Reduced contact-inhibition and substratum adhesion in epithelial cells expressing G1cNAc-transferase V

Abstract

Malignant transformation of fibroblast and epithelial cells is accompanied by increased β1-6 N-acetylglucosaminyltransferase V (GlcNAc-TV) activity, a Golgi N-linked oligosaccharide processing enzyme. Herein, we report that expression of GlcNAc-TV in Mv1Lu cells, an immortalized lung epithelial cell line results in loss of contact-inhibition of cell growth, an effect that was blocked by swainsonine, an inhibitor of Golgi processing enzyme α-mannosidase II. In serumdeprived and high density monolayer cultures, the GlcNAc-TV transfectants formed foci, maintained microfilaments characteristic of proliferating cells, and also experienced accelerated cell death by apoptosis. Injection of the GlcNAc-TV transfectants into nude mice produced a 50% incidence of benign tumors, and progressively growing tumors in 2:12 mice with a latency of 6 mo, while no growth was observed in mice injected with control cells. In short term adhesion assays, the GlcNAc-TV expressing cells were less adhesive on surfaces coated with fibronectin and collagen type IV, but no changes were observed in levels of cell surface α5β1 or αvβ3 integrins. The larger apparent molecular weights of the LAMP-2 glycoprotein and integrin glycoproteins α5, αv and β1 in the transfected cells indicates that their oligosaccharide chains are substrates for GlcNAc-TV. The results suggest that β1-6GlcNAc branching of N-linked oligosaccharides contributes directly to relaxed growth controls and reduce substratum adhesion in premalignant epithelial cells.