ABSTRACT
IRAK-M is a negative regulator of innate immunity signaling processes. Although attenuation of innate immunity may help to prevent excessive inflammation, it may also lead to compromised immune surveillance of tumor cells and contribute to tumor formation and growth. Here, we demonstrate that IRAK-M(-/-) mice are resistant to tumor growth upon inoculation with transplantable tumor cells. Immune cells from IRAK-M(-/-) mice are responsible for the anti-tumor effect, since adoptive transfer of splenocytes from IRAK-M(-/-) mice to wild type mice can transfer the tumor-resistant phenotype. Upon tumor cell challenge, there are elevated populations of CD4(+) and CD8(+) T cells and a decreased population of CD4(+) CD25(+)Foxp3(+) regulatory T cells in IRAK-M(-/-) splenocytes. Furthermore, we observe that IRAK-M deficiency leads to elevated proliferation and activation of T cells and B cells. Enhanced NFkappaB activation directly caused by IRAK-M deficiency may explain elevated activation of T and B cells. In addition, macrophages from IRAK-M(-/-) mice exhibit enhanced phagocytic function toward acetylated LDL and apoptotic thymocytes. Collectively, we demonstrate that IRAK-M is directly involved in the regulation of both innate and adaptive immune signaling processes, and deletion of IRAK-M enhances host anti-tumor immune response.
Subject(s)
Immunity, Innate/immunology , Interleukin-1 Receptor-Associated Kinases/deficiency , Neoplasms/immunology , Animals , Apoptosis , B-Lymphocytes/cytology , B-Lymphocytes/immunology , CD4-Positive T-Lymphocytes/cytology , CD4-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/cytology , CD8-Positive T-Lymphocytes/immunology , Cell Proliferation , Cytotoxicity, Immunologic , I-kappa B Proteins/metabolism , Lymphocyte Activation , Macrophages/immunology , Male , Mice , Mice, Inbred C57BL , NF-KappaB Inhibitor alpha , NF-kappa B/metabolism , Neoplasm Transplantation , Phagocytosis , Protein Processing, Post-Translational , Spleen/cytology , Spleen/immunologyABSTRACT
Toll-like-receptor mediated signaling is finely regulated by a complex intracellular protein network including the interleukin-1 receptor associate kinases (IRAKs). IRAK-4, 1, and 2 may positively regulate innate immunity signaling through the activation of various downstream kinases such as MAPKs. In contrast, IRAK-M plays an inhibitory role through unknown mechanism. In this report, we show that IRAK-M is ubiquitously present in the cell, and becomes exclusively cytoplasmic upon bacterial lipoprotein Pam(3)CSK(4) challenge. Furthermore, using bone marrow derived macrophages (BMDM) from wild type, IRAK1(-/-), and IRAK-M(-/-) mice, we have herein demonstrated that IRAK-M selectively attenuates bacterial lipopeptide Pam(3)CSK(4)-induced p38 activation, but not ERK or JNK. IRAK1(-/-) and IRAK-M(-/-)BMDM display distinct activation profile of various MAP kinases upon Pam(3)CSK(4) challenge, indicating that IRAK-M exerts its inhibitory effect through an IRAK1 independent pathway. Pam(3)CSK(4) challenge leads to rapid decrease of MKP-1 protein level in IRAK-M(-/-)BMDM as well as THP-1 cells with decreased IRAK-M expression through siRNA interference. Our findings indicate that IRAK-M selectively attenuates p38 activation and inhibits innate immunity through stabilizing MKP-1.
Subject(s)
Immunity, Innate/immunology , Interleukin-1 Receptor-Associated Kinases/metabolism , Signal Transduction , Active Transport, Cell Nucleus/drug effects , Animals , Cell Cycle Proteins/metabolism , Cell Nucleus/drug effects , Cell Nucleus/enzymology , Cells, Cultured , Dual Specificity Phosphatase 1 , Enzyme Activation/drug effects , Extracellular Signal-Regulated MAP Kinases/metabolism , Humans , Immediate-Early Proteins/metabolism , JNK Mitogen-Activated Protein Kinases/metabolism , Leukocytes, Mononuclear/drug effects , Leukocytes, Mononuclear/enzymology , Lipopeptides , Macrophages/drug effects , Macrophages/enzymology , Mice , Models, Immunological , Peptides/pharmacology , Phosphoprotein Phosphatases/metabolism , Protein Phosphatase 1 , Protein Tyrosine Phosphatases/metabolism , Signal Transduction/drug effects , p38 Mitogen-Activated Protein Kinases/metabolismABSTRACT
The activation of ATP-sensitive potassium (K ATP) ion channels in the heart is thought to exert a cardioprotective effect under low oxygen conditions, possibly enhancing tolerance of environmental hypoxia in aquatic vertebrates. The purpose of this study was to examine the possibility that hypoxia-induced activation of cardiac K ATP channels, whether in the sarcolemma (sarcK ATP) or mitochondria (mitoK ATP), enhances viability in cardiac muscle cells from a species highly tolerant of low oxygen environments, the goldfish Carassius auratus. During moderate hypoxia (6-7 kPa), the activation of sarcK ATP channels was indicated by a reduction in transmembrane action potential duration (APD). This response to hypoxia was mimicked by the NO-donor SNAP (100 micromol l(-1)) and the stable cGMP analog 8-Br-cGMP, but abolished by glibenclamide or l-NAME, an inhibitor of NO synthesis. The mitoK ATP channel opener diazoxide did not affect APD. Isolated ventricular muscle cells were then incubated under normoxic and hypoxic conditions. Cell viability was decreased in hypoxia; however, the negative effects of low oxygen were reduced during simultaneous exposure to SNAP, 8-Br-cGMP, and diazoxide. The cardioprotective effect of diazoxide, but not 8-Br-cGMP, was reduced by the mitoK ATP channel blocker 5-HD. These data suggest that hypoxia-induced activation of sarcK ATP or mitoK ATP channels could enhance tolerance of low-oxygen environments in this species, and that sarcK ATP activity is increased through a NO and cGMP-dependent pathway.
