Laminin interactions with ductal pancreatic adenocarcinoma cells: Identification of laminin- and collagen-binding proteins

Abstract

Laminin promotes the modulation of human pancreatic adenocarcinoma cells from a proliferative to a resting phenotype. This process includes restoration of cell polarity, increase of protein biosynthesis, and increase of glycoprotein secretion. The growth correlates with the amount of laminin coated on the culture dish. Adenocarcinoma cells do not synthesize collagen type I, fibronectin or laminin. Prolonged propagation of the cells on laminin substratum enhances the expression of laminin-binding sites on the cell surface. Laminin binds to cell plasma membrane vesicles with a KB of about 2.2 x 10(10). By affinity chromatography of [35S]methionine-labeled, detergent-extracted, cells on immobilized laminin, a Mr 82,000 polypeptide could be enriched. By simultaneous chromatography on immobilized collagen type I, a Mr 34,000 polypeptide was retained. In laminin overlay experiments on transblotted plasma membrane proteins, Mr 82,000 and 70,000 polypeptides were labeled. Affinity chromatography on laminin-Sepharose of tumor cell membranes from cells grown in nude mice tumors retained Mr 100,000, 82,000, 70,000 and 55,000 polypeptides bound to the column. Endoglycosidase F treatment of these proteins reduced the number of higher Mr proteins, leaving a Mr 70,000 polypeptide, together with smaller peptides. Using the enriched binding protein fraction as antigens, monoclonal antibodies (mAbs) were prepared in mice. Two of the mAbs were further analysed; they recognized simultaneously the complete pattern of high and low Mr polypeptides identified to date by the other methods. Antibody 2A1-H7 was capable of inhibiting attachment and spreading of the cells on laminin and collagen I, but not on tissue-culture plastic. These data may indicate a molecular heterogeneity, partly based on diverse glycosylation, responsible for the variations in the molecular weight of the binding proteins. The adaptation processes of the tumor cells during growth on the extracellular matrix may indicate a regulatory function on tumor growth and metastasis in vivo.