Glycolipid sialyltransferases in normal and neoplastic murine thymocytes

Total labeled glycolipids from thymocytes of leukemic AKR/J mouse thymus incubated for 24 h in the presence of the precursors [3H] galactose or [14C] glucosamine were found to exceed those from non-leukemic thymocytes. The amount of labeled compounds that co-migrated with monosialogangliosides (GM3 and GM2) and disialogangliosides (GD1a and GD1b) was higher, whereas incorporation into monosialoganglioside (GM1) and trisialoganglioside (GT1) was lower in leukemic than in non-leukemic thymocytes. Consistent with this altered pattern of ganglioside distribution was the finding of a higher activity of two of the sialyltransferase activities in homogenates of leukemic thymus as compared to normal thymus. About 2-fold higher activities of the enzymes CMP-AcNeu: lactosylceramide sialyltransferase and CMP-AcNeu: GM1 sialyltransferase were observed in leukemic thymus homogenate compared to homogenates of non-leukemic cells. The substrate affinity of sialyltransferase with GM1 as acceptor from the leukemic thymus was similar to that of the enzyme from normal thymus. Thus, our studies reveal an enzymatic basis for the enhanced rate of synthesis and altered ganglioside profile observed in malignant thymocytes, and are consistent with the general view on the pattern of acidic glycolipids in tumorigenesis.