Myat M M, Anderson S, Allen L A, Aderem A
University of Washington, Department of Immunology, Seattle 98195-7650, USA.
Curr Biol. 1997 Aug 1;7(8):611-4. doi: 10.1016/s0960-9822(06)00262-4.
The dynamic rearrangement of the actin cytoskeleton is fundamental to most biological processes including embryogenesis, morphogenesis, cell movement, wound healing and metastasis [1]. Membrane ruffling and reversible cell-substratum interactions underlie actin-driven cell movement. Protein kinase C (PKC) stimulates membrane ruffling and adhesion [2], but the mechanism by which this occurs is unknown. Myristoylated alaninerich C kinase substrate (MARCKS) is a PKC substrate that cycles on and off membranes by a mechanism termed the myristoyl-electrostatic switch [3-6]. While at the membrane, MARCKS binds to and sequesters acidic phospholipids including phosphatidyl-inositol-4,5-bisphosphate (PIP2) [7]. MARCKS also binds and cross-links filamentous actin, an activity which is regulated by PKC-dependent phosphorylation and calcium-calmodulin [3]. In this report, we demonstrate that expression, in fibroblasts, of MARCKS containing a mutation which abrogates the myristoyl-electrostatic switch prevents cell spreading. The MARCKS mutant arrests the cell during an early stage of spreading, characterized by profuse membrane blebbing, and prevents the formation of membrane ruffles and lamellae usually found at the leading edge of spreading cells. This defect in the regulation of the actin cytoskeleton is accompanied by a decrease in cell-substratum adhesion. Our results provide direct evidence that MARCKS and PKC regulate actin-dependent membrane ruffling and cell adhesion, perhaps via a PIP2-dependent mechanism.
肌动蛋白细胞骨架的动态重排是大多数生物过程的基础，包括胚胎发育、形态发生、细胞运动、伤口愈合和转移[1]。膜皱褶和可逆的细胞与基质相互作用是肌动蛋白驱动的细胞运动的基础。蛋白激酶C（PKC）刺激膜皱褶和黏附[2]，但其发生机制尚不清楚。肉豆蔻酰化富含丙氨酸的C激酶底物（MARCKS）是一种PKC底物，通过一种称为肉豆蔻酰静电开关的机制在膜上循环开启和关闭[3-6]。在膜上时，MARCKS结合并隔离酸性磷脂，包括磷脂酰肌醇-4,5-二磷酸（PIP2）[7]。MARCKS还结合并交联丝状肌动蛋白，这种活性受PKC依赖性磷酸化和钙调蛋白调节[3]。在本报告中，我们证明，在成纤维细胞中表达含有消除肉豆蔻酰静电开关突变的MARCKS可阻止细胞铺展。MARCKS突变体在铺展的早期阶段使细胞停滞，其特征是大量膜泡形成，并阻止通常在铺展细胞前缘发现的膜皱褶和片状伪足的形成。肌动蛋白细胞骨架调节的这种缺陷伴随着细胞与基质黏附的减少。我们的结果提供了直接证据，表明MARCKS和PKC可能通过一种依赖PIP2的机制调节肌动蛋白依赖性膜皱褶和细胞黏附。
