title: Mitogen-activated protein kinases p38 and JNK mediate Actinobacillus pleuropneumoniae exotoxin ApxI-induced apoptosis in porcine alveolar macrophages.
abstract: Actinobacillus pleuropneumoniae exotoxins (Apx) are major virulence factors that play important roles in the pathogenesis of pleuropneumonia in swine. A previous study has demonstrated that native ApxI at low concentrations induces apoptosis in primary porcine alveolar macrophages (PAMs) via a caspase-3-dependent pathway. However, the molecular mechanisms underlying ApxI-induced apoptosis remain largely unknown. In this study, it was shown that ApxI treatment in PAMs rapidly induced phosphorylation of both p38 and JNK, members of the mitogen-activated protein kinase family. Application of a selective p38 or JNK inhibitor significantly reduced ApxI-induced apoptosis, indicating the involvement of p38 and JNK pathways in this event. Furthermore, activation of both caspase-8 and -9 were observed in ApxI-stimulated PAMs. Inhibition of caspase-8 and caspase-9 activity significantly protected PAMs from ApxI-induced apoptosis. In addition, Bid activation was also noted in ApxI-treated PAMs, and inhibition of caspase-8 suppressed the activation of Bid and caspase-9, suggesting that ApxI was able to activate the caspases-8-Bid-caspase-9 pathway. Notably, inhibition of p38 or JNK pathway greatly attenuated the activation of caspases-3, -8, and -9. This study is the first to demonstrate that ApxI-induced apoptosis of PAMs involves the activation of p38 and JNK, and engages the extrinsic and intrinsic apoptotic pathways.
authors.affiliation: Graduate Institute of Veterinary Pathobiology, College of Veterinary Medicine, National Chung Hsing University, 250 Kuo Kuang Road, Taichung 402, Taiwan, ROC.
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Wu
authors.forename: Zeng-Weng
authors.initials: ZW
authors.lastname: Chen
authors.forename: Ter-Hsin
authors.initials: TH
authors.lastname: Chen
authors.forename: Jiunn-Wang
authors.initials: JW
authors.lastname: Liao
authors.forename: Cheng-Chung
authors.initials: CC
authors.lastname: Lin
authors.forename: Maw-Sheng
authors.initials: MS
authors.lastname: Chien
authors.forename: Wei-Cheng
authors.initials: WC
authors.lastname: Lee
authors.forename: Shih-Ling
authors.initials: SL
authors.lastname: Hsuan
mesh_terms: D016977:Actinobacillus pleuropneumoniae / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism; D001426:Bacterial Proteins / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation; D005098:Exotoxins / Q000494:pharmacology*; D006460:Hemolysin Proteins / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D016676:Macrophages, Alveolar / Q000166:cytology* / Q000382:microbiology; D010766:Phosphorylation; D013552:Swine; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; D001426:Bacterial Proteins; D005098:Exotoxins; D006460:Hemolysin Proteins; C087744:ApxI toxin, Bacteria; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9