Promotion of human oral squamous cell carcinoma adhesion in vitro by the carboxy-terminal globular domain of laminin

The domains of laminin utilized by cells from human squamous-cell carcinoma (SCC) to promote adhesion were investigated. The ability of cultured SCC cells to adhere to surfaces adsorbed with laminin, laminin fragments, or laminin peptides was examined in a direct, solid-phase adhesion assay. The cells adhered in a concentration-dependent and saturable manner to laminin and E3 and E8 fragments of elastase-digested laminin. These results suggest that SCC cells adhere to at least two distinct sites within the carboxy terminal long arm of laminin. In contrast, SCC cells adhered poorly to the 440-kDa chymotrypsin-resistant fragment of laminin, and the E1′ and E4 elastase-digested fragments of laminin, suggesting that the short arms, including the cross-region, of laminin does not contain binding sites for these cells. Synthetic peptides GD-2 and -6, comprised of amino acid sequences derived from the E3 fragment, promoted the adhesion of SCC cells in a concentration-dependent and saturable manner. The specific interaction of SCC cells with GD-2 was demonstrated by competition assays in which soluble GD-2 and anti-peptide GD-2 IgG inhibited cell adhesion to GD-2. The anti-peptide GD-2 IgG partially inhibited the adhesion of SCC cells to the E3 fragment and intact laminin, but not to fibronectin. These results suggest that SCC cells recognize the sequence of GD-2 within laminin. The role of integrins in mediating the adhesion of SCC cells to laminin and GD-2 was then investigated. In competition assays, monoclonal antibodies raised against integrin subunits β1, α2, α3, and α6 decreased SCC cell adhesion to laminin but not to GD-2. Therefore, integrins α2β1, α3β1, and α6β1 actively mediate SCC cell adhesion to laminin, but may not play a major part in SCC cell adhesion to GD-2.