METTL3 preferentially enhances non-m6A translation of epigenetic factors and promotes tumourigenesis.

METTL3 encodes the predominant catalytic enzyme to promote m6A methylation in nucleus. Recently, accumulating evidence has shown the expression of METTL3 in cytoplasm, but its function is not fully understood. Here we demonstrated an m6A-independent mechanism for METTL3 to promote tumour progression. In gastric cancer, METTL3 could not only facilitate cancer progression via m6A modification, but also bind to numerous non-m6A-modified mRNAs, suggesting an unexpected role of METTL3. Mechanistically, cytoplasm-anchored METTL3 interacted with PABPC1 to stabilize its association with cap-binding complex eIF4F, which preferentially promoted the translation of epigenetic factors without m6A modification. Clinical investigation showed that cytoplasmic distributed METTL3 was highly correlated with gastric cancer progression, and this finding could be expanded to prostate cancer. Therefore, the cytoplasmic METTL3 enhances the translation of epigenetic mRNAs, thus serving as an oncogenic driver in cancer progression, and METTL3 subcellular distribution can assist diagnosis and predict prognosis for patients with cancer.

YTHDF1 Promotes Gastric Carcinogenesis by Controlling Translation of FZD7.

N6-methyladenosine (m6A) is the most prevalent internal RNA modification in mammals that regulates homeostasis and function of modified RNA transcripts. Here, we aimed to investigate the role of YTH m6A RNA-binding protein 1 (YTHDF1), a key regulator of m6A methylation in gastric cancer tumorigenesis. Multiple bioinformatic analyses of different human cancer databases identified key m6A-associated genetic mutations that regulated gastric tumorigenesis. YTHDF1 was mutated in about 7% of patients with gastric cancer, and high expression of YTHDF1 was associated with more aggressive tumor progression and poor overall survival. Inhibition of YTHDF1 attenuated gastric cancer cell proliferation and tumorigenesis in vitro and in vivo. Mechanistically, YTHDF1 promoted the translation of a key Wnt receptor frizzled7 (FZD7) in an m6A-dependent manner, and mutated YTHDF1 enhanced expression of FZD7, leading to hyperactivation of the Wnt/ß-catenin pathway and promotion of gastric carcinogenesis. Our results demonstrate the oncogenic role of YTHDF1 and its m6A-mediated regulation of Wnt/ß-catenin signaling in gastric cancer, providing a novel approach of targeting such epigenetic regulators in this disease. SIGNIFICANCE: This study provides a rationale for controlling translation of key oncogenic drivers in cancer by manipulating epigenetic regulators, representing a novel and efficient strategy for anticancer treatment. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/10/2651/F1.large.jpg.

MiRNA-221-3p desensitizes pancreatic cancer cells to 5-fluorouracil by targeting RB1.

Pancreatic cancer is a highly lethal disease due to its rapid dissemination and resistance to conventional chemotherapy. MicroRNAs (miRNAs) are emerging as novel regulators of chemoresistance, which modulate the expression of drug resistance-related genes. MiRNA-221 has been reported to be associated with chemoresistance in various types of cancer. But the detailed molecular mechanism about miR-221-3p regulating 5-fluorouracil (5-FU) resistance in human pancreatic cancer remains to be clarified. In this study, we investigated the association between miR-221-3p expression and 5-FU sensitivity. Studies on pancreatic cancer cell lines suggested an increased 5-FU resistance with miR-221-3p over-expression. In addition, the results indicated that miR-221-3p down-regulated RB1 expression by directly binding to its 3'-UTR and therefore caused increased several aspects of pancreatic cancer pathogenesis, including proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT). Collectively, our findings revealed the important role of miR-221-3p in promoting 5-FU resistance of pancreatic cancer cells and provided a potential therapeutic target for pancreatic cancer.

MicroRNA-320a promotes 5-FU resistance in human pancreatic cancer cells.

The drug-resistance of pancreatic cancer cells results in poor therapeutic effect. To predict the therapeutic effect of the chemotherapy drugs to specific patients and to reverse the resistance of pancreatic cancer cells are critical for chemotherapy of pancreatic cancer. MicroRNAs (miRNAs) have been reported to play important roles in the genesis of drug-resistance of various cancer types. There are also many advantages of miRNAs in diagnosis and therapy of disease. Although several miRNAs regulating 5-Fluorouracil (5-FU) resistance in human pancreatic cancer have been reported, the detailed molecular mechanism remains to be determined. In this study, we found that miR-320a was significantly up-regulated in 5-FU resistant pancreatic cancer cells. Over-expression of miR-320a strongly contributed to pathogenesis of pancreatic cancer, which was represented by the increased proliferation, invasion, metastasis, drug-resistance characteristics and the epithelial-to-mesenchymal transition. Furthermore, we demonstrated that miR-320a was able to bind to 3'UTR of PDCD4 mRNA, and mediated its down-regulation in 5-FU resistance of human pancreatic cancer cells. Whereas restoration of PDCD4 expression could partially attenuate the function of miR-320a in pancreatic cancer. Taken together, our study demonstrated that miR-320a played important role in regulating 5-FU resistance by targeting PDCD4 and might be developed as new therapeutic target for pancreatic cancer.

MicroRNA-21 induces 5-fluorouracil resistance in human pancreatic cancer cells by regulating PTEN and PDCD4.

Pancreatic cancer patients are often resistant to chemotherapy treatment, which results in poor prognosis. The objective of this study was to delineate the mechanism by which miR-21 induces drug resistance to 5-fluorouracil (5-FU) in human pancreatic cancer cells (PATU8988 and PANC-1). We report that PATU8988 cells resistant to 5-FU express high levels of miR-21 in comparison to sensitive primary PATU8988 cells. Suppression of miR-21 expression in 5-Fu-resistant PATU8988 cells can alleviate its 5-FU resistance. Meanwhile, lentiviral vector-mediated overexpression of miR-21 not only conferred resistance to 5-FU but also promoted proliferation, migration, and invasion of PATU8988 and PANC-1 cells. The proresistance effects of miR-21 were attributed to the attenuated expression of tumor suppressor genes, including PTEN and PDCD4. Overexpression of PTEN and PDCD4 antagonized miR-21-induced resistance to 5-FU and migration activity. Our work demonstrates that miR-21 can confer drug resistance to 5-FU in pancreatic cancer cells by regulating the expression of tumor suppressor genes, as the target genes of miR-21, PTEN and PDCD4 can rescue 5-FU sensitivity and the phenotypic characteristics disrupted by miR-21.

Functional screen reveals essential roles of miR-27a/24 in differentiation of embryonic stem cells.

MicroRNAs play important roles in controlling the embryonic stem cell (ESC) state. Although much is known about microRNAs maintaining ESC state, microRNAs that are responsible for promoting ESC differentiation are less reported. Here, by screening 40 microRNAs pre-selected by their expression patterns and predicted targets in Dgcr8-null ESCs, we identify 14 novel differentiation-associated microRNAs. Among them, miR-27a and miR-24, restrained by c-Myc in ESC, exert their roles of silencing self-renewal through directly targeting several important pluripotency-associated factors, such as Oct4, Foxo1 and Smads. CRISPR/Cas9-mediated knockout of all miR-27/24 in ESCs leads to serious deficiency in ESC differentiation in vitro and in vivo. Moreover, depleting of them in mouse embryonic fibroblasts can evidently promote somatic cell reprogramming. Altogether, our findings uncover the essential role of miR-27 and miR-24 in ESC differentiation and also demonstrate novel microRNAs responsible for ESC differentiation.

The up-regulation of miR-199b-5p in erythroid differentiation is associated with GATA-1 and NF-E2.

MicroRNAs (miRNAs) represent a class of small non-coding regulatory RNAs that play important roles in normal hematopoiesis, including erythropoiesis. Although studies have identified several miRNAs that regulate erythroid commitment and differentiation, we do not understand the mechanism by which the crucial erythroid transcription factors, GATA-1and NF-E2 directly regulate and control differentiation via miRNA pathways. In this study, we identified miR-199b-5p as a key regulator of human erythropoiesis, and its expression was up-regulated during the erythroid differentiation of K562 cells. Furthermore, the increase of miR-199b-5p in erythroid cells occurred in a GATA-1- and NF-E2-dependent manner during erythrocyte maturation. Both GATA-1 and NF-E2 bound upstream of the miR-199b gene locus and activated its transcription. Forced expression of miRNA-199b-5p in K562 cells affected erythroid cell proliferation and maturation. Moreover, we identified c-Kit as a direct target of miR-199b-5p in erythroid cells. Taken together, our results establish a functional link among the erythroid transcription factors GATA-1/NF-E2, miR-199b-5p and c-Kit, and provide new insights into the coupling of transcription and post-transcription regulation in erythroid differentiation.