title: TGFβ-induced deptor suppression recruits mTORC1 and not mTORC2 to enhance collagen I (α2) gene expression.
abstract: 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 TGFβ treatment. Importantly, downregulation of deptor by TGFβ increased the expression of Hif1α by increasing translation of its mRNA. TGFβ-induced deptor downregulation promotes Hif1α 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 Hif1α while inhibition of rictor to prevent selectively mTORC2 activation did not have any effect. Critically, our data provide evidence for the requirement of TGFβ-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.
authors.affiliation: Departments of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.
authors.forename: Falguni
authors.initials: F
authors.lastname: Das
authors.affiliation: Departments of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.
authors.forename: Amit
authors.initials: A
authors.lastname: Bera
authors.affiliation: Department of Pathology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America; VA Research, South Texas Veterans Health Care System, San Antonio, Texas, United States of America.
authors.forename: Nandini
authors.initials: N
authors.lastname: Ghosh-Choudhury
authors.affiliation: Departments of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America; VA Research, South Texas Veterans Health Care System, San Antonio, Texas, United States of America.
authors.forename: Hanna E
authors.initials: HE
authors.lastname: Abboud
authors.affiliation: Departments of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America; VA Research, South Texas Veterans Health Care System, San Antonio, Texas, United States of America.
authors.forename: Balakuntalam S
authors.initials: BS
authors.lastname: Kasinath
authors.affiliation: Departments of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America; Geriatric Research, Education and Clinical Center, South Texas Veterans Health Care System, San Antonio, Texas, United States of America; VA Research, South Texas Veterans Health Care System, San Antonio, Texas, United States of America.
authors.forename: Goutam Ghosh
authors.initials: GG
authors.lastname: Choudhury
mesh_terms: D000818:Animals; D002460:Cell Line; D024042:Collagen Type I / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D051379:Mice; D046912:Multiprotein Complexes / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*
chemical_list: D024042:Collagen Type I; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047908:Intracellular Signaling Peptides and Proteins; D046912:Multiprotein Complexes; D053773:Transforming Growth Factor beta1; C556139:DEPTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D058570:TOR Serine-Threonine Kinases