Extracellular calcium elicits feedforward regulation of the Toll-like receptor-triggered innate immune response.
Despite the expanding knowledge on feedback regulation of Toll-like receptor (TLR) signaling, the feedforward regulation of TLR signaling for the proper innate response to invading microbes is not fully understood. Here, we report that extracellular calcium can coordinate the activation of the small GTPases Ras and Ras-proximate-1 (Rap1) upon TLR stimulation which favors activation of macrophages through a feedforward mechanism. We show that different doses of TLR agonists can trigger different levels of cytokine production, which can be potentiated by extracellular calcium but are impaired by the chelating reagent ethylene glycol tetraacetic acid (EGTA) or by knockdown of stromal interaction molecule 1 (STIM1). Upon TLR engagement, GTP-bound Ras levels are increased and GTP-bound Rap1 is decreased, which can be reversed by EGTA-mediated removal of extracellular calcium. Furthermore, we demonstrate that Rap1 knockdown rescues the inhibitory effects of EGTA on the TLR-triggered innate response. Examination of the TLR signaling pathway reveals that extracellular calcium may regulate the TLR response via feedforward activation of the extracellular signal-regulated kinase signaling pathway. Our data suggest that an influx of extracellular calcium, mediated by STIM1-operated calcium channels, may transmit the information about the intensity of extracellular TLR stimuli to initiate innate responses at an appropriate level. Our study may provide mechanistic insight into the feedforward regulation of the TLR-triggered innate immune response.
Institute of Immunology, Zhejiang University School of Medicine, Hangzhou 310058, China.|National Key Laboratory of Medical Immunology & Institute of Immunology, Second Military Medical University, Shanghai 200433, China.
Songqing
S
Tang
National Key Laboratory of Medical Immunology & Institute of Immunology, Second Military Medical University, Shanghai 200433, China.
Taoyong
T
Chen
National Key Laboratory of Medical Immunology & Institute of Immunology, Second Military Medical University, Shanghai 200433, China.|National Key Laboratory of Medical Molecular Biology & Department of Immunology, Chinese Academy of Medical Sciences, Beijing 100005, China.
Mingjin
M
Yang
National Key Laboratory of Medical Molecular Biology & Department of Immunology, Chinese Academy of Medical Sciences, Beijing 100005, China.
Lei
L
Wang
Institute of Immunology, Zhejiang University School of Medicine, Hangzhou 310058, China.
Zhou
Z
Yu
Institute of Immunology, Zhejiang University School of Medicine, Hangzhou 310058, China.|National Key Laboratory of Medical Immunology & Institute of Immunology, Second Military Medical University, Shanghai 200433, China.
Bin
B
Xie
National Key Laboratory of Medical Immunology & Institute of Immunology, Second Military Medical University, Shanghai 200433, China.
Cheng
C
Qian
National Key Laboratory of Medical Immunology & Institute of Immunology, Second Military Medical University, Shanghai 200433, China.
Sheng
S
Xu
National Key Laboratory of Medical Immunology & Institute of Immunology, Second Military Medical University, Shanghai 200433, China.
Nan
N
Li
Institute of Immunology, Zhejiang University School of Medicine, Hangzhou 310058, China.|National Key Laboratory of Medical Immunology & Institute of Immunology, Second Military Medical University, Shanghai 200433, China.|National Key Laboratory of Medical Molecular Biology & Department of Immunology, Chinese Academy of Medical Sciences, Beijing 100005, China.
Xuetao
X
Cao
Institute of Immunology, Zhejiang University School of Medicine, Hangzhou 310058, China.
Jianli
J
Wang
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D005110:Extracellular Space / Q000737:chemistry*; D055785:Gene Knockdown Techniques; D007113:Immunity, Innate / Q000187:drug effects*; D015850:Interleukin-6 / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008262:Macrophage Activation / Q000187:drug effects; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D008810:Mice, Inbred C57BL; D009000:Monocytes / Q000166:cytology; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D000071737:Stromal Interaction Molecule 1 / Q000378:metabolism; D051193:Toll-Like Receptors / Q000378:metabolism*
D015850:Interleukin-6; C100757:Stim1 protein, mouse; D000071737:Stromal Interaction Molecule 1; D051193:Toll-Like Receptors; D020559:Monomeric GTP-Binding Proteins; D002118:Calcium