Indoxyl sulfate enhances p53-TGF-β1-Smad3 pathway in proximal tubular cells

Am J Nephrol. 2013;37(2):97-103. doi: 10.1159/000346420. Epub 2013 Jan 25.


Background/aim: Indoxyl sulfate-induced activation of nuclear factor (NF)-ĸB promotes transforming growth factor (TGF)-β1 in human proximal tubular cells (HK-2 cells). The present study aimed to elucidate the cross talk among indoxyl sulfate, p53 and TGF-β1-Smad3 signaling in proximal tubular cells.

Methods: The effects of indoxyl sulfate on the expression of TGF-β1, Smad3, and α-smooth muscle actin (α-SMA) were determined using HK-2 cells. As for in vivo experiments the following animals were used: Dahl salt-resistant normotensive rats (DN) and indoxyl sulfate-administered Dahl salt-resistant normotensive rats (DN+IS).

Results: Both indoxyl sulfate and nutlin-3, a specific p53 inducer, stimulated TGF-β1 expression, which was suppressed by pifithrin-α, p-nitro, a p53 inhibitor. Further, indoxyl sulfate stimulated TGF-β1-induced expression of α-SMA by enhancing Smad3 expression and TGF-β1-induced Smad3 phosphorylation. Indoxyl sulfate induced phosphorylation of extracellular signal-regulated kinase (ERK). U0126, an inhibitor of ERK pathway, prevented indoxyl sulfate-induced upregulation of Smad3 expression. Immunohistochemistry demonstrated that TGF-β1 and Smad3 were localized in renal tubular cells, and that indoxyl sulfate increased the TGF-β1 and Smad3-positive area in the kidney.

Conclusion: Indoxyl sulfate stimulates p53-induced TGF-β1 expression and TGF-β1-induced α-SMA expression in proximal tubular cells. Indoxyl sulfate-induced Smad3 accelerates TGF-β1-induced α-SMA expression through ERK activation. Thus, indoxyl sulfate enhances p53-TGF-β1-Smad3 pathway in proximal tubular cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / genetics
  • Actins / metabolism*
  • Analysis of Variance
  • Animals
  • Benzothiazoles / pharmacology
  • Cells, Cultured
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Humans
  • Imidazoles / pharmacology
  • Indican / pharmacology*
  • Kidney Tubules, Proximal / cytology
  • Kidney Tubules, Proximal / metabolism*
  • Male
  • Phosphorylation / drug effects
  • Piperazines / pharmacology
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Inbred Dahl
  • Signal Transduction / drug effects*
  • Smad3 Protein / genetics
  • Smad3 Protein / metabolism*
  • Toluene / analogs & derivatives
  • Toluene / pharmacology
  • Transforming Growth Factor beta1 / genetics
  • Transforming Growth Factor beta1 / metabolism*
  • Tumor Suppressor Protein p53 / metabolism*
  • Up-Regulation / drug effects


  • ACTA2 protein, human
  • Actins
  • Benzothiazoles
  • Imidazoles
  • Piperazines
  • RNA, Messenger
  • SMAD3 protein, human
  • Smad3 Protein
  • Transforming Growth Factor beta1
  • Tumor Suppressor Protein p53
  • Toluene
  • nutlin 3
  • pifithrin
  • Extracellular Signal-Regulated MAP Kinases
  • Indican