Transcriptional repression of the transforming growth factor β (TGF-β) Pseudoreceptor BMP and activin membrane-bound inhibitor (BAMBI) by Nuclear Factor κB (NF-κB) p50 enhances TGF-β signaling in hepatic stellate cells.
TLR4 signaling induces down-regulation of the bone morphogenic protein (BMP) and activin membrane-bound inhibitor (BAMBI), which enhances TGF-β signaling during hepatic stellate cell (HSC) activation. We investigated the mechanism by which TLR4 signaling down-regulates BAMBI expression in HSCs and found that TLR4- and TNF-α-mediated BAMBI down-regulation is dependent on regulation of BAMBI promoter activity through the interaction with NF-κBp50 and HDAC1 in HSCs. Bambi was predominantly expressed in HSCs, at high levels in quiescent HSCs but at low levels in in vivo-activated and LPS-stimulated HSCs. In human HSCs, BAMBI expression was down-regulated in response to LPS and TNF-α. A BAMBI reporter assay demonstrated that the regulatory element to repress BAMBI transcription is located between 3384 and 1560 bp upstream from the transcription start site. LPS stimulation down-regulated BAMBI expression in cells with NF-κBp65 knockdown. However, it failed to down-regulate BAMBI in cells with inactivation of NF-κB or NF-κBp50 silencing, indicating that NF-κBp50 is a factor for BAMBI down-regulation. ChIP analysis revealed that LPS and TNF-α induced binding of the NF-κBp50/p50 homodimer to the BAMBI promoter region. We also found that HDAC1 is bound to this region as part of the NF-κBp50-HDAC1 complex, repressing transcriptional activity of the BAMBI promoter. Finally, we confirmed that LPS does not repress BAMBI reporter activity using a BAMBI reporter construct with a mutation at 3166 bp upstream of the coding region. In summary, our study demonstrates that LPS- and TNF-α-induced NF-κBp50-HDAC1 interaction represses BAMBI transcriptional activity, which contributes to TLR4-mediated enhancement of TGF-β signaling in HSCs during liver fibrosis.
Division of Gastroenterology, Department of Medicine, University of California San Diego, School of Medicine, La Jolla, California 92093; Scientific Research Center, Shanghai 201508, China; Department of Traditional Chinese Medicine, Shanghai Public Clinical Health Center, Shanghai 201508, China.
Cheng
C
Liu
Department of Traditional Chinese Medicine, Shanghai Public Clinical Health Center, Shanghai 201508, China.
Xiaorong
X
Chen
Division of Gastroenterology, Department of Medicine, University of California San Diego, School of Medicine, La Jolla, California 92093.
Ling
L
Yang
Division of Gastroenterology, Department of Medicine, University of California San Diego, School of Medicine, La Jolla, California 92093.
Tatiana
T
Kisseleva
Division of Gastroenterology, Department of Medicine, University of California San Diego, School of Medicine, La Jolla, California 92093.
David A
DA
Brenner
Division of Gastroenterology, Department of Medicine, University of California San Diego, School of Medicine, La Jolla, California 92093. Electronic address: ekseki@ucsd.edu.
Ekihiro
E
Seki
D002460:Cell Line; D015536:Down-Regulation; D005786:Gene Expression Regulation; D055166:Hepatic Stellate Cells / Q000378:metabolism*; D056284:Histone Deacetylase 1 / Q000378:metabolism; D006801:Humans; D008070:Lipopolysaccharides / Q000378:metabolism; D008103:Liver Cirrhosis / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics*; D052002:NF-kappa B p50 Subunit / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D055503:Protein Multimerization; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*
C485671:BAMBI protein, human; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D052002:NF-kappa B p50 Subunit; C489548:NFKB1 protein, human; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D016212:Transforming Growth Factor beta; C110550:HDAC1 protein, human; D056284:Histone Deacetylase 1
Hepatic Stellate Cells; Lipopolysaccharide (LPS); NF-κB; Toll-like Receptors (TLR); Transcription Promoter; Transforming Growth Factor β (TGF-β)