SIGNAL TRANSDUCTION PATHWAYS IN RESPONSE TO STRESS

工作总结：本课题研究的重点是信号转导 哺乳动物细胞中调节应激反应的途径。关于中国的研究 过去的一年集中在三个主题上。 (1)识别ERK信号的上游调控因子 亚砷酸盐。我们之前已经证明了亚砷酸盐可以 差异激活ERK、JNK和p38 MAP激酶。激活 ERK依赖RAS。现在我们发现亚砷酸盐可以刺激 Shc的酪氨酸磷酸化及其与接头的相互作用 Grb2蛋白。Shc的酪氨酸磷酸化与 一种未知的高分子量蛋白质的酪氨酸磷酸化， 它与之相互作用。该蛋白可能是Shc的激活剂 在应激过程中，启动RAS/ERK信号通路。 (2)应激反应中p90RSK的激活及其与 IKB。P90RSK是一种丝氨酸/苏氨酸蛋白激酶，位于 ERK，因此被有丝分裂刺激激活。我们发现 P90RSK可以被包括亚砷酸盐在内的许多应激条件激活， 双氧水和甲烷磺酸甲酯。P90RSK激活被发现 与IKB的磷酸化和降解有关，IKB是一种 转录因子核因子-kB。P90RSK可能作为IKB激酶发挥作用 在应激过程中促进核因子-kB的激活。 (3)EGF刺激的肝细胞中p70S6K的表达随年龄增长而下降。老龄化 与细胞增殖能力下降有关。 在此之前，我们发现这与ERK降低有关 有丝分裂刺激的激活。我们现在观察到还有 P70S6K活性随增龄而显著下降。因此，缺陷 在至少两条不同的信号转导途径中可能解释了 增殖力与年龄相关的缺陷。对上游的分析 这两条途径共有的监管机构可能会为 衰老的基本机制。

Summary of work: This project focusses on the signal transduction pathways mediating stress responses in mammalian cells. Studies over the past year have concentrated on three topics. (1) Identification of upstream regulators of ERK signaling in response to arsenite. We have previously demonstrated that arsenite can differentially activate ERK, JNK and p38 MAP kinases. The activation of ERK is dependent on Ras. Now we have found that arsenite can stimulate the tyrosine phosphorylation of Shc and its interaction with the adaptor protein Grb2. Tyrosine phosphorylation of Shc was concommitant with tyrosine phosphorylation of an unidentified high molecular weight protein, with which it interacts. This protein may function as an activator of Shc during stress, initiating the Ras/ERK signaling cascade. (2) p90RSK activation in response to stress and its relationship with IkB. p90RSK is a serine/threonine protein kinase which lies downstream of ERK, and is therefore activated by mitogenic stimuli. We found that p90RSK can be activated by many stressful conditions including arsenite, H2O2 and methyl methanesulfonate. p90RSK activation was found to correlate with the phosphorylation and degradation of IkB, an inhibitor of the transcription factor NF-kB. p90RSK may function as an IkB kinase and contribute to NF-kB activation during stress. (3) Age-associated decline in p70S6k in EGF-stimulated hepatocytes. Aging is associated with a decline in the proliferative capacity of cells. Previously we showed that this was correlated with decreased ERK activation by mitogenic stimuli. We have now observed that there is also a significant decline in the activity of p70S6k with aging. Thus, defects in at least two distinct signal transduction pathways may account for the age-associated defect in proliferative capacity. Analysis of the upstream regulators common to both pathways may provide important insights into the basic mechanisms of the aging.