Cell membrane sialoglycopeptides of corticoid-sensitive and -resistant lymphosarcoma P1798.

Cells of corticoid-sensitive (CS) and corticoid-resistant (CR) lymphosarcoma P1798 were labeled in vivo with either [14C]- or [3H]fucose before and after treatment with 9-alpha-fluoroprednisolone (9-FP). Labeled glycopeptides, derived from isolated, Pronase-digested cell membranes of both tumors were separated by gel filtration on Bio-Gel P-10 by a double-label technique. Elution profiles of CS and CR fractions showed significant differences in early eluting material. Desialylation of glycopeptides by neuraminidase lowered the molecular weight of both CS and CR fractions, and altered 3H:14C ratios indicated that CS and CR sialoglycopeptides are different. 9-FP treatment for 7 hr increased the density of isolated P1798-CS and -CR cell membranes. All CS and CR glycopeptides from treated tumors eluted faster than did those of untreated preparations. Both CS and CR sialoglycopeptides were altered, although differences in CS and CR profiles persisted. Histochemical investigations indicated that negative charge, present on surfaces of untreated CS cells, is lost between 6 and 8 hr after exposure in vivo to 9-FP. CR cells had no or few anionic sites on their surfaces before and after steroid administration. We demonstrated that glycopeptides of both CS and CR tumors contain sialic acid, although only CS cells carry a surface-exposed negative charge that is lost after 9-FP treatment. Glucocorticoids alter both P1798-CS and -CR sialoglycopeptides, but the consistent differences between their chromatographic patterns suggest that steroid-induced changes in cell membranes of the two tumors are not identical. Cell death or survival of glucocorticoid-treated P1798 cells may, therefore, be influenced by specific structural characteristics involving cell surface sialoglycoproteins.