title: Infection with influenza A viruses causes changes in promoter DNA methylation of inflammatory genes.
abstract: BACKGROUND
  Replication of influenza virus in the host cells results in production of immune mediators like cytokines. Excessive secretion of cytokines (hypercytokinemia) has been observed during highly pathogenic avian influenza virus (HPAI-H5N1) infections resulting in high fatality rates.
  
  
  OBJECTIVE
  The exact mechanism of hypercytokinemia during influenza virus infection is still not known completely. As promoter DNA methylation changes are linked with expression changes in genes, we intend to identify whether changes in promoter DNA methylation have any role in expression of cytokines during influenza A virus infection.
  
  
  METHODS
  A panel of 24 cytokine genes and genes known to be involved in inflammatory response were analyzed for their promoter DNA methylation changes during influenza A virus infections. Four different strains of influenza A viruses, viz. H5N1, H1N1, pandemic (2009) H1N1, and a vaccine strain of H5N1, were used for the study.
  
  
  RESULTS
  We found seven of the total 24 inflammatory genes studied, showing significant changes in their promoter methylation levels in response to virus infection. These genes included proinflammatory cytokines CXCL14, CCL25, CXCL6, and interleukines IL13, IL17C, IL4R. The changes in DNA methylation levels varied across different strains of influenza viruses depending upon their virulence. Significant promoter hypomethylation in IL17C and IL13 genes was observed in cells infected with HPAI-H5N1 virus compared with other influenza viruses. This decrease in methylation was found to be positively correlating with the increased expression of these genes. Analysis of IL17C promoter region using bisulfite sequencing resulted in identification of a CpG site within Retinoid X receptor-alpha (RXR-α) transcription factor binding site undergoing demethylation specifically in H5N1-infected cells but not in other influenza-infected cells.
  
  
  CONCLUSIONS
  Thus, the study could demonstrate that changes in promoter methylation in certain specific cytokine genes actually have a possible role in their expression changes during influenza A virus infection.
authors.affiliation: National Institute of Virology, Pune, India.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Mukherjee
authors.forename: Veena C
authors.initials: VC
authors.lastname: Vipat
authors.forename: Alok K
authors.initials: AK
authors.lastname: Chakrabarti
mesh_terms: D002460:Cell Line; D016207:Cytokines / Q000096:biosynthesis*; D019175:DNA Methylation; D004847:Epithelial Cells / Q000276:immunology / Q000821:virology; D005786:Gene Expression Regulation; D054884:Host-Pathogen Interactions; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000254:growth & development* / Q000276:immunology; D053124:Influenza A Virus, H5N1 Subtype / Q000254:growth & development* / Q000276:immunology; D011401:Promoter Regions, Genetic
chemical_list: D016207:Cytokines
keywords: Cytokines; DNA methylation; host gene; influenza A viruses; pathogenicity; subtypes