CRM1 and IFN-α1 mRNA: nuclear export partners

In general, the nuclear import and export of proteins and nucleic acids requires transport receptors known collectively as karyopherins. However, nuclear export of most mRNAs is mediated by the non-karyopherin mRNA receptor TAP. Now, on p. 2259, Jun-Ichi Fujisawa and colleagues report that the nuclear export of interferon-α1 (IFN-α1) mRNA is mediated by CRM1, a karyopherin more often involved in the export of proteins (including the HIV-1 Rev protein), U-rich small nuclear RNAs, and rRNAs. The authors show that the nuclear export of IFN-α1 mRNA is inhibited by overexpression of Rev, provided the protein carries an intact nuclear export signal, and by two inhibitors of CRM1 function. In addition, IFN-α1 mRNA colocalizes with CRM1 but not TAP in the nucleus. Surprisingly, the adenylate/uridylate-rich element (ARE) in the 3′ untranslated region of IFN-α1 mRNA is not required for its nuclear export; in other mRNAs whose export is CRM1 dependent, the RNA adaptor HuR mediates export by binding to the ARE. Thus, a new RNA adaptor may be required for CRM-1-dependent nuclear export of IFN-α1 mRNA.