Novel role for molecular transporter importin 9 in posttranscriptional regulation of IFN-ε expression

J Immunol. 2013 Aug 15;191(4):1907-15. doi: 10.4049/jimmunol.1201925. Epub 2013 Jul 12.

Abstract

IFN-ε is a unique type I IFN whose constitutive expression in lung, brain, small intestine, and reproductive tissues is only partially understood. Our previous observation that posttranscriptional events participate in the regulation of IFN-ε mRNA expression led us to investigate whether the 5' and/or 3' untranslated regions (UTR) have regulatory functions. Surprisingly, we found that full-length IFN-ε 5'UTR markedly suppressed mRNA expression under basal conditions. Analysis of the secondary structure of this region predicted formation of two stable stem-loop structures, loops 1 and 2. Studies using luciferase constructs harboring various stretches of IFN-ε 5'UTR and mutant constructs in which the conformation of loop structures was disrupted showed that loop 1 is essential for regulation of mRNA expression. Incubation of HeLa cell extracts with agarose-bound RNAs harboring IFN-ε loop structures identified importin 9 (IPO9), a molecular transporter and chaperone, as a candidate that associates with these regions of the 5'UTR. IPO9 overexpression decreased, and IPO9 silencing increased basal IFN-ε expression. Our studies uncover a previously undescribed function for IPO9 as a specific, and negative, posttranscriptional regulator of IFN-ε expression, and they identify key roles for IFN-ε stem-loop structure 1 in this process. IPO9-mediated effects on 5'UTRs appear to extend to additional mRNAs, including hypoxia-inducible factor-1α, that can form specific loop structures.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5' Untranslated Regions / genetics*
  • Animals
  • Base Sequence
  • Consensus Sequence
  • Down-Regulation
  • Female
  • Gene Expression Regulation / physiology*
  • Genes, Reporter
  • HeLa Cells
  • Humans
  • Interferons / biosynthesis
  • Interferons / genetics*
  • Inverted Repeat Sequences / genetics*
  • Karyopherins / genetics
  • Karyopherins / physiology*
  • Mammals / genetics
  • Molecular Sequence Data
  • Nucleic Acid Conformation
  • RNA Interference*
  • RNA Stability
  • RNA, Messenger / biosynthesis
  • RNA, Small Interfering / pharmacology
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Sequence Alignment
  • Sequence Homology, Nucleic Acid
  • Uterine Cervical Neoplasms / pathology

Substances

  • 5' Untranslated Regions
  • Karyopherins
  • RNA, Messenger
  • RNA, Small Interfering
  • Recombinant Fusion Proteins
  • importin 9, human
  • interferon-epsilon, human
  • Interferons