MicroRNA-181a downregulates deptor for TGF?-induced glomerular mesangial cell hypertrophy and matrix protein expression.
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ABSTRACT: TGF? contributes to mesangial cell hypertrophy and matrix protein increase in various kidney diseases including diabetic nephropathy. Deptor is an mTOR-interacting protein and suppresses mTORC1 and mTORC2 activities. We have recently shown that TGF?-induced inhibition of deptor increases the mTOR activity. The mechanism by which TGF? regulates deptor expression is not known. Here we identify deptor as a target of the microRNA-181a. We show that in mesangial cells, TGF? increases the expression of miR-181a to downregulate deptor. Decrease in deptor augments mTORC2 activity, resulting in phosphorylation/activation of Akt kinase. Akt promotes inactivating phosphorylation of PRAS40 and tuberin, leading to stimulation of mTORC1. miR-181a-mimic increased mTORC1 and C2 activities, while anti-miR-181a inhibited them. mTORC1 controls protein synthesis via phosphorylation of translation initiation and elongation suppressors 4EBP-1 and eEF2 kinase. TGF?-stimulated miR-181a increased the phosphorylation of 4EBP-1 and eEF2 kinase, resulting in their inactivation. miR-181a-dependent inactivation of eEF2 kinase caused dephosphorylation of eEF2. Consequently, miR-181a-mimic increased protein synthesis and hypertrophy of mesangial cells similar to TGF?. Anti-miR-181a blocked these events in a deptor-dependent manner. Finally, TGF?-miR-181a-driven deptor downregulation increased the expression of fibronectin. Our results identify a novel mechanism involving miR-181a-driven deptor downregulation, which contributes to mesangial cell pathologies in renal complications.
SUBMITTER: Maity S
PROVIDER: S-EPMC5825286 | biostudies-literature | 2018 Mar
REPOSITORIES: biostudies-literature
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