EXPRESSION OF GLYCOPHOSPHATIDYLINOSITOL-ANCHORED AND GLYCOPHOSPHATIDYLINOSITOL-NONANCHORED ISOFORMS OF VASCULAR CELL-ADHESION MOLECULE-1 INMURINE STROMAL AND ENDOTHELIAL-CELLS

Monoclonal antibodies to murine vascular cell adhesion molecule-1 (VCA M-1, CD106) revealed not only the expected VCAM-1 molecule with an app arent molecular weight of 100 kDa, but also a molecule with a smaller size of 46 kDa in stromal cells and stimulated endothelial cells. Pept ide mapping suggested the 46 kDa and 100 kDa proteins were closely rel ated. The 46 kDa, but not 100 kDa protein, was cleaved from the cell s urface with phosphatidylinositol-specific phospholipase C (PI-PLC), sh owing that the 46 kDa protein was a GPI-linked molecule. The 46 kDa an d 100 kDa isoforms of VCAM-1 were shown to be N-glycosylated, have sim ilar kinetics of biosynthesis, and to be partially shed from the cell surface with a slight reduction of size. TNF-alpha induced both isofor ms of VCAM-1 with a similar time course of appearance on the surface o f endothelial cells. The relative amounts of the 46 kDa and 100 kDa is oforms depended on the cell type examined. The GPI-anchored isoform is functionally important, because on a cell on which it was expressed a lmost as well as the 100 kDa isoform, treatment with PI-PLC reduced VL A-4-dependent conjugate formation.