| Abstract: |
G(M2) and G(D2) gangliosides are sialic acid-containing glycosphingolipids expressed in some normal tissues such as brain and in various tumors such as neuroblastomas, astrocytomas, and malignant melanomas. We used a eukaryotic cell transient expression system to isolate cDNA clones that determine G(M2) expression. We developed a new cell line from murine melanoma line B16 by transfecting with the polyoma T antigen gene that was suitable for this purpose. Two cDNA clones, both of which have a continuous open reading frame of 1683 base pairs, were isolated. Although the cloned cDNAs had no primary sequence similarity to reported glycosyltransferases, the deduced amino acid sequence predicted a type II transmembrane protein with an overall structure similar to other glycosyltransferases. The cDNA clones, when stably transfected, determined the expression of G(M2) in B16 cells and G(M2) and G(D2) in the human melanoma line MeWo. Northern blot analysis revealed two transcripts in all cells that expressed either G(M2) or G(D2) or both. These findings indicate that the cDNAs catalyze the transfer of GalNAc onto G(M3) and G(D2) by a beta-1,4 linkage, resulting in the synthesis of G(M2) and G(D2), respectively. Namely they suggest that these cDNAs derive from the UDP-GalNAc: G(M3)/B(D3) beta-1,4 N-acetylgalactosaminyltransferase (EC 2.4.1.92) gene. |
