Rat Small Intestinal Laminin-Binding Proteins

Abstract

Mucosal intestinal cells migrate and differentiate simultaneously as they move out of the crypts to their functional site along the villus. Interactions between the enterocyte basal membrane domain and the extracellular intestinal basement membrane (IBM) have been suggested to be essential to both cell migration and differentiation. The IBM is composed primarily of collagen IV, laminin, fibronectin and heparan sulfate proteoglycans. It is likely that enterocytes possess receptors to various IBM components as they adhere to this IBM, an essential scaffold for villus structural integrity. In addition, the enterocyte must have mechanisms of altering this adherence to IBM as the cell moves up the villus and is eventually expelled into the lumen. To understand these processes, enterocyte membrane proteins involved in cell to IBM adhesion need to be defined. In the present study, laminin-binding proteins have been identified in enterocyte membranes. These binding proteins were isolated and purified. Antibodies raised against these binding proteins were used to further characterize these enterocyte membrane proteins. A major antigen at 67-69 kD was detected from both villus and crypt cells, although upper crypt cell membranes appeared to have more. Other antigens at 41, 43, 52, 100 and 130 kD were also detected. Immunofluorescent studies showed antigens present in the basal domain of the crypt enterocyte. These laminin-binding proteins may prove important as inducers of differentiation and in the dynamic alterations required for cell movement.