Protein kinase C mediation of Ca2+-independent contractions of vascular smooth muscle
Protein kinase C mediation of Ca2+-independent contractions of vascular smooth muscle
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DOI：
10.1139/o96-053
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发表时间：
1996-01-01
影响因子：
2.9
通讯作者：
Morgan, KG
中科院分区：
文献类型：
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作者：
Walsh, MP;Horowitz, A;Morgan, KG
促肿瘤的佛波醇酯诱导血管平滑肌缓慢、持续的收缩，表明蛋白激酶C（PKC）可能在平滑肌收缩性的调节中起作用。在某些情况下，例如，在雪貂主动脉平滑肌中，佛波酯诱导的收缩在[Ca 2 +]（i）或肌球蛋白磷酸化没有变化的情况下发生。PKC参与的直接证据来自于使用单一皂苷透化的雪貂主动脉细胞。一个组成性活性的PKC催化片段诱导一个缓慢的，持续的收缩类似于苯肾上腺素引发的。这两种反应都被PKC的肽抑制剂所消除。即使当[Ca 2 +]减少到接近于零时，也会发生类似幅度的收缩，这意味着PKC的Ca 2+非依赖性同工酶。在雪貂主动脉中发现的两种不依赖Ca ~（2+）的PKC同工酶中，PKC β更可能介导收缩反应，因为（i）PKC β，而不是PKC ζ，对佛波酯有反应;（ii）在苯肾上腺素刺激下，PKC β从肌浆易位到肌膜，而PKC ζ从核周定位易位到核内部;和（iii）当加入到pCa 9的渗透化的雪貂主动脉单细胞中时，PKC β，而不是PKC ζ，诱导了与苯肾上腺素类似的收缩反应。PKC β的一种可能底物是平滑肌特异性细丝相关蛋白，钙调蛋白。钙调蛋白在完整的平滑肌条中被卡巴胆碱、内皮素-1、佛波酯或冈田酸磷酸化。在体外通过PKC（α、β和γ同工酶的混合物）磷酸化钙调蛋白显著降低其对F-肌动蛋白的亲和力，并增强其对跨桥循环速率的抑制。钙调蛋白在体外被PKC β磷酸化，但它是PKC zeta的一种非常差的底物。提出了一种信号转导途径来解释雪貂主动脉的Ca 2+非依赖性收缩，从而细胞外信号触发甘油二酯的产生，而无需Ca 2+瞬变。随后的PKC β的激活将导致钙调蛋白磷酸化，其从细丝中释放，并减轻对跨桥循环的抑制。由于肌球蛋白轻链磷酸化的基础水平（约为0.1 mol P-i/mol轻链），缓慢、持续的收缩是由缓慢的跨桥循环速率引起的。我们还认为，通过PKC β的信号转导是由激活磷酸肌醇周转的激动剂触发的收缩反应的一个组成部分;这可以解释为什么平滑肌经常在反应中产生更大的力量，例如，对α（1）-肾上腺素能激动剂的反应比对K+的反应要大。
Tumour-promoting phorbol esters induce slow, sustained contractions of Vascular smooth muscle, suggesting that protein kinase C (PKC) may play a role in the regulation of smooth muscle contractility. In some cases, e.g., ferret aortic smooth muscle, phorbol ester induced contractions occur without a change in [Ca2+](i) or myosin phosphorylation. Direct evidence for the involvement of PKC came from the use of single saponin-permeabilized ferret aortic cells. A constitutively active catalytic fragment of PKC induced a slow, sustained contraction similar to that triggered by phenylephrine. Both responses were abolished by a peptide inhibitor of PKC. Contractions of similar magnitude occurred even when the [Ca2+] was reduced to close to zero, implicating a Ca2+-independent isoenzyme of PKC. Of the two Ca2+-independent PKC isoenzymes, epsilon and zeta, identified in ferret aorta, PKC epsilon is more likely to mediate the contractile response because (i) PKC epsilon, but not PKC zeta, is responsive to phorbol esters; (ii) upon stimulation with phenylephrine, PKC epsilon translocates from the sarcoplasm to the sarcolemma, whereas PKC zeta translocates from a perinuclear localization to the interior of the nucleus; and (iii) when added to permeabilized single cells of the ferret aorta at pCa 9, PKC epsilon, but not PKC zeta, induced a contractile response similar to that induced by phenylephrine. A possible substrate of PKC epsilon is the smooth muscle specific, thin filament associated protein, calponin. Calponin is phosphorylated in intact smooth muscle strips in response to carbachol, endothelin-1, phorbol esters, or okadaic acid. Phosphorylation of calponin in vitro by PKC (a mixture of alpha, beta, and gamma isoenzymes) dramatically reduces its affinity for F-actin and alleviates its inhibition of the cross-bridge cycling rate. Calponin is phosphorylated in vitro by PKC epsilon but is a very poor substrate of PKC zeta. A signal transduction pathway is proposed to explain Ca2+-independent contraction of ferret aorta whereby extracellular signals trigger diacylglycerol production without a Ca2+ transient. The consequent activation of PKC epsilon would result in calponin phosphorylation, its release from the thin filaments, and alleviation of inhibition of cross-bridge cycling. Slow, sustained contraction then results from a slow rate of cross-bridge cycling because of the basal level of myosin light chain phosphorylation (approximate to 0.1 mol P-i/mol light chain). We also suggest that signal transduction through PKC epsilon is a component of contractile responses triggered by agonists that activate phosphoinositide turnover; this may explain why smooth muscles often develop more force in response, e.g., to alpha(1)-adrenergic agonists than to K+.