The expression pattern of laminin (Ln) alpha1 chain has been a controversial topic due to discrepancies between mRNA and protein studies. Recently it was reported that the monoclonal antibody 4C7, previously thought to recognize Ln alpha1 chain, actually detects Ln alpha5 chain. This finding makes it necessary to reestimate the role of Ln alpha1 chain and to compare the expression and functions of Ln alpha1 and alpha5 chains. We studied the expression of Ln alpha1 and alpha5 chains and production of Ln-1 and Ln-10 in cultured human carcinoma cells. Ln alpha1 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 lines did not express or produce Ln alpha1 chain, suggesting that Ln-1 (alpha1 beta1 gamma1) is produced only by certain carcinoma cells. Ln alpha5 chain mRNA was expressed in all carcinoma cells, but was not incorporated into extracellular matrix in vitro, as shown with JAR cells. Immunoprecipitation of metabolically labeled cells showed that cells expressing Ln alpha1 mRNA also produced 400-kDa Ln alpha1 chain, whereas all cells produced 380-kDa Ln alpha5 chain. Adhesion to Ln-1 was inhibited by a functionally blocking antibody against alpha6-integrin subunit, whereas adhesion to Ln-10 was inhibited by an antibody against alpha6-integrin in JAR cells and by an antibody against alpha3-integrin in PANC-1 cells. The results suggest that Ln-10 is a ubiquitously expressed Ln isoform in carcinoma cells, and the mechanism of adhesion to Ln-10 is cell-type specific.
Copyright 1999 Academic Press.