MYOSIN AND CALDESMON PHOSPHORYLATION IN NONMUSCLE CELLS

Caldesmon是一种肌动蛋白结合蛋白，可能调节基于肌动蛋白的 细胞过程。这些活动包括胞质分裂、形状 改变，细胞运动，细胞与细胞的相互作用，对底物的黏附和 分泌物。体外研究表明，钙离子通道阻滞剂可以抑制 肌球蛋白的肌动蛋白激活的镁ATPase活性，这种抑制可以 通过钙调素与钙调蛋白结合而逆转。Caldesmon是一种底物 各种不同的激酶，已被证明在平滑过程中被磷酸化 肌肉收缩。当人类血小板被激活时，它也会被磷酸化 用佛波酯处理过的。 我们已经检测了治疗后钙调蛋白的磷酸化。 含有凝血酶、ADP和胶原等生理激动剂的血小板 在前列腺素PGI2治疗后，它会提高cAMP水平。 钙调蛋白的磷酸化水平或位置没有增加。 在用凝血酶、ADP或胶原治疗血小板后，但 用PGI2处理后，磷酸化水平增加。胰酶 磷酸多肽图谱显示，这种磷酸化主要发生在 在体外也被cAMP依赖性磷酸化的两个位点 蛋白激酶。

Caldesmon is an actin-binding protein which may modulate actin-based cellular processes. These include activities such as cytokinesis, shape change, cell motility, cell to cell interactions, adhesion to substrata and secretion. In vitro studies have shown that caldesmon can inhibit the actin-activated MgATPase activity of myosin and that this inhibition can be reversed by calmodulin binding to caldesmon. Caldesmon is a substrate for various kinases and has been shown to be phosphorylated during smooth muscle contraction. It is also phosphorylated when human platelets are treated with phorbol esters. We have examined the phosphorylation of caldesmon following treatment of platelets with physiological agonists such as thrombin, ADP and collagen and after treatment with the prostaglandin, PGI2, which raises cAMP levels. There is no increase in the level or sites of phosphorylation of caldesmon following treatment of platelets with thrombin, ADP or collagen, but treatment with PGI2 results in an increase in phosphorylation. Tryptic phosphopeptide maps show that this phosphorylation is primarily occurring at two sites which are also phosphorylated in vitro by cAMP-dependent protein kinase.