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Regulation of NFkB‐dependent Interleukin‐8 in Human Macrophages By Nuclear IkBa and Proteasome Inhibition
Author(s) -
Sanacora Shan,
Manna Subrata,
Singha Bipradeb,
Chang TzuPei,
Ramaswami Sitharam,
Vancurova Ivana
Publication year - 2013
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.27.1_supplement.550.17
Subject(s) - transcription factor , proinflammatory cytokine , biology , proteasome , nfkb1 , microbiology and biotechnology , nf κb , proteasome inhibitor , phosphorylation , chemokine , gene expression , iκbα , tumor necrosis factor alpha , signal transduction , inflammation , immunology , gene , biochemistry
Transcription of NFkB‐dependent genes is regulated by the nuclear translocation and accumulation of IkBa. In the nucleus, IkBa suppresses transcription of NFkB‐dependent pro‐inflammatory and anti‐apoptotic genes providing potential therapeutic targets. Post‐induction repression in stimulated cells, inhibition of the CRM1‐ dependent nuclear IkBa export by leptomycin B (LMB), and the inhibition of the 26S proteasome have all been found to induce nuclear IkBa accumulation. However, studies from our laboratory have shown that the inhibition of NFkB‐dependent transcription by nuclear IkBa is promoter specific. Transcription is also dependent on the subunit composition of NFkB dimers and post‐translational modifications of the recruited NFkB proteins. In this study, we have investigated the mechanisms responsible for the regulation of gene expression of the NFkB‐dependent proinflammatory chemokine interleukin‐8 (IL‐8) by nuclear IkBa and proteasome inhibition in human macrophages. Our results show that a different mechanism regulates the NFkB‐dependent transcription of IL‐8 compared to other NFkB‐dependent proinflammatory and antiapoptotic cytokines, such as TNFa, IL‐1 and IL‐6. While both IL‐8 and TNFa promoters are occupied by p65/65 homodimers in LPS‐stimulated macrophages, TNFa expression is inhibited by the LMB‐induced nuclear IkBa and proteasome inhibitor bortezomib, yet the IL‐8 expression is not inhibited by the nuclear IkBa, and is significantly up‐regulated by bortezomib. In addition, while the p65 NFkB homodimers recruited to IL‐8 promoter are phosphorylated on S536, p65 NFkB recruited to TNFa promoter is not phosphorylated. Together, our data indicate that the S536 p65 phosphorylation plays a crucial role in the regulation of IL‐8 transcription by nuclear IkBa in human macrophages. * Funded by NIH grants GM079581 and AI085497 to IV.