Abstract
Heme oxygenase (HO)-1 is the inducible isoform of the rate-limiting enzyme of heme degradation and provides cytoprotection against oxidative stress by its products carbon monoxide and biliverdin. More recently, HO-1 has also been shown to exert immunomodulatory functions via cell type-specific anti-inflammatory effects in myeloid/macrophage cells. In the current study, it is demonstrated that Bruton's tyrosine kinase (Btk), the gene of which is mutated in the human immunodeficiency X-linked agammaglobulinemia, is involved in the upregulation of HO-1 gene expression via TLR signaling in macrophages. The specific Btk inhibitor LFM-A13 blocked HO-1 induction by the classical TLR4 ligand LPS in cell cultures of RAW264.7 monocytic cells and primary mouse alveolar macrophages. Moreover, upregulation of HO-1 gene expression was abrogated in LPS-stimulated alveolar macrophages from Btk(-/-) mice. Transfection studies with luciferase reporter gene constructs demonstrated that LPS-dependent induction of HO-1 promoter activity was attenuated by pharmacological Btk inhibition and by an overexpressed dominant-negative mutant of Btk. This induction was mediated by the transcription factor Nrf2, which is a master regulator of the antioxidant cellular defense. Accordingly, nuclear translocation of Nrf2 in LPS-treated macrophages was reduced by Btk inhibition. The generation of reactive oxygen species, but not that of NO, was involved in this regulatory pathway. Btk-dependent induction of HO-1 gene expression was also observed upon macrophage stimulation with ligands of TLR2, TLR6, TLR7, and TLR9, suggesting that Btk is required for HO-1 gene activation by major TLR pathways.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Agammaglobulinaemia Tyrosine Kinase
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Agammaglobulinemia / enzymology
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Agammaglobulinemia / genetics
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Agammaglobulinemia / immunology
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Amides / pharmacology
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Animals
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Cell Line
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Cells, Cultured
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Gene Expression Regulation, Enzymologic / drug effects
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Gene Expression Regulation, Enzymologic / immunology
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Genetic Diseases, X-Linked / enzymology
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Genetic Diseases, X-Linked / genetics
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Genetic Diseases, X-Linked / immunology
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Heme Oxygenase-1 / antagonists & inhibitors
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Heme Oxygenase-1 / biosynthesis
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Heme Oxygenase-1 / genetics*
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Lipopolysaccharides / physiology
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Macrophages, Alveolar / drug effects
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Macrophages, Alveolar / enzymology*
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Macrophages, Alveolar / immunology*
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Membrane Proteins / antagonists & inhibitors
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Membrane Proteins / biosynthesis
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Membrane Proteins / genetics*
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Mice
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Mice, Inbred C57BL
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Mice, Knockout
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Mutation
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NF-E2-Related Factor 2 / physiology*
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Nitriles / pharmacology
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Protein Kinase Inhibitors / pharmacology
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Protein-Tyrosine Kinases / antagonists & inhibitors
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Protein-Tyrosine Kinases / deficiency
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Protein-Tyrosine Kinases / physiology*
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Signal Transduction / drug effects
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Signal Transduction / immunology
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Toll-Like Receptors / physiology*
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Transcriptional Activation / drug effects
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Transcriptional Activation / genetics
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Transcriptional Activation / immunology*
Substances
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Amides
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LFM A13
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Lipopolysaccharides
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Membrane Proteins
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NF-E2-Related Factor 2
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NFE2L2 protein, human
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Nitriles
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Protein Kinase Inhibitors
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Toll-Like Receptors
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Heme Oxygenase-1
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Hmox1 protein, mouse
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Protein-Tyrosine Kinases
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Agammaglobulinaemia Tyrosine Kinase
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BTK protein, human
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Btk protein, mouse
Supplementary concepts
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Bruton type agammaglobulinemia