Our long range goal is to understand how to regulate glutathione (GSH) biosynthesis and thereby protect lungs from oxidative damage. Adaptation to oxidative stress in the lung involves an increase in the ability of cells to remove reactive and toxic molecules. Perhaps the most common mechanism for this is an increase in the ability to synthesize the endogenous antioxidant, GSH, which is essential for adaptation as it is critical in removal of hydroperoxides and toxic lipid peroxidation products, such as 4-hydroxynonenal (HNE). HNE is produced during exposure to any kind of oxidative stress but, interestingly, is one of the strongest inducers of GSH synthesis through increased transcription of both the regulatory and catalytic subunits of glutamate cysteine ligase (GCL). GCL catalyzes the rate limiting and first step in GSH synthesis. There is much evidence supporting roles for TRE and EpRE cis elements in regulation of the two GCL genes. We found that a little explored mode of activation of the EpRE and TRE elements is transcription factor (TF) switching. Our results also indicated that inhibition of the stress activated protein kinase, JNK, results in complete suppression of GCL induction by HNE. Thus, we hypothesize that HNE induced transcription of the two GCL genes involves switching from inactive or suppressing EpRE and TRE TF complexes to transcriptionally active complexes. We also hypothesize that HNE activation of the JNK signaling pathway is critical to both EpRE and AP-1 activation in GCL gene expression.
The aims are: 1) to determine how the changes in the transcription factor binding complexes that bind to EpRE and TRE binding complexes in response to HNE cause increased transcription of both GCL genes and 2) to determine the mechanism of JNK activation by HNE. Both normal human bronchial epithelial cells (NHBE) and HBE1 cells will be used in exposures to subtoxic concentrations of HNE.
In Aim 1, we will identify potential TFs by DNA affinity chromatography and LC-MS/MS analysis and then use chromatin immunoprecipitation (ChiP) assays to identify the EpRE and TRE TF complexes in the context of the whole GCL genes in situ. """"""""NoShift"""""""" and Shift-Western assays will be used to quantify changes in TF binding and TF functionality will be determined by silencing TF genes and measuring EpRE and TRE driven luciferase reporters.
In Aim 2, the effect of JNK inhibition on binding and function of TFs bound to EpRE will be examined along with a determination of which protein in the JNK pathway binds HNE. Relevance: Oxidative damage is a major component of lung injury during inflammation, other respiratory diseases and in exposure to air pollutants. The endogenous antioxidant glutathione increases during adaptation to sublethal oxidative stress through induction of the enzyme, GCL. In this investigation, the mechanism through which GCL increases in response to a toxic product of membrane oxidation will be investigated, hopefully leading to understanding of how to increase GSH without the use of toxic agents. ? ? ?
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