Smad7 mediates transforming growth factor-beta-induced apoptosis in mesangial cells.
BACKGROUND
In addition to inhibiting cell growth, transforming growth factor-beta (TGF-beta) has recently been reported to induce apoptosis in various cell lines. Smad proteins are the downstream effectors of TGF-beta signaling. Among them, Smad7 exerts negative feedback control over the action of TGF-beta. However, we do not know how the Smad proteins contribute to TGF-beta-induced apoptosis in mesangial cells. To investigate the function of Smad proteins, we examined the effect of Smad overexpression using adenoviral vector in mesangial cells.


METHODS
Primary cultured rat mesangial cells were transfected with Smad7-promoter-luciferase-plasmid by electroporation. Smad7 promoter activity was investigated by luciferase assay. The apoptotic phenomena elicited by TGF-beta and Smad7 overexpression were investigated using adenoviral vector (AdCMV-Smad7). Apoptosis was detected by the cell death detection ELISA assay, CPP32/caspase-3 assay, and nucleosomal DNA laddering.


RESULTS
TGF-beta significantly increased the protein expression and the promoter activity of Smad7 in rat mesangial cells. Overexpression of Smad7 induced DNA fragmentation and significant increases in cell death ELISA and CPP32/caspase-3 assay. On the other hand, overexpression of Smad2 and Smad3 did not elicit any significant increases in CPP32/caspase-3 activity. Furthermore, the antisense oligonucleotide to Smad7 prevented the TGF-beta-induced apoptosis. Overexpression of Smad7 did not affect nuclear factor-kappaB activity in mesangial cells.


CONCLUSIONS
These data indicate that TGF-beta-induced apoptosis in mesangial cells is mediated through the activation of caspase-3 by Smad7, but not by Smad2 or Smad3. Our results provide new clarification on the function of Smad7 in TGF-beta signaling in mesangial cells.
Okado
Tomokazu
T
Homeostasis Medicine and Nephrology, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan.
Terada
Yoshio
Y
Tanaka
Hiroyuki
H
Inoshita
Seiji
S
Nakao
Atsuhito
A
Sasaki
Sei
S
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D005920:Glomerular Mesangium / Q000166:cytology* / Q000502:physiology; D008297:Male; D016328:NF-kappa B / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D051899:Smad2 Protein; D051900:Smad3 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D004268:DNA-Binding Proteins; D016328:NF-kappa B; D016376:Oligonucleotides, Antisense; D051899:Smad2 Protein; C497784:Smad2 protein, rat; D051900:Smad3 Protein; C497787:Smad3 protein, rat; D051906:Smad7 Protein; C497808:Smad7 protein, rat; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases