MYOSIN AND CALDESMON PHOSPHORYLATION IN NONMUSCLE CELLS

肌动蛋白和肌球蛋白参与了许多收缩活动 在非肌肉细胞中，包括胞质分裂、吞噬和细胞 运动 这两种蛋白质相互作用的调节是 对正常细胞功能至关重要 至少有两种可能 监管体系在其中。 其中之一是肌球蛋白光 链激酶依赖的肌球蛋白磷酸化。 该激酶 由钙和钙调素调节。 肌球蛋白必须磷酸化 命令被激活。 另一个系统涉及钙调素，一种肌动蛋白， 钙调素结合蛋白在体外可抑制肌球蛋白的活性。 这种抑制作用可以通过钙调素与钙调素结合而逆转。 钙调素是各种激酶的底物，并且已被证明是 在平滑肌收缩期间磷酸化。 也是 当人血小板以100 μ mol/L的浓度用海兰素处理时， cAMP依赖性蛋白激酶体外磷酸化位点。 我们有 检测了钙调素上被这种激酶磷酸化的位点，发现 它们位于分子的氨基末端区域。 我们也开始研究收缩蛋白的作用 激动剂诱导的人类微小梁细胞收缩。 这些 细胞有许多特性使它们非常适合这些， 类型的研究。 它们含有大量的肌球蛋白， 在培养物中传播表型，收缩至其原始表型约一半 在约20分钟的时间范围内加入激动剂后的表面积 并且可以容易地在培养物中生长。

Actin and myosin are involved in a host of contractile events in nonmuscle cells including cytokinesis, phagocytosis and cell locomotion. The regulation of the interaction of these two proteins is critical to normal cell function. There are at least two possible regulatory systems involved in this. One of these is the myosin light chain kinase-dependent phosphorylation of myosin. This kinase is regulated by calcium and calmodulin. Myosin must be phosphorylated in order to be activated. The other system involves caldesmon, an actin and calmodulin binding protein which can inhibit myosin's activity in vitro. The 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 prostaglandins at sites phosphorylated in vitro by cAMP-dependent protein kinase. We have examined the sites phosphorylated on caldesmon by this kinase and find that they are in the amino-terminal region of the molecule. We have also started to study the role of contractile proteins in the agonist-induced contraction of human microtrabecular cells. These cells have many characteristics that make them very suitable for these, types of studies. They contain a large amount of myosin, have a well spread phenotype in culture, contract to about one-half of their original surface area upon addition of agonist in a time frame of about 20 minutes and can be easily grown in culture.