title: Overexpression of USP14 protease reduces I-κB protein levels and increases cytokine release in lung epithelial cells.
abstract: The ubiquitin-proteasome system is the major pathway of non-lysosomal intracellular protein degradation, playing an important role in a variety of cellular responses including cell division, proliferation, and apoptosis. Ubiquitin-specific protease 14 (USP14) is a component of proteasome regulatory subunit 19 S that regulates deubiquitinated proteins entering inside the proteasome core 20 S. The role of USP14 in protein degradation is still controversial. Several studies suggest that USP14 plays an inhibitory role in protein degradation. Here, in contrast, overexpression of USP14 induced I-κB degradation, which increased cytokine release in lung epithelial cells. Overexpression of HA-tagged USP14 (HA-USP14) reduced I-κB protein levels by increasing the I-κB degradation rate in mouse lung epithelial cells (MLE12). I-κB polyubiquitination was reduced in HA-USP14-overexpressed MLE12 cells, suggesting that USP14 regulates I-κB degradation by removing its ubiquitin chain, thus promoting the deubiquitinated I-κB degradation within the proteasome. Interestingly, we found that USP14 was associated with RelA, a binding partner of I-κB, suggesting that RelA is the linker between USP14 and I-κB. Lipopolysaccharide (LPS) treatment induced serine phosphorylation of USP14 as well as further reducing I-κB levels in HA-USP14-overexpressed MLE12 cells as compared with empty vector transfected cells. Further, overexpression of HA-USP14 increased the LPS-, TNFα-, or Escherichia coli-induced IL-8 release in human lung epithelial cells. This study suggests that USP14 removes the ubiquitin chain of I-κB, therefore inducing I-κB degradation and increasing cytokine release in lung epithelial cells.
authors.affiliation: Department of Medicine and the Acute Lung Injury Center of Excellence, the University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Rachel K
authors.initials: RK
authors.lastname: Mialki
authors.forename: Jing
authors.initials: J
authors.lastname: Zhao
authors.forename: Jianxin
authors.initials: J
authors.lastname: Wei
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Mallampalli
authors.forename: Yutong
authors.initials: Y
authors.lastname: Zhao
mesh_terms: D000818:Animals; D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D004926:Escherichia coli; D006801:Humans; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism*; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D059748:Proteolysis; D020545:Respiratory Mucosa / Q000166:cytology / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D043222:Ubiquitin Thiolesterase / Q000096:biosynthesis* / Q000235:genetics; D054875:Ubiquitination / Q000187:drug effects / Q000235:genetics
chemical_list: C508606:CXCL8 protein, human; D020672:I-kappa B Proteins; D016209:Interleukin-8; D008070:Lipopolysaccharides; C498143:RELA protein, human; C498144:Rela protein, mouse; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; C509299:USP14 protein, human; D025801:Ubiquitin; C469268:Usp14 protein, mouse; D043222:Ubiquitin Thiolesterase
keywords: Cytokine; Deubiquitination; NF-κB Transcription Factor; Protein Phosphorylation; Protein degradation; USP14