Elucidation of the activation mechanisms and functions of ASK1

细胞持续暴露于来自外部和内部环境的各种物理，化学和生物应激源。为了适应或抵抗压力，细胞配备了多种信号系统，引起广泛的压力反应。作为这种信号系统的一个组成部分，我们集中在细胞凋亡信号调节激酶1（ASK 1），c-Jun N-末端激酶（JNK）和p38 MAPK通路的丝裂原活化蛋白激酶（MAPK）激酶（MAP 3 K）。本课题主要研究了ASK 1的激活及其在细胞存活、凋亡和分化中的作用。最后，我们证明了以下几点：1）内源性ASK 1形成高分子量复合物。ASK 1通过抑制因子从ASK 1复合物上解离，随后激活因子相互募集到复合物上而被激活（J. Biol. Chem.，2005）。2）我们已经鉴定了一种新的MAP 3 K，ASK 2，其与ASK 1相互作用。ASK 2通过与ASK 1形成功能性异聚复合物在应激反应中起重要作用，其中ASK 1和ASK 2通过不同的机制促进彼此的活性（J. Biol. Chem.，3）我们已经鉴定了一种新的蛋白磷酸酶PGLM作为ASK 1的相互作用蛋白。PGLM似乎通过抑制ASK 1活性的磷酸化位点的直接去磷酸化来激活ASK 1。4）ASK 1通过在TLR 4下游产生的ROS响应于脂多糖（LPS）而被激活，并且通过p38途径在先天免疫应答中起关键作用（Nat. Immunol.，2005）. 5）ASK 1是创伤诱导的巨噬细胞浸润和活化所必需的，并且在小鼠中作为创伤诱导的毛发生长的诱导物起作用。这些发现强烈地表明，ASK 1作为细胞内信号传导系统的中间体在细胞对各种应激源的反应中起关键作用。

Cells are continuously exposed to a wide variety of physical, chemical, and biological stressors from both the external and internal environments. In order to adapt to or resist stress, cells are equipped with multiple signaling systems that elicit a wide range of stress responses. As a component of such signaling systems, we focused on apoptosis signal-regulating kinase 1 (ASK1), a mitogen-activated protein kinase (MAPK) kinase kinase (MAP3K) of the c-Jun N-terminal kinase (JNK) and p38 MAPK pathways. In this project, we investigated the molecular mechanisms of ASK1 activation and its function in cell survival and apoptosis as well as cell differentiation. Finally, we demonstrated the following:1) Endogenous ASK1 forms a high molecular mass complex. ASK1 is activated through the dissociation of inhibitory factors from the ASK1 complex followed by the reciprocal recruitment of activation factors to the complex (J. Biol. Chem., 2005).2) We have identified a novel MAP3K, ASK2, which interacts with ASK1. ASK2 plays important roles in stress responses by forming a functional heteromeric complex with ASK1, in which ASK1 and ASK2 facilitate each other's activity by distinct mechanisms (J. Biol. Chem., 2007).3) We have identified a novel protein phosphatase, PGLM, as an interacting protein of ASK1. PGLM appears to activate ASK1 by direct dephosphorylation of the phosphorylation site(s) that inhibits ASK1 activity.4) ASK1 is activated in response to lipopolysaccharide (LPS) through ROS that are produced downstream of TLR4, and plays critical roles in innate immune response through the p38 pathway (Nat. Immunol., 2005).5) ASK1 is required for wounding-induced infiltration and activation of macrophages, and functions as an inducer of wounding-induced hair growth in mice.These findings strongly suggest that ASK1 plays critical roles in cellular response to a variety of stressors as an intermediate of the intracellular signaling system.