BIPHASIC REGULATION OF ADENYLATE-CYCLASE BY CHOLERA-TOXIN IN NEUROBLASTOMA X GLIOMA HYBRID-CELLS IS DUE TO THE ACTIVATION AND SUBSEQUENT LOSS OF THE ALPHA-SUBUNIT OF THE STIMULATORY GTP BINDING-PROTEIN (GS)

Exposure of neuroblastoma × glioma hybrid (NG108-15) cells to low concentrations of cholera toxin produced a stimulation of both basal and forskolin-amplified adenylate cyclase activity in membranes prepared from these cells. Higher concentrations of cholera-toxin revesed this effect. Mn2+ activation of adenylate cyclase indicated that this effect was not due to a modification of the intrinsic activity of this enzyme. Cholera toxin was demonstrated to produce a concentration and time-dependent loss of Gsα from membranes of these cells. Loss of Gsα from membranes of these cells was preceded by its ADP-ribosylation. The effects of cholera toxin were specific for Gsα, as no alterations in levels of the pertussis toxin-sensitive G-proteins Gi2, Gi3 and G0, were noted in parallel. Equally, no alteration in levels of G-protein β-subunit were produced by the cholera toxin treatment. These experiments demonstrate that cholera toxin-catalysed ADP-ribosylation does not simply maintain an activated population of Gs at the plasma membrane and that alterations in levels of Gs at the plasma membrane can modify adenylate cyclase activity. © 1990.