Requirement of phospholipase C‐γ2 (PLCγ2) for Dectin‐1‐induced antigen presentation and induction of T_H1/T_H17 polarization

Abstract

DC recognize microbial components through an array of receptors known as PRR. PRR initiate intracellular signals, which engender DC with the capacity to stimulate T-cell responses. Dectin-1 is a PRR that recognizes b-glucan, a major constituent of many fungi's outer cell wall. Here we show that Dectin-1 activates DC through phospholipase (PLC)c2 signaling. PLCc2-deficient DC were unable to expand antigen-specific T cells and induce T H 1 and T H 17 differentiation in response to b-glucan. Mechanistically, PLCc2-deficiency impaired the capacity of DC to secrete polarizing cytokines following exposure to b-glucan. Dectin-1 required PLCc2 to activate MAPK, AP-1 and NF-jB, which induce cytokine gene expression. Moreover, PLCc2 controlled Dectin-1-mediated NFAT activation and induction of NFAT-dependent genes such as IL-2, cyclooxigenase-2 and Egr transcription factors. We conclude that PLCc2 is a crucial signaling mediator that modifies DC gene expression program to activate DC responses to b-glucan-containing pathogens.Key words: DC . Dectin-1 . PLCg . Signaling Supporting Information available online Introduction DC play a key role in gathering information from the surrounding environment and initiating appropriate immune responses when needed [1,2]. Because they bridge innate and adaptive immunity, DC are equipped with a multitude of intracellular and cell surface receptors that sense microbial components and trigger host responses to invading pathogens. These receptors, collectively known as PRR, include TLR [3], C-type lectins such as Dectin-1 [4], scavenger receptors [5], the nucleotide-binding oligomerization domain (NOD) proteins NOD1 and NOD2, the NOD-like receptors and the RIG-like receptors [6].Dectin-1 recognizes b-glucan, a major constituent of many fungi's outer cell wall [4,7] and triggers intracellular signals through a cytoplasmic tyrosine motif resembling the ITAM. Upon ligand binding, this motif is phosphorylated by src family kinases [8] and recruits the tyrosine kinase Syk [9], which initiates a signaling cascade leading to NF-kB [10], NFAT [11] and MAPK [12] activation. Along with Bcl-10 and MALT1, CARD9 is a crucial mediator in the ITAM-signaling pathway that links recognition of b-glucan by Dectin-1 to NF-kB and MAPK activation [13,14]. Overall, the Syk-CARD9 pathway is essential for [20,21]. Syk, together with the tyrosine kinases BTK and Src, activate PLCg through tyrosine phosphorylation [22]. Another downstream ITAM mediator, PI-3K, activates PLCg by generating phosphatidylinositol 3,4,5 trisphosphate, which binds the pleckstrin homology domain of PLCg, promoting PLCg recruitment to the cell membrane. Thus, the ability of Dectin-1 to initiate an ITAM-Syk-signaling pathway [9] provides a rationale for studying the role of PLCg in Dectin-1-mediated antimicrobial responses in DC.PLCg includes two isoforms, PLCg1 and PLCg2, which hydrolyze membrane phosphatidylinositol 4,5-biphosphate into inositol 1,4,5-trisphosphate and diacylglicerol (DAG) [20]. Inositol 1,4,5-trisphosphate triggers the ...

Dectin-1-mediated Signaling Leads to Characteristic Gene Expressions and Cytokine Secretion via Spleen Tyrosine Kinase (Syk) in Rat Mast Cells

“…The list of the significantly up-regulated genes in RBL-2H3 cells overexpressing Dectin-1 WT after 2 h of curdlan stimulation is shown in Table 1. Consistent with previous studies in macrophages and DCs, gene expressions of TNF-␣ (12, 13, 15), IL-4/IL-13 (38,39), early growth response transcription factor 3 (40,41), and suppressor of cytokine signaling 1 (42) were also up-regulated in curdlan-stimulated mast cells. Interestingly, curdlan did not stimulate gene expressions that were previously reported in macrophages and DCs, such as IL-1␤ (43, 44), IL-2 (18), [18][19][20], and IL-12 (18,20).…”

Differential Control of Mincle-Dependent Cord Factor Recognition and Macrophage Responses by the Transcription Factors C/EBPβ and HIF1α

“…The Egrs were rapidly induced, direct targets of Mincle triggering, as shown by CHX-blockade experiments. Several reports have indicated that Egr family members are induced by Dectin-1 ligands in macrophages and DCs (34,58) or neutrophils (59) in a calcineurin/NF-AT-dependent manner, which is likely also the case after Mincle stimulation. Although there are a number of reports on genes regulated by EGR family members in innate immune cells (60)(61)(62), the direct targets of EGRs in macrophages and DCs, especially in response to CLR activation, are currently unknown.…”

The Syk–NFAT–IL-2 Pathway in Dendritic Cells Is Required for Optimal Sterile Immunity Elicited by Alum Adjuvants

“…NFAT was linked to IL-2 release upon microbial challenge (15,27,29,30). Therefore, we asked whether NFAT also regulates IL-2 secretion in response to sterile stimuli, such as alum.…”