Aldosterone-induced and GTP-stimulated methylation of a 90-kDa polypeptide in the apical membrane of A6 epithelia.
Aldosterone treatment of A6 cultured renal epithelial cells methylates the apical membrane, and we examined the aldosterone-induced carboxymethylation of the apical membrane of these cells to determine the targeted polypeptides. Methionine-deprived A6 cells were incubated with aldosterone and [3H]methionine. Homogenates and apical membranes were solubilized and analyzed by SDS-polyacrylamide gel electrophoresis. Label incorporation in a 90-kDa polypeptide was more intense (4-fold) in membranes after aldosterone compared to control. For in vitro methylation, membranes were isolated, incubated with S-adenosyl-L-[methyl-3H]methionine, and analyzed for 3H-methyl uptake. Label incorporation was low in control membranes but markedly stimulated (4-fold) in membrane preparations from aldosterone-treated cells. Guanosine 5'-O-(3-thiotriphosphate) increased in vitro methylation of a 90-kDa polypeptide 5-fold in control membranes but after aldosterone, where methylation was already stimulated, little change was observed. We conclude that aldosterone induces methylation of an apical membrane 90-kDa polypeptide, possibly a subunit of the epithelial Na+ channel, in a GTP-dependent manner, and this may be one of the final steps in a cascade of reactions leading to the natriferic action of this hormone.
Sariban-Sohraby
S
S
Laboratoire de Physiopathologie, Université Libre de Bruxelles, Belgium.
Fisher
R S
RS
Abramow
M
M
D000450:Aldosterone / Q000502:physiology*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004848:Epithelium / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000502:physiology*; D007668:Kidney / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008745:Methylation; D010455:Peptides / Q000378:metabolism; D014982:Xenopus laevis
D008565:Membrane Proteins; D010455:Peptides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000450:Aldosterone