Sequential regulation of α4β1 and α5β1 integrin avidity by CC chemokines in monocytes: Implications for transendothelial chemotaxis

Abstract

Leukocyte emigration possibly requires dynamic regulation of integrin adhesiveness for endothelial and extracellular matrix ligands. Adhesion assays on purified vascular cell adhesion molecule (VCAM)-1, fibronectin, and fibronectin fragments revealed distinct kinetic patterns for the regulation of very late antigen (VLA)-4 (α4β1) and VLA-5 (α5β1) avidity by the CC chemokines monocyte inflammatory protein (MIP)-1α, RANTES (regulated on activation, normal T expressed and secreted), or monocyte chemoattractant protein (MCP)-1 in monocytes. CC chemokines induced early activation and subsequent deactivation of VLA-4, whereas upregulation of VLA-5 avidity occurred later and persisted. Controlled detachment assays in shear flow suggested that adhesive strength of VLA-4 for VCAM-1 or the 40-kD fragment of fibronectin (FN40) is more rapidly increased and subsequently reduced by MCP- 1 than by MIP-1α, and confirmed late and sustained activation of the adhesive strength of VLA-5 for the 120-kD fragment of fibronectin (FN120). Mn2+ or the stimulating β1 mAb TS2/16 strongly and stably enhanced monocyte binding to VCAM-1 or fibronectin, and locked β1 integrins in a high avidity state, which was not further modulated by CC chemokines. Mn2+ and mAb TS2/16 inhibited CC chemokine-induced transendothelial migration, particularly chemotaxis across stimulated endothelium that involved VLA-4 and VCAM-1. VLA-4 on Jurkat cells is of constitutively high avidity and interfered with migration across barriers expressing VCAM-1. Low but not high site densities of VCAM-1 or FN40 promoted, while FN120 impaired, β1 integrin-dependent monocyte chemotaxis to MCP-1 across filters coated with these substrates. Thus, we show that CC chemokines can differentially and selectively regulate avidity of integrins sharing common β subunits. Transient activation and deactivation of VLA-4 may serve to facilitate transendothelial diapedesis, whereas late and prolonged activation of VLA-5 may mediate subsequent interactions with the basement membrane and extracellular matrix.