Dysregulation of epithelial Na+ absorption induced by inhibition of the kinases TORC1 and TORC2

• Published in: British journal of pharmacology Vol. 161; no. 8; pp. 1778 - 1792
• Main Authors: Mansley, Morag K, Wilson, Stuart M
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.2010; Nature Publishing Group
• Subjects: Absorption - physiology; Aldosterone - pharmacology; Animals; Arginine Vasopressin - pharmacology; Biological and medical sciences; Cells, Cultured; cortical collecting duct; Dexamethasone - pharmacology; Epithelial Cells - metabolism; epithelial Na+ channel; Immediate-Early Proteins - antagonists & inhibitors; Immediate-Early Proteins - metabolism; Insulin - pharmacology; Kidney Tubules, Collecting - drug effects; Kidney Tubules, Collecting - enzymology; kinase inhibitors; Kinases; Medical sciences; Membrane Potentials - drug effects; Mice; Naphthyridines - pharmacology; Pharmacology. Drug treatments; phosphoinositide‐3‐kinase; Phosphorylation; Phosphorylation - drug effects; PP242; Protein-Serine-Threonine Kinases - antagonists & inhibitors; Protein-Serine-Threonine Kinases - metabolism; Research Papers; Rodents; serum and glucocorticoid‐inducibleprotein kinase 1; Sirolimus - pharmacology; Sodium; Sodium - metabolism; TOR Serine-Threonine Kinases - physiology; TORIN1; epithelial Na; Biological fluid; Phosphoinositide; TORIN1; Enzyme; Transferases; Non-specific serine/threonine protein kinase; channel; Ionic channel; Glucocorticoid; Kidney; Absorption; kinase inhibitors; Urinary system; Sodium; Kinase; serum and glucocorticoid-inducible protein kinase 1; Serum; phosphoinositide-3-kinase; Inhibitor; cortical collecting duct; Collecting duct; Pharmacokinetics; PP242
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.2010.01003.x

BACKGROUND AND PURPOSE Although the serum and glucocorticoid‐inducible protein kinase 1 (SGK1) appears to be involved in controlling epithelial Na+ absorption, its role in this physiologically important ion transport process is undefined. As SGK1 activity is dependent upon target of rapamycin complex 2 (TORC2)‐catalysed phosphorylation of SGK1‐Ser422, we have explored the effects of inhibiting TORC2 and/or TORC1 upon the hormonal control of Na+ absorption. EXPERIMENTAL APPROACH Na+ absorption was quantified electrometrically in mouse cortical collecting duct cells (mpkCCD) grown to confluence on permeable membranes. Kinase activities were assessed by monitoring endogenous protein phosphorylation, with or without TORC1/2 inhibitors (TORIN1 and PP242) and the TORC1 inhibitor: rapamycin. KEY RESULTS Inhibition of TORC1/2 (TORIN1, PP242) suppressed basal SGK1 activity, prevented insulin‐ and dexamethasone‐induced SGK1 activation, and caused modest (10–20%) inhibition of basal Na+ absorption and substantial (∼80%) inhibition of insulin/dexamethasone‐induced Na+ transport. Inhibition of TORC1 did not impair SGK1 activation or insulin‐induced Na+ transport, but did inhibit (∼80%) dexamethasone‐induced Na+ absorption. Arginine vasopressin stimulated Na+ absorption via a TORC1/2‐independent mechanism. CONCLUSION AND IMPLICATIONS Target of rapamycin complex 2, but not TORC1, is important to SGK1 activation. Signalling via phosphoinositide‐3‐kinase/TORC2/SGK1 can explain insulin‐induced Na+ absorption. TORC2, but not TORC1, is also involved in glucocorticoid‐induced SGK1 activation but its role is permissive. Glucocorticoid‐induced Na+ transport displayed a requirement for TORC1 activity. Therefore, TORC1 and TORC2 contribute to the regulation of Na+ absorption. Pharmacological manipulation of TORC1/2 signalling may provide novel therapies for Na+‐sensitive hypertension.