Role of PARP-1 in Regulating Cytokine-Mediated Pro-Inflammatory Transcriptional Responses in Macrophages

Presentation Number: MON 581
Date of Presentation: April 3rd, 2017

Rebecca Gupte*, Tulip Sunil Nandu and W Lee Kraus
University of Texas Southwestern Medical Center, Dallas, TX

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-γ (IFNg) are highly effective at resolving infections. Aberrant activation of MF, however, results in excessive inflammation, which may lead to autoimmune diseases. Mice lacking the nuclear gene regulatory protein Poly(ADP-ribose) Polymerase-1 (PARP-1) are resistant to septic shock due to decreased serum levels of pro-inflammatory cytokines. Moreover, PARP-1 modulates the activity of NF-κB, a key proinflammatory transcription factor. Although these observations implicate PARP-1 in the regulation of inflammation, its role in innate immune signaling is relatively unexplored. We hypothesize that PARP-1 potentiates proinflammatory responses by mediating signal-dependent transcriptional changes in MF. To test this hypothesis, we assessed the effect of PARP-1 inhibition on proinflammatory signaling in MF using the PARP inhibitor PJ34. RNA-seq analysis revealed that PARP inhibition induces significant changes in the LPS- and TNFa-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 proinflammatory cytokines and chemokines. In this regard, we observed that PARP-1 associates with nuclear STAT1, a key downstream mediator of IFNg signaling, 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 STAT1, 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 STAT1 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.

 

Nothing to Disclose: RG, TSN, WLK