Structural requirement of carboxyl-terminal globular domains of laminin α3 chain for promotion of rapid cell adhesion and migration by laminin-5

Abstract

The basement membrane protein laminin-5, a heterotrimer of laminin α3, β3, and γ2 chains, potently promotes cellular adhesion and motility. It has been supposed that the carboxyl-terminal globular region of the α3 chain consisting of five distinct domains (G1 to G5) is important for its interaction with integrins. To clarify the function of each G domain, we transfected cDNAs for the full-length (wild type (WT)) and five deletion derivatives (ΔGs) of the α3 chain into human fibrosarcoma cell line HT1080, which expressed and secreted the laminin β3 and γ2 chains but not the α3 chain. The transfectants with the α3 chain cDNAs lacking G5 (ΔG5), G4-5 (ΔG4-5), G3-5 (ΔG3-5), and G2-5 (ΔG2-5) secreted laminin-5 variants at levels comparable to that with WT cDNA. However, the transfectant with the cDNA without any G domains (ΔG1-5) secreted little laminin-5, suggesting that the G domains are essential for the efficient assembly and secretion of the heterotrimer α3β3γ2. The transfectants with WT, ΔG5, and ΔG4-5 cDNAs survived in serum-free medium longer than those with ΔG3-5, ΔG2-5, and ΔG1-5 cDNAs. The transfectants with WT, ΔG5, and ΔG4-5 cDNAs secreted apparently the same size of laminin-5, which lacked G4 and G5 due to proteolytic cleavage between G3 and G4, and these laminin-5 forms potently promoted integrin α3β1-dependent cell adhesion and migration. However, the laminin-5 forms of ΔG3-5 and ΔG2-5 hardly promoted the cell adhesion and motility. These findings demonstrate that the G3 domain, but not the G4 and G5 domains, of the α3 chain is essential for the potent promotion of cell adhesion and motility by laminin-5.