An Increase in GM1 Ganglioside in Plasma Membranes of Skin Fibroblasts from GM1 Gangliosidosis as Demonstrated by Cholera Toxin-Induced cAMP Production

Cholera toxin (CT) has been reported to bind specifically to GM1 ganglioside on cell surface plasma membranes and activates adenylate cyclase. We examined whether or not GM1 ganglioside (ga-lactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosyl-glucosylceramide) accumulates in plasma membranes of cultured skin fibroblasts from GM1 gangliosidosis patients by measuring cyclic AMP (adenosine 3’,5'-cyclic monophosphate; cAMP) production elicited by CT. Optimal conditions for the assay were determined to be 1 μg/ml of CT and 1 h incubation at 37°C. The responses of intracellular cAMP level to a direct activator of adenylate cyclase, forskolin, and to phorbol 12-myristate 13-acetate (PMA) were not different between patients and controls. Insertion of exogenous GM1 ganglioside into the cell membrane caused a linear increase in the cAMP production triggered by CT in control cells. Under the optimal conditions, intracellular cAMP production in response to CT was estimated as 544.3+16.3 pmol/h per mg protein in the patients’ cells and 284.8 + 46.8 pmol/h per mg protein in the control ones. These data are the first indication of the accumulation of GM1 ganglioside in cell surface membranes of patients with GM1 gangliosidosis.