Uncoordinated Regulation of Stress Fibers and Focal Adhesions and Suppression of Integrin Activity and ECM Survival Signals by DAPK.

Ruey-Hwa Chen

《Journal of Genetics and Molecular Biology》 13卷4期 (2002/12) Pp. 296-296

https://doi.org/10.30047/JGMB.200212.0010

並列摘要

Death associated protein kinase (DAPK) is a calcium/calmodulin-dependent serine/threonine kinase, and participates in a variety of apoptotic systems. However, its pro-apoptotic mechanism and intracellular substrates have not been well studied. Here, we demonstrate that DAPK phosphorylates the requlatory light chain of myosin II (MLC) at Ser19. DAPK triggers the assembly or stabilization of stress fibers in quiescent fibroblasts through its phosphorylation of MLC, and is required for serum-induced stress fiber formation. However, it 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. These results identify a novel and unique function of DPK in the uncoupling of stress fibers and focal adhesions, which may lead to a perturbation of the balance between contractile and adhesion forces and subsequent cell detachment. Indeed, we found that DAPK suppresses integrin-mediated cell adhesion by downregulatino of integrin activity through an inside-out mechanism. We present several lines of evidence indicating that this adhesion-inhibitory effect accounts for a major mechanism of the apoptosis induced by DAPK. First, in growth-arrested fibroblasts, DAPK triggers apoptosis in cells plated on fibronectin, but does not affect the death of cells on poly-L-lysine. Second, in epithelial cells, DAPK induces apoptosis in the anoikis-sensitive cells, but not in the anoikis-resistant cells. Most importantly, the apoptosis-promoting effect of DAPK is completely abolished by enforced acrivation of integrin-mediated signaling pathways from either integrin itself or its downstream effector FAK. Finally, FAK activaton blocks the ability of DAPK to upregulate p53. Altogether, our results indicate that DAPK exerts apoptotic effect by perturbation of cytokeletal architecture and suppression of integrin-mediated cell dhesion, thereby activating a p53-dependent apoptotic pathway.