Takeya Kosuke, Wang Xuemei, Sutherland Cindy, Kathol Iris, Loutzenhiser Kathy, Loutzenhiser Rodger D, Walsh Michael P
Department of Physiology, Asahikawa Medical College, Hokkaido, Japan.
J Smooth Muscle Res. 2014;50:18-28. doi: 10.1540/jsmr.50.18.
Smooth muscle contraction is activated primarily by phosphorylation at Ser19 of the regulatory light chain subunits (LC20) of myosin II, catalysed by Ca(2+)/calmodulin-dependent myosin light chain kinase. Ca(2+)-independent contraction can be induced by inhibition of myosin light chain phosphatase, which correlates with diphosphorylation of LC20 at Ser19 and Thr18, catalysed by integrin-linked kinase (ILK) and zipper-interacting protein kinase (ZIPK). LC20 diphosphorylation at Ser19 and Thr18 has been detected in mammalian vascular smooth muscle tissues in response to specific contractile stimuli (e.g. endothelin-1 stimulation of rat renal afferent arterioles) and in pathophysiological situations associated with hypercontractility (e.g. cerebral vasospasm following subarachnoid hemorrhage). Comparison of the effects of LC 20 monophosphorylation at Ser19 and diphosphorylation at Ser19 and Thr18 on contraction and relaxation of Triton-skinned rat caudal arterial smooth muscle revealed that phosphorylation at Thr18 has no effect on steady-state force induced by Ser19 phosphorylation. On the other hand, the rates of dephosphorylation and relaxation are significantly slower following diphosphorylation at Thr18 and Ser19 compared to monophosphorylation at Ser19. We propose that this diphosphorylation mechanism underlies the prolonged contractile response of particular vascular smooth muscle tissues to specific stimuli, e.g. endothelin-1 stimulation of renal afferent arterioles, and the vasospastic behavior observed in pathological conditions such as cerebral vasospasm following subarachnoid hemorrhage and coronary arterial vasospasm. ILK and ZIPK may, therefore, be useful therapeutic targets for the treatment of such conditions.
平滑肌收缩主要由肌球蛋白轻链激酶（受Ca(2+)/钙调蛋白依赖性激活）催化肌球蛋白II调节轻链亚基（LC20）的Ser19位点磷酸化而激活。抑制肌球蛋白轻链磷酸酶可诱导不依赖Ca(2+)的收缩，这与整合素连接激酶（ILK）和拉链相互作用蛋白激酶（ZIPK）催化的LC20在Ser19和Thr18位点的双磷酸化有关。在哺乳动物血管平滑肌组织中，已检测到在特定收缩刺激（如内皮素-1刺激大鼠肾入球小动脉）以及与过度收缩相关的病理生理情况（如蛛网膜下腔出血后的脑血管痉挛）下，LC20在Ser19和Thr18位点的双磷酸化。比较LC20在Ser19位点的单磷酸化以及在Ser19和Thr18位点的双磷酸化对用曲拉通处理的大鼠尾动脉平滑肌收缩和舒张的影响，结果显示Thr18位点的磷酸化对由Ser19磷酸化诱导的稳态力没有影响。另一方面，与Ser19位点的单磷酸化相比，Thr18和Ser19位点双磷酸化后的去磷酸化速率和舒张速率明显更慢。我们认为，这种双磷酸化机制是特定血管平滑肌组织对特定刺激（如内皮素-1刺激肾入球小动脉）产生延长收缩反应以及在诸如蛛网膜下腔出血后的脑血管痉挛和冠状动脉痉挛等病理状况下观察到的血管痉挛行为的基础。因此，ILK和ZIPK可能是治疗此类病症的有用治疗靶点。
