Dysregulation of epithelial Na+ absorption induced by inhibition of the kinases TORC1 and TORC2.
OBJECTIVE
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-Ser(422) , we have explored the effects of inhibiting TORC2 and/or TORC1 upon the hormonal control of Na(+) absorption.


METHODS
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.


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.


CONCLUSIONS
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.
Mansley
Morag K
MK
Centre for Cardiovascular and Lung Biology, Division of Medical Sciences, College of Medicine, Dentistry and Nursing, University of Dundee, Dundee, UK.
Wilson
Stuart M
SM
D000042:Absorption / Q000502:physiology*; D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism; D017874:Immediate-Early Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000201:enzymology; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009287:Naphthyridines / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000502:physiology*; D000099184:Serum-Glucocorticoid Regulated Kinases
D000450:Aldosterone; D001127:Arginine Vasopressin; D003907:Dexamethasone; D017874:Immediate-Early Proteins; D007328:Insulin; D009287:Naphthyridines; D017346:Protein Serine-Threonine Kinases; D020123:Sirolimus; D012964:Sodium; D058570:TOR Serine-Threonine Kinases; D000099184:Serum-Glucocorticoid Regulated Kinases; C553294:1-(4-(4-propionylpiperazin-1-yl)-3-(trifluoromethyl)phenyl)-9-(quinolin-3-yl)benzo(h)(1,6)naphthyridin-2(1H)-one; C546843:mTOR protein, mouse