CRNKL1 is a highly selective regulator of intron-retaining HIV-1 and cellular mRNAs

The HIV-1 Rev protein is a nuclear export factor for unspliced and incompletely-spliced HIV-1 RNAs. Without Rev, these intron-retaining RNAs are trapped in the nucleus. A genome-wide screen identified nine proteins of the spliceosome which all enhanced expression from the HIV-1 unspliced RNA after CRISPR/Cas knock-down. Depletion of DHX38, WDR70 and four proteins of the Prp19-associated complex (ISY1, BUD31, XAB2, CRNKL1) resulted in a more than 20-fold enhancement of unspliced HIV-1 RNA levels in the cytoplasm. Targeting of CRNKL1, DHX38, and BUD31 affected nuclear export efficiencies of the HIV-1 unspliced RNA to a much larger extent than splicing. Transcriptomic analyses further revealed that CRNKL1 also suppresses cytoplasmic levels of cellular mRNAs with selectively retained introns. Thus, CRNKL1 dependent nuclear retention seems to be a novel mechanism for the regulation of cytoplasmic levels of intron-retaining cellular mRNAs that is harnessed by HIV-1 to direct its complex splicing pattern.