Translational Reprogramming by Self-RNA Decay in the Interferon Response

Abstract

The innate immune response is the body’s first line of defense against invasion or damage. One of its main actors is RNase L, which cleaves various RNAs and inhibits translation in response to double-stranded RNA (dsRNA) detection. Its mechanism of inhibition remains unclear. To further characterize RNase L function in the innate immune response, we investigated the following: RNase L influence in comparison to another downstream effector of dsRNA, protein kinase RNA-activated (PKR); the apparent conflict between global translation block by RNase L and expression of in- terferon response genes; and the influence of mRNA cleavage on translation block. We found that RNase L acts rapidly and robustly to arrest translation before PKR action and before interferon induction of interferon-stimulated genes (ISGs). Despite this fact, our results show that the interferon response is dependent on translation activity in order to be successful. We do not have a clear mechanism for interferon and ISG evasion of translation block, but we do show that the 5’ untranslated region (5’ UTR) of their mRNA transcripts is not required. We also provide evidence that there are two pools of mRNA in the cell: one that can be cleaved by RNase L, and one that cannot. Our data suggest that the latter pool is comprised of mRNA that is sequestered in cytosolic foci, rendering it inaccessible to both RNase L and the trans- lation machinery. These results indicate that RNase L achieves translation inhibition through the cleavage and depletion of free, intact mRNAs that are not sequestered in cytosolic foci. Our findings provide vital information for further investigation of innate immune gene expression during RNase L-induced translational arrest.