Multiple tumor-associated microRNAs modulate the survival and longevity of dendritic cells by targeting YWHAZ and Bcl2 signaling pathways.

Tumors use a wide array of immunosuppressive strategies, such as reducing the longevity and survival of dendritic cells (DCs), to diminish immune responses and limit the effect of immunotherapy. In this study, we found that tumors upregulate the expression of multiple microRNAs (miRNAs), such as miR-16-1, miR-22, miR-155, and miR-503. These tumor-associated miRNAs influenced the survival and longevity of DCs by affecting the expression of multiple molecules that are associated with apoptotic signaling pathways. Specifically, miR-22 targeted YWHAZ to interrupt the PI3K/Akt and MAPK signaling pathways, and miR-503 downregulated Bcl2 expression. The result of the increased expression of miR-22 and miR-503 in the tumor-associated DCs was their reduced survival and longevity. Thus, tumor-associated miRNAs can target multiple intracellular signaling molecules to cause the apoptosis of DCs in the tumor environment. Use of miR-22 and miR-503 as inhibitors may therefore represent a new strategy to improve DC-based immunotherapies against tumors.

Identification and characterization of a unique leucine-rich repeat protein (LRRC33) that inhibits Toll-like receptor-mediated NF-κB activation.

Toll-like receptors (TLRs) are important initiators in innate immune responses against pathogenic microbes such as viruses, intracellular bacteria or parasites. Although the innate immune system is designed to fight infectious pathogens, excessive activation of TLR signaling may lead to unwarranted inflammation with hazardous outcomes. Mechanisms of restraining excessive inflammation and controlling homeostasis for innate immunity are the focus of intense study. Here we showed that LRRC33, a novel member of leucine-rich repeat (LRR) protein family, plays a critical role in desensitizing TLR signaling. LRRC33 is TLR homolog that contains 17 putative LRRs in the extracellular region but lacks a cytoplasmic Toll/IL-1 receptor (TIR) domain. Expression of LRRC33 appears to be ubiquitous with high level of expression found in bone marrow, thymus, liver, lung, intestine and spleen. The LRRs of LRRC33 is required for the interaction with TLR and its inhibitory effect on NF-κB and AP-1 activation as well as cytokine production. Our study sheds new insight into the TLR signaling and inflammatory response in development and human diseases.

miR-223 suppresses differentiation of tumor-induced CD11b⁺ Gr1⁺ myeloid-derived suppressor cells from bone marrow cells.

Tumor-associated factors are related to increased accumulation of CD11b(+) Gr1(+) myeloid-derived suppressor cells (MDSCs). However, the exact mechanism of how genetic factors control the expansion of MDSCs in tumor-bearing hosts remains elusive. Herein, we found that tumor-associated MDSCs and their subsets, mononuclear MDSCs and polymorphonuclear MDSCs, have decreased expression of miR-223 when compared to CD11b(+) Gr1(+) cells from the spleen of disease-free mice. With the differentiation of CD11b(+) Gr1(+) MDSCs from bone marrow cells (BMCs) upon exposure to tumor-associated factors, the expression of both pri-miR-223 and mature miR-223 was downregulated, indicating that the expression of miR-223 could be regulated by tumor-associated factors. Interestingly, miR-223 remarkably inhibits differentiation of BMCs into CD11b(+) Gr1(+) MDSCs in the presence of tumor-associated factors by targeting myocyte enhancer factor 2C (MEF2C). Using reconstituted s.c. tumor models, miR-223 also suppresses accumulation of CD11b(+) Gr1(+) MDSCs, whereas its targeting molecule MEF2C increases the number of MDSCs. Tumor growth is slower in mice infused by miR223-engineered BMCs than in mice infused with control transfected BMCs. As miR-223 and its target molecule MEF2C are highly conserved between mice and humans, the modulation of miR-223 in tumor-induced CD11b(+) Gr1(+) MDSCs may exert an important role in controlling the increased accumulation of CD11b(+) Gr1(+) MDSCs in patients with tumor.

TNF-α-mediated microRNA-136 induces differentiation of myeloid cells by targeting NFIA.

Immune cell-lineage specification and function are influenced by progenitor origin and environmental factors. The mechanism of differentiation of immune cells, such as neutrophils, monocytes, and myeloid-derived suppressor cells, in inflammatory environments has not been elucidated completely. In this study, we have identified human microRNA-136 as a positive regulator of the differentiation of granulocytes and monocytes. Ectopic microRNA-136 induced cells to express higher levels of CD11b, CD14, and C/EBPε, secrete more cytokines, and synthesize higher levels of reactive oxygen species and H(2)O(2). microRNA-136 was shown to target and degrade multiple differentiation-associated molecules, such as the transcription factor NFIA, which induced the release of another microRNA, microRNA-223, with the ability to promote CD11b expression. Furthermore, microRNA-136 expression was remarkably increased by TNF-α, which activated NF-κB to bind to the DNA-promoter region controlling microRNA-136 expression. Additionally, TNF-α may alter NFIA expression through its modulation of microRNA-136 expression. Thus, TNF-α-mediated microRNA-136 may play a critical role in the generation and differentiation of inflammatory immune cells.

Dendritic cell-associated miRNAs are modulated via chromatin remodeling in response to different environments.

INTRODUCTION: Epigenetic modification plays a critical role in regulating gene expression. To understand how epigenetic modification alters miRNA expression in monocyte-derived dendritic cells (moDCs) in different environments, we analyzed the connections between H3K4me3 and H3K27me3 modification and the expression of miRNAs in LPS- and TGF-ß-conditioned moDCs. RESULTS: In moDCs, H3K4me3 modification was strongly associated with the expression of activating miRNAs, whereas H3K27me3 was related to repressive miRNAs. The regulation of miRNA expression by H3K4me3 and H3K27me3 was further confirmed by silencing or inhibiting methyltransferases or methylation-associated factors in LPS- and TGF-ß-conditioned moDCs. siRNAs targeting H3K4me3-associated mixed lineage leukemia (MLL) and retinoblastoma binding protein 5 (RBBP5) reduced H3K4me3 enrichment and downregulated miRNA expression; conversely, silencing H3K27me3-associated enhancer of zeste homolog 2 (EZH2) and embryonic ectoderm development (EED) genes upregulated the DC-associated miRNAs. However, LPS-mediated miRNAs were often associated with H3K4me3 redistribution from the transcription start site (TSS) to the miRNA-coding region. Silencing LPS-associated NF-κB p65 and CBP/p300 not only inhibited H3K4m3 redistribution but also reduced miRNA expression. LPS-upregulated RBBP4 and RBBP7, which are involved in chromatin remodeling, also affected the redistribution of H3K4me3 and reduced the expression of miRNAs. CONCLUSION: In LPS- and TGF-ß-conditioned moDCs, miRNAs may be modulated not only by H3K4m3 and H3K27me3 modification but also by redistribution of H3K4me3 around the transcriptional start site of miRNAs. Thus, H3K4me3 and H3K27me3 epigenetic modification may play an important role in regulating DC differentiation and function in the presence of tumor or inflammatory environments.

LRRC19 expressed in the kidney induces TRAF2/6-mediated signals to prevent infection by uropathogenic bacteria.

The innate immune-dependent bactericidal effects are critical for preventing microbial colonization in the urinary system. However, the mechanisms involved in establishing innate immune responses in kidney are not completely understood. Here we describe the role of a novel member of the LRR (leucine-rich repeat) class of transmembrane proteins, LRRC19 (LRR-containing 19) in eliminating uropathogenic bacteria. LRRC19 is predominantly expressed in human and mouse kidney tubular epithelial cells and LRRC19-deficient mice are more susceptible to uropathogenic Escherichia coli (UPEC) infection than wild-type or TLR4 knockout mice. Recognition of UPEC by LRRC19 induces the production of cytokines, chemokines and antimicrobial substances through TRAF2- and TRAF6-mediated NF-κB and MAPK signalling pathways. Thus, LRRC19 may be a critical pathogen-recognition receptor in kidney mediating the elimination of UPEC infection.