Expression of Laminins 1 and 10 in Carcinoma Cells and Comparison of Their Roles in Cell Adhesion

Abstract

The expression pattern of laminin (Ln) α1 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 α1 chain, actually detects Ln α5 chain. This finding makes it necessary to reestimate the role of Ln α1 chain and to compare the expression and functions of Ln α1 and α5 chains. We studied the expression of Ln α1 and α5 chains and production of Ln-1 and Ln-10 in cultured human carcinoma cells. Ln α1 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 α1 chain, suggesting that Ln-1 (α1β1γ1) is produced only by certain carcinoma cells. Ln α5 chain mRNA was expressed in all carcinoma cells, but was not incorporated into extracellular matrixin vitro,as shown with JAR cells. Immunoprecipitation of metabolically labeled cells showed that cells expressing Ln α1 mRNA also produced 400-kDa Ln α1 chain, whereas all cells produced 380-kDa Ln α5 chain. Adhesion to Ln-1 was inhibited by a functionally blocking antibody against α6-integrin subunit, whereas adhesion to Ln-10 was inhibited by an antibody against α6-integrin in JAR cells and by an antibody against α3-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.