Kuo Jean-Cheng, Lin Jia-Ren, Staddon James M, Hosoya Hiroshi, Chen Ruey-Hwa
Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
J Cell Sci. 2003 Dec 1;116(Pt 23):4777-90. doi: 10.1242/jcs.00794.
Death-associated protein kinase (DAP kinase) is a proapoptotic, calcium/calmodulin-dependent serine/threonine kinase. Here, we report that DAP kinase phosphorylates the regulatory light chain of myosin II (MLC) both in vitro and in vivo, and that this phosphorylation occurs preferentially at residue Ser19. In quiescent fibroblasts, DAP kinase stabilizes stress fibers through phosphorylation of MLC, but it is dispensable for the formation of peripheral microfilament bundles. This cytoskeletal effect of DAP kinase occurs before the onset of apoptosis and does not require an intact death domain. In addition, DAP kinase is required for serum-induced stress-fiber formation, which is associated with the upregulation of its catalytic activity. Despite being both sufficient and necessary for the assembly or maintenance of stress fibers, DAP kinase is incapable of stimulating the formation of focal adhesions in quiescent cells. Moreover, it promotes the disassembly of focal adhesions but not stress fibers in cells receiving serum factors. Together, our results identify a novel and unique function of DAP kinase in the uncoupling of stress fibers and focal adhesions. Such uncoupling would lead to a perturbation of the balance between contractile and adhesion forces and subsequent cell detachment, which might contribute to its pro-apoptotic activity.
死亡相关蛋白激酶（DAP激酶）是一种促凋亡的、钙/钙调蛋白依赖性丝氨酸/苏氨酸激酶。在此，我们报告DAP激酶在体外和体内均能磷酸化肌球蛋白II的调节轻链（MLC），且这种磷酸化优先发生在丝氨酸19位点。在静止的成纤维细胞中，DAP激酶通过磷酸化MLC来稳定应力纤维，但它对于外周微丝束的形成并非必需。DAP激酶的这种细胞骨架效应发生在细胞凋亡开始之前，且不需要完整的死亡结构域。此外，血清诱导的应力纤维形成需要DAP激酶，这与其催化活性的上调相关。尽管DAP激酶对于应力纤维的组装或维持既充分又必要，但它无法刺激静止细胞中粘着斑的形成。而且，在接受血清因子的细胞中，它促进粘着斑的解体而非应力纤维的解体。总之，我们的结果确定了DAP激酶在应力纤维和粘着斑解偶联中的一种新的独特功能。这种解偶联将导致收缩力和粘附力之间平衡的扰动以及随后的细胞脱离，这可能有助于其促凋亡活性。
