title: Proteasomal inhibition upregulates the endogenous MAPK deactivator MKP-1 in human airway smooth muscle: mechanism of action and effect on cytokine secretion.
abstract: Asthma is a chronic inflammatory condition. Inhibition of the ubiquitin-proteasome system offers promise as a anti-inflammatory strategy, being responsible for the degradation of key proteins involved in crucial cellular functions, including gene expression in inflammation (e.g. inhibitory IkappaB-alpha and the endogenous MAPK deactivator - MKP-1). As MKP-1 inhibits MAPK-mediated pro-remodeling functions in human airway smooth muscle (ASM; a pivotal immunomodulatory cell in asthma) in this study we investigate the effect of the proteasome inhibitor MG-132 on MKP-1 and evaluate the anti-inflammatory effect of MG-132 on cytokine secretion from ASM cells. Examining the time-course of induction of MKP-1 mRNA and protein by MG-132 (10microM) we show that MKP-1 mRNA was first detected at 30min, increased to significant levels by 4h, resulting in a 12.6+/-1.5-fold increase in MKP-1 mRNA expression by 24h (P<0.05). MKP-1 protein levels corroborate the mRNA results. Investigating the effect of MG-132 on secretion of the cytokine IL-6 we show that while short-term pretreatment with MG-132 (30min) partially reduced TNFalpha-induced IL-6 via inhibition of IkappaB-alpha degradation and the NF-kappaB pathway, longer-term proteasome inhibition (up to 24h) robustly upregulated MKP-1 and was temporally correlated with repression of p38-mediated IL-6 secretion from ASM cells. Moreover, utilizing a cytokine array we show that MG-132 represses the secretion of multiple cytokines implicated in asthma. Taken together, our results demonstrate that MG-132 upregulates MKP-1 and represses cytokine secretion from ASM and highlight the potential of the proteasome as a therapeutic target in asthma.
authors.affiliation: Respiratory Research Group, Faculty of Pharmacy, University of Sydney, NSW 2006 Australia.
authors.forename: John P
authors.initials: JP
authors.lastname: Moutzouris
authors.forename: Wenchi
authors.initials: W
authors.lastname: Che
authors.forename: Emma E
authors.initials: EE
authors.lastname: Ramsay
authors.forename: Melanie
authors.initials: M
authors.lastname: Manetsch
authors.forename: Hatem
authors.initials: H
authors.lastname: Alkhouri
authors.forename: Anna M
authors.initials: AM
authors.lastname: Bjorkman
authors.forename: Friederike
authors.initials: F
authors.lastname: Schuster
authors.forename: Qi
authors.initials: Q
authors.lastname: Ge
authors.forename: Alaina J
authors.initials: AJ
authors.lastname: Ammit
mesh_terms: D001249:Asthma / Q000276:immunology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D016207:Cytokines / Q000378:metabolism*; D054638:Dual Specificity Phosphatase 1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D020545:Respiratory Mucosa / Q000033:anatomy & histology*; D015398:Signal Transduction / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D015853:Cysteine Proteinase Inhibitors; D016207:Cytokines; D015850:Interleukin-6; D016209:Interleukin-8; D007976:Leupeptins; D061988:Proteasome Inhibitors; D014409:Tumor Necrosis Factor-alpha; D020928:Mitogen-Activated Protein Kinases; D054638:Dual Specificity Phosphatase 1; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde