Role of MAP Kinase Cascade in the Regulation of Diverse Cellular Fuctions.

(1) MEK特异性抑制剂PD98059阻断ERK-MAP激酶通路，完全抑制了该通路组成性激活的肿瘤细胞的生长。PD98059治疗这些肿瘤细胞后，观察到p27^<Klp1>的选择性上调。p27^<Klp1>的上调与p27^<Klp1>与周期蛋白E-CDK2复合物的关联增加相关，同时抑制周期蛋白E-CDK2激酶活性，随后RB磷酸化状态降低，最终在这些肿瘤细胞中观察到明显的G1细胞周期阻滞。这些结果表明，肿瘤细胞中ERK-MAP激酶通路被特异性阻断后的完全生长抑制是由p27^<Klp1>上调介导的。(2) HGF诱导MDCK细胞的扩散、解离和散射。HGF诱导细胞中ERK-MAP激酶的持续激活。我们进一步研究了hgf诱导的MDCK细胞散射是否需要细胞核中的ERK-MAP激酶活性。为了进行分析，我们通过表达一种无活性的MKP-3细胞质磷酸酶，迫使细胞中ERK-MAP激酶在细胞质中保留。活化的ERK-MAP激酶在细胞质中的强制保留明显抑制了MDCK细胞对HGF的散射反应。这些结果表明，细胞核中的ERK-MAP激酶活性是HGF诱导的mdck细胞运动反应所必需的。(3) NGF具有诱导PC12细胞神经元分化的能力。NGF诱导p38 MAP激酶通路和ERK-MAP激酶通路持续激活。用SB203580 （p38 MAP激酶特异性抑制剂）或PD98059预处理PC12细胞部分抑制ngf诱导的神经突生长，而PD98059和SB203580联合预处理细胞几乎完全抑制ngf诱导的神经突生长。这些结果表明，在NGF刺激PC12细胞后，激活ERK-MAP激酶途径和激活p38 MAP激酶途径是充分诱导神经突生长的必要条件。ERK-MAP激酶参与了神经丝蛋白（NFs）的磷酸化，而p38 MAP激酶参与了NF基因的表达。少

(1) Blockade of the ERK-MAP kinase pathway by treatment with PD98059, a specific inhibitor of MEK, completely suppressed the growth of tumor cells in which the pathway is constitutively activated. Selective up-regulation of p27^<Klp1> was observed after PD98059 treatment of these tumor cells. The up-regulation of p27^<Klp1> correlated with increased association of p27^<Klp1> with cyclin E-CDK2 complexes, a concomitant inhibition of cyclin E-CDK2 kinase activity, and consequent decrease in the phosphorylation state of RB, which would culminate in the marked G1 cell cycle arrest observed in these tumor cells. These results suggest that the complete growth suppression that follows specific blockade of the ERK-MAP kinase pathway in tumor cells in which the pathway is constitutively activated is mediated by up-regulation of p27^<Klp1>.(2) HGF induced the spreading, dissociation and scattering of MDCK cells. HGF induced the sustained activation of ERK-MAP kinases in the cells. We have examin … More ed whether or not the ERK-MAP kinase activity in the nucleus is required for HGF-induced scattering of MDCK cells. For the analysis, we forced cytoplasmic retention of ERK-MAP kinases in the cells by expressing an inactive form of the MKP-3 cytoplasmic phosphatase. The enforced cytoplasmic retention of the activated ERK-MAP kinases apparently inhibited the scattering response of MDCK cells in response to HGF.These results indicate that the ERK-MAP kinase activity in the nucleus is required for the motility response of MDCKcells induced by HGF.(3) NGF has the capacity to induce the neuronal differentiation of PC12 cells. NGF induced the sustained activation of p38 MAP kinase pathway as well as of ERK-MAP kinase pathway. Pretreatment of PC12 cells with SB203580 (a specific inhibitor of p38 MAP kinase) or PD98059 partially inhibited the NGF-induced neurite outgrowth formation, while pretreatment of the cells with a combination of PD98059 and SB203580 resulted in almost complete inhibition of NGF-induced neurite outgrowth. These results suggest that activation of the ERK-MAP kinase pathway together with activation of p38 MAP kinase pathway are required for full induction of neurite outgrowth following stimulation of PC12 cells with NGF.ERK-MAP kinases are suggestively involved in the phosphorylation of neurofilament proteins (NFs), while p38 MAP kinase is involved in the expression of NF genes. Less