A hallmark of the antiviral response is the induction of interferons. First discovered in 1957 by Issac and Lindeman, interferons are noted for their ability to interfere with viral replication. Interferons act via autocrine and paracrine pathways to induce an antiviral state in infected cells and in neighboring cells containing interferon receptors. Interferons are the frontline defenders against viral infection and their primary function is to locally restrict viral propagation. Viruses have evolved mechanisms to escape the host interferon response, thus gaining a replicative advantage in host cells. This review will discuss recent findings on the mechanisms viruses use to evade the host interferon response. This knowledge is important because the treatment of viral infections is a challenge of global proportions and a better understanding of the mechanisms viruses use to persist in the host may uncover valuable insights applicable to the discovery of novel drug targets.

Purpose To investigate whether mild heat stress at 39.5°C altered Dicer protein and miRNA expression patterns in several cell types. Methods Multiple human and mouse cell types were cultured during the course of 9 h at temperatures from 37°C to 39.5°C. Dicer mRNA levels and microRNAs were quantified by TaqMan RT-qPCR assays and Dicer protein by western blotting. Results Dicer protein was substantially elevated on western analysis in response to heat stress at 39.5°C in the absence of significant changes in Dicer mRNA by RT-qPCR. Conclusions Heat-induced regulation of Dicer expression occurs primarily post-transcriptionally, and the expression levels of Dicer protein are increased and often oscillate in response to fever-range hyperthermia in multiple mouse and human cells. Our studies suggest a potential role for Dicer and microRNAs in the response to mild thermal stress. Additional studies on the mechanisms involved in the stress-induced oscillations of Dicer protein and microRNAs will be of interest.

Dicer is an enzyme of the RNase III endoribonuclease family, which is crucial for RNA interference (RNAi) in eukaryotes. Dicer is a component of the protein machinery (the RNA Induced Silencing Complex [RISC]) which is involved in catalyzing the formation of mature microRNAs from their precursors in the process of microRNA biogenesis. RISC-associated microRNAs bind to specific sequences in the 3’ untranslated region of cognate mRNAs largely through complementary base pairing, resulting in either translational inhibition and/or the degradation of a specific mRNA pool. MicroRNAs epigenetically regulate the cellular levels of receptors, transcription factors and signaling proteins that govern the developmental pathways and functions of multiple cellular processes. The pivotal role played by Dicer in microRNA formation has also piqued the interest of molecular immunologists who have sought to understand the biological relevance of microRNAs in the development and function of the immune system. Here, we review the major findings of these studies and provide an overview of the role of Dicer and microRNAs in immune cell development and function. Additionally, we highlight deficiencies in our knowledge and new research areas that may enhance our understanding of the role of Dicer and microRNAs in immunity.

Cellular exposure to mild stress (39.5°C - 41.5°C) induces thermotolerance, rendering cells resistant to a subsequent heat shock (>42°C) insult. We found that mild hyperthermia at 39.5°C leads to elevations in dicer, a protein well-known for its role in microRNA processing and for its role in cellular stress responses. However, whether elevated dicer protein levels play a role in sustaining a thermotolerant phenotype has, to our knowledge, not been reported. Here we demonstrate that elevated dicer protein is linked to a thermotolerant phenotype in the cervical carcinoma cell line HeLa and in murine embryonic fibroblasts (MEF), and demonstrate that dicer plays a role in mediating PKR and eIF2α phosphorylation. These findings suggest that dicer's role in thermotolerance may be to relay signals to key ER stress pathway components. Moreover, utilizing a MEF cell line defective in microRNA processing, we suggest that dicer's influence on PKR and eIF2α phosphorylation is likely distinct from its microRNA processing role. ATF4 and CHOP are well characterized stress response factors proximal to eIF2α. Evidence is presented that elevated dicer protein in thermotolerant cells differentially modulates ATF4 and CHOP levels to promote a pro-survival phenotype. This work contributes new information on dicer's role in cellular stress responses by defining a pro-survival phenotype in heat stress resistant cells which is sustained, at least in part, by elevated dicer protein levels. Our results suggest an ancillary role for dicer in the cellular stress pathways activated by mild hyperthermia that is likely distinct from its role in microRNA processing.