Cell‐Cycle Dependence of a Ganglioside Glycosyltransferase Activity and Its Inhibition by Enkephalin in a Neurotumor Cell Line

Abstract

Rat glioma X mouse neuroblastoma hybrid neurotumor cells (NG108-15), synchronized by amino acid deprivation, showed a cell-cycle-dependent peak of activity of a ganglioside N-acetylgalactosaminyl transferase 14-24 h following release from the cell cycle block (S/G2 phase). Maximal expression of two typical lysosomal hydrolases, N-acetyl-beta-hexosaminidase and beta-galactosidase, occurred between 18 and 21 h following release (S phase), declining to G1 phase levels during the peak of N-acetylgalactosamine (GalNAc) transferase activity. In addition, glycosyltransferase activity in G2 phase cells showed an increase in apparent Vmax (suggesting the presence of more enzyme/mg of cell protein) and apparent binding affinity for uridine diphosphate N-acetylgalactosamine (UDP-GalNAc) (32 versus 14 microM) when compared to transferase activity in the G1 phase. However, the opioid peptide enkephalin [D-Ala2, D-Leu5], which inhibits ganglioside GalNAc transferase activity in unsynchronized NG108-15 cultures, was much more inhibitory in whole cells 8 h after release from the cell cycle block (G1 phase) than in cells 20 h after release (G2 phase), with 50% inhibition occurring at 2 X 10(-9) M and 2 X 10(-7) M, respectively. These results suggest that the GalNAc transferase activity is regulated in more than one way during the cell cycle, since both Vmax and Km changes are observed, and that the cyclic AMP-dependent mechanism by which opiates reduce transferase activity is receptor mediated and cell cycle dependent.

Differential expression of receptors for Shiga and Cholera toxin is regulated by the cell cycle

“…An UDP-N-acetyl-galactosyl transferase converts lactosylceramide to GA2, and GM3 to GM2, both precursors of the CTXreceptor GM1. It has been reported in a hybrid rat gliomaneuroblastoma cell line, that the activity of this enzyme reaches a maximum during S-and G2-phase (Scheideler et al, 1984). This is not in line with our observation that the expression of CTX receptors on the cell surface reaches a minimum during S-and G2-phase.…”

Coordinate Regulation of Ganglioside Glycosyltransferases in Differentiating NG108‐15 Neuroblastoma X Glioma Cells

“…In addition to the above changes, previous work by this and other laboratories have shown differentiation-REG ULA TION OF GANG LIOSID E G L YCOS YL TRA NSFERASES 1543 induced modulation of the ganglioside pattern of NG108-15 cells (Dawson et al, 1980;Dahms and Schnaar, 1983;Scheideler et al, 1984). These cells have been reported to contain four gangliosides: GDla, GM 1, GM2, and GM3 (we find no gangliosides more complex than these under any growth condition).…”

Possible Role of Gangliosides in Regulating an Adenylate Cyclase‐Linked 5‐Hydroxytryptamine (5‐HT1) Receptor

“…Thus, gangliosides may play a role in 5-HT1 receptor function, either after direct incorporation into the neuronal membrane or after incorporation into the membrane as a result of modulation of cyclic AMP levels following the interaction of cells with other neurotransmitters. This system may suggest a possible mechanism for neurotransmitter modulation of neuronal responses to other neurotransmitters, as we had previously shown (Dawson et al, 1980McLawhon et al, 1981;Scheideler et al, 1984) that cyclic AMP can in turn stimulate ganglioside synthesis in neurotumor cells.…”