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Aldosterone induces ras methylation in A6 epithelia
N F Al-Baldawi1, J D Stockand, O K Al-Khalili
1Center for Cell and Molecular Signaling, Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
American Journal of Physiology. Cell Physiology
|July 27, 2000
Summary
Aldosterone enhances sodium reabsorption through protein methylation, particularly targeting Ras proteins. Inhibiting Ras methylation or expression blocks this crucial sodium channel activity.
Area of Science:
- Renal Physiology
- Molecular Endocrinology
- Cellular Biology
Background:
- Aldosterone is a key hormone regulating sodium reabsorption in the kidneys.
- Acute effects of aldosterone (<4 hours) are linked to protein methylation.
- Understanding the molecular mechanisms of aldosterone action is crucial for renal physiology.
Purpose of the Study:
- To investigate the relationship between protein methylation and aldosterone's action.
- To identify aldosterone-mediated targets for protein methylation in cultured renal cells.
- To elucidate the role of protein methylation in aldosterone-induced sodium transport.
Main Methods:
- Measurement of protein methylation levels and methyltransferase activity in cultured renal cells (A6).
- Utilizing methyltransferase inhibitors, including a specific inhibitor for isoprenyl-cysteine methyltransferase (S-trans, trans-farnesylthiosalicylic acid).
- Analysis of aldosterone-induced protein methylation at specific molecular weights and assessment of Ras protein and its methylation.
- Investigating the effect of Ras antisense oligonucleotides on Na(+) channel activity.
Main Results:
- Aldosterone significantly increased protein methylation and methyltransferase activity.
- A specific methyltransferase inhibitor completely blocked aldosterone-induced protein methylation and short-circuit current.
- Aldosterone induced protein methylation near 90 kDa and 20 kDa, with the latter corresponding to small G proteins like Ras.
- Aldosterone increased Ras protein levels and methylation, and Ras inhibition reduced Na(+) channel activity.
Conclusions:
- Protein methylation is essential for aldosterone-induced increases in sodium transport.
- p21(Ras) is identified as a key target for aldosterone-mediated protein methylation.
- Inhibition of Ras expression or methylation significantly impairs Na(+) channel activity, highlighting its role in aldosterone signaling.