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


CONCLUSIONS
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.
Department of Advanced Medicine for Uremia, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Hidehisa
H
Shimizu
Maimaiti
M
Yisireyili
Fuyuhiko
F
Nishijima
Toshimitsu
T
Niwa
D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D052160:Benzothiazoles / Q000494:pharmacology; D002478:Cells, Cultured; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007200:Indican / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D008297:Male; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020303:Rats, Inbred Dahl; D015398:Signal Transduction / Q000187:drug effects*; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism*; D014050:Toluene / Q000031:analogs & derivatives / Q000494:pharmacology; D053773:Transforming Growth Factor beta1 / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects
C541116:ACTA2 protein, human; D000199:Actins; D052160:Benzothiazoles; D007093:Imidazoles; D010879:Piperazines; D012333:RNA, Messenger; C497790:SMAD3 protein, human; D051900:Smad3 Protein; D053773:Transforming Growth Factor beta1; D016159:Tumor Suppressor Protein p53; D014050:Toluene; C482205:nutlin 3; C121565:pifithrin; D048049:Extracellular Signal-Regulated MAP Kinases; D007200:Indican