VCAM-1 is internalized by a clathrin-related pathway in human endothelial cells but its alpha 4 beta 1 integrin counter-receptor remains associated with the plasma membrane in human T lymphocytes.
Lymphocyte extravasation involves a step(s) of de-adhesion to allow trans- and subendothelial migration in response to inflammatory signals. We show here that ligated VCAM-1 was rapidly internalized (t1/2 14.5 min) in ECV 304 endothelial cells and in TNF-alpha-primed human umbilical vein-derived endothelial cells (t1/2 11.2 min). The process required energy (ATP), intracellular Ca2+, an intact cytoskeletal network and active protein kinases. The internalization of VCAM-1 involved a clathrin-dependent pathway based on the observations that 1) it was inhibited in cells treated with lysosomotropic agents or with a hypertonic concentration of sucrose, and 2) internalized VCAM-1 colocalized with clathrin. In contrast, the cross-linked alpha 4 beta 1 integrin counter-receptor of VCAM-1 remained associated with the plasma membrane of purified peripheral T and Jurkat cells. Our results suggest a model where VCAM-1 would initially participate in the retention of T cells to the endothelium by binding alpha 4 beta 1 integrin. Lymphocyte de-adhesion would be facilitated as a result of the internalization of VCAM-1. The persistent cell surface expression of alpha 4 beta 1 integrin would allow the migrating T cells to interact with and receive signal(s) from its fibronectin ligand of the extracellular matrix.
Ricard
I
I
Department of Biochemistry, Faculty of Medicine, University of Sherbrooke, Quebec, Canada.
Payet
M D
MD
Dupuis
G
G
D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002966:Clathrin / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000032:analysis / Q000378:metabolism*; D019169:Jurkat Cells; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000378:metabolism; D016201:Receptors, Lymphocyte Homing / Q000032:analysis / Q000378:metabolism*; D013601:T-Lymphocytes / Q000378:metabolism*; D013997:Time Factors; D014471:Umbilical Veins; D019010:Vascular Cell Adhesion Molecule-1 / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*
D002966:Clathrin; D039041:Integrin alpha4beta1; D016023:Integrins; D011500:Protein Synthesis Inhibitors; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D016201:Receptors, Lymphocyte Homing; D019010:Vascular Cell Adhesion Molecule-1