The macrophage scavenger receptor SR-AI binds to host tissue debris to perform clearance and it binds to bacteria for phagocytosis.In addition,SR-AI modulates macrophage activation through cell signaling.However,inves...The macrophage scavenger receptor SR-AI binds to host tissue debris to perform clearance and it binds to bacteria for phagocytosis.In addition,SR-AI modulates macrophage activation through cell signaling.However,investigation of SR-AI signaling on macrophages is complicated due to its promiscuous ligand specificity that overlaps with other macrophage receptors.Therefore,we expressed SR-AI on HEK 293T cells to investigate its ligand binding and signaling.On 293T cells,SR-AI could respond to E.coli DH5α,leading to NF-κB activation and IL-8 production.However,this requires E.coli DH5αto be sensitized by fresh serum that is treated with heat-inactivation or complement C3 depletion.Anti-C3 antibody inhibits the binding of SR-AI to serum-sensitized DH5αand blocks DH5αstimulation of SR-AI signaling.Further analysis showed that SR-AI can directly bind to purified iC3b but not C3 or C3b.By mutagenesis,The SRCR domain of SR-AI was found to be essential in SR-AI binding to serum-sensitized DH5α.These results revealed a novel property of SR-AI as a complement receptor for iC3b-opsonized bacteria that can elicit cell signaling.展开更多
基金This project is support by the Singapore Biomedical Research Council grant R-182-000-089-305National Medical Research Council grants R-364-000-019-213.JWKG received a scholarship from the National University of Singapore.
文摘The macrophage scavenger receptor SR-AI binds to host tissue debris to perform clearance and it binds to bacteria for phagocytosis.In addition,SR-AI modulates macrophage activation through cell signaling.However,investigation of SR-AI signaling on macrophages is complicated due to its promiscuous ligand specificity that overlaps with other macrophage receptors.Therefore,we expressed SR-AI on HEK 293T cells to investigate its ligand binding and signaling.On 293T cells,SR-AI could respond to E.coli DH5α,leading to NF-κB activation and IL-8 production.However,this requires E.coli DH5αto be sensitized by fresh serum that is treated with heat-inactivation or complement C3 depletion.Anti-C3 antibody inhibits the binding of SR-AI to serum-sensitized DH5αand blocks DH5αstimulation of SR-AI signaling.Further analysis showed that SR-AI can directly bind to purified iC3b but not C3 or C3b.By mutagenesis,The SRCR domain of SR-AI was found to be essential in SR-AI binding to serum-sensitized DH5α.These results revealed a novel property of SR-AI as a complement receptor for iC3b-opsonized bacteria that can elicit cell signaling.
