PRAS40 acts as a nodal regulator of high glucose‐induced TORC1 activation in glomerular mesangial cell hypertrophy

Abstract

Diabetic nephropathy manifests aberrant activation of TORC1, which senses key signals to modulate protein synthesis and renal hypertrophy. PRAS40 has recently been identified as a raptor-interacting protein and is a component and a constitutive inhibitor of TORC1. The mechanism by which high glucose stimulates TORC1 activity is not known. PRAS40 was identified in the mesangial cells in renal glomeruli and in tubulointerstitium of rat kidney. Streptozotocin-induced diabetic renal hypertrophy was associated with phosphorylation of PRAS40 in the cortex and glomeruli. In vitro, high glucose concentration increased PRAS40 phosphorylation in a PI 3 kinase-and Akt-dependent manner, resulting in dissociation of raptor-PRAS40 complex in mesangial cells. High glucose augmented the inactivating and activating phosphorylation of 4EBP-1 and S6 kinase, respectively with concomitant induction of protein synthesis and hypertrophy. Expression of TORC1-nonphosphorylatable mutant of 4EBP-1 and dominant negative S6 kinase significantly inhibited high glucose-induced protein synthesis and hypertrophy. PRAS40 knockdown mimicked the effect of high glucose on phosphorylation of 4EBP-1 and S6 kinase, protein synthesis and hypertrophy. To elucidate the role of PRAS40 phosphorylation, we used phosphorylation-deficient mutant of PRAS40, which in contrast to PRAS40 knockdown inhibited phosphorylation of 4EBP-1 and S6 kinase, leading to reduced mesangial cell hypertrophy. Thus our data identify high glucose-induced phosphorylation and inactivation of PRAS40 as a central node for mesangial cell hypertrophy in diabetic nephropathy.

Hydrogen Sulfide Inhibits High Glucose-induced Matrix Protein Synthesis by Activating AMP-activated Protein Kinase in Renal Epithelial Cells

“…High glucose recruits mTORC1 to promote protein synthesis and hypertrophy in kidney epithelial and mesangial cells (13,19,35,(52)(53)(54). One mechanism by which mTOR complex 1 is stimulated by high glucose in the GECs involves inhibition of AMPK phosphorylation and activity (12,13).…”

MicroRNA-214 Reduces Insulin-like Growth Factor-1 (IGF-1) Receptor Expression and Downstream mTORC1 Signaling in Renal Carcinoma Cells

“…More recently we and others have shown that phosphorylation of PRAS40 regulates protein synthesis leading to an increase in the size of normal renal cells (42)(43)(44). However, its role in renal cancer cells has not been investigated.…”

Knockdown of PRAS40 inhibits insulin action via proteasome-mediated degradation of IRS1 in primary human skeletal muscle cells

“…PRAS40 is a component of mTORC1 [16,17]. Yet studies of the function of this protein within mTORC1 have yielded conflicting results [18][19][20][21][22][23]. Silencing and overexpression studies, mostly in immortalised cultured cell lines, have ascribed both inhibitory and stimulatory functions to PRAS40 in the regulation of mTORC1 activity [18][19][20][21][22][23].…”

“…Yet studies of the function of this protein within mTORC1 have yielded conflicting results [18][19][20][21][22][23]. Silencing and overexpression studies, mostly in immortalised cultured cell lines, have ascribed both inhibitory and stimulatory functions to PRAS40 in the regulation of mTORC1 activity [18][19][20][21][22][23]. Importantly, a recent study conducted in Drosophila melanogaster shed light on these seemingly contrasting findings, demonstrating that D. melanogaster dPRAS40 acts as an inhibitor of TORC1 signalling in a tissue-specific way that depends on post-translational modification of the protein [24].…”