N6-methyladenosine (m6A) is a reversible mRNA modification that has been shown to play important roles in various biological processes. However, the roles of m6A modification in macrophages are still unknown. Here, we discover that ablation of Mettl3 in myeloid cells promotes tumour growth and metastasis in vivo. In contrast to wild-type mice, Mettl3-deficient mice show increased M1/M2-like tumour-associated macrophage and regulatory T cell infiltration into tumours. m6A sequencing reveals that loss of METTL3 impairs the YTHDF1-mediated translation of SPRED2, which enhances the activation of NF-kB and STAT3 through the ERK pathway, leading to increased tumour growth and metastasis. Furthermore, the therapeutic efficacy of PD-1 checkpoint blockade is attenuated in Mettl3-deficient mice, identifying METTL3 as a potential therapeutic target for tumour immunotherapy.

Circular RNAs (circRNAs) are novel clusters of endogenous noncoding RNAs (ncRNAs) that are widely expressed in eukaryotic cells. In contrast to the generation of linear RNA transcripts, circRNAs undergo a “back-splicing” process to form a continuous, covalently closed, stable loop structure without 5ʹ or 3ʹ polarities and poly (A) tails during posttranscriptional modification. Due to the widespread availability of several technologies, especially high-throughput RNA sequencing, numerous circRNAs have been discovered not only in mammals but also in plants and insects. Notably, due to their abilities to serve as microRNA (miRNA) “sponges”, miRNA “reservoirs”, regulate gene expression and encode proteins, circRNAs participate in the development and progression of different immune responses and immune diseases by enriching various forms of epigenetic modification. CircRNAs have been demonstrated to be expressed in a tissue-specific and pathogenesis-related manner during the occurrence of multiple immune diseases. Additionally, because of their circular configurations, expression in blood and peripheral tissues and coexistence with exosomes, circRNAs show inherent conservation along with environmental resistance stability and may be regarded as potential biomarkers or therapeutic targets for some immune diseases. In this review, we summarize the characteristics, functions and mechanisms of circRNAs and their involvement in immune responses and diseases. Although our knowledge of circRNAs remains preliminary, this field is worthy of deeper exploration and greater research efforts.

Resistance to trastuzumab and concomitantly distal metastasis are leading causes of mortality in HER2‐positive breast cancers, the molecular basis of which remains largely unknown. Here, we generated trastuzumab‐resistant breast cancer cells with increased tumorigenicity and invasiveness compared with parental cells, and observed robust epithelial–mesenchymal transition (EMT) and consistently elevated TGF‐β signaling in these cells. MiR‐200c, which was the most significantly downregulated miRNA in trastuzumab‐resistant cells, restored trastuzumab sensitivity and suppressed invasion of breast cancer cells by concurrently targeting ZNF217, a transcriptional activator of TGF‐β, and ZEB1, a known mediator of TGF‐β signaling. Given the reported backward inhibition of miR‐200c by ZEB1, ZNF217 also exerts a feedback suppression of miR‐200c via TGF‐β/ZEB1 signaling. Restoration of miR‐200c, silencing of ZEB1 or ZNF217 or blockade of TGF‐β signaling increased trastuzumab sensitivity and suppressed invasiveness of breast cancer cells. Therefore, our study unraveled nested regulatory circuits of miR‐200c/ZEB1 and miR‐200c/ZNF217/TGF‐β/ZEB1 in synergistically promoting trastuzumab resistance and metastasis of breast cancer cells. These findings provide novel insights into the common role of EMT and related molecular machinery in mediating the malignant phenotypes of breast cancers.

Glioma, characterized by its undesirable prognosis and poor survival rate, is a serious threat to human health and lives. MicroRNA-9 (miR-9) is implicated in the regulation of multiple tumors, while the mechanisms underlying its aberrant expression and functional alterations in human glioma are still controversial. Expressions of miR-9 were measured in GEO database, patient specimens and glioma cell lines. Gain- and loss-of-function assays were applied to identify the effects of miR-9 on glioma cells and HUVECs in vitro and in vivo. Potential targets of miR-9 were predicted by bioinformatics and further verified via in vitro experiments. Transcriptional regulation of miR-9 by MYC and OCT4 was determined in glioma cells. MiR-9 was frequently up-regulated in glioma specimens and cells, and could significantly enhance proliferation, migration and invasion of glioma cells. In addition, miR-9 could be secreted from glioma cells via exosomes and was then absorbed by vascular endothelial cells, leading to an increase in angiogenesis. COL18A1, THBS2, PTCH1 and PHD3 were verified as the direct targets of miR-9, which could elucidate the miR-9-induced malignant phenotypes in glioma cells. MYC and OCT4 were able to bind to the promoter region of miR-9 to trigger its transcription. Our results highlight that miR-9 is pivotal for glioma pathogenesis and can be treated as a potential therapeutic target for glioma.

The MYC oncogene is overexpressed in hepatocellular carcinoma (HCC) and has been associated with widespread microRNA (miRNA) repression; however, the underlying mechanisms are largely unknown. Here, we report that the c-Myc oncogenic transcription factor physically interacts with enhancer of zeste homolog 2 (EZH2), a core enzymatic unit of polycomb repressive complex 2 (PRC2). Furthermore, miR-101, an important tumor-suppressive miRNA in human hepatocarcinomas, is epigenetically repressed by PRC2 complex in a c-Myc-mediated manner. miR-101, in turn, inhibits the expression of two subunits of PRC2 ( EZH2 and EED ), thus creating a double-negative feedback loop that regulates the process of hepatocarcinogenesis. Restoration of miR-101 expression suppresses multiple malignant phenotypes of HCC cells by coordinate repression of a cohort of oncogenes, including STMN1 , JUNB , and CXCR7 , and further increases expression of endogenous miR-101 by inhibition of PRC2 activation. In addition, co-overexpression of c-Myc and EZH2 in HCC samples was closely associated with lower expression of miR-101 ( P < 0.0001) and poorer prognosis of HCC patients ( P < 0.01). Conclusions : c-Myc collaborates with EZH2-containing PRC2 complex in silencing tumor-suppressive miRNAs during hepatocarcinogenesis and provides promising therapeutic candidates for human HCC. (Hepatology 2014;59:1850–1863)

Psoriasis is a chronic inflammatory skin disease that severely affects patients physiologically and psychologically. The pathogenesis involving communication between psoriatic keratinocytes and infiltrated immune cells such as neutrophils remains unclear. Exosomes are emerging mediators of intercellular communication. Herein we aim to investigate the release and function of psoriatic keratinocyte exosomes, which have not been illustrated to any extent. We first isolated exosomes from both healthy and psoriasis‐like keratinocytes treated with psoriatic cytokine cocktail. These exosomes were observed to be endocytosed by neutrophils. Unlike non‐cytokine‐treated keratinocyte exosomes, cytokine‐treated keratinocyte exosomes significantly induced NETosis (the process by which neutrophils produce and release neutrophil extracellular traps) and the expressions of IL‐6, IL‐8, and TNF‐α in neutrophils. Proteomic analysis showed that cytokine‐treated keratinocyte exosomes exhibited a specific protein profile with proteins enriched in immune‐related pathways. We then confirmed that NF‐κB and p38 MAPK signaling pathways were activated in neutrophils stimulated by cytokine‐treated keratinocyte exosomes and were responsible for the expressions of proinflammatory factors mentioned above. Finally, we verified in vivo that cytokine‐treated keratinocyte exosomes participated in the skin lesion development of imiquimod‐induced psoriasis‐like mouse model. Collectively, we reveal that the release of exosomes works as a way of keratinocyte‐neutrophil communication, indicating that keratinocyte exosomes, with their specific cargoes, are therapeutic candidates for psoriasis.—Jiang, M., Fang, H., Shao, S., Dang, E., Zhang, J., Qiao, P., Yang, A., Wang, G. Keratinocyte exosomes activate neutrophils and enhance skin inflammation in psoriasis. FASEB J. 33, 13241–13253 (2019). www.fasebj.org