TY - JOUR
T1 - TGFβ-induced deptor suppression recruits mTORC1 and not mTORC2 to enhance collagen i (α2) gene expression
AU - Das, Falguni
AU - Bera, Amit
AU - Ghosh-Choudhury, Nandini
AU - Abboud, Hanna E.
AU - Kasinath, Balakuntalam S.
AU - Choudhury, Goutam Ghosh
PY - 2014/10/15
Y1 - 2014/10/15
N2 - Enhanced TGFβ activity contributes to the accumulation of matrix proteins including collagen I (α2) by proximal tubular epithelial cells in progressive kidney disease. Although TGFβ rapidly activates its canonical Smad signaling pathway, it also recruits noncanonical pathway involving mTOR kinase to regulate renal matrix expansion. The mechanism by which chronic TGFβ treatment maintains increased mTOR activity to induce the matrix protein collagen I (α2) expression is not known. Deptor is an mTOR interacting protein that suppresses mTOR activity in both mTORC1 and mTORC2. In proximal tubular epithelial cells, TGFβ reduced deptor levels in a time-dependent manner with concomitant increase in both mTORC1 and mTORC2 activities. Expression of deptor abrogated activity of mTORC1 and mTORC2 resulting in inhibition of collagen I (α2) mRNA and protein expression via transcriptional mechanism. In contrast, neutralization of endogenous deptor by shRNAs increased activity of both mTOR complexes and expression of collagen I (α2) similar to TGFb treatment. Importantly, downregulation of deptor by TGFβ increased the expression of Hif1a by increasing translation of its mRNA. TGFb-induced deptor downregulation promotes Hif1a binding to its cognate hypoxia responsive element in the collagen I (α2) gene to control its protein expression via direct transcriptional mechanism. Interestingly, knockdown of raptor to specifically block mTORC1 activity significantly inhibited expression of collagen I (α2) and Hif1a while inhibition of rictor to prevent selectively mTORC2 activation did not have any effect. Critically, our data provide evidence for the requirement of TGFb-activated mTORC1 only by deptor downregulation, which dominates upon the bystander mTORC2 activity for enhanced expression of collagen I (α2). Our results also suggest the presence of a safeguard mechanism involving deptor-mediated suppression of mTORC1 activity against developing TGFβ-induced renal fibrosis.
AB - Enhanced TGFβ activity contributes to the accumulation of matrix proteins including collagen I (α2) by proximal tubular epithelial cells in progressive kidney disease. Although TGFβ rapidly activates its canonical Smad signaling pathway, it also recruits noncanonical pathway involving mTOR kinase to regulate renal matrix expansion. The mechanism by which chronic TGFβ treatment maintains increased mTOR activity to induce the matrix protein collagen I (α2) expression is not known. Deptor is an mTOR interacting protein that suppresses mTOR activity in both mTORC1 and mTORC2. In proximal tubular epithelial cells, TGFβ reduced deptor levels in a time-dependent manner with concomitant increase in both mTORC1 and mTORC2 activities. Expression of deptor abrogated activity of mTORC1 and mTORC2 resulting in inhibition of collagen I (α2) mRNA and protein expression via transcriptional mechanism. In contrast, neutralization of endogenous deptor by shRNAs increased activity of both mTOR complexes and expression of collagen I (α2) similar to TGFb treatment. Importantly, downregulation of deptor by TGFβ increased the expression of Hif1a by increasing translation of its mRNA. TGFb-induced deptor downregulation promotes Hif1a binding to its cognate hypoxia responsive element in the collagen I (α2) gene to control its protein expression via direct transcriptional mechanism. Interestingly, knockdown of raptor to specifically block mTORC1 activity significantly inhibited expression of collagen I (α2) and Hif1a while inhibition of rictor to prevent selectively mTORC2 activation did not have any effect. Critically, our data provide evidence for the requirement of TGFb-activated mTORC1 only by deptor downregulation, which dominates upon the bystander mTORC2 activity for enhanced expression of collagen I (α2). Our results also suggest the presence of a safeguard mechanism involving deptor-mediated suppression of mTORC1 activity against developing TGFβ-induced renal fibrosis.
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U2 - 10.1371/journal.pone.0109608
DO - 10.1371/journal.pone.0109608
M3 - Article
C2 - 25333702
AN - SCOPUS:84908110053
SN - 1932-6203
VL - 9
JO - PloS one
JF - PloS one
IS - 10
M1 - e109608
ER -