Abstract
DNA Damage Response (DDR) and DNA repair pathways are emerging as potent, ubiquitous suppressors of innate immune signaling in human cells. Here, we show that human cells surviving depletion of the Single Strand Break (SSB) repair protein PARP1 undergo p21-dependent senescence or cell cycle checkpoint activation in the context of activation of innate immune signaling, or viral mimicry. Specifically, we observe induction of a large number of interferon-stimulated genes (ISGs) and multiple pattern recognition receptors (PRRs; including RIG-I, MDA-5, MAVS, TLR3 and STING) and increased nuclear IRF3 staining. Mechanistically, depletion of the double-stranded RNA (dsRNA) helicase RIG-I or its downstream effector MAVS specifically rescues ISG induction in PARP1-depleted cells, suggesting that the RIG-I/MAVS pathway is required for sustained ISG expression in this context. Experiments with conditioned media or a neutralizing antibody to the α/β-IFN receptor revealed that persistent ISG expression additionally requires an autocrine/paracrine loop. Finally, loss of PARP1 and radiation-induced DNA damage strongly synergize in the induction of p21 and ISGs. Overall, these findings increase our understanding of how PARP1 may suppress deleterious phenotypes associated to aging, inflammation and cancer in humans.
Highlights
In response to viral infection, human cells activate an interferon (IFN)-dependent antiviral program [1]
For experiments aimed at generating Knock out (KO) lines, cells were subjected to sequential rounds of transfection/selection, cells were kept in conditions of exponential growth after the first selection and retransfected when puromycin sensitivity was restored
To “knock out” (KO) PARP1 in human cells, we introduced double-strand break (DSB) at PARP1 exon 2 using a pair of gRNAs coupled to Cas9D10A (“double nicking” [30])
Summary
In response to viral infection, human cells activate an interferon (IFN)-dependent antiviral program [1]. Secreted IFNs bind to their common IFN receptor, triggering JAK/STAT signaling and the coordinated induction of hundreds of interferon-inducible genes (ISGs)[4]. The products of these genes execute the antiviral response via direct interaction with viral molecules as well as with many cellular factors that control cell cycle progression, apoptosis and other key cellular functions [1]. Type I IFN signaling can be activated by cytoplasmic nucleic acids in the absence of viral infection (“viral mimicry”) In this context, DNA damaging agents are well-known to induce IFNs via multiple mechanisms (reviewed in [5]).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
