Compound signaling activates endogenous retroviruses by inducing enhancer and gene-neighborhood transcription

Abstract

SummaryMultiple sclerosis (MS) is a neuroinflammatory and autoimmune disease, in which various immune cell types and autoreactive T cells exert a pathogenic activity. This disease is also associated with increased transcription of several endogenous retroviruses (HERVs) normally kept in check by heterochromatin. Here, we have uncovered an organic pollutant dieldrin that activates several HERVs associated with MS and allowing us to examine the mechanism of their activation. Dieldrin singles out by its ability to simultaneously activate the MAP kinase and the PI3K pathways, while also triggering calcium dependent peptidylarginine deiminase activity. It was this association of pathways that caused HERV activation, a phenomenon that was only part of more generally increased transcription of heterochromatic regions. The HERV transcripts were generally not polyadenylated. Some arose as a consequence of activation of HERV-based enhancers, while others were the result of unusually strong activation at some mostly transcription factor genes causing transcription to leak out of the HERV-free region that surrounds them. Altogether, our data emphasized the hazard associated with simultaneous activation of multiples signaling pathways by xenobiotics, while also providing a very general toolbox for the interpretation of HERV transcription.