CR3 and Dectin-1 Collaborate in Macrophage Cytokine Response through Association on Lipid Rafts and Activation of Syk-JNK-AP-1 Pathway

Abstract

Collaboration between heterogeneous pattern recognition receptors (PRRs) leading to synergistic coordination of immune response is important for the host to fight against invading pathogens. Although complement receptor 3 (CR3) and Dectin-1 are major PRRs to detect fungi, crosstalk between these two receptors in antifungal immunity is largely undefined. Here we took advantage of Histoplasma capsulatum which is known to interact with both CR3 and Dectin-1 and specific particulate ligands to study the collaboration of CR3 and Dectin-1 in macrophage cytokine response. By employing Micro-Western Array (MWA), genetic approach, and pharmacological inhibitors, we demonstrated that CR3 and Dectin-1 act collaboratively to trigger macrophage TNF and IL-6 response through signaling integration at Syk kinase, allowing subsequent enhanced activation of Syk-JNK-AP-1 pathway. Upon engagement, CR3 and Dectin-1 colocalize and form clusters on lipid raft microdomains which serve as a platform facilitating their cooperation in signaling activation and cytokine production. Furthermore, in vivo studies showed that CR3 and Dectin-1 cooperatively participate in host defense against disseminated histoplasmosis and instruct adaptive immune response. Taken together, our findings define the mechanism of receptor crosstalk between CR3 and Dectin-1 and demonstrate the importance of their collaboration in host defense against fungal infection.

Immunity against fungi

“…These data can be reconciled if the major role of dectin-1/CARD9 is to modulate NADPH oxidase and fungal killing via soluble mediators, rather than by cell-intrinsic activation. β2 integrins and TLR signaling can collaborate with dectin-1 to mount macrophage inflammatory responses to H. capsulatum and other fungi (44,45).…”

Antifungal Innate Immunity: A Perspective from the Last 10 Years

“…There have also been many studies describing synergistic or antagonistic intracellular signaling between PRR in antifungal immunity. Through association with lipid rafts, dectin-1 and CR3, for example, can collaboratively trigger macrophage IL-6 and TNF-α production via the Syk-JNK-AP1 pathway and subsequently induce host defense against disseminated histoplasmosis [79]. More recently, it has been suggested that dectin-1 can also interact with dectin-2 and trigger the Syk-JNK pathway to activate the NLRP3 inflammasome in response to H. capsulatum [80].…”

Molecular Functions of Glycoconjugates in Autophagy

“…Dectin 1 is a C-type lectin receptor found on macrophages, dendritic cells, and neutrophils that activates LAP in response to fungal challenge [91–95]. The Dectin 1 carbohydrate recognition domain binds to fungal β-glucan, essentially a glucose polymer found in the cell walls of pathogenic bacteria and fungi [92].…”

“…The Dectin 1 carbohydrate recognition domain binds to fungal β-glucan, essentially a glucose polymer found in the cell walls of pathogenic bacteria and fungi [92]. Recognition of this PAMP (pathogen associated molecular pattern) initiates phagocytosis as well as respiratory burst and inflammation for the purpose of eliminating the pathogen [91, 92, 94]. The offending pathogen is internalized in a single-membraned phagocytic vacuole or phagosome (distinct from an autophagosome), which undergoes a series of phenotypic changes to gain the necessary degradative potential.…”

“…It is unclear how phagosomal ROS leads to the generation of LC3-II and association at the phagosome. However, the mechanism(s) of Dectin 1 cytokine induction offers viable avenues to uncover the downstream signaling involved in LAP [88, 91]. Many of the signaling proteins implicated in Dectin 1 cytokine induction, including JNK (c-Jun N-terminal kinase), p38 MAPK, TAK1 (Transforming growth factor-beta-activated kinase 1) and NFκB (nuclear factor kappa-light-chain-enhancer of activated B cells), are known regulators of autophagy [88].…”