Role of MARCKS in regulating endothelial cell proliferation

Myristoylated alanine-rich C kinase substrate (MARCKS), as a specificprotein kinase C (PKC) substrate, mediates PKC signaling through itsphosphorylation and subsequent modification of its association withfilamentous actin (F-actin) and calmodulin (CaM). PKC has long beenimplicated in cell proliferation, and recent studies have suggestedthat MARCKS may function as a cell growth suppressor. Therefore, in thepresent study, we investigated MARCKS protein expression, distribution,and phosphorylation in preconfluent and confluent bovine pulmonarymicrovascular endothelial cells (BPMEC) in the presence or absence ofthe vascular endothelial growth factor (VEGF). In addition, we examinedfunctional alterations of MARCKS in these cells by studying theassociation of MARCKS with F-actin and CaM-dependent myosin light chain(MLC) phosphorylation. Our results indicate that MARCKS protein isdownregulated during BPMEC proliferation. Decreased MARCKSassociation with F-actin, increased actin polymerization, andCaM-dependent MLC phosphorylation appear to mediate cell shape changesand motility during BPMEC growth. In contrast, VEGF stimulated MARCKSphosphorylation without alteration of protein expression during BPMECproliferation, which may result in reduced interaction between MARCKSand actin or CaM, leading to actin reorganization and MLCphosphorylation. Our data suggest a regulatory role of MARCKS duringendothelial cell proliferation.