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MicroRNA-181a downregulates deptor for TGF?-induced glomerular mesangial cell hypertrophy and matrix protein expression.

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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microRNA-181a downregulates deptor for TGFβ-induced glomerular mesangial cell hypertrophy and matrix protein expression.

Maity Soumya S Bera Amit A Ghosh-Choudhury Nandini N Das Falguni F Kasinath Balakuntalam S BS Choudhury Goutam Ghosh GG

Experimental cell research 20180201 1

TGFβ 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 TGFβ-induced inhibition of deptor increases the mTOR activity. The mechanism by which TGFβ regulates deptor expression is not known. Here we identify deptor as a target of the microRNA-181a. We show that in mesangial cells, TGFβ increases the expression o ...[more]

PMID: 29397070

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Project description:Interaction of transforming growth factor-β (TGFβ)-induced canonical signaling with the noncanonical kinase cascades regulates glomerular hypertrophy and matrix protein deposition, which are early features of glomerulosclerosis. However, the specific target downstream of the TGFβ receptor involved in the noncanonical signaling is unknown. Here, we show that TGFβ increased the catalytic loop phosphorylation of platelet-derived growth factor receptor β (PDGFRβ), a receptor tyrosine kinase expressed abundantly in glomerular mesangial cells. TGFβ increased phosphorylation of the PI 3-kinase-interacting Tyr-751 residue of PDGFRβ, thus activating Akt. Inhibition of PDGFRβ using a pharmacological inhibitor and siRNAs blocked TGFβ-stimulated phosphorylation of proline-rich Akt substrate of 40 kDa (PRAS40), an intrinsic inhibitory component of mTORC1, and prevented activation of mTORC1 in the absence of any effect on Smad 2/3 phosphorylation. Expression of constitutively active myristoylated Akt reversed the siPDGFRβ-mediated inhibition of mTORC1 activity; however, co-expression of the phospho-deficient mutant of PRAS40 inhibited the effect of myristoylated Akt, suggesting a definitive role of PRAS40 phosphorylation in mTORC1 activation downstream of PDGFRβ in mesangial cells. Additionally, we demonstrate that PDGFRβ-initiated phosphorylation of PRAS40 is required for TGFβ-induced mesangial cell hypertrophy and fibronectin and collagen I (α2) production. Increased activating phosphorylation of PDGFRβ is also associated with enhanced TGFβ expression and mTORC1 activation in the kidney cortex and glomeruli of diabetic mice and rats, respectively. Thus, pursuing TGFβ noncanonical signaling, we identified how TGFβ receptor I achieves mTORC1 activation through PDGFRβ-mediated Akt/PRAS40 phosphorylation to spur mesangial cell hypertrophy and matrix protein accumulation. These findings provide support for targeting PDGFRβ in TGFβ-driven renal fibrosis.

Project description:Transforming growth factor-? (TGF?) promotes glomerular hypertrophy and matrix expansion, leading to glomerulosclerosis. MicroRNAs are well suited to promote fibrosis because they can repress gene expression, which negatively regulate the fibrotic process. Recent cellular and animal studies have revealed enhanced expression of microRNA, miR-21, in renal cells in response to TGF?. Specific miR-21 targets downstream of TGF? receptor activation that control cell hypertrophy and matrix protein expression have not been studied. Using 3'UTR-driven luciferase reporter, we identified the tumor suppressor protein PTEN as a target of TGF?-stimulated miR-21 in glomerular mesangial cells. Expression of miR-21 Sponge, which quenches endogenous miR-21 levels, reversed TGF?-induced suppression of PTEN. Additionally, miR-21 Sponge inhibited TGF?-stimulated phosphorylation of Akt kinase, resulting in attenuation of phosphorylation of its substrate GSK3?. Tuberin and PRAS40, two other Akt substrates, and endogenous inhibitors of mTORC1, regulate mesangial cell hypertrophy. Neutralization of endogenous miR-21 abrogated TGF?-stimulated phosphorylation of tuberin and PRAS40, leading to inhibition of phosphorylation of S6 kinase, mTOR and 4EBP-1. Moreover, downregulation of miR-21 significantly suppressed TGF?-induced protein synthesis and hypertrophy, which were reversed by siRNA-targeted inhibition of PTEN expression. Similarly, expression of constitutively active Akt kinase reversed the miR-21 Sponge-mediated inhibition of TGF?-induced protein synthesis and hypertrophy. Furthermore, expression of constitutively active mTORC1 prevented the miR-21 Sponge-induced suppression of mesangial cell protein synthesis and hypertrophy by TGF?. Finally, we show that miR-21 Sponge inhibited TGF?-stimulated fibronectin and collagen expression. Suppression of PTEN expression and expression of both constitutively active Akt kinase and mTORC1 independently reversed this miR-21-mediated inhibition of TGF?-induced fibronectin and collagen expression. Our results uncover an essential role of TGF?-induced expression of miR-21, which targets PTEN to initiate a non-canonical signaling circuit involving Akt/mTORC1 axis for mesangial cell hypertrophy and matrix protein synthesis.

Dataset Information

MicroRNA-181a downregulates deptor for TGF?-induced glomerular mesangial cell hypertrophy and matrix protein expression.

Publications

microRNA-181a downregulates deptor for TGFβ-induced glomerular mesangial cell hypertrophy and matrix protein expression.

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