Role of Src kinases in the ADAM-mediated release of L1 adhesion molecule from human tumor cells

The ectodomain of certain transmembrane molecules can be released by proteo lysis, and the solubilized antigens often exert important biological functi ons. We demonstrated before that the L1 adhesion molecule is shed from the cell surface. Here we show that L1 release in AR breast carcinoma cells is mediated by a member of the disintegrin metalloproteinase (ADAM) family of proteinases, Up-regulation of L1 shedding by phorbol ester or pervanadate i nvolved distinct mechanisms. Pervanadate induced shedding and rounding-up o f cells from the substrate, which was blocked by the Src kinase inhibitor P P2. Tyr phosphorylation of the L1 cytoplasmic tail and the Src kinase Fyn w as observed following pervanadate treatment. Up-regulation of L1 release an d activation of Fyn occurred also when cells were detached by EDTA suggesti ng that the regulation of L1 shedding by this pathway was linked to cell mo rphology and adhesion. The phorbol 12-myristate 13-acetate-induced shedding was inhibited by the protein kinase C inhibitor bisindolylnaleimide I and by PD98059, a specific inhibitor of the mitogen-activated protein kinase pa thway. Soluble L1 binds to the proteoglycan neurocan and in bound form coul d support integrin-mediated cell adhesion and migration. We propose that th e release of cell-associated adhesion molecules such as L1 may be relevant to promote cell migration.