Pathogen-Mediated Proteolysis of the Cell Death Regulator RIPK1 and the Host Defense Modulator RIPK2 in Human Aortic Endothelial Cells

Abstract

Porphyromonas gingivalis is the primary etiologic agent of periodontal disease that is associated with other human chronic inflammatory diseases, including atherosclerosis. The ability of P. gingivalis to invade and persist within human aortic endothelial cells (HAEC) has been postulated to contribute to a low to moderate chronic state of inflammation, although how this is specifically achieved has not been well defined. In this study, we demonstrate that P. gingivalis infection of HAEC resulted in the rapid cleavage of receptor interacting protein 1 (RIPK1), a mediator of tumor necrosis factor (TNF) receptor-1 (TNF-R1)-induced cell activation or death, and RIPK2, a key mediator of both innate immune signaling and adaptive immunity. The cleavage of RIPK1 or RIPK2 was not observed in cells treated with apoptotic stimuli, or cells stimulated with agonists to TNF-R1, nucleotide oligomerization domain receptor 1(NOD1), NOD2, Toll-like receptor 2 (TLR2) or TLR4. P. gingivalis-induced cleavage of RIPK1 and RIPK2 was inhibited in the presence of a lysine-specific gingipain (Kgp) inhibitor. RIPK1 and RIPK2 cleavage was not observed in HAEC treated with an isogenic mutant deficient in the lysine-specific gingipain, confirming a role for Kgp in the cleavage of RIPK1 and RIPK2. Similar proteolysis of poly (ADP-ribose) polymerase (PARP) was observed. We also demonstrated direct proteolysis of RIPK2 by P. gingivalis in a cell-free system which was abrogated in the presence of a Kgp-specific protease inhibitor. Our studies thus reveal an important role for pathogen-mediated modification of cellular kinases as a potential strategy for bacterial persistence within target host cells, which is associated with low-grade chronic inflammation, a hallmark of pathogen-mediated chronic inflammatory disorders.

The diverse role of RIP kinases in necroptosis and inflammation

“…3). Bacteria have also evolved to inhibit RIPK1 signaling; for example, Porphyromonas gingivalis has been shown to specifically cleave RIPK1 via its lysine-specific (Kgp) protease 100 .…”

Periodontitis: from microbial immune subversion to systemic inflammation

“…P. gingivalis can indeed invade human aortic endothelial cells by means of its FimA fimbriae and subsequently suppresses the levels of key intracellular molecules involved in cell death and host defence ( such as NLRP3 and RIPK1) leading to a permissive intracellular environment 6,94,111,112 . FimA fimbriae also induce TLR2-dependent expression of endothelial adhesion molecules (ICAM-1, VCAM-1 and E-selectin) and chemokines (MCP-1 and CXCL8) involved in leukocyte recruitment, as well as TLR2 inside-out signalling that activates leukocyte integrins that mediate transendothelial migration 6,113,114 .…”

LRRK2 and RIPK2 Variants in the NOD 2-Mediated Signaling Pathway Are Associated with Susceptibility to Mycobacterium leprae in Indian Populations

“…Dysregulation in NOD2 signalling is associated with pathogenesis of many inflammatory disorders [13] and is also associated with triggering of IL-32 dependent dendritic cell programming in leprosy [14]. The cytosolic pattern recognition receptor NOD1 and NOD2 also activates the RIPK2 gene [15]. The gene encoding receptor- interacting serine-threonine kinase 2 ( RIPK2 ) located on the long arm of chromosome 8 (8q21) is essential for signaling through the Toll-like receptors [15], [16].…”