The basement membrane protein laminin-5, a heterotrimer of laminin ␣3, ␤3, and ␥2 chains, potently promotes cellular adhesion and motility. It has been supposed that the carboxyl-terminal globular region of the ␣3 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 (⌬Gs) of the ␣3 chain into human fibrosarcoma cell

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... e HT1080, which expressed and secreted the laminin ␤3 and ␥2 chains but not the ␣3 chain. The transfectants with the ␣3 chain cDNAs lacking G5 (⌬G 5 ), G4 -5 (⌬G 4 -5 ), G3-5 (⌬G 3-5 ), and G2-5 (⌬G 2-5 ) secreted laminin-5 variants at levels comparable to that with WT cDNA. However, the transfectant with the cDNA without any G domains (⌬G 1-5 ) secreted little laminin-5, suggesting that the G domains are essential for the efficient assembly and secretion of the heterotrimer ␣3␤3␥2. The transfectants with WT, ⌬G 5 , and ⌬G 4 -5 cDNAs survived in serum-free medium longer than those with ⌬G 3-5 , ⌬G 2-5 , and ⌬G 1-5 cDNAs. The transfectants with WT, ⌬G 5 , and ⌬G 4 -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 ␣ 3 ␤ 1 -dependent cell adhesion and migration. However, the laminin-5 forms of ⌬G 3-5 and ⌬G 2-5 hardly promoted the cell adhesion and motility. These findings demonstrate that the G3 domain, but not the G4 and G5 domains, of the ␣3 chain is essential for the potent promotion of cell adhesion and motility by laminin-5.