Wang Ruping, Li Qing-Fen, Anfinogenova Yana, Tang Dale D
Center for Cardiovascular Sciences, Albany Medical College, 47 New Scotland Ave., MC-8, Albany, NY 12208, USA.
Am J Physiol Lung Cell Mol Physiol. 2007 Jan;292(1):L240-8. doi: 10.1152/ajplung.00199.2006. Epub 2006 Sep 22.
The intermediate filament protein vimentin has been shown to be required for smooth muscle contraction. The adapter protein p130 Crk-associated substrate (CAS) participates in the signaling processes that regulate force development in smooth muscle. However, the interaction of vimentin filaments with CAS has not been well elucidated. In the present study, ACh stimulation of tracheal smooth muscle strips increased the ratio of soluble to insoluble vimentin (an index of vimentin disassembly) in association with force development. ACh activation also induced vimentin phosphorylation at Ser(56) as assessed by immunoblot analysis. More importantly, CAS was found in the cytoskeletal vimentin fraction, and the amount of CAS in cytoskeletal vimentin was reduced in smooth muscle strips on contractile stimulation. CAS redistributed from the myoplasm to the periphery during ACh activation of smooth muscle cells. The ACh-elicited decrease in CAS distribution in cytoskeletal vimentin was attenuated by the downregulation of p21-activated kinase (PAK) 1 with antisense oligodeoxynucleotides. Vimentin phosphorylation at this residue, the ratio of soluble to insoluble vimentin, and active force in smooth muscle strips induced by ACh were also reduced in PAK-depleted tissues. These results suggest that PAK may regulate CAS release from the vimentin intermediate filaments by mediating vimentin phosphorylation at Ser(56) and the transition of cytoskeletal vimentin to soluble vimentin. The PAK-mediated dissociation of CAS from the vimentin network may participate in the cellular processes that affect active force development during ACh activation of tracheal smooth muscle tissues.
中间丝蛋白波形蛋白已被证明是平滑肌收缩所必需的。衔接蛋白p130 Crk相关底物（CAS）参与调节平滑肌中力量产生的信号传导过程。然而，波形蛋白丝与CAS之间的相互作用尚未得到充分阐明。在本研究中，乙酰胆碱（ACh）刺激气管平滑肌条增加了可溶性波形蛋白与不可溶性波形蛋白的比例（波形蛋白解聚的指标），这与力量产生相关。免疫印迹分析评估显示，ACh激活还诱导了波形蛋白在丝氨酸（56）位点的磷酸化。更重要的是，在细胞骨架波形蛋白组分中发现了CAS，并且在收缩刺激下，气管平滑肌条中细胞骨架波形蛋白中的CAS量减少。在平滑肌细胞的ACh激活过程中，CAS从肌浆重新分布到外周。用反义寡脱氧核苷酸下调p21激活激酶（PAK）1可减弱ACh引起的细胞骨架波形蛋白中CAS分布的减少。在PAK缺失的组织中，ACh诱导的波形蛋白在该位点的磷酸化、可溶性波形蛋白与不可溶性波形蛋白的比例以及平滑肌条中的主动力也降低。这些结果表明，PAK可能通过介导波形蛋白在丝氨酸（56）位点的磷酸化以及细胞骨架波形蛋白向可溶性波形蛋白的转变来调节CAS从波形蛋白中间丝的释放。PAK介导的CAS从波形蛋白网络的解离可能参与了影响气管平滑肌组织ACh激活过程中主动力产生的细胞过程。
