Human vascular adhesion protein-1 in smooth muscle cells

Human vascular adhesion protein-1 (VAP-1) is a dual-function molecule with adhesive and enzymatic properties. In addition to synthesis in endothelial cells, where it mediates lymphocyte binding, VAP-1 is expressed in smooth m uscle cells. Here we studied the expression, biochemical structure, and fun ction of VAP-1 in muscle cells and compared it to those in endothelial cell s. VAP-1 is expressed on the plasma membrane of all types of smooth muscle cells, but it is completely absent from cardiac and skeletal muscle cells. In tumors, VAP-1 is retained on all leiomyoma cells, whereas it is lost in half of leiomyosarcoma samples. In smooth muscle VAP-1 predominantly exists as a similar to 165-kd homodimeric glycoprotein, but a trimeric (similar t o 250 kd) form of VAP-1 is also found. It contains N-linked oligosaccharide side chains and abundant sialic acid decorations. In comparison, in endoth elial cells dimeric VAP-1 is larger, no trimeric forms are found, and VAP-1 does not have N-glycanase-sensitive oligosaccharides. Unlike endothelial V AP-1, VAP-1 localized on smooth muscle cells does not support binding of ly mphocytes. Instead, it deaminates exogenous and endogenous primary amines. In conclusion, VAP-1 in smooth muscle cells is structurally and functionall y distinct from VAP-1 present on endothelial cells.