Porphyromonas gingivalis attenuates ATP-mediated inflammasome activation and HMGB1 release through expression of a nucleoside-diphosphate kinase

Abstract

Many intracellular pathogens evade the innate immune response in order to survive and proliferate within infected cells. We show that Porphyromonas gingivalis, an intracellular opportunistic pathogen, uses a nucleoside-diphosphate kinase (NDK) homolog to inhibit innate immune responses due to stimulation by extracellular ATP, which acts as a danger signal that binds to P2X7 receptors and induces activation of an inflammasome and caspase-1. Thus, infection of gingival epithelial cells (GECs) with wild-type P. gingivalis results in inhibition of ATP-induced caspase-1 activation. However, ndk-deficient P. gingivalis is less effective than wild-type P. gingivalis in reducing ATP-mediated caspase-1 activation and secretion of the proinflammatory cytokine, IL-1β, from infected GECs. Furthermore, P. gingivalis NDK modulates release of high-mobility group protein B1 (HMGB1), a pro-inflammatory danger signal, which remains associated with chromatin in healthy cells. Unexpectedly, infection with either wild-type or ndk-deficient P. gingivalis causes release of HMGB1 from the nucleus to the cytosol. But HMGB1 is released to the extracellular space when uninfected GECs are further stimulated with ATP, and there is more HMGB1 released from the cells when ATP-treated cells are infected with ndk-deficient mutant than wild-type P. gingivalis. Our results reveal that NDK plays a significant role in inhibiting P2X7-dependent inflammasome activation and HMGB1 release from infected GECs.

Porphyromonas gingivalis activates NFκB and MAPK pathways in human oral epithelial cells

“…HMGB1 is released into the extracellular area after stimulation of uninfected GECs with ATP instead of being translocated from the nucleus into the cytosol. In comparison to wild-type P. gingivalis higher amounts of HMGB1 are released when cells are infected with a NDK-deficient mutant stimulated with ATP, suggesting that NDK is crucial in inhibiting the initiation of the P2X7-dependent inflammasome and HMGB1 release from infected GECs [21]. …”

Fusobacterium nucleatuminfection of gingival epithelial cells leads to NLRP3 inflammasome-dependent secretion of IL-1β and the danger signals ASC and HMGB1

“…Furthermore, periodontitis is more prevalent and severe in developing countries because of poorer oral hygiene and greater plaque retention (Pilot, 1998; Pihlstrom et al , 2005). Untreated periodontitis can lead to damage of the gum tissue surrounding the tooth and alveolar bone damage, resulting in tooth loss (Han et al , 2000; Saini et al , 2009; Atanasova and Yilmaz, 2015). …”

“…While epithelial cells are not typically considered to be specialized innate immune cells, they can also recognize infection and respond by secreting chemokines and cytokines such as IL-8 and IL-1β, as in the case of GECs (Yilmaz et al , 2010; Hung et al , 2013; Johnson et al , 2015) and other epithelial cells (Santana et al , 2015). Receptors on both immune cells and epithelial cells recognize microbial products such as lipopolysaccharide and peptidoglycan, also known as pathogen-associated molecular patterns (PAMPs), through pattern recognition receptors such as toll-like receptors, which stimulate expression of antimicrobial genes, and inflammatory cytokines and chemokines (Janeway and Medzhitov, 2002; Takeda and Akira, 2005; Cassel et al , 2009; Said-Sadier and Ojcius, 2012).…”

Nucleoside-Diphosphate-Kinase of P. gingivalis is Secreted from Epithelial Cells In the Absence of a Leader Sequence Through a Pannexin-1 Interactome

“…The extracellular translocation of P. gingivalis -NDK from GECs was shown to modulate and inhibit key immune responses, such as eATP-induced NADPH-oxidase, as well as mitochondria-mediated reactive oxygen species (ROS) generation mediating oxidative stress and clearance of intracellular bacteria1182124. Secretion of P. gingivalis -NDK also interferes with eATP/P2X 7 -receptor mediated activation of the NLRP3 inflammasome in GECs, and suppresses the secretion of a pro-inflammatory cytokine, interleukin-1β (IL-1β), via ATP scavenging1821252627. Despite the emerging importance of NDK secretion in a number of severe human chronic conditions, currently the extracellular translocation pathways of NDKs from host cells have not been identified1589.…”