Identification of homologous biologically active sites on the N-terminal domain of laminin alpha chains.

Laminin, a multifunctional glycoprotein of the basement membrane, consists of three different subunits, alpha, beta, and gamma chains. To date, five different alpha chains have been identified. N-terminal domain VI in the alpha1 chain has various biological activities. Here we screened biologically active sequences on domain VI of the laminin alpha2, alpha3, and alpha5 chains using a large number of overlapping peptides. HT-1080 human fibrosarcoma cell attachment to the peptides was evaluated using peptide-coated plastic plates and peptide-conjugated Sepharose beads. We identified four cell adhesive sequences from laminin alpha2 chain domain VI, two sequences from the alpha3 chain, and two sequences from the laminin alpha5 chain. Sequences homologous to A13 (RQVFQVAYIIIKA, alpha1 chain 121-133) on all the alpha chains (FQIAYVIVKA, alpha2 chain 130-139; GQLFHVAYILIKF, alpha3 chain 96-108; FHVAYVLIKA, alpha5 chain 74-83) showed strong cell attachment activity. A5-16 (LENGEIVVSLVNGR, alpha5 chain 147-160) showed the strongest cell attachment activity in the plate assay, and the homologous peptide in the alpha3 chain promoted similar strong cell attachment activity. A5-16 and its homologous peptide in the alpha2 chain promoted moderate cell attachment, while the homologous peptide to A5-16 in the alpha1 chain did not show activity. A2-7 (SPSIKNGVEYHYV, alpha2 chain 108-120) showed cell attachment activity only in the plate assay, but homologous sequences in the alpha1, alpha3, and alpha5 chains did not promote activity. A2-7 promoted endothelial cell sprouting from aortic rings in vitro and melanoma colonization to murine lungs in vivo. However, none of the homologous peptides of A2-7 promoted experimental pulmonary metastasis by B16-BL6 melanoma cells. These results indicate that there are chain-specific active sites in domain VI of the laminin alpha chains, some of which contain conserved activities.