Helicobacter pylori protein HP0986 (TieA) interacts with mouse TNFR1 and triggers proinflammatory and proapoptotic signaling pathways in cultured macrophage cells (RAW 264.7)

Abstract

HP0986 protein of Helicobacter pylori has been shown to trigger induction of proinflammatory cytokines (IL-8 and TNF-α) through the activation of NF-κB and also to induce Fas mediated apoptosis of human macrophage cells (THP-1). In this study, we unravel mechanistic details of the biological effects of this protein in a murine macrophage environment. Up regulation of MCP-1 and TNF-α in HP0986-induced RAW 264.7 cells occurred subsequent to the activation and translocation of NF-κB to the cell nucleus. Further, HP0986 induced apoptosis of RAW 264.7 cells through Fas activation and this was in agreement with previous observations made with THP-1 cells. Our studies indicated activation of TNFR1 through interaction with HP0986 and this elicited the aforementioned responses independent of TLR2, TLR4 or TNFR2. We found that mouse TNFR1 activation by HP0986 facilitates formation of a complex comprising of TNFR1, TRADD and TRAF2, and this occurs upstream of NF-κB activation. Furthermore, FADD also forms a second complex, at a later stage, together with TNFR1 and TRADD, resulting in caspase-8 activation and thereby the apoptosis of RAW 264.7 cells. In summary, our observations reveal finer details of the functional activity of HP0986 protein in relation to its behavior in a murine macrophage cell environment. These findings reconfirm the proinflammatory and apoptotic role of HP0986 signifying it to be an important trigger of innate responses. These observations form much needed baseline data entailing future in vivo studies of the functions of HP0986 in a murine model.