Project description:DC-SIGN+ monocyte-derived dendritic cells (mo-DCs) play important roles in bacterial infections and inflammatory diseases, but the factors regulating their differentiation and proinflammatory status remain poorly defined. Here, we identify a micro-RNA, miR-181a, and a molecular mechanism that simultaneously regulate the acquisition of DC-SIGN+ expression and the activation state of DC-SIGN+ mo-DCs. Specifically, we show that miR-181a promotes DC-SIGN expression during terminal mo-DC differentiation and limits its sensitivity and responsiveness to TLR triggering and CD40 ligation. Mechanistically, miR-181a sustains ERK-MAPK signaling in mo-DCs, thereby enabling the maintenance of high levels of DC-SIGN and a high activation threshold. Low miR-181a levels during mo-DC differentiation, induced by inflammatory signals, do not support the high phospho-ERK signal transduction required for DC-SIGNhi mo-DCs and lead to development of proinflammatory DC-SIGNlo/- mo-DCs. Collectively, our study demonstrates that high DC-SIGN expression levels and a high activation threshold in mo-DCs are linked and simultaneously maintained by miR-181a.
Project description:The molecular requirements that guide the differentiation of monocytes into macrophages or monocyte-derived dendritic cells (Mo-DCs) are poorly understood. Here, we demonstrate that the nuclear orphan receptor NR4A3 guides monocyte fate and is essential for Mo-DC differentiation. Nr4a3-/- mice are impaired in the in vivo generation of DC-SIGN+ Mo-DCs following LPS stimulation and, as such, are defective at priming a CD8+ T cell response to gram negative bacteria. We also demonstrate that NR4A3 is an essential downstream effector of IRF4 during in vitro differentiation of Mo-DCs with GM-CSF and IL-4 and that, in absence of NR4A3, monocytes are diverted to macrophages. Our transcriptomic analysis of the genes regulated by NR4A3 reveals that the acquisition of the Mo-DC differentiation program is intertwined with the acquisition of a migratory signature. Furthermore, NR4A3 is critical for steady-state migration of non-lymphoid tissue conventional DCs to lymph nodes. Altogether, our results highlight a unique role for NR4A3 in Mo-DC differentiation and in the acquisition of migratory properties.
Project description:DC-SIGN is a C-type lectin expressed by dendritic cells (DCs) that binds HIV-1, sequestering it within multivesicular bodies to facilitate transmission to CD4+ T cells. Here we characterize the molecular basis of signalling through DC-SIGN by large-scale gene expression profiling and phosphoproteome analysis. Solitary DC-SIGN activation leads to a phenotypically disparate transcriptional program from Toll-like receptor (TLR) triggering with downregulation of MHC II, CD86, and interferon response genes and with induction of the TLR negative regulator ATF3. Phosphoproteome analysis reveals DC-SIGN signals through the leukemia-associated Rho guanine nucleotide exchange factor (LARG) to induce Rho activity. This LARG activation also occurs on DC HIV exposure and is required for effective HIV viral synapse formation. Taken together HIV mediated DC-SIGN signalling provides a mechanism by which HIV evades the immune response yet induces viral spread. Experiment Overall Design: Circulating monocyte derived DCs were isolated from buffy coats by adherence and culture in IL-4 and granulocyte-macrophage colony-stimulating factor (GM-CSF). DC preparations analyzed were more than 98% pure. At day four 10 million immature DCs were either left unstimulated or stimulated using plate bound anti-DC-SIGN antibody for 2 hr. Three replicates of non-stimulated or stimulated cells were taken and used to extract total RNA.
Project description:DC-SIGN is a C-type lectin expressed by dendritic cells (DCs) that binds HIV-1, sequestering it within multivesicular bodies to facilitate transmission to CD4+ T cells. Here we characterize the molecular basis of signalling through DC-SIGN by large-scale gene expression profiling and phosphoproteome analysis. Solitary DC-SIGN activation leads to a phenotypically disparate transcriptional program from Toll-like receptor (TLR) triggering with downregulation of MHC II, CD86, and interferon response genes and with induction of the TLR negative regulator ATF3. Phosphoproteome analysis reveals DC-SIGN signals through the leukemia-associated Rho guanine nucleotide exchange factor (LARG) to induce Rho activity. This LARG activation also occurs on DC HIV exposure and is required for effective HIV viral synapse formation. Taken together HIV mediated DC-SIGN signalling provides a mechanism by which HIV evades the immune response yet induces viral spread. Keywords: Activation state, signalling, Toll-like Receptor (TLR)
Project description:Monocytes can differentiate into macrophages or dendritic cells. When treated with granulocyte-macrophage colony-stimulating factor (GM-CSF) monocytes differentiate into macrophage-like cells. Here, we report that pharmacological blockade of the nuclear receptor PPARγ in monocytes turns GM-CSF into a potent inducer of dendritic cell (Mo-DC) differentiation. Remarkably, simultaneous blockade of PPARγ and mTORC1 in the presence of GM-CSF promoted the differentiation of Mo-DCs with a stronger phenotypic stability and immunogenic profile when compared with canonical Mo-DCs differentiated by treatment with GM-CSF and IL-4. Moreover, and in contrast with the observations made with GM-CSF and IL-4, blockade of PPARγ and mTORC1 was shown to be able to induce the differentiation of monocyte-derived macrophages (Mo-Macs) into Mo-DCs. Transcriptional profiling performed at either early time points, as well as at the end of the differentiation process, revealed marked differences in the gene expression signature between Mo-DCs induced by GM-CSF and IL-4 and Mo-DCs induced by GM-CSF in the presence of PPARγ and/or mTORC1 inhibitors, thus suggesting diverging differentiation pathways. Our observations might contribute, not only to a better understanding of the mechanisms involved in Mo-DCs differentiation but also to improving the efficacy of both, DC vaccines and therapies focusing on the modulation of myeloid cell functions.
Project description:Cross-presentation of cell-associated antigens is carried out by classical DCs (cDCs) and monocyte-derived DCs (Mo-DCs), but whether a similar or distinct program exists for this process is unknown. In examining this issue, we discovered that only Ly-6ChiTremL4– monocytes, but not Ly-6ChiTremL4+ monocytes, can differentiate into Zbtb46+ Mo-DCs in response to GM-CSF and IL-4. However, Ly-6ChiTremL4+ monocytes were committed to Nur77-dependent development of Ly-6CloTremL4+ monocytes. Further, differentiation of monocytes with GM-CSF required addition of IL-4 to generate Zbtb46+ Mo-DCs that cross-presented as efficiently as CD24+ cDCs, which was accompanied by increased Batf3 and Irf4 expression. Unlike cDCs, Mo-DCs required only IRF4, and not Batf3, for cross-presentation. Further, Irf4–/– monocytes failed to develop into Zbtb46+ Mo-DCs, and instead developed into macrophages. Thus, cDCs and Mo-DCs use distinct transcriptional programs for cross-presentation that may drive different antigen-processing pathways. These differences may influence development of therapeutic DC vaccines based on Mo-DCs.
Project description:Cross-presentation of cell-associated antigens is carried out by classical DCs (cDCs) and monocyte-derived DCs (Mo-DCs), but whether a similar or distinct program exists for this process is unknown. In examining this issue, we discovered that only Ly-6ChiTremL4– monocytes, but not Ly-6ChiTremL4+ monocytes, can differentiate into Zbtb46+ Mo-DCs in response to GM-CSF and IL-4. However, Ly-6ChiTremL4+ monocytes were committed to Nur77-dependent development of Ly-6CloTremL4+ monocytes. Further, differentiation of monocytes with GM-CSF required addition of IL-4 to generate Zbtb46+ Mo-DCs that cross-presented as efficiently as CD24+ cDCs, which was accompanied by increased Batf3 and Irf4 expression. Unlike cDCs, Mo-DCs required only IRF4, and not Batf3, for cross-presentation. Further, Irf4–/– monocytes failed to develop into Zbtb46+ Mo-DCs, and instead developed into macrophages. Thus, cDCs and Mo-DCs use distinct transcriptional programs for cross-presentation that may drive different antigen-processing pathways. These differences may influence development of therapeutic DC vaccines based on Mo-DCs.
Project description:Cross-presentation of cell-associated antigens is carried out by classical DCs (cDCs) and monocyte-derived DCs (Mo-DCs), but whether a similar or distinct program exists for this process is unknown. In examining this issue, we discovered that only Ly-6ChiTremL4– monocytes, but not Ly-6ChiTremL4+ monocytes, can differentiate into Zbtb46+ Mo-DCs in response to GM-CSF and IL-4. However, Ly-6ChiTremL4+ monocytes were committed to Nur77-dependent development of Ly-6CloTremL4+ monocytes. Further, differentiation of monocytes with GM-CSF required addition of IL-4 to generate Zbtb46+ Mo-DCs that cross-presented as efficiently as CD24+ cDCs, which was accompanied by increased Batf3 and Irf4 expression. Unlike cDCs, Mo-DCs required only IRF4, and not Batf3, for cross-presentation. Further, Irf4–/– monocytes failed to develop into Zbtb46+ Mo-DCs, and instead developed into macrophages. Thus, cDCs and Mo-DCs use distinct transcriptional programs for cross-presentation that may drive different antigen-processing pathways. These differences may influence development of therapeutic DC vaccines based on Mo-DCs.
Project description:Recently, we showed that increased miR-181a expression was associated with improved outcomes in cytogenetically normal acute myeloid leukemia (CN-AML). Interestingly, miR-181a expression was increased in CN-AML patients harboring CEBPA mutations, which are usually biallelic and associate with better prognosis. CEBPA encodes the C/EBP? transcription factor. We demonstrate here that the presence of N-terminal CEBPA mutations and miR-181a expression are linked. Indeed, the truncated C/EBP?-p30 isoform, which is produced from the N-terminal mutant CEBPA gene or from the differential translation of wild-type CEBPA mRNA and is commonly believed to have no transactivation activity, binds to the miR-181a-1 promoter and upregulates the microRNA expression. In xenograft mouse models, ectopic miR-181a expression inhibits tumor growth. This regulatory pathway may explain an increased sensitivity to apoptosis-inducing chemotherapy in subsets of AML patients. Altogether, our data provide a potential explanation for the improved clinical outcomes observed in CEBPA-mutated CN-AML patients.
Project description:Dendritic cells (DCs) are the most potent antigen (Ag)-presenting cells. Whereas immature DCs down-regulate T cell responses to induce/maintain immunological tolerance, mature DCs promote immunity. To amplify their functions, DCs communicate with neighboring DCs through soluble mediators, cell-to-cell contact and vesicle exchange. Transfer of nanovesicles (<100nm) derived from the endocytic pathway (termed exosomes) represents a novel mechanism of DC-to-DC communication. The facts that exosomes contain exosome-shuttle microRNAs (miRNAs), and DC functions can be regulated by exogenous miRNAs, suggest that DC-to-DC interactions could be mediated through exosome-shuttle miRNAs, an hypothesis that remains to be tested. Importantly, the mechanism of transfer of exosome-shuttle miRNAs from the exosome lumen to the cytosol of target cells is unknown. Here, we demonstrate that DCs release exosomes with different miRNAs depending on the maturation of the DCs. By visualizing spontaneous transfer of exosomes between DCs, we demonstrate that exosomes fused with the target DCs, the latter followed by release of the exosome content into the DC cytosol. Importantly, exosome-shuttle miRNAs are functional, as they repress target mRNAs of acceptor DCs. Our findings unveil a mechanism of transfer of exosome-shuttle miRNAs between DCs and its role as a means of communication and post-transcriptional regulation between DCs.