Expression of laminins 1 and 10 in carcinoma cells and comparison of theirroles in cell adhesion

The expression pattern of laminin (Ln) alpha 1 chain has been a controversi al topic due to discrepancies between mRNA and protein studies. Recently it was reported that the monoclonal antibody 4C7, previously thought to recog nize Ln alpha 1 chain, actually detects Ln alpha 5 chain. This finding make s it necessary to reestimate the role of Ln alpha 1 chain and to compare th e expression and functions of Ln alpha 1 and alpha 5 chains. We studied the expression of Ln alpha 1 and alpha 5 chains and production of Ln-l and Ln- 10 in cultured human carcinoma cells. Ln alpha 1 chain mRNA was detected in JAR choriocarcinoma cells and in all four renal cell carcinoma cell lines studied. In contrast, pancreatic, colon, and lung alveolar carcinoma cell l ines did not express or produce Ln alpha 1 chain, suggesting that Ln-l (alp ha 1 beta 1 gamma 1) is produced only by certain carcinoma cells. Ln alpha 5 chain mRNA was expressed in all carcinoma cells, but was not incorporated into extracellular matrix in vitro, as shown with JAR cells. Immunoprecipi tation of metabolically labeled cells showed that cells expressing Ln alpha 1 mRNA also produced 400-kDa Ln alpha 1 chain, whereas all cells produced 380-kDa Ln alpha 5 chain. Adhesion to Ln-l was inhibited by a functionally blocking antibody against alpha(6)-integrin subunit, whereas adhesion to Ln -10 was inhibited by an antibody against alpha(6)-integrin in JAR cells and by an antibody against alpha(3)-integrin in PANC-1 cells. The results sugg est that Ln-10 is a ubiquitously expressed Ln isoform in carcinoma cells, a nd the mechanism of adhesion to Ln-lO is cell-type specific. (C) 1999 Acade mic Press.