Differential expression of laminin-5/ladsin subunits in human tissues and cancer cell lines and their induction by tumor promoter and growth factors.

We previously reported a new laminin variant containing laminin gamma 2 (or B2t) chain, ladsin, which exerted prominent cell-scattering, cell-adhesion, and cell-migration activities. In the present study, this laminin was further characterized, and gene expression of its three subunits in various human tissues and cancer cell lines was examined by Northern blotting. cDNA cloning of the largest subunit of ladsin and partial amino acid sequencing of its beta (or B1) subunit revealed that ladsin was identical to laminin-5 (kalinin/epiligrin/ nicein). Among various human tissues, placenta, lung, and fetal kidney expressed high levels of mRNAs for the three subunits of laminin-5 (laminin alpha 3EPA, beta 3, and gamma 2 chains). Most gastric and squamous carcinoma cell lines constitutively expressed all of the three subunit mRNAs, while other types of carcinoma cell lines expressed one or two of them. The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and epidermal growth factor (EGF) strongly enhanced the gene expression of the three subunits, increasing 2 to 8-fold the secretion of laminin-5 from carcinoma cells into culture medium. However, TPA treatment did not increase the secretion of laminin beta 1 chain, a subunit of laminins-1, -3, and -6. The unique properties and inducibility by TPA and EGF of laminin-5 suggest that it is associated with growth and migration of cancer cells.