title: A redox microenvironment is essential for MAPK-dependent secretion of pro-inflammatory cytokines: modulation by glutathione (GSH/GSSG) biosynthesis and equilibrium in the alveolar epithelium.
abstract: The characterization of oxidant (glutathione)-dependent regulation of MAPK(p38/RK)-mediated TNF-α secretion was undertaken in vitro, and the ramifications of the influence of a redox microenvironment were unraveled. Intermittent exposure of alveolar epithelial cells (FATEII) to LPS (endotoxin) transiently and temporally induced the expression of MAPK(p38/RK). This upregulation was associated with the activation of MAPKAP-K(2), manifested by the specific phosphorylation of the downstream heat-shock protein (Hsp)-27. Selective blockading of the MAPK(p38/RK) pathway using the pyridinyl imidazole SB-203580 abrogated the LPS-dependent release of TNF-α. N-acetyl-l-cysteine (NAC), a precursor of glutathione, reduced TNF-α secretion and increased [GSH]. Conversely, l-buthionine-(S,R)-sulfoximine (BSO), an irreversible inhibitor of γ-glutamylcysteine synthetase (γ-GCS), the rate-limiting enzyme in the pathway mediating GSH biosynthesis, augmented the secretion of TNF-α and [GSSG] accumulation. Whereas NAC abrogated the phosphorylation of MAPK(p38/RK), BSO reversibly amplified this effect. Furthermore, intermittent exposure of FATEII cells to the exogenous oxidants X/XO and H(2)O(2) upregulated the secretion of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α; this upregulation was correlated with increasing activity of key glutathione-related enzymes, closely involved with maintaining the cyclic GSH/GSSG equilibrium. These results indicate that a redox microenvironment plays a major role in regulating MAPK-dependent production of cytokines in the alveolar epithelium.
authors.affiliation: Cellular and Molecular Signaling Research Group, Department of Medical Laboratory Technology, Faculty of Health Sciences, Beirut Arab University, Beirut, Lebanon. john.haddad@yahoo.co.uk
authors.forename: John J
authors.initials: JJ
authors.lastname: Haddad
mesh_terms: D000111:Acetylcysteine / Q000378:metabolism / Q000494:pharmacology; D056809:Alveolar Epithelial Cells / Q000378:metabolism*; D019328:Buthionine Sulfoximine / Q000378:metabolism / Q000494:pharmacology; D002478:Cells, Cultured; D004789:Enzyme Activation; D005721:Glutamate-Cysteine Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism; D019803:Glutathione Disulfide / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D053583:Interleukin-1beta / Q000096:biosynthesis; D015850:Interleukin-6 / Q000096:biosynthesis; D020935:MAP Kinase Signaling System / Q000187:drug effects; D010084:Oxidation-Reduction; D010766:Phosphorylation; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D007093:Imidazoles; D053583:Interleukin-1beta; D015850:Interleukin-6; D011725:Pyridines; D014409:Tumor Necrosis Factor-alpha; D019328:Buthionine Sulfoximine; D048051:p38 Mitogen-Activated Protein Kinases; D005721:Glutamate-Cysteine Ligase; C093642:SB 203580; D019803:Glutathione Disulfide; D000111:Acetylcysteine