? Redox dependent upregulation of hepatocyte inducible nitric oxide synthase (iNOS) expression serves anti-oxidant and anti-apoptotic functions in sepsis and shock. However, in the setting of oxidative stress and pro-inflammatory cytokines which characterize sepsis and shock, the redox-sensitive mechanisms which enhance hepatocyte iNOS expression are unknown. In interleukin-1 beta (IL-1) stimulated rat hepatocytes exposed to superoxide, we demonstrated that iNOS protein expression and gene transcription is increased by oxidative stress. Subsequently, we characterized a redox-sensitive DR1 cis-acting enhancer element in the iNOS promoter. We then identified hepatocyte nuclear factor-4 alpha (HNF-4) as the corresponding transcription factor, confirmed its redox-sensitive enhancement of IL-1 induced iNOS gene transcription, and demonstrated that redox-sensitive HNF-4 DNA binding and transactivation are dependent upon its phosphorylation state. We hypothesize that a redox-dependent kinase pathway phosphorylates HNF-4 to enhance its DNA binding/ transactivation potential and increase hepatocyte iNOS gene transcription. Previous studies have not addressed a redox dependent signaling pathway which targets HNF-4 to enhance iNOS expression. We will focus on the following specific aims which are critical to defining the mechanisms underlying redox-induced phosphorylation of HNF-4 and its role as a redox-dependent enhancer of iNOS promoter activity in IL-1 stimulated rat hepatocytes. We will: 1) identify the amino acid residues of HNF-4 specifically phosphorylated in the presence of IL-1 and superoxide, 2) mutate the candidate amino acid residues to ablate phosphorylation and characterize mutations which inhibit HNF-4 DNA binding and/or transactivation in the presence of IL-1 and superoxide, 3) identify the kinase(s) which phosphorylate the amino acid residues that mediate redox-dependent HNF-4 DNA binding/ transactivation and confirm in vitro hepatocellular kinase functionality, and 4) confirm in vivo function of HNF-4 and its corresponding kinase in a murine model of endotoxemia. Our studies will define a novel and, as yet, poorly described redox-dependent signal transduction pathway which regulates iNOS as an antioxidant mechanism in hepatocytes. ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI044629-09
Application #
6895601
Study Section
Surgery, Anesthesiology and Trauma Study Section (SAT)
Program Officer
Rathbun, Gary
Project Start
1998-06-01
Project End
2008-05-30
Budget Start
2005-06-01
Budget End
2006-05-31
Support Year
9
Fiscal Year
2005
Total Cost
$346,500
Indirect Cost
Name
Duke University
Department
Surgery
Type
Schools of Medicine
DUNS #
044387793
City
Durham
State
NC
Country
United States
Zip Code
27705
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