An RNA-binding protein alphaCP-1 is involved in the STAT3-mediated suppression of NF-kappaB transcriptional activity.
Signal transducer and activator of transcription 3 (STAT3) has been shown to mediate the anti-inflammatory effect of IL-10. Activated STAT3 suppresses LPS-induced IL-6, tumor necrosis factor-alpha and IL-12 gene expression in macrophages and dendritic cells. However, the mechanism of Toll-like receptor (TLR) signal suppression by STAT3 has not been clarified. In this study, we investigated the effect of constitutively activated STAT3 (STAT3C) on LPS-induced nuclear factor-kappaB (NF-kappaB) activation. The forced expression of STAT3C in HEK293/TLR4 cells, but neither wild-type STAT3 nor dominant-negative form of STAT3, suppressed LPS-TLR4-mediated NF-kappaB reporter activation. The over-expression of STAT3C did not affect the signal transduction of TLR4, such as the phosphorylation of inhibitory nuclear factor-kappaBalpha and mitogen-activated protein kinases and the DNA-binding activity of NF-kappaB. Thus, STAT3C could suppress the transcriptional and/or translational activity of NF-kappaB. To define the molecular mechanism, we searched STAT3C-binding proteins by using a proteomic approach and found that a novel RNA-binding protein, alphaCP-1, interacted with STAT3C. alphaCP-1 is a K-homology domain-containing RNA-binding protein with specificity for C-rich pyrimidine tracts. Such proteins play pivotal roles in a broad-spectrum of transcriptional and translational events. The over-expression of alphaCP-1 augmented the suppressive effect of STAT3C on NF-kappaB activation in HEK293/TLR4 cells. Furthermore, the forced expression of alphaCP-1 enhanced the antagonistic effect of IL-10 on IL-6 production in RAW264.7 cells, while small interfering RNA against alphaCP-1 reduced it. These data suggest that alphaCP-1 is involved in the STAT3-mediated suppression of NF-kappaB activity.
Nishinakamura
Hitomi
H
Division of Molecular and Cellular Immunology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Minoda
Yasumasa
Y
Saeki
Kazuko
K
Koga
Keiko
K
Takaesu
Giichi
G
Onodera
Masafumi
M
Yoshimura
Akihiko
A
Kobayashi
Takashi
T
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins; D003713:Dendritic Cells; D005786:Gene Expression Regulation; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000378:metabolism*; D006801:Humans; D016753:Interleukin-10 / Q000235:genetics / Q000378:metabolism; D015850:Interleukin-6 / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000235:genetics; D034741:RNA, Small Interfering / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D051193:Toll-Like Receptors / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D015850:Interleukin-6; D016328:NF-kappa B; C094604:PCBP1 protein, human; C121375:Pcbp1 protein, mouse; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D050796:STAT3 Transcription Factor; D051193:Toll-Like Receptors; D018808:Transcription Factor AP-1; D016753:Interleukin-10