DNA-Demethylating Agents Target Colorectal Cancer Cells by Inducing Viral Mimicry by Endogenous Transcripts

Abstract

Summary DNA demethylating agents have shown clinical anti-tumor efficacy via an unknown mechanism of action. Using a combination of experimental and bioinformatics analysis in colorectal cancer cells, we demonstrate that low-dose 5-AZA-CdR targets colorectal cancer initiating cells (CICs) by inducing viral mimicry. This is associated with induction of dsRNAs derived at least in part from endogenous retroviral elements, activation of the MDA5/MAVS RNA recognition pathway and downstream activation of IRF7. Indeed, disruption of virus recognition pathways, by individually knocking down MDA5, MAVS or IRF7, inhibits the ability of 5-AZA-CdR to target colorectal CICs and significantly decreases 5-AZA-CdR long-term growth effects. Moreover, transfection of dsRNA into CICs can mimic the effects of 5-AZA-CdR. Together; our results represent a major shift in understanding the antitumor mechanisms of DNA-demethylating agents and highlight the MDA5/MAVS/IRF7 pathway as a potentially druggable target against CICs.

Function of HNRNPC in breast cancer cells by controlling the dsRNA‐induced interferon response

“…These elevated dsRNA species were mostly found in introns, corroborating known transcriptome‐wide HNRNPC binding regions (Konig et al , 2010; Zarnack et al , 2013). This differs from previous observation of elevated dsRNA derived from normally hypermethylated endogenous retroviruses (ERVs) that are activated by anti‐tumor inhibitors to trigger the IFN response as a therapeutic approach (Chiappinelli et al , 2015; Roulois et al , 2015; Goel et al , 2017). Heterogeneous nuclear ribonucleoprotein C is well known for its function in regulating RNA splicing by binding with introns, especially the introns containing Alu (Konig et al , 2010; Zarnack et al , 2013).…”

“…However, in our work done in different types of breast cancer cells, expression profiles of the down‐stream genes indicated that NOTCH3 signaling was not amplified when interferon signaling was activated. On the other hand, several other studies have reported that up‐regulated dsRNA from endogenous retrovirus (ERV) in tumor cells, triggered by DNA methyltransferase inhibitors or CDK4/6 inhibitors, induced IFN responses and thus inhibited tumor development (Chiappinelli et al , 2015; Roulois et al , 2015; Goel et al , 2017). Our proposed model is similar to these studies, even though the dsRNA species in our study were originated from a different resource than ERV.…”

“…Recent studies showed transcriptional activations of the ERVs triggered by several anti‐tumor drugs, which in turn resulted in ERV‐originated dsRNA accumulation, potent interferon responses, and significant tumor inhibition (Chiappinelli et al , 2015; Roulois et al , 2015; Goel et al , 2017). In contrast, our study showed that upon perturbation of the RBP HNRNPC, the non‐ERV pre‐mRNA introns gave rise to dsRNA, which triggered the interferon response and tumor growth arrestment as well.…”

“…These interferon responses have been shown to be involved in regulating tumor development due to its well‐characterized pro‐apoptotic and anti‐proliferative effects in various types of cancer cells, including myeloma cell lines (Chen et al , 2001), lymphoma (Yang et al , 2013), liver cancer cells (Maeda et al , 2014; Murata et al , 2006; Sangfelt et al , 1997), and sarcoma cell lines (Sanceau et al , 2000). In fact, recent studies have shown that the IFN response triggered by endogenous dsRNA plays a central role in executing the therapeutic effects of anti‐tumor drugs such as DNA methyltransferase inhibitors and CDK4/6 inhibitors in multiple types of cancer (Chiappinelli et al , 2015; Roulois et al , 2015; Goel et al , 2017). …”

Targeting the epigenome in malignant pleural mesothelioma

“…This "DNA methylation paradox", recapitulates epigenomic states in normal germ cells, and provides the rationale for the development of epigenetic regimens that induce growth arrest/apoptosis via restoration of tumor suppressor gene expression (106)(107)(108), while simultaneously augmenting antitumor immunity by up-regulation of CTAs (79), induction of viral mimicry by de-repression of endogenous retroviruses (109,110), and modulation of the tumor microenvironment (111)(112)(113).…”