cGMP-dependent relaxation of smooth muscle is coupled with the change in the phosphorylation of myosin phosphatase
cGMP-dependent relaxation of smooth muscle is coupled with the change in the phosphorylation of myosin phosphatase
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DOI：
10.1161/circresaha.107.153981
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发表时间：
2007-09-28
影响因子：
20.1
通讯作者：
Ikebe, Mitsuo
中科院分区：
文献类型：
--
作者：
Nakamura, Kensei;Koga, Yasuhiko;Ikebe, Mitsuo
一氧化氮/cGMP通路诱导血管舒张，但其潜在机制尚不清楚。在本研究中，我们研究了环鸟苷酸（cGMP）诱导的平滑肌收缩装置松弛的机制，使用透化的兔股动脉平滑肌。8-Br-cGMP诱导的舒张伴随着肌球蛋白轻链（MLC）磷酸化的减少。MLC磷酸酶（MLCP）的活性，一旦激动剂刺激下降，恢复到静息水平上添加8-Br-cGMP。由于MLCP活性受MLCP特异性抑制剂（Thr 38处的CPI 17和Thr 696处的MBS（MLCP的肌球蛋白结合亚基））的磷酸化调节，因此我们检查了8-Br-cGMP对这些MLCP调节剂磷酸化的影响。而CPI 17磷酸化在加入8-Br-cGMP后没有变化，MBS在Thr 696的磷酸化被8-Br-cGMP显著降低。我们发现，8-Br-cGMP显着增加MBS磷酸化的Ser 695在纤维中预处理苯肾上腺素。MBS磷酸化Thr 696磷酸化MBS的Ser 695部分恢复MLCP活性抑制Thr 696磷酸化。而Ser 695磷酸化显着增加，在纤维中的Ser 695和Thr 696的二磷酸化MBS的程度是不变的cGMP刺激后。我们发现，MBS磷酸酶活性在动脉中的二磷酸化MBS和单磷酸化MBS在Thr 696显着增加8-Br-cGMP，而MBS激酶活性不变。这些结果表明，由cGMP诱导的Ser 640磷酸化使Thr 641磷酸化的平衡向去磷酸化方向移动，从而增加MLCP活性。这导致MLC磷酸化和平滑肌松弛的减少。
Nitric oxide/cGMP pathway induces vasodilatation, yet the underlying mechanism is obscure. In the present study, we studied the mechanism of cGMP-induced relaxation of the smooth muscle contractile apparatus using permeabilized rabbit femoral arterial smooth muscle. 8-Br-cGMP-induced relaxation was accompanied with a decrease in myosin light chain (MLC) phosphorylation. MLC phosphatase (MLCP) activity, once decreased by agonist-stimulation, recovered to the resting level on addition of 8-Br-cGMP. Because MLCP activity is regulated by the phosphorylation of a MLCP-specific inhibitor, CPI17 at Thr38 and MBS (myosin binding subunit of MLCP) at Thr696, we examined the effect of 8-Br-cGMP on the phosphorylation of these MLCP modulators. Whereas CPI17 phosphorylation was unchanged after addition of 8-Br-cGMP, MBS phosphorylation at Thr696 was significantly decreased by 8-Br-cGMP. We found that 8-Br-cGMP markedly increased MBS phosphorylation at Ser695 in the fiber pretreated with phenylephrine. MBS phosphorylation of Thr696 phosphorylated MBS at Ser695 partially resumed MLCP activity inhibited by Thr696 phosphorylation. Whereas Ser695 phosphorylation was markedly increased, the extent of diphosphorylated MBS at Ser695 and Thr696 in fibers was unchanged after cGMP-stimulation. We found that MBS phosphatase activity in arteries for both diphosphorylated MBS and monophosphorylated MBS at Thr696 significantly increased by 8-Br-cGMP, whereas MBS kinase activity was unchanged. These results suggest that the phosphorylation at Ser640 induced by cGMP shifted the equilibrium of the Thr641 phosphorylation toward dephosphorylation, thus increasing MLCP activity. This results in the decrease in MLC phosphorylation and smooth muscle relaxation.