Interaction of (α4 β1) integrin/VCAM‐1 induces Myosin Light Chain phosphorylation in monocytes and endothelial cells

Abstract

We undertook this study to investigate the role of actin cytoskeleton and Myosin Light Chain (MLC) phosphorylation in transendothelial migration (TEM) of monocytes. Our studies demonstrated that exposure of THP‐1 to integrin‐activating antibody induced both Extracellular Signal‐Regulated Kinase (ERK) and MLC phosphorylation. These inductions were more pronounced in the presence of α4β1 ligand, CS‐1fibronectin. Exposure of THP‐1 cells to chemokines (MCP‐1, SDF‐1) induced MLC‐phosphorylation by activation of MLC kinase and inactivation of MLC phosphatase. The chemokine‐induced MLC phosphorylation was accompanied by ERK‐phosphorylation and was inhibited by pre‐exposure of the cells to the inhibitors of MLC kinase, protein kinase C and MEK/ERK. The integrin‐mediated clustering of VCAM‐1 on the endothelial cells (ECs) is mimicked by the crosslinking of antibodies to VCAM‐1. Our studies demonstrated that crosslinking of VCAM‐1 on ECs induces ERK and MLC phosphorylation. The induction of phosphorylation of MLC was attenuated when the cells were pre‐exposed to the inhibitors of MLC kinase, protein kinase C and MEK/ERK. Experiments in the transwell system showed that TEM of monocytes were reduced and enhanced after inhibition and induction of MLC phosphorylation in THP‐1 cells. Our studies demonstrated that interaction of α4β1/VCAM‐1 leads to a critical reaction in TEM of monocytes, phosphorylation of MLC.