A study of the intracellular and secreted forms of the MUC2 mucin from thePC AA intestinal cell line

In this study we present data on the entire population of MUC2 molecules se creted from and within the cell layer of an intestinal cell line. The molec ular size distribution of the extracted molecules and their reactivity with two different MUC2 polypeptide antibodies indicated the presence of precur sor and mature forms of the mucin. Oligomerized forms of the mucin were fou nd in both the cell layer and medium; however, precursor forms were confine d to the cell layer. Isopycnic density gradient centrifugation gave good re solution of mature and precursor forms of MUC2 as assessed by agarose gel e lectrophoresis. Three different populations of MUC2 were identified: one at low density (>1.3 g/ml) containing the N-glycosylated, non-O-glycosylated polypeptide; a second at intermediate density (1.3-1.35 g/ml) which may rep resent partially O-glycosylated intermediates; and a third at high density (1.36-1.48 g/ml) containing the mature MUC2 mucins, Rate-zonal centrifugati on and agarose electrophoretic analysis of the low-density fraction indicat ed that the N-glycosylated MUC2 polypeptide was present as putative monomer and dimer/oligomer species, The combination of isopycnic density gradient centrifugation with agarose electrophoresis pro,ides a new and simple appro ach that allows us to follow the MUC2 gene product from polypeptide through to the mature glycosylated mucin.