title: TGF-β/Smad3 activates mammalian target of rapamycin complex-1 to promote collagen production by increasing HIF-1α expression.
abstract: Transforming growth factor (TGF)-β is a major mediator of kidney fibrosis. In the past decade it was recognized that, besides canonical Smad signaling, many other signaling pathways participate in the process of TGF-β-induced fibrogenesis. One such pathway involves mammalian target of rapamycin complex (mTORC)1. We recently reported that the hypoxia-inducible factor (HIF)-1 is essential for TGF-β-induced collagen expression regardless of ambient oxygen tension. A modulator of HIF expression other than oxygen tension is mTORC1. We therefore sought to evaluate a possible role for mTORC1 activity in TGF-β-induced fibrogenesis. mTORC1 activity was increased in human mesangial cells treated with TGF-β in a TGF-β receptor-dependent manner. Short hairpin (sh)RNA to Smad3 decreased, while overexpression of Smad3 increased, the mTORC1 activity, suggesting that TGF-β stimulation of mTORC1 also requires Smad3. Pretreatment with rapamycin or shRNA for a regulatory molecule of mTORC1, Raptor, reduced TGF-β-induced COL1A2-luc activity and collagen I protein expression. mTORC1 inhibition also prevented the TGF-β-stimulated increase in both hypoxia-responsive element (HRE) activity and HIF-1α protein expression, while activation of mTORC1 by active Rheb increased basal but not TGF-β-induced HRE activity. shRNA to Smad3 reduced HRE activity, while overexpression of Smad3 increased HIF-1α protein expression and activity in an mTORC1-dependent manner. Lastly, overexpression of HIF-1α bypassed the inhibitory effect of mTORC1 blockade on collagen expression. These results suggest that Smad3/mTORC1 interaction to promote HIF-1 expression is a key step in normoxic kidney fibrogenesis.
authors.affiliation: Dept. of Pediatrics, 310 E. Superior St. Chicago, IL 60611. benayarz@gmail.com.
authors.forename: Benaya
authors.initials: B
authors.lastname: Rozen-Zvi
authors.forename: Tomoko
authors.initials: T
authors.lastname: Hayashida
authors.forename: Susan C
authors.initials: SC
authors.lastname: Hubchak
authors.forename: Christian
authors.initials: C
authors.lastname: Hanna
authors.forename: Leonidas C
authors.initials: LC
authors.lastname: Platanias
authors.forename: H William
authors.initials: HW
authors.lastname: Schnaper
mesh_terms: D015153:Blotting, Western; D018929:Cell Culture Techniques; D003094:Collagen / Q000187:drug effects / Q000378:metabolism*; D005355:Fibrosis / Q000378:metabolism*; D005920:Glomerular Mesangium / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D000860:Hypoxia / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D047468:Immunoprecipitation; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D051900:Smad3 Protein / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology
chemical_list: C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D046912:Multiprotein Complexes; D034741:RNA, Small Interfering; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D003094:Collagen; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus
keywords: HIF; Smad3; TGF-β; collagen; fibrosis; mTOR; rapamycin