Smad7 and Smad6 bind to discrete regions of Pellino-1 via their MH2 domains to mediate TGF-beta1-induced negative regulation of IL-1R/TLR signaling.
Transforming growth factor-beta1 (TGF-beta1) performs diverse cellular functions, including anti-inflammatory activity. The inhibitory Smad (I-Smad) Smad6 was previously shown to play an important role in TGF-beta1-induced negative regulation of Interleukin-1/Toll-like receptor (IL-1R/TLR) signaling through binding to Pellino-1, an adaptor protein of interleukin-1 receptor associated kinase 1(IRAK1). However, it is unknown whether Smad7, the other inhibitory Smad, also has a role in regulating IL-1R/TLR signaling. Here, we demonstrate that endogeneous Smad7 and Smad6 simultaneously bind to discrete regions of Pellino-1 upon TGF-beta1 treatment, via distinct regions of the Smad MH2 domains. In addition, the Smad7-Pellino-1 interaction abrogated NF-kappaB activity by blocking formation of the IRAK1-mediated IL-1R/TLR signaling complex, subsequently causing reduced expression of pro-inflammatory genes. Double knock-down of endogenous Smad6 and Smad7 genes by RNA interference further reduced the anti-inflammatory activity of TGF-beta1 than when compared with single knock-down of Smad7. These results provide evidence that the I-Smads, Smad6 and Smad7, act as critical mediators for effective TGF-beta1-mediated suppression of IL-1R/TLR signaling, by simultaneous binding to discrete regions of Pellino-1.
Lee
Youn Sook
YS
Department of Biological Sciences, Sungkyunkwan University, Suwon 440-746, Republic of Korea.
Kim
Jun Hwan
JH
Kim
Shin-Tae
ST
Kwon
Jae Young
JY
Hong
Suntaek
S
Kim
Seong-Jin
SJ
Park
Seok Hee
SH
D000818:Animals; D002460:Cell Line; D005260:Female; D055785:Gene Knockdown Techniques; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D017472:Receptors, Interleukin-1 / Q000378:metabolism*; D015398:Signal Transduction; D051899:Smad2 Protein / Q000235:genetics / Q000378:metabolism*; D051905:Smad6 Protein / Q000235:genetics / Q000378:metabolism*; D051193:Toll-Like Receptors / Q000378:metabolism*; D053773:Transforming Growth Factor beta1 / Q000378:metabolism* / Q000494:pharmacology; D044767:Ubiquitin-Protein Ligases
D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D017472:Receptors, Interleukin-1; D051899:Smad2 Protein; D051905:Smad6 Protein; D051193:Toll-Like Receptors; D053773:Transforming Growth Factor beta1; C485959:PELI1 protein, human; D044767:Ubiquitin-Protein Ligases