Stabilization of human interferon-α1 mRNA by its antisense RNA

Antisense transcription is a widespread phenomenon in the mammalian genome and is believed to play a role in regulating gene expression. However, the exact functional significance of antisense transcription is largely unknown. Here, we show that natural antisense (AS) RNA is an important modulator of interferon-α1 (IFN-α1) mRNA levels. A ~4-kb, spliced IFN-α1 AS RNA targets a single-stranded region within a conserved secondary structure element of the IFN-α1 mRNA, an element which was previously reported to function as the nuclear export element. Following infection of human Namalwa lymphocytes with Sendai virus or infection of guinea pig 104C1 fetal fibroblasts with influenza virus A/PR/8/34, expression of IFN-α1 AS RNA becomes elevated. This elevated expression results in increased IFN-α1 mRNA stability because of the cytoplasmic (but not nuclear) interaction of the AS RNA with the mRNA at the single-stranded region. This results in increased IFN-α protein production. The silencing of IFN-α1 AS RNA by sense oligonucleotides or over-expression of antisense oligoribonucleotides, which were both designed from the target region, confirmed the critical role of the AS RNA in the post-transcriptional regulation of IFN-α1 mRNA levels. This AS RNA stabilization effect is caused by the prevention of the microRNA (miRNA)-induced destabilization of IFN-α1 mRNA due to masking of the miR-1270 binding site. This discovery not only reveals a regulatory pathway for controlling IFN-α1 gene expression during the host innate immune response against virus infection but also suggests a reason for the large number of overlapping complementary transcripts with previously unknown function.