Interleukin-1beta up-regulation of Smad7 via NF-kappaB activation in human chondrocytes.
OBJECTIVE
We have previously shown that interleukin-1beta (IL-1beta) impairs transforming growth factor beta (TGFbeta) signaling through TGFbeta receptor type II (TGFbetaRII) down-regulation and Smad7 up-regulation. This mechanism could account for the reduced responsiveness of osteoarthritic chondrocytes to TGFbeta and the cartilage breakdown linked to this disease. The aim of this study was to investigate the molecular mechanism underlying the IL-1beta-induced stimulation of Smad7 in human articular chondrocytes.


METHODS
Human articular chondrocytes were treated with IL-1beta in the presence of TGFbeta1, pyrrolidine dithiocarbamate (a repressor of the NF-kappaB pathway), or cycloheximide. Then, steady-state messenger RNA and protein levels were estimated by real-time reverse transcription-polymerase chain reaction and immunocytology. In addition, transient transfections of p65 expression vector or p65-targeted short hairpin RNA were performed to define the effect of NF-kappaB on Smad7 expression.


RESULTS
TGFbetaRII overexpression restored the TGFbeta response of human articular chondrocytes. However, this effect was transient, implying that a secondary mechanism was responsible for the alteration of the TGFbeta response with long-term exposure to IL-1beta. Moreover, IL-1beta caused a late induction of the inhibitory Smad7. This effect was direct, since it did not require de novo synthesis. In addition, we established, by experiments with gain/loss of function, that the up-regulation of Smad7 by IL-1beta is mediated through the NF-kappaB pathway, especially the p65 subunit.


CONCLUSIONS
These findings clarify the regulatory process of IL-1beta on Smad7 expression. Understanding the molecular basis of IL-1beta induction of Smad7 and the reduction of chondrocyte responsiveness to TGFbeta provides new insights into the molecular mechanisms of osteoarthritis and may facilitate the identification of novel approaches for its treatment.
Baugé
C
C
University of Caen Lower Normandy, Faculty of Medicine, Caen, France.
Attia
J
J
Leclercq
S
S
Pujol
J-P
JP
Galéra
P
P
Boumédiene
K
K
D000368:Aged; D000369:Aged, 80 and over; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000502:physiology*; D006801:Humans; D053583:Interleukin-1beta / Q000378:metabolism* / Q000494:pharmacology; D008875:Middle Aged; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D051906:Smad7 Protein / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D053583:Interleukin-1beta; D017395:Plasminogen Activator Inhibitor 1; D018125:Receptors, Transforming Growth Factor beta; C051321:SERPINE1 protein, human; C497806:SMAD7 protein, human; D051906:Smad7 Protein; D051996:Transcription Factor RelA; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II