Peckham M, Miller G, Wells C, Zicha D, Dunn G A
School of Biomedical Sciences, Worsley Building, University of Leeds, Leeds LS2 9JT, UK.
J Cell Sci. 2001 Apr;114(Pt 7):1367-77. doi: 10.1242/jcs.114.7.1367.
Overexpression of beta-actin is known to alter cell morphology, though its effect on cell motility has not been documented previously. Here we show that overexpressing beta-actin in myoblasts has striking effects on motility, increasing cell speed to almost double that of control cells. This occurs by increasing the areas of protrusion and retraction and is accompanied by raised levels of beta-actin in the newly protruded regions. These regions of the cell margin, however, show decreased levels of polymerised actin, indicating that protrusion can outpace the rate of actin polymerisation in these cells. Moreover, the expression of beta*-actin (a G244D mutant, which shows defective polymerisation in vitro) is equally effective at increasing speed and protrusion. Concomitant changes in actin binding proteins show no evidence of a consistent mechanism for increasing the rate of actin polymerisation in these actin overexpressing cells. The increase in motility is confined to poorly spread cells in both cases and the excess motility can be abolished by blocking myosin function with butanedione monoxime (BDM). Our observations on normal myoblasts are consistent with the view that they protrude by the assembly and cross linking of actin filaments. In contrast, the additional motility shown by cells overexpressing beta-actin appears not to result from an increase in the rate of actin polymerisation but to depend on myosin function. This suggests that the additional protrusion arises from a different mechanism. We discuss the possibility that it is related to retraction-induced protrusion in fibroblasts. In this phenomenon, a wave of increased protrusion follows a sudden collapse in cell spreading. This view could explain why it is only the additional motility that depends on spreading, and has implications for understanding the differences in locomotion that distinguish tissue cells from highly invasive cell types such as leucocytes and malignant cells.
已知β-肌动蛋白的过表达会改变细胞形态，不过其对细胞运动性的影响此前尚无文献记载。在此我们表明，在成肌细胞中过表达β-肌动蛋白对运动性有显著影响，使细胞速度增加至几乎是对照细胞的两倍。这是通过增加细胞突出和回缩的面积实现的，并且新突出区域的β-肌动蛋白水平升高。然而，细胞边缘的这些区域显示出聚合肌动蛋白水平降低，表明在这些细胞中突出速度可能超过肌动蛋白聚合速度。此外，β*-肌动蛋白（一种G244D突变体，在体外显示出聚合缺陷）的表达在增加速度和突出方面同样有效。肌动蛋白结合蛋白的伴随变化没有显示出在这些肌动蛋白过表达细胞中增加肌动蛋白聚合速率的一致机制的证据。在这两种情况下，运动性的增加都局限于铺展不良的细胞，并且通过用丁二酮单肟（BDM）阻断肌球蛋白功能可以消除过度的运动性。我们对正常成肌细胞的观察结果与它们通过肌动蛋白丝的组装和交联而突出的观点一致。相比之下，过表达β-肌动蛋白的细胞所显示的额外运动性似乎并非源于肌动蛋白聚合速率的增加，而是取决于肌球蛋白功能。这表明额外的突出源于不同的机制。我们讨论了它与成纤维细胞中回缩诱导突出相关的可能性。在这种现象中，细胞铺展突然塌陷后会出现一波突出增加的情况。这种观点可以解释为什么只有额外的运动性依赖于铺展，并且对于理解区分组织细胞与高度侵袭性细胞类型（如白细胞和恶性细胞）的运动差异具有启示意义。
