The 2-5A/RNase L/RNase L inhibitor (RNI) pathway regulates mitochondrial mRNAs stability in interferon α-treated H9 cells

Interferon alpha (IFN alpha) belongs to a cytokine family that exhibits antiviral properties, immuno-modulating effects, and antiproliferative activity on normal and neoplasic cells in vitro and in vivo. IFN alpha exerts antitumor action by inducing direct cytotoxicity against tumor cells. This toxicity is at least partly due to induction of apoptosis. Although the molecular basis of the inhibition of cell growth by IFN alpha is only partially understood, there is a direct correlation between the sensitivity of cells to the antiproliferative action of IFN alpha and the down-regulation of their mitochondrial mRNAs. Here, we studied the role of the 2-5A/RNase L system and its inhibitor RLI in this regulation of the mitochondrial mRNAs by IFNa. We found that a fraction of cellular RNase L and RLI is localized in the mitochondria. Thus, we down-regulated RNase L activity in human H9 cells by stably transfecting (i) RNase L antisense cDNA or (ii) RLI sense cDNA constructions. In contrast to control cells, no post-transcriptional down-regulation of mitochondrial mRNAs and no cell growth inhibition were observed after IFN alpha treatment in these transfectants. These results demonstrate that IFNa exerts its antiproliferative effect on H9 cells at least in part via the degradation of mitochondrial mRNAs by RNase L.