Cell surface oligosaccharide modulation during differentiation: V. Partial characterization of the regulated surface...

In previous studies with IMR-90 human fetal lung fibroblasts, it was shown that modulation of a small finite number of unique cell surface oligosaccharide structural specificities (as defined by reaction with specific lectins and monoclonal antibodies) define the cellular senescence phenotype. The cell surface oligosaccharide display can be characterized by assessing the epitope density and conformational arrangement of three or four individual carbohydrate specificities. Development of the senescence morphological phenotype was preceded by specific alterations in the cell surface oligosaccharide display. The senescence-dependent changes in these displays are primarily related to the binding affinity (the Kij of the Scatchard analyses) rather than the epitope density (the binding capacity, Rij of the Scatchard analyses). These alterations involve rearrangements within specific carbohydrate classes. In the course of these studies, the observation was made that low-density and contact-inhibited growth-retarded Phase II cells showed similar surface modulation of the oligosaccharide display. This suggests a broader significance for the date in growth regulation. These data suggest a structural/functional relationship between cellular senescence mechanisms and growth control in general. In this study we have investigated the possible role of cell surface oligosaccharide regulation in substrate interactions. Trypsinized cells were studied during substrate adherence, spreading and initiation of growth on control and poly-L-ornithine-treated polystyrene substrate. The cell surface oligosaccharide display was characterized using both biological assays and NMR-based measurements of the mobility of water at the cell surface. Results show that trypsinization does not remove or diminish the oligosaccharide display. The initial adherence of the cells to unmodified substrate is mediated by oligosaccharides. Cellular spreading results in specific changes in the display. Initiation of growth corresponds to further specific changes in the display. These data suggest a mechanistic connection between the cell surface oligosaccharide display and growth control of these fibroblasts.