Analysis of interferon-λ1 gene activation and function

Abstract

The class II cytokine family consists of structurally homologous receptors and their ligands, including type I and type II interferons (IFNs), interleukin-10 (IL-10) and IL-10 related factors, such as IL-24, IL-26 and IL-22. They exert a broad range of functions on the immune system, such as anti-viral, anti-inflammatory and immuno-regulatory effects. The recent sequencing and annotation of the human genome led to identification of several additional members of this cytokine family, including interferon-λ1 (or IL-29), λ2 (IL-28A) and λ3 (IL-28B). An understanding of the function and biological relevance of these novel class II cytokines is important to expand our knowledge of the immune system and to potentially open the door for new therapeutic possibilities. This thesis aimed to analyse how the expression of the human IFN-λ1 gene is regulated and what role this cytokine plays during acute and chronic inflammation. It revealed that the gene is rapidly and strongly induced in human monocyte-derived dendritic cells in response to LPS. Using a combination of RNA-interference and over-expression studies, it was found that this induction was strongly dependent on specific transcription factors of the NF-[kappa]B and Interferon Regulatory Factor (IRF) families, such as RelA and IRF3/7. Furthermore, gene reporter and bio-informatic analyses suggested that IRF3/7 activity is mediated via interactions with the proximal part of the IFN-λ1 promoter, whereas the majority of RelA activity is mediated via a distal cluster of putative NF-[kappa]B binding sites located between -1106 and -1901 nucleotides upstream of the gene. A combination of electrophoretic mobility shift assay and chromatin immunoprecipitation confirmed that RelA could efficiently bind to binding sites within this cluster. Interestingly, these distal NF-[kappa]B binding sites in the IFN-λ1 promoter are contained within transposable elements of Alu and LTR families, and the evolutionary significance of this is discussed. This thesis also shows that a specific chain of the IFN-λ1 receptor complex (IFN-λR1) is expressed in a cell-type specific manner, with primary human myeloid cells and synoviocytes derived from rheumatoid arthritis patients expressing only a modest level of the receptor. Consequently IFN-λ1 had limited effect on inflammatory cytokine production by these cells. The role of this restricted IFN system and its potential therapeutic benefits in inflammatory diseases will be discussed.