Interleukin-1 homologues IL-1F7b and IL-18 contain functional mRNA instability elements within the coding region responsive to lipopolysaccharide.
IL-1F7b, a novel homologue of the IL-1 (interleukin 1) family, was discovered by computational cloning. We demonstrated that IL-1F7b shares critical amino acid residues with IL-18 and binds to the IL-18-binding protein enhancing its ability to inhibit IL-18-induced interferon-gamma. We also showed that low levels of IL-1F7b are constitutively present intracellularly in human blood monocytes. In this study, we demonstrate that similar to IL-18, both mRNA and intracellular protein expression of IL-1F7b are up-regulated by LPS (lipopolysaccharide) in human monocytes. In stable transfectants of murine RAW264.7 macrophage cells, there was no IL-1F7b protein expression despite a highly active CMV promoter. We found that IL-1F7b-specific mRNA was rapidly degraded in transfected cells, via a 3'-UTR (untranslated region)-independent control of IL-1F7b transcript stability. After LPS stimulation, there was a rapid transient increase in IL-1F7b-specific mRNA and concomitant protein levels. Using sequence alignment, we found a conserved ten-nucleotide homology box within the open reading frame of IL-F7b, which is flanking the coding region instability elements of some selective genes. In-frame deletion of downstream exon 5 from the full-length IL-1F7b cDNA markedly increased the levels of IL-1F7b mRNA. A similar coding region element is located in IL-18. When transfected into RAW264.7 macrophages, IL-18 mRNA was also unstable unless treated with LPS. These results indicate that both IL-1F7b and IL-18 mRNA contain functional instability determinants within their coding region, which influence mRNA decay as a novel mechanism to regulate the expression of IL-1 family members.
Bufler
Philip
P
Division of Infectious Diseases, University of Colorado Health Sciences Center, 4200 East Ninth Ave., Denver, CO 80262, USA. Philip.Bufler@med.uni-muenchen.de
Gamboni-Robertson
Fabia
F
Azam
Tania
T
Kim
Soo-Hyun
SH
Dinarello
Charles A
CA
D000818:Animals; D001483:Base Sequence / Q000235:genetics; D016466:CHO Cells / Q000737:chemistry / Q000378:metabolism; D019556:COS Cells / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D002522:Chlorocebus aethiops; D017124:Conserved Sequence / Q000235:genetics; D006224:Cricetinae; D005091:Exons / Q000235:genetics / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D007375:Interleukin-1 / Q000235:genetics* / Q000276:immunology / Q000378:metabolism / Q000502:physiology; D020382:Interleukin-18 / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology*; D008264:Macrophages / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009000:Monocytes / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D020871:RNA Stability / Q000502:physiology*; D012333:RNA, Messenger / Q000502:physiology*; D017384:Sequence Deletion / Q000235:genetics / Q000502:physiology; D012689:Sequence Homology, Nucleic Acid; D014162:Transfection / Q000379:methods; D015854:Up-Regulation / Q000502:physiology
D007375:Interleukin-1; D020382:Interleukin-18; D008070:Lipopolysaccharides; D012333:RNA, Messenger; C471352:interleukin-1 homolog 4, human