Cell surface oligosaccharide modulation during differentiation. II. Membrane mobility of oligosaccharide lectin conjugates

Abstract

The quantitative, population doubling level (PDL) dependent changes in cell surface oligosaccharides on IMR-90 cells, were investigated from the perspective of membrane mobility of the lectin-oligosaccharide conjugates. Concanavalin-A (CON-A), wheat germ agglutinin (WGA), Ricinus communis agglutinin (RCA-120), and Dolichos biflorus agglutinin (DBA) were all observed to cluster, cap, and endocytose in cultured human diploid fibroblasts (IMR-90). Quantitative photometry at 37°C over defined periods of time indicated that as the IMR-90s approached cellular senescence a specific lectin-dependent inability to either endocytose or process the capped complex occurred. The development of a biotin/avidin/enzyme amplification assay permitted the assignment of the accumulating signal to the internal compartment. Kinetic data indicate that there are at least three separate (and separable) mechanisms for the PDL related changes in lectin binding. Data for the CON-A complex indicates that at least two classes of functional complexes are present. Regression analysis of the kinetic data for the RCA-120 complex indicates a similar membrane clearance for the IMR-90s at all population doubling levels (PDL), suggesting that the quantitative differences observed earlier were due to simple quantitative reductions in the RCA complexing molecules. Data for WGA mobility on the membrane indicates that they are both changes in the number and mobility status of the complexes. These results indicate that the quantitative changes in lectin binding observed previously as IMR-90 cells approach senescence are correlated with alterations in membrane mobility patterns of the lectin oligosaccharide conjugates.