Human Neural Cell Adhesion Molecule L1 and Rat Homologue NILE are Ligands for Integrin

Integrin Otv~3 is distinct in its capacity to recognize the sequence Arg-Gly-Asp (RGD) in many extra-cellular matrix (ECM) components. Here, we demonstrate that in addition to the recognition of ECM components, ave3 can interact with the neural cell adhesion molecule L1-CAM; a member of the immunoglobulin superfamily (IgSF). M21 melanoma cells displayed significant Ca++-dependent adhesion and spreading on immunopurified rat L1 (NILE). This adhesion was found to be dependent on the expression of the Otv-integrin subunit and could be significantly inhibited by an antibody to the av~33 heterodimer. M21 cells also displayed some av133-dependent adhesion and spreading on immunopurified human L1. Ligation between this ligand and e~vl33 was also observed to promote significant haptotactic cell migration. To map the site of ~v~33 ligation we used recombinant L1 fragments comprising the entire extraceUular domain of human L1. Significant av133-dependent adhesion and spreading was evident on a L1 fragment containing Ig-like domains 4, 5, and 6. Importantly, mutation of an RGD sequence present in the sixth Iglike domain of L1 abrogated M21 cell adhesion. We conclude that av133-dependent recognition of human L1 is dependent on ligation of this RGD site. Despite high levels of L1 expression the M21 melanoma cells did not display significant adhesion via a homophilic L1-L1 interaction. These data suggest that M21 melanoma cells recognize and adhere to L1 through a mechanism that is primarily heterophilic and integrin dependent. Finally, we present evidence that melanoma cells can shed and deposit L1 in occluding ECM. In this regard, av133 may recognize L1 in a cellcell or cell-substrate interaction. T HE neural cell adhesion molecule L1 is a multidomain glycoprotein and a member of the IgSF (Moos et al, 1988). This cell adhesion molecule (CAM) 1 was first described in the mouse, but homologous molecules have now been reported in man, rat (NILE), chick (NgCAM, 8D9, G4), and Drosphila (neuroglian) (Grumet et al., 1984; Bock et al., 1985; Lemmon and McLoon, 1986; Mujoo et al., 1986). These Ll-related glycoproteins have an extracellular region that consists of six immunoglobulin (Ig)-like domains followed by five fibronectin type III-like repeats. There is a single transmembrane region that is linked to a short, highly conserved cytoplasmic domain (Moos et al, 1988; Sonderegger and Rathjen, 1992). Considerable sequence homology has been found between the mammalian Ll-related CAMs. Thus, the deduced identity Address correspondence to Anthony Montgomery, Department of Immunology, R218, The Scripps Research Institute, La Jolla, CA 92037. Tel.: (619) 554-8109. Fax: (619) 554-6705. 1. Abbrevia t ions used in this paper:. CAM, cell adhesion molecule; IgSF, Immunoglobulin superfamily; ECM, extracellular matrix; NILE, nerve growth factor-inducible large external glycoprotein; NCAM, neural CAM. between the amino acid sequences of human and mouse L1 is 87% (Reid and Hemperly, 1992), while the amino acid homology between rat and mouse L1 is 96% (Miura et al., 1991). Reference to L1 as a neural CAM is based on its distribution on post-mitotic neurons of the central and peripheral nervous systems and on preor non-myelinating Schwann cells of the peripheral nervous system (Lindner et al., 1983; Rathjen and Schachner, 1984; Martini and Schachner, 1986). L1 has also been described on non-neural ceils, including granulocytes, lymphocytes, and epithelial cells of the intestine and urogenital tract (Thor et al., 1987; Kowitz et al., 1992; Kujat et al., 1995). This CAM is further expressed on transformed cells of diverse histological origin, including melanoma, neuroblastoma, embryonal carcinoma, osteogenic sarcoma, squamous lung carcinoma, squamous skin carcinoma, pheochromocytoma, rhabdomyosarcoma, and retinoblastoma cell lines (Mujoo et al., 1986; Linnemann et al., 1989; Reid and Hemperly, 1992). Surprisingly, despite widespread expression of L1 on many highly malignant tumors, little is known of the function of this CAM with respect to tumor progression © The Rockefeller University Press, 0021-9525/96/02/475/11 $2.00 The Journal of Cell Biology, Volume 132, Number 3, February 1996 475~185 475 on Jne 7, 2017 D ow nladed fom Published February 1, 1996