SHEDDING OF THE 67-KD LAMININ RECEPTOR BY HUMAN CANCER-CELLS

The 67-kD laminin receptor (67LR) is a cell membrane-associated molecu le exhibiting high affinity for the basement membrane glycoprotein, la minin. While export of the 67LR toward the extracellular matrix has be en recently suggested by electron microscopy studies, there is to date no evidence of shedding of the 67LR from cells. Using two monoclonal antibodies directed against the 67LR, we developed a double-determinan t radioimmunoassay that demonstrates that the 67LR is released from ca ncer cells into the culture medium. The shed molecule exhibited the sa me apparent molecular weight as that of the membrane-associated 67LR, suggesting that no proteolytic cleavage is involved in the process. Fu rthermore, we demonstrate that the 67LR is not anchored to the membran e through a glycolsyl-phosphatidylinositol bridge. However, the observ ation that lactose increased the release of 67LR suggests that a lecti n-type interaction is involved in the cell membrane association of thi s laminin binding protein and the cell surface. Interestingly, the rel eased 67LR recovered after HPLC gel filtration was found free as well as associated to high molecular weight complexes. The free 67LR retain ed its ability to bind to the cell surface. Our study is the first dem onstration that the 67LR is effectively shed by cancer cells. The rele ased free 67LR could play an important role in modulating interactions between cancer cells and laminin during tumor invasion and metastasis . (C) 1996 Wiley-Liss, Inc.