Cholera toxin treatment produces down-regulation of the alpha-subunit of the stimulatory guanine-nucleotide-binding protein (Gs).
The effect of activation of the alpha-subunit(s) of the stimulatory guanine-nucleotide-binding protein, Gs, on levels of this polypeptide(s) associated with the plasma membrane of L6 skeletal myoblasts was ascertained. Incubation of these cells with cholera toxin led to a time- and concentration-dependent 'down-regulation' of both 44 and 42 kDa forms of Gs alpha as assessed by immunoblotting with an anti-peptide antiserum (CS1) able to identify the extreme C-terminus of Gs. The effect of cholera toxin was specific for Gs; levels of Gi alpha in membranes of cholera toxin-treated cells were not different from untreated cells. Down-regulation of Gs was absolutely dependent upon prior ADP-ribosylation, and hence activation of Gs and was not mimicked by other agents which elevate intracellular levels of cyclic AMP. Pretreatment with pertussis toxin, which catalyses ADP-ribosylation of Gi but not of Gs, did not down-regulate either Gi or Gs, demonstrating that covalent modification by ADP-ribosylation is alone not a signal for removal of G-proteins from the plasma membrane.
Milligan
G
G
Department of Biochemistry, University of Glasgow, Scotland, U.K.
Unson
C G
CG
Wakelam
M J
MJ
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002772:Cholera Toxin / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007739:L Cells; D051379:Mice; D009124:Muscle Proteins / Q000378:metabolism; D009132:Muscles / Q000187:drug effects* / Q000648:ultrastructure
D009124:Muscle Proteins; D002772:Cholera Toxin; D019204:GTP-Binding Proteins