title: Activating protein phosphatase 2A (PP2A) enhances tristetraprolin (TTP) anti-inflammatory function in A549 lung epithelial cells.
abstract: Chronic respiratory diseases are driven by inflammation, but some clinical conditions (severe asthma, COPD) are refractory to conventional anti-inflammatory therapies. Thus, novel anti-inflammatory strategies are necessary. The mRNA destabilizing protein, tristetraprolin (TTP), is an anti-inflammatory molecule that functions to induce mRNA decay of cytokines that drive pathogenesis of respiratory disorders. TTP is regulated by phosphorylation and protein phosphatase 2A (PP2A) is responsible for dephosphorylating (and hence activating) TTP, amongst other targets. PP2A is activated by small molecules, FTY720 and AAL(S), and in this study we examine whether these compounds repress cytokine production in a cellular model of airway inflammation using A549 lung epithelial cells stimulated with tumor necrosis factor α (TNFα) in vitro. PP2A activators significantly increase TNFα-induced PP2A activity and inhibit mRNA expression and protein secretion of interleukin 8 (IL-8) and IL-6; two key pro-inflammatory cytokines implicated in respiratory disease and TTP targets. The effect of PP2A activators is not via an increase in TNFα-induced TTP mRNA expression; instead we demonstrate a link between PP2A activation and TTP anti-inflammatory function by showing that specific knockdown of TTP with siRNA reversed the repression of TNFα-induced IL-8 and IL-6 mRNA expression and protein secretion by FTY720. Therefore we propose that PP2A activators affect the dynamic equilibrium regulating TTP; shifting the equilibrium from phosphorylated (inactive) towards unphosphorylated (active) but unstable TTP. PP2A activators boost the anti-inflammatory function of TTP and have implications for future pharmacotherapeutic strategies to combat inflammation in respiratory disease.
authors.affiliation: Faculty of Pharmacy, University of Sydney, NSW 2006, Australia.
authors.forename: Md Mostafizur
authors.initials: MM
authors.lastname: Rahman
authors.affiliation: Faculty of Pharmacy, University of Sydney, NSW 2006, Australia.
authors.forename: Nowshin N
authors.initials: NN
authors.lastname: Rumzhum
authors.affiliation: Priority Research Centre for Respiratory Diseases, Hunter Medical Research Institute, University of Newcastle, NSW 2308, Australia.
authors.forename: Philip M
authors.initials: PM
authors.lastname: Hansbro
authors.affiliation: School of Chemistry, University of NSW, NSW 2052, Australia.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Morris
authors.affiliation: Centre for Translational Inflammation Research, School of Immunity and Infection, University of Birmingham, Edgbaston B15 2TT, United Kingdom.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Clark
authors.affiliation: School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, University of Newcastle, NSW 2308, Australia.
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Verrills
authors.affiliation: Faculty of Pharmacy, University of Sydney, NSW 2006, Australia. Electronic address: alaina.ammit@sydney.edu.au.
authors.forename: Alaina J
authors.initials: AJ
authors.lastname: Ammit
mesh_terms: D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D004847:Epithelial Cells / Q000378:metabolism*; D000068876:Fingolimod Hydrochloride / Q000494:pharmacology; D006801:Humans; D008168:Lung / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000378:metabolism*; D051816:Tristetraprolin / Q000235:genetics / Q000378:metabolism*
chemical_list: D051816:Tristetraprolin; C497552:ZFP36 protein, human; D054648:Protein Phosphatase 2; D000068876:Fingolimod Hydrochloride
keywords: Asthma; Inflammation; Protein phosphatase 2A; TNFα; Tristetraprolin