Yang Chia-Ping Huang, Horwitz Susan Band
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Biochim Biophys Acta. 2002 Jun 12;1590(1-3):76-83. doi: 10.1016/s0167-4889(02)00200-8.
Nanomolar concentrations of Taxol, and other antimitotic agents that interact with microtubules, mediate serine phosphorylation of the 66-kDa Shc isoform (p66shc) in A549 human lung carcinoma cells, 9-18 h after drug treatment. This event coincides with the release of PARP cleavage fragments that are early indicators of apoptosis. Taxol-induced serine phosphorylation of p66shc results from a MEK-independent signaling pathway that is activated in A549 cells that have a prolonged or abnormal mitotic phase of the cell cycle [Cancer Res. 60 (2000) 5171]. In contrast, in murine macrophage RAW 264.7 cells, micromolar concentrations of Taxol but not other microtubule-interacting agents induced serine phosphorylation of p66shc that correlated with the phosphorylation of Raf-1 and extracellular signal-regulated kinase (ERK1/2), within 15-30 min after Taxol treatment. This event also was induced by lipopolysaccharide (LPS). The MEK-inhibitor, U0126, that specifically inhibits the activation of ERK also blocked the phosphorylation of p66shc and Raf-1, suggesting that these processes were MEK-dependent, quite different from that which was observed in A549 cells. Taxol also induced phosphorylation of p38 and JNK MAP kinases within 8-15 min after drug treatment. It is known that Taxol, but not other microtubule-interacting agents, induces the production of cytokines, such as tumor necrosis factor alpha (TNF-alpha) in mouse macrophages. The time course of Taxol-induced TNF-alpha expression coincides with that of Taxol-induced p66shc phosphorylation, and U0126 inhibits significantly Taxol-induced TNF-alpha expression in RAW 264.7 cells. Our data indicate that the Taxol-induced serine phosphorylation of p66shc in RAW 264.7 cells is microtubule-independent and may be related to increased TNF-alpha expression after Taxol and LPS treatment. It is concluded that the mechanisms involved in Taxol-induced p66shc phosphorylation are distinct in A549 and RAW 264.7 cells.
纳摩尔浓度的紫杉醇以及其他与微管相互作用的抗有丝分裂剂，在药物处理9 - 18小时后，可介导A549人肺癌细胞中66-kDa Shc亚型（p66shc）的丝氨酸磷酸化。这一事件与聚（ADP-核糖）聚合酶（PARP）裂解片段的释放同时发生，而PARP裂解片段是细胞凋亡的早期指标。紫杉醇诱导的p66shc丝氨酸磷酸化源于一条不依赖丝裂原活化蛋白激酶（MEK）的信号通路，该通路在细胞周期有延长或异常有丝分裂期的A549细胞中被激活[《癌症研究》60 (2000) 5171]。相比之下，在鼠巨噬细胞RAW 264.7细胞中，微摩尔浓度的紫杉醇而非其他与微管相互作用的药物，在紫杉醇处理后15 - 30分钟内可诱导p66shc的丝氨酸磷酸化，这与Raf-1和细胞外信号调节激酶（ERK1/2）的磷酸化相关。这一事件也可由脂多糖（LPS）诱导。特异性抑制ERK激活的MEK抑制剂U0126，也可阻断p66shc和Raf-1的磷酸化，这表明这些过程依赖MEK，与在A549细胞中观察到的情况截然不同。紫杉醇在药物处理后8 - 15分钟内还可诱导p38和应激活化蛋白激酶（JNK）的磷酸化。已知紫杉醇而非其他与微管相互作用的药物，可诱导小鼠巨噬细胞中细胞因子的产生，如肿瘤坏死因子α（TNF-α）。紫杉醇诱导TNF-α表达的时间进程与紫杉醇诱导p66shc磷酸化的时间进程一致，且U0126可显著抑制RAW 264.7细胞中紫杉醇诱导的TNF-α表达。我们的数据表明，RAW 264.7细胞中紫杉醇诱导的p66shc丝氨酸磷酸化不依赖微管，可能与紫杉醇和LPS处理后TNF-α表达增加有关。得出的结论是，紫杉醇诱导p66shc磷酸化的机制在A549细胞和RAW 264.7细胞中是不同的。
