PI3Kγ is a molecular switch that controls immune suppression.

Macrophages play critical, but opposite, roles in acute and chronic inflammation and cancer. In response to pathogens or injury, inflammatory macrophages express cytokines that stimulate cytotoxic T cells, whereas macrophages in neoplastic and parasitic diseases express anti-inflammatory cytokines that induce immune suppression and may promote resistance to T cell checkpoint inhibitors. Here we show that macrophage PI 3-kinase γ controls a critical switch between immune stimulation and suppression during inflammation and cancer. PI3Kγ signalling through Akt and mTor inhibits NFκB activation while stimulating C/EBPß activation, thereby inducing a transcriptional program that promotes immune suppression during inflammation and tumour growth. By contrast, selective inactivation of macrophage PI3Kγ stimulates and prolongs NFκB activation and inhibits C/EBPß activation, thus promoting an immunostimulatory transcriptional program that restores CD8+ T cell activation and cytotoxicity. PI3Kγ synergizes with checkpoint inhibitor therapy to promote tumour regression and increased survival in mouse models of cancer. In addition, PI3Kγ-directed, anti-inflammatory gene expression can predict survival probability in cancer patients. Our work thus demonstrates that therapeutic targeting of intracellular signalling pathways that regulate the switch between macrophage polarization states can control immune suppression in cancer and other disorders.

Bruton Tyrosine Kinase-Dependent Immune Cell Cross-talk Drives Pancreas Cancer.

UNLABELLED: Pancreas ductal adenocarcinoma (PDAC) has one of the worst 5-year survival rates of all solid tumors, and thus new treatment strategies are urgently needed. Here, we report that targeting Bruton tyrosine kinase (BTK), a key B-cell and macrophage kinase, restores T cell-dependent antitumor immune responses, thereby inhibiting PDAC growth and improving responsiveness to standard-of-care chemotherapy. We report that PDAC tumor growth depends on cross-talk between B cells and FcRγ(+) tumor-associated macrophages, resulting in T(H)2-type macrophage programming via BTK activation in a PI3Kγ-dependent manner. Treatment of PDAC-bearing mice with the BTK inhibitor PCI32765 (ibrutinib) or by PI3Kγ inhibition reprogrammed macrophages toward a T(H)1 phenotype that fostered CD8(+) T-cell cytotoxicity, and suppressed PDAC growth, indicating that BTK signaling mediates PDAC immunosuppression. These data indicate that pharmacologic inhibition of BTK in PDAC can reactivate adaptive immune responses, presenting a new therapeutic modality for this devastating tumor type. SIGNIFICANCE: We report that BTK regulates B-cell and macrophage-mediated T-cell suppression in pancreas adenocarcinomas. Inhibition of BTK with the FDA-approved inhibitor ibrutinib restores T cell-dependent antitumor immune responses to inhibit PDAC growth and improves responsiveness to chemotherapy, presenting a new therapeutic modality for pancreas cancer.

Rapid CD4+ T-cell responses to bacterial flagellin require dendritic cell expression of Syk and CARD9.

Toll-like receptors (TLRs) can recognize microbial patterns and utilize adaptor molecules, such as-MyD88 or (TRIF TIR-domain-containing adapter-inducing interferon-ß), to initiate downstream signaling that ultimately affects the initiation of adaptive immunity. In addition to this inflammatory role, TLR5 expression on dendritic cells can favor antigen presentation of flagellin peptides and thus increase the sensitivity of flagellin-specific T-cell responses in vitro and in vivo. Here, we examined the role of alternative signaling pathways that might regulate flagellin antigen presentation in addition to MyD88. These studies suggest a requirement for spleen tyrosine kinase, a noncanonical TLR-signaling adaptor molecule, and its downstream molecule CARD9 in regulating the sensitivity of flagellin-specific CD4(+) T-cell responses in vitro and in vivo. Thus, a previously unappreciated signaling pathway plays an important role in regulating the dominance of flagellin-specific T-cell responses.

CARD9 mediates Dectin-1-induced ERK activation by linking Ras-GRF1 to H-Ras for antifungal immunity.

Dectin-1 functions as a pattern recognition receptor for sensing fungal infection. It has been well-established that Dectin-1 induces innate immune responses through caspase recruitment domain-containing protein 9 (CARD9)-mediated NF-κB activation. In this study, we find that CARD9 is dispensable for NF-κB activation induced by Dectin-1 ligands, such as curdlan or Candida albicans yeast. In contrast, we find that CARD9 regulates H-Ras activation by linking Ras-GRF1 to H-Ras, which mediates Dectin-1-induced extracellular signal-regulated protein kinase (ERK) activation and proinflammatory responses when stimulated by their ligands. Mechanistically, Dectin-1 engagement initiates spleen tyrosine kinase (Syk)-dependent Ras-GRF1 phosphorylation, and the phosphorylated Ras-GRF1 recruits and activates H-Ras through forming a complex with CARD9, which leads to activation of ERK downstream. Finally, we show that inhibiting ERK activation significantly accelerates the death of C. albicans-infected mice, and this inhibitory effect is dependent on CARD9. Together, our studies reveal a molecular mechanism by which Dectin-1 induces H-Ras activation that leads to ERK activation for host innate immune responses against fungal infection.

USP18 inhibits NF-κB and NFAT activation during Th17 differentiation by deubiquitinating the TAK1-TAB1 complex.

Reversible ubiquitin modification of cell signaling molecules has emerged as a critical mechanism by which cells respond to extracellular stimuli. Although ubiquitination of TGF-ß-activated kinase 1 (TAK1) is critical for NF-κB activation in T cells, the regulation of its deubiquitination is unclear. We show that USP18, which was previously reported to be important in regulating type I interferon signaling in innate immunity, regulates T cell activation and T helper 17 (Th17) cell differentiation by deubiquitinating the TAK1-TAB1 complex. USP18-deficient T cells are defective in Th17 differentiation and Usp18(-/-) mice are resistant to experimental autoimmune encephalomyelitis (EAE). In response to T cell receptor engagement, USP18-deficient T cells exhibit hyperactivation of NF-κB and NFAT and produce increased levels of IL-2 compared with the wild-type controls. Importantly, USP18 is associated with and deubiquitinates the TAK1-TAB1 complex, thereby restricting expression of IL-2. Our findings thus demonstrate a previously uncharacterized negative regulation of TAK1 activity during Th17 differentiation, suggesting that USP18 may be targeted to treat autoimmune diseases.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) and TGFß-activated kinase 1 (TAK1) play essential roles in the C-type lectin receptor signaling in response to Candida albicans infection.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) and TGFß-activated kinase 1 (TAK1) are considered as key intermediates in Toll-like receptor (TLR) signaling. However, the role of TRAF6 and TAK1 in C-type lectin receptors (CLRs) in response to fungal infection has not been studied. In this study, we have utilized macrophages derived from TRAF6 knock-out mice and myeloid-specific TAK1-deficient mice and determined the role of TRAF6 and TAK1 in CLR-induced signal transduction events. We demonstrate that TRAF6 and TAK1 are required for NF-κB and JNK activation, and expression of proinflammatory cytokines in response to Candida albicans infection. Our results highlight TRAF6 and TAK1 as key components in the signaling cascade downstream of C-type lectin receptors and as critical mediators of the anti-fungal immune response. Therefore, our studies provide a mechanistic understanding of the host immune response to C. albicans, which has a significant impact for the development of anti-fungal therapeutics and in understanding risk-factors and determining susceptibility to C. albicans infection.

Phospholipase Cγ2 (PLCγ2) is key component in Dectin-2 signaling pathway, mediating anti-fungal innate immune responses.

C-type lectin receptors (CLRs) such as Dectin-2 function as pattern recognition receptors to sense fungal infection. However, the signaling pathways induced by these receptors remain largely unknown. Previous studies suggest that the CLR-induced signaling pathway may utilize similar signaling components as the B cell receptor-induced signaling pathway. Phospholipase Cγ2 (PLCγ2) is a key component in B cell receptor signaling, but its role in other signaling pathways has not been fully characterized. Here, we show that PLCγ2 functions downstream of Dectin-2 in response to the stimulation by the hyphal form of Candida albicans, an opportunistic pathogenic fungus. Using PLCγ2- and PLCγ1-deficient macrophages, we found that the lack of PLCγ2, but not PLCγ1, impairs cytokine production in response to infection with C. albicans. PLCγ2 deficiency results in the defective activation of NF-κB and MAPK and a significantly reduced production of reactive oxygen species following fungal challenge. In addition, PLCγ2-deficient mice are defective in clearing C. albicans infection in vivo. Together, these findings demonstrate that PLCγ2 plays a critical role in CLR-induced signaling pathways, governing antifungal innate immune responses.