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E1A repression of IL-6-induced gene activation by blocking the assembly of IL-6 response element binding complexes
T Takeda1, K Nakajima, H Kojima
1Division of Molecular Oncology, Osaka University Medical School, Japan.
Abstract:
Some viral products interfere with host antiviral defense mechanisms. Adenovirus E1A represses IFN signal transduction pathways which induces gene activation and an antiviral state. Both IFN and IL-6 activate Jak/Tyk protein tyrosine kinases and the STAT (signal transducer and activator of transcription) family proteins. We showed that 12S E1A repressed IL-6 signals activating the junB promoter and the two IL-6 response elements (REs), JRE-IL6 and type II IL-6 RE (also called acute phase response element), required for IL-6-induced activation of the junB promoter and the type II acute phase reactant genes, respectively, in hepatocytes. Conserved region 1 of the 12S E1A was responsible for the repression. Target molecules of the repression by E1A appeared to be IL-6-inducible DNA-binding proteins acting on the IL-6 REs. In a rat 3Y1 cell line stably expressing E1A, the levels of IL-6-induced IL-6 RE binding proteins were severely reduced compared with those in a parental 3Y1 cell line. Moreover, we found that the levels of the STAT family proteins including Stat1-alpha (p91), Stat1-beta (p84), Stat2 (p113), and Stat3 were decreased by the stable expression of adenovirus E1A. The E1A-induced reduction in the amount of DNA-binding proteins seemed to be partly responsible for the decreased transcriptional activity of the IL-6 RE-driven gene expression in response to IL-6. This repression mechanism may be applicable to the E1A repression of IFN-gamma-induced gene activation.
Insights
Adenovirus E1A protein inhibits host antiviral responses by repressing interleukin-6 (IL-6) signaling pathways. This repression involves reducing STAT protein levels and IL-6-inducible DNA-binding proteins, impacting gene activation.
Area of Science:
- Molecular Virology
- Immunology
- Cellular Biology
Background:
- Viral proteins can disrupt host antiviral defenses.
- Adenovirus E1A is known to interfere with interferon (IFN) signal transduction.
- Interleukin-6 (IL-6) and IFN pathways activate Janus kinases (Jak/Tyk) and Signal Transducer and Activator of Transcription (STAT) proteins.
Purpose of the Study:
- To investigate how adenovirus 12S E1A represses IL-6 signaling in hepatocytes.
- To identify the specific regions of E1A involved in this repression.
- To determine the molecular targets of E1A-mediated repression.
Main Methods:
- Reporter gene assays using junB promoter and IL-6 response elements (REs).
- Analysis of E1A conserved region 1 function.
- Western blot analysis to assess STAT protein levels in E1A-expressing cells.
- Electrophoretic mobility shift assays to detect IL-6-inducible DNA-binding proteins.
Main Results:
- 12S E1A repressed IL-6-induced activation of the junB promoter and IL-6 REs in hepatocytes.
- Conserved region 1 of 12S E1A was responsible for the observed repression.
- Stable expression of E1A reduced IL-6-induced DNA-binding proteins and STAT family proteins (Stat1-alpha, Stat1-beta, Stat2, Stat3).
Conclusions:
- Adenovirus E1A represses IL-6 signaling by decreasing STAT protein levels and IL-6-inducible DNA-binding proteins.
- This mechanism contributes to the reduced transcriptional activity of IL-6-responsive genes.
- The repression mechanism may also apply to E1A's inhibition of IFN-gamma-induced gene activation.