Extracellular calcium elicits feedforward regulation of the Toll-like receptor-triggered innate immune response

Abstract

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. Cellular & Molecular Immunology

Signal Integration at Elongation Factor 2 Kinase

“…4E). Feed-forward systems involving Ca 2ϩ have been shown to be important for driving biological phenotypes, such as cancer cell invasion (57) and the innate immune response (58), and are important regulatory components of cell signaling. Under basal conditions (i.e.…”

Integration of Rap1 and Calcium Signaling

“…The intensity of pathogenic TLR stimuli and the corresponding intensity of Ca 2+ signal has been linked with differential activation signaling by Ras and Rap1 as well as a differential effect on ERK activation and cytokine production [116,117]. Induced by low-intensity TLR stimuli, low-intensity Ca 2+ influx mediated by stromal interaction molecule 1 (STIM1) favors Rap1 inhibition and ERK activation, while high-intensity TLR stimuli trigger more intense Ca 2+ influx, leading to Ras activation and cytokine production [116] (Figure 3). Interestingly, this effect is mediated by CalDAG-GEFIII, which limits TLR-mediated cytokine production by activating Rap1 and ERK in response to a low level of antagonists and, in vivo, limits the inflammatory response [117].…”

“…In addition to the regulation of migration, Rap1 signaling is an important modulator of Ca 2+ -dependent regulation of toll-like receptor (TLR) signaling in immune cells [115,116]. The intensity of pathogenic TLR stimuli and the corresponding intensity of Ca 2+ signal has been linked with differential activation signaling by Ras and Rap1 as well as a differential effect on ERK activation and cytokine production [116,117].…”

“…In addition to the regulation of migration, Rap1 signaling is an important modulator of Ca 2+ -dependent regulation of toll-like receptor (TLR) signaling in immune cells [115,116]. The intensity of pathogenic TLR stimuli and the corresponding intensity of Ca 2+ signal has been linked with differential activation signaling by Ras and Rap1 as well as a differential effect on ERK activation and cytokine production [116,117]. Induced by low-intensity TLR stimuli, low-intensity Ca 2+ influx mediated by stromal interaction molecule 1 (STIM1) favors Rap1 inhibition and ERK activation, while high-intensity TLR stimuli trigger more intense Ca 2+ influx, leading to Ras activation and cytokine production [116] (Figure 3).…”

Biofunctionalized Materials Featuring Feedforward and Feedback Circuits Exemplified by the Detection of Botulinum Toxin A

“…These circuit designs are fundamental motifs in signal transduction pathways [16][17][18] and are harnessed for the programming of synthetic biological circuits. We exemplified this concept by a positive feedforward and a positive feedback topology.…”