Koga Yasuhiko, Ikebe Mitsuo
Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
J Biol Chem. 2005 Feb 11;280(6):4983-91. doi: 10.1074/jbc.M410909200. Epub 2004 Nov 14.
p116Rip was originally found to be a RhoA-binding protein, but its function has been unknown. Here, we clarify the function of p116Rip. Two critical findings were made. First, we found that p116Rip activated the GTPase activity of RhoA in vitro and that p116Rip overexpression in cells consistently diminished the epidermal growth factor-induced increase in GTP-bound RhoA. Second, p116Rip activated the myosin light chain phosphatase (MLCP) activity of the holoenzyme. p116Rip did not activate the catalytic subunit alone, indicating that the activation is due to the binding of p116Rip to the myosin phosphatase targeting subunit MYPT1. Interestingly, the activation of phosphatase was specific to myosin as substrate, and p116Rip directly bound to myosin, thus facilitating myosin/MLCP interaction. The gene silencing of p116Rip consistently and significantly increased myosin phosphorylation as well as stress fiber formation in cells. Based upon these findings, we propose that p116Rip is an important regulatory component that controls the RhoA signaling pathway, thus regulating MLCP activity and myosin phosphorylation in cells.
p116Rip最初被发现是一种与RhoA结合的蛋白质，但其功能尚不清楚。在此，我们阐明了p116Rip的功能。有两个关键发现。第一，我们发现p116Rip在体外激活了RhoA的GTP酶活性，并且在细胞中过表达p116Rip持续降低了表皮生长因子诱导的结合GTP的RhoA增加。第二，p116Rip激活了全酶的肌球蛋白轻链磷酸酶（MLCP）活性。p116Rip单独不能激活催化亚基，这表明激活是由于p116Rip与肌球蛋白磷酸酶靶向亚基MYPT1结合所致。有趣的是，磷酸酶的激活以肌球蛋白为底物具有特异性，并且p116Rip直接与肌球蛋白结合，从而促进肌球蛋白/MLCP相互作用。p116Rip的基因沉默持续且显著增加了细胞中的肌球蛋白磷酸化以及应力纤维形成。基于这些发现，我们提出p116Rip是控制RhoA信号通路的重要调节成分，从而调节细胞中的MLCP活性和肌球蛋白磷酸化。
