GANGLIOSIDE COMPOSITION AND BIOSYNTHESIS IN CULTURED CELLS DERIVED FROM CNS

Abstract

Abstract— Cultured mouse neuroblastoma cells (clone N18) contained a homologous series of gangliosides, G M3 , G M2 , G M1 and G D1a ; the total lipid bound sialic acid (LBSA) was 3.3 nmol per mg of protein, of which G D1a comprised two‐thirds. In contrast, neonatal hamster astrocytes (clone NN) and human glioblastoma cells (Cox clone) contained mainly G M3 , which represented 95% of the 2 nmol of LBSA per mg protein in these cells. When the cells were grown in the presence of [ 14 C]galactose, label was incorporated into all of the gangliosides isolated from the cells. The labeling pattern corresponded to the ganglioside composition of the cell lines; G D1a was more extensively labeled in N18 cells and G M3 was the major labeled ganglioside extracted from glial cells. In addition to in rivo biosynthesis, in vitro synthesis of gangliosides was also determined. The activities of five glycosyltransferases of the ganglioside biosynthetic pathway were measured in homogenates of the three cell lines. The neuroblastoma cells contained all five enzyme activities whereas the two glial cell lines were deficient in UDP‐ N ‐acetylgalactosamine: G M3 N ‐acetylgalactosaminyltransferase activity, which catalyzes the synthesis of G M2 from G M3 . The results indicated that cells of neuronal origin contain the more complex gangliosides associated with CNS and the requisite biosynthetic enzymes and that cells of glial origin are missing these complex gangliosides and the key glycosyltransferase required for their synthesis.