Bruton’s Tyrosine Kinase Is Required for TLR-Dependent Heme Oxygenase-1 Gene Activation via Nrf2 in Macrophages

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.

The Renal Mononuclear Phagocytic System

“…30,93 More recent studies show that bone marrow-derived Mø or rMoPh display biphasic expression of proinflammatory factors followed by anti-inflammatory and reparative factors in response to challenge with lipopolysaccharide or ischemic injury, respectively. 62,92,94,95 Within the kidney, specific paracrine factors released from renal parenchymal cells, such as IL-10, DAMPs, or apoptotic bodies, initiate or augment this phenotypic reprogramming of rMoPh. 90,96,97 Figure 2.…”

PRIMA1 ile lösemi hücrelerinde Bruton tirozin kinaz inhibisyonu aracılığı apoptoz uyarımı

“…Indeed, Btk has been shown to be an important regulator for the activity of several transcription factors including NF-кB, STAT5, FOXO1, Nrf2 and BRIGHT 42,[60][61][62][63] . Notably, Btk contains an NLS-like sequence in the PH domain, but it has been shown to be functionally inactive 43 .…”

“…Previously, it has been shown that Btk regulates the expression level of Nrf2 gene 42 . To examine the effect of Btk on Nrf2/HO-1 expression in response to PRIMA-1 exposure, we probed the membranes with both Nrf2 and HO-1 antibodies.…”

Bruton's Tyrosine Kinase Is Required for Apoptotic Cell Uptake via Regulating the Phosphorylation and Localization of Calreticulin

“…In the context of phagocytosis, TLR stimulation has been shown to differentially affect the uptake and cross-presentation of cellular Ags by monocyte-derived dendritic cells (20). Although Btk has been shown to be involved in TLR7 mediated responses in myeloid cells (11), the effect of loss of Btk on TLR7-induced changes to myeloid cells has not yet been fully explored.…”

“…Recent studies, however, have focused on its role in regulating innate immune responses in myeloid cells, acting downstream of TLR4 and the antiviral TLRs, TLR3, -7, and -9, to regulate proinflammatory cytokine and type I IFN production (6)(7)(8)(9)(10)(11). Btk has also been shown to interact with and become activated following ligation of TLR8 and -9 in the monocytic cell line THP-1 (8).…”