Objectives: PARPs, which are members of the poly(ADP-ribose) polymerase superfamily, promote tumorigenesis and tumour-associated inflammation and are thus therapeutic targets for several cancers. The aim of the present study is to investigate the mechanistic insight into the roles PARPs for inflammation.
Methods: Primary murine macrophages were cultured in the presence or absence of the PARP5 inhibitor NVP-TNKS656 to examine the role of PARP5 for cytokine production.
Results: In contrast to the roles of other PARPs for induction of inflammation, we found in the present study that pharmacologic inhibition of PARP5 induces production of inflammatory cytokines in primary murine macrophages. We found that treatment with the PARP5 inhibitor NVP-TNKS656 in macrophages enhanced steady-state and LPS-mediated cytokine production through degradation of IκBα and subsequent nuclear translocation of NF-κB. We also found that pharmacologic inhibition of PARP5 stabilises the adaptor protein 3BP2, a substrate of PARP5, and that accelerated cytokine production induced by PARP5 inhibition was rescued in 3BP2-deleted macrophages. Additionally, we found that LPS increases the expression of 3BP2 and AXIN1, a negative regulator of β-catenin, through suppression of PARP5 transcripts in macrophages, leading to further activation of cytokine production and inhibition of β-catenin-mediated cell proliferation, respectively. Lastly, we found that PARP5 inhibition in macrophages promotes osteoclastogenesis through stabilisation of 3BP2 and AXIN1, leading to activation of SRC and suppression of β-catenin, respectively.
Conclusions: Our results show that pharmacologic inhibition of PARP5 against cancers unexpectedly induces adverse autoinflammatory side effects through activation of innate immunity, unlike inhibition of other PARPs.