Aldosterone induces Ras methylation in A6 epithelia

Aldosterone increases Na+ reabsorption by renal epithelial cells: the acute actions (<4 h) appear to be promoted by protein methylation. This paper de scribes the relationship between protein methylation and aldosterone's acti on and describes aldosterone-mediated targets for methylation in cultured r enal cells (A6). Aldosterone increases protein methylation from 7.90 +/- 0. 60 to 20.1 +/- 0.80 methyl ester cpm/mu g protein. Aldosterone stimulates p rotein methylation by increasing methyltransferase activity from 14.0 +/- 0 .64 in aldosterone-depleted cells to 31.8 +/- 2.60 methyl ester cpm/mu g pr otein per hour in aldosterone-treated cells. Three known methyltransferase inhibitors reduce the aldosterone-induced increase in methyltransferase act ivity. One of these inhibitors, the isoprenyl-cysteine methyltransferase-sp ecific inhibitor, S-trans, trans-farnesylthiosalicylic acid, completely blo cks aldosterone-induced protein methylation and also aldosterone-induced sh ort-circuit current. Aldosterone induces protein methylation in two molecul ar weight ranges: near 90 kDa and around 20 kDa. The lower molecular weight range is the weight of small G proteins, and aldosterone does increase bot h Ras protein 1.6-fold and Ras methylation almost 12-fold. Also, Ras antise nse oligonucleotides reduce the activity of Na+ channels by about fivefold. We conclude that 1) protein methylation is essential for aldosterone-induc ed increases in Na+ transport; 2) one target for methylation is p21(ras); a nd 3) inhibition of Ras expression or Ras methylation inhibits Na+ channel activity.