Transforming growth factor β integrates Smad 3 to mechanistic target of rapamycin complexes to arrest deptor abundance for glomerular mesangial cell hypertrophy.
In many renal diseases, transforming growth factor β (TGFβ)-stimulated canonical Smad 3 and noncanonical mechanistic target of rapamycin (mTOR) promote increased protein synthesis and mesangial cell hypertrophy. The cellular underpinnings involving these signaling molecules to regulate mesangial cell hypertrophy are not fully understood. Deptor has recently been identified as an mTOR interacting protein and functions as an endogenous inhibitor of the kinase activity for both TORC1 and TORC2. Prolonged incubation of mesangial cells with TGFβ reduced the levels of deptor concomitant with an increase in TORC1 and TORC2 activity. Sustained TGFβ activation was required to inhibit association of deptor with mTOR, whereas rapid activation had no effect. Using the mTOR inhibitor PP242, we found that TGFβ-induced both early and sustained activation of TORC1 and TORC2 was necessary for deptor suppression. PP242-induced reversal of deptor suppression by TGFβ was associated with a significant inhibition of TGFβ-stimulated protein synthesis and hypertrophy. Interestingly, expression of siRNA against Smad 3 or Smad 7, which blocks TGFβ receptor-specific Smad 3 signaling, prevented TGFβ-induced suppression of deptor abundance and TORC1/2 activities. Furthermore, overexpression of Smad 3 decreased deptor expression similar to TGFβ stimulation concomitant with increased TORC1 and TORC2 activities. Finally, knockdown of deptor reversed Smad 7-mediated inhibition of protein synthesis and mesangial cell hypertrophy induced by TGFβ. These data reveal the requirement of both early and late activation of mTOR for TGFβ-induced protein synthesis. Our results support that TGFβ-stimulated Smad 3 acts as a key node to instill a feedback loop between deptor down-regulation and TORC1/2 activation in driving mesangial cell hypertrophy.
Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229.
Falguni
F
Das
Department of Pathology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229; Veterans Affairs Research, South Texas Veterans Health Care System, San Antonio, Texas 78229.
Nandini
N
Ghosh-Choudhury
Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229.
Amit
A
Bera
Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229.
Nirmalya
N
Dey
Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229; Veterans Affairs Research, South Texas Veterans Health Care System, San Antonio, Texas 78229.
Hanna E
HE
Abboud
Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229; Veterans Affairs Research, South Texas Veterans Health Care System, San Antonio, Texas 78229.
Balakuntalam S
BS
Kasinath
Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229; Veterans Affairs Research, South Texas Veterans Health Care System, San Antonio, Texas 78229; Geriatric Research, Education and Clinical Center, South Texas Veterans Health Care System, San Antonio, Texas 78229. Electronic address: choudhuryg@uthscsa.edu.
Goutam Ghosh
GG
Choudhury
D000256:Adenoviridae / Q000378:metabolism; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D005920:Glomerular Mesangium / Q000473:pathology*; D006801:Humans; D006984:Hypertrophy; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D051900:Smad3 Protein / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D046912:Multiprotein Complexes; D011994:Recombinant Proteins; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; C546842:MTOR protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases