Elucidation of the activation mechanisms and functions of ASK1

细胞不断地暴露在来自外部和内部环境的各种物理、化学和生物应激源中。为了适应或抵抗压力，细胞配备了多种信号系统，这些信号系统可以引发广泛的应激反应。作为这类信号系统的一个组成部分，我们重点研究了凋亡信号调节激酶1(ASK1)、c-jun氨基末端激酶(JNK)的丝裂原活化蛋白激酶(MAP3K)和p38 MAPK通路。在本项目中，我们研究了ASK1激活的分子机制及其在细胞存活、凋亡和细胞分化中的作用。结果表明：1)内源性ASK1形成了一个高分子质量的复合体。ASK1是通过从ASK1复合体中解离抑制因子，然后激活因子相互补充到复合体中而被激活的(J.Biol。我们已经鉴定出一种新的MAP3K，ASK2，它与ASK1相互作用。ASK2通过与ASK1形成功能性异构体复合体，在胁迫反应中发挥重要作用，其中ASK1和ASK2通过不同的机制促进彼此的活性(J.Biol.3)我们已经鉴定出一种新的蛋白磷酸酶PGLm，它是ASK1的相互作用蛋白。4)ASK1通过TLR4下游产生的ROS被激活，并通过p38途径(NAT)在先天性免疫反应中发挥关键作用。5)ASK1是创伤诱导巨噬细胞渗入和激活所必需的，也是创伤诱导小鼠毛发生长的诱导剂。这些发现有力地表明，ASK1作为细胞内信号系统的中介，在细胞对各种应激源的反应中发挥着关键作用。

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.