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TAK1-mediated induction of nitric oxide synthase gene expression in glial cells
Narayan R Bhat1, Qin Shen, Fan Fan
1Department of Neurology, Medical University of South Carolina, Charleston, South Carolina 29425, USA. bhatnr@musc.edu
Abstract:
Inflammatory cell signaling leading to transcriptional activation is primarily mediated by signal transduction via mitogen-activated protein kinase (MAPK) and NFkappaB pathways. A common upstream kinase that signals the activation of these pathways is TGFbeta-activated kinase 1 (TAK1), which itself becomes activated in response to cytokines and upon engagement of a class of cell surface receptors involved in innate immunity, that is Toll-like receptors (TLRs) by bacterial and viral pathogens. This study directly tests the role of TAK1 in the induction of inducible nitric oxide (NO) synthase (iNOS) in glial cells, which represent immune-regulatory cells of the CNS, by transient transfection assays. Transfection of C-6 glia, primary astrocytes and a rat microglial cell line with TAK1 (but not its inactive form) along with its activator protein, TAK1-binding protein 1 (TAB1) resulted in a marked stimulation of a co-transfected rat iNOS promoter-reporter construct (iNOS-Luc). TAK1-induced iNOS-Luc activity was substantially inhibited by pharmacological inhibitors of the known downstream kinases, p38 MAPK and JNK (SB203580 and SP620125), and was almost completely blocked by co-expression of a phosphorylation mutant of IkappaB. TAK1/TAB1 also induced the production of NO and the expression of iNOS in microglial cells in a p38 MAPK-, JNK- and NFkappaB-dependent manner. The results of these studies provide evidence for an important role for TAK1-mediated intracellular signaling, via p38 MAPK, JNK and NFkappaB, in the transcriptional activation of iNOS in glial cells.
Insights
TGFbeta-activated kinase 1 (TAK1) activates inducible nitric oxide synthase (iNOS) in glial cells. This signaling pathway involves p38 MAPK, JNK, and NFkappaB, crucial for central nervous system immune responses.
Area of Science:
- Neuroimmunology
- Cellular signaling
- Molecular biology
Background:
- Inflammatory responses involve cell signaling pathways like MAPK and NFkappaB.
- TGFbeta-activated kinase 1 (TAK1) is a key upstream kinase in these pathways.
- Glial cells are immune-regulatory cells in the central nervous system (CNS).
Purpose of the Study:
- To investigate the role of TAK1 in inducing inducible nitric oxide synthase (iNOS) in glial cells.
- To elucidate the specific signaling molecules downstream of TAK1 involved in iNOS induction.
Main Methods:
- Transient transfection assays in C-6 glia, primary astrocytes, and a rat microglial cell line.
- Co-transfection with TAK1, TAK1-binding protein 1 (TAB1), and an iNOS promoter-reporter construct (iNOS-Luc).
- Inhibition studies using pharmacological inhibitors of p38 MAPK and JNK, and co-expression of a phosphorylation mutant of IkappaB.
Main Results:
- TAK1 and TAB1 co-expression significantly stimulated iNOS promoter activity.
- TAK1-induced iNOS activity was inhibited by p38 MAPK and JNK inhibitors.
- iNOS induction by TAK1/TAB1 was blocked by inhibiting NFkappaB signaling.
- TAK1/TAB1 induced nitric oxide (NO) production and iNOS expression in microglial cells.
Conclusions:
- TAK1 plays a critical role in the transcriptional activation of iNOS in glial cells.
- The signaling pathway involves TAK1 activating p38 MAPK, JNK, and NFkappaB.
- This pathway is important for immune regulation within the CNS.