Association of C-Type Lectin Mincle with FcεRIβγ Subunits Leads to Functional Activation of RBL-2H3 Cells through Syk

Abstract

Macrophage-inducible C-type lectin (Mincle) interacts with the γ-subunit of high-affinity IgE receptor (FcεRIγ) and activates Syk by recognizing its specific ligand, trehalose-6,6′-dimycolate, a glycolipid produced by Mycobacterium tuberculosis. It has been suggested that mast cells participate in the immune defense against pathogenic microbes including M. tuberculosis, although the functions are still uncertain. In this study, we examined the Mincle-mediated signaling pathway and cellular responses using RBL-2H3 cells. Mincle formed a protein complex with not only FcεRIγ but also FcεRIβ in a stable cell line expressing myc-tagged Mincle. In addition, engagement of Mincle increased the levels of protein tyrosine phosphorylation and ERK phosphorylation. A pull-down assay demonstrated that cross-linking of Mincle induced binding of FcεRIβγ subunits to the Src homology 2 domain of Syk. Pharmacological and genetic studies indicated that activation of Syk was critical for Mincle-mediated activation of phospholipase Cγ2, leading to the activation of ERK and nuclear factor of activated T cells. Moreover, engagement of Mincle efficiently induced up-regulation of characteristic mast cell genes in addition to degranulation. Taken together, our present results suggest that mast cells contribute to Mincle-mediated immunity through Syk activation triggered by association with the FcεRIβγ complex.

Phospholipase C‐γ2 promotes intracellular survival of mycobacteria

“…Entry of Ca 2+ via TRPC1 enhances macrophage's inflammatory responses as evident by decreased Ca 2+ entry and increased infection susceptibility in macrophages with TRPC1 deficiency. 26 It was also reported that binding of TDM to Mincle delayed phagosomal maturation and promoted intracellular survival of Mtb within macrophages. Augmented level of inflammatory cytokines may then provide effective protection from invading pathogens.…”

“…Stimulation with Mtb also induced tyrosine phosphorylation of PLC-γ2. Considering the fact that phosphorylation of PLC-γ2 at tyrosine 1217 led to the activation of the enzyme, 26 it might be speculated that interaction of pathogenic mycobacteria with macrophages directs the activation of PLC-γ2, which subsequently culminates in the survival of the pathogen inside the host cells. 16 Transient receptor potential channel 1 (TRPC1) and its associated endogenous Ca 2+ channel regulate cytokine production by lung alveolar macrophages and epithelial cells.…”

Expression and function of macrophage-inducible C-type lectin (Mincle) in inflammation driven parturition in fetal membranes and myometrium

“…We found no effect of Mincle siRNA knock‐out on NF‐κB transcriptional activity in myometrial cells, suggesting that Mincle regulates proinflammatory and pro‐labour mediators in gestational tissues by other downstream transcription factors. NFAT, MAPK and AP‐1 have also been shown to be involved in Mincle‐induced gene transcription . Notably, a few recent studies indicate a potential role for NFAT in mediating stretch or oxytocin‐induced gene expression in myometrium .…”

“…Mincle binding to its ligands initiates a cascade of events that leads to the recruitment of spleen tyrosine kinase (Syk) which activates a cascade of signalling events that leads to the induction of inflammatory genes via NF‐κB, mitogen‐activated protein kinase (MAPK), activator protein 1 (AP‐1) or nuclear factor of activated T cells (NFAT) . Numerous studies have implicated Mincle in regulating inflammation.…”

C-Type Lectin-Like Receptors: Head or Tail in Cell Death Immunity

“…MINCLE is largely described to recognize glycolipids from pathogens (88), but binds also ligands released by dead cells such as spliceosomeassociated protein 130 (SAP130) (21,89), β-glucosylceramide (β-GlcCer) (90), cholesterol sulfate and crystals (82, 91) ( Table 1 and Figure 1). This triggers the recruitment of SYK and the activation of NF-κB, mitogen-activated protein kinase (MAPK), activator protein 1 (AP-1) or nuclear factor of activated T cells (NFAT) and downstream transcription of inflammatory genes (21,88,(92)(93)(94)(95)(96)(97). MINCLE induces the expression of several cytokines and chemokines such as TNF-α, IL-6, MIP-2, and CXCL1 (21,28,29).…”