Peptide G, containing the binding site of the 67-kDa laminin receptor, increases and stabilizes laminin binding to cancer cells

We investigated the effect of peptide G, a synthetic peptide derived from the sequence of the 37-kDa laminin receptor precursor, on the interaction of laminin in two tumor cell lines one of which produces laminin and one of which does not, Addition of peptide G to the culture medium induced a significant increase in the amount of endogenous laminin detectable on the cell membrane of both cell lines, Moreover, pretreatment of exogenous laminin with peptide G dramatically increased laminin binding on both cell lines, Kinetics analysis of membrane-bound labeled laminin revealed a 3-fold decrease in the k(d) of peptide G-treated laminin compared with untreated or unrelated or scrambled peptide-treated laminin, Moreover, the affinity constant of peptide cr-treated laminin increased S-fold, with a doubling of the number of laminin binding sites, as de termined by Scatchard analysis, Expression of the VLA6 integrin receptor on the cell membrane increased after incubation with peptide G-treated laminin, However, the lower binding inhibition of peptide G-treated laminin after anti-VLA6 antibody or cation chelation treatment indicates that membrane molecules in addition to integrin receptors are involved in the recognition of peptide G-modified laminin, These ''new'' laminin-binding proteins also mediated cell adhesion to laminin, the first step in tumor invasion, Together, the data suggest that peptide G increases and stabilizes laminin binding on tumor cells, involving surface receptors that normally do not take part in this interaction, This might explain the abundant clinical and experimental data suggesting a key role for the 67-kDa laminin receptor in the interaction between cancer cells and the basement membrane glycoprotein laminin during tumor invasion and metastasis.