreased, in mTOR knockout heart tissues, indicating the existence of other kinase(s) contributing to AKT phosphorylation. Here we show that the atypical IκB kinase ε and TANK-binding kinase 1 (IKKε/TBK1) phosphorylate AKT on both the hydrophobic motif and the activation loop in a manner dependent on PI3K signaling. This dual phosphorylation results in a robust AKT activation in vitro. Consistently, we found that growth factors can induce AKT (S473) phosphorylation in Rictor(-/-) cells, and this effect is insensitive to mTOR inhibitor Torin1. In IKKε/TBK1 double-knockout cells, AKT activation by growth factors is compromised. We also observed that TBK1 expression is elevated in the mTOR knockout heart tissues, and that TBK1 is required for Ras-induced mouse embryonic fibroblast transformation. Our observations suggest a physiological function of IKKε/TBK1 in AKT regulation and a possible mechanism of IKKε/TBK1 in oncogenesis by activating AKT.