LAUSR

Abstract Macrophages (MF) are major components of the innate immune system involved in mounting inflammatory responses against infection or injury in the host. MF activated by microbial agents, cytokines, or interferon-gamma (IFNg) are highly effective at resolving infections. Mice lacking in the enzyme Poly(ADP-ribose) Polymerase-1 (PARP-1) are resistant to septic shock due to an attenuated pro-inflammatory response. Moreover, PARP-1 modulates the activity of NF-κB, a key pro-inflammatory transcription factor. Although these observations implicate PARP-1 in the regulation of inflammation, its role in innate immune signaling is relatively unexplored. We hypothesized that PARP-1 potentiates pro-inflammatory responses by mediating signal-dependent transcriptional changes in MF. To test this hypothesis, we assessed the effect of PARP-1 inhibition on pro-inflammatory signaling in MF. RNA-seq analysis revealed that PARP inhibition induces significant changes in the LPS- and TNFα-stimulated transcriptomes. Moreover, PARP inhibition, as well as PARP-1 depletion, significantly alters the global expression of IFNg-regulated genes, including a number of key pro-inflammatory cytokines and chemokines. In this regard, we observed that PARP-1 associates with nuclear STAT1α and triggers its poly(ADP-ribosyl)ation (PARylation) in an IFNg-dependent manner. Using a mass spectrometric approach, we identified the sites of PARylation on STAT1α, including a number of glutamate and aspartate residues in its DNA binding and transactivation domains. Using ChIP-seq, we observe significant changes in IFNg-induced STAT1α genomic localization upon treatment with PJ34. Furthermore, PARP inhibition attenuates IFNg-dependent phosphorylation of STAT1. These results suggest that PARP-1-driven PARylation affects DNA-binding and transactivation by STAT1, consequently altering IFNg responses in MF. These studies may open new avenues for using PARP inhibitors to treat autoimmune and inflammatory diseases. This work is supported by the American Heart Association postdoctoral fellowship to RG and a grant (DK069710) from the NIH/NIDDK to WLK.