CLUSTERING THE ADHESION MOLECULES VLA-4 (CD49D CD29) IN JURKAT T-CELLS OR VCAM-1 (CD106) IN ENDOTHELIAL (ECV-304) CELLS ACTIVATES THE PHOSPHOINOSITIDE PATHWAY AND TRIGGERS CA2+ MOBILIZATION/

Ligation of very late antigen (VLA)-4 (alpha(4) beta(1) integrin) with a cross-linked anti-alpha(4) subunit monoclonal antibody (mAb) trigge red a biphasic Ca2+ response in Jurkat cell populations and in periphe ral human lymphocytes. Cross-linking vascular cell adhesion molecule ( VCAM)-1 (the counter-receptor of VLA-4) in ECV 304 endothelial cells g enerated a biphasic Ca2+ response. Tumor necrosis factor-alpha-primed human umbilical cord vascular endothelial cells also responded to the cross-linked mAb with a biphasic Ca2+ profile. Ligated VLA-4 (Jurkat c ells) or VCAM-1 (ECV 304) stimulated the production of myo-inositol 1, 4,5-trisphosphate. ECV 304 cells induced a biphasic Ca2+ response in F ura2-loaded Jurkat cells, whereas a transient response was observed wh en Jurkat cells were added to Fura2-loaded ECV 304 cells. The Ca2+ res ponses in these experiments involved VLA-4/VCAM-1 interactions since t hey were significantly reduced (similar to 80 %) by prior treatment of the target cells with the relevant noncross-linked mAb. Close contact between the cells triggered mutual Ca2+ signaling as shown by spectro fluorimetric and confocal microscopy time-dependent recordings. Fibron ectin and its CS-1 fragment (V25) triggered a sustained Ca2+ response in Jurkat cells (confocal microscopy). Our results suggest that the VL A-4 and VCAM-1 adhesion molecules can transduce a signal that involves activation of the phosphoinositide pathway and the mobilization of Ca 2+.