N 6-Methyladenosine (m6A) is the most abundant RNA modification in mammal mRNAs and increasing evidence suggests the key roles of m6A in human tumorigenesis. However, whether m6A, especially its ‘reader’ YTHDF1, targets a gene involving in protein translation and thus affects overall protein production in cancer cells is largely unexplored. Here, using multi-omics analysis for ovarian cancer, we identified a novel mechanism involving EIF3C, a subunit of the protein translation initiation factor EIF3, as the direct target of the YTHDF1. YTHDF1 augments the translation of EIF3C in an m6A-dependent manner by binding to m6A-modified EIF3C mRNA and concomitantly promotes the overall translational output, thereby facilitating tumorigenesis and metastasis of ovarian cancer. YTHDF1 is frequently amplified in ovarian cancer and up-regulation of YTHDF1 is associated with the adverse prognosis of ovarian cancer patients. Furthermore, the protein but not the RNA abundance of EIF3C is increased in ovarian cancer and positively correlates with the protein expression of YTHDF1 in ovarian cancer patients, suggesting modification of EIF3C mRNA is more relevant to its role in cancer. Collectively, we identify the novel YTHDF1-EIF3C axis critical for ovarian cancer progression which can serve as a target to develop therapeutics for cancer treatment.

N 6-methyladenosine (m 6 A) 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 N6-methyladenosine RNA binding protein 1 (YTHDF1), a key regulator of m 6 A methylation in gastric cancer (GC) tumorigenesis. Multiple bioinformatic analyses of different human cancer databases identified key m 6 A-associated genetic mutations that regulated gastric tumorigenesis. YTHDF1 was mutated in about 7% of gastric cancer patients and high expression of YTHDF1 was associated with more aggressive tumor progression and poor overall survival. Inhibition of YTHDF1 attenuated GC cell proliferation and tumorigenesis in vitro and in vivo. Mechanistically, YTHDF1 promoted the translation of a key Wnt receptor frizzled7 (FZD7) in an m 6 A-dependent manner, and mutated YTHDF1 enhanced expression of FZD7, leading to hyper-activation of the Wnt/β-catenin pathway and promotion of gastric carcinogenesis. Our results demonstrate the oncogenic role of YTHDF1 and its m 6 A-mediated regulation of Wnt/β-catenin signaling in gastric cancer, providing a novel approach of targeting such epigenetic regulators in this disease. Research.

Strand-selection is the final step of microRNA biogenesis in which functional mature miRNAs are generated from one or both arms of precursor. The preference of strand-selection is diverse during development and tissue formation, however, its pathological effect is still unknown. Here we find that two miRNA arms from the same precursor, miR-574-5p and miR-574-3p, are inversely expressed and play exactly opposite roles in gastric cancer progression. Higher-5p with lower-3p expression pattern is significantly correlated with higher TNM stages and poor prognosis of gastric cancer patients. The increase of miR-574-5p/-3p ratio, named miR-574 arm-imbalance is partially due to the dynamic expression of their highly complementary targets in gastric carcinogenesis, moreover, the arm-imbalance of miR-574 is in turn involved and further promotes gastric cancer progression. Our results indicate that miR-574 arm-imbalance contribute to gastric cancer progression and re-modification of the miR-574-targets homeostasis may represent a promising strategy for gastric cancer therapy.

MicroRNA (miRNA) biogenesis is finely controlled by complex layers of post-transcriptional regulators, including RNA-binding proteins (RBPs). Here, we show that an RBP, QKI5, activates the processing of primary miR-124-1 (pri-124-1) during erythropoiesis. QKI5 recognizes a distal QKI response element and recruits Microprocessor through interaction with DGCR8. Furthermore, the recruited Microprocessor is brought to pri-124-1 stem loops by a spatial RNA-RNA interaction between two complementary sequences. Thus, mutations disrupting their base-pairing affect the strength of QKI5 activation. When erythropoiesis proceeds, the concomitant decrease of QKI5 releases Microprocessor from pri-124-1 and reduces mature miR-124 levels to facilitate erythrocyte maturation. Mechanistically, miR-124 targets TAL1 and c-MYB, two transcription factors involved in normal erythropoiesis. Importantly, this QKI5-mediated regulation also gives rise to a unique miRNA signature, which is required for erythroid differentiation. Taken together, these results demonstrate the pivotal role of QKI5 in primary miRNA processing during erythropoiesis and provide new insights into how a distal element on primary transcripts affects miRNA biogenesis.

Alternative pre-mRNA splicing is a key mechanism for increasing proteomic diversity and modulating gene expression. Emerging evidence indicated that the splicing program is frequently dysregulated during tumorigenesis. Cancer cells produce protein isoforms that can promote growth and survival. The RNA-binding protein QKI5 is a critical regulator of alternative splicing in expanding lists of primary human tumors and tumor cell lines. However, its biological role and regulatory mechanism are poorly defined in gastric cancer (GC) development and progression. In this study, we demonstrated that the downregulation of QKI5 was associated with pTNM stage and pM state of GC patients. Re-introduction of QKI5 could inhibit GC cell proliferation, migration, and invasion in vitro and in vivo, which might be due to the altered splicing pattern of macroH2A1 pre-mRNA, leading to the accumulation of macroH2A1.1 isoform. Furthermore, QKI5 could inhibit cyclin L1 expression via promoting macroH2A1.1 production. Thus, this study identified a novel regulatory axis involved in gastric tumorigenesis and provided a new strategy for GC therapy.

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N6‐methyladenosine (m6A) modulators decide the fate of m6A‐modified transcripts and drive cancer development. RNA interference targeting m6A modulators promise to be an emerging cancer therapy but is challenging due to its poor tumor targeting and high systematic toxicity. Here engineered small extracellular vesicles (sEVs) with high CD47 expression and cyclic arginine–glycine–aspartic (c(RGDyC)) modification are developed for effective delivery of short interfering RNA against m6A reader YTH N6‐methyladenosine RNA binding protein 1 (YTHDF1) to treat gastric cancer via epigenetic and immune regulation. This nanosystem efficiently depletes YTHDF1 expression and suppresses gastric cancer progression and metastasis through hampering frizzled7 translation and inactivating Wnt/β‐catenin pathway in an m6A dependent manner. Loss of YTHDF1 mediates overexpression of interferon (IFN)‐γ receptor 1 and enhances IFN‐γ response, promoting expression of major histocompatibility complex class I on tumor cells to achieve self‐presentation of the immunogenic tumor cells to stimulate strong cytotoxic T lymphocytes responses. CD47 expression on the engineered sEVs can competitively bind with signal regulatory protein α to enhance phagocytosis of the tumor cells by tumor‐associated macrophages. This versatile nanoplatform provides an efficient and low toxic strategy to inhibit epigenetic regulators and holds great potential in promoting immunotherapy.

In article number 2204910, Jia Yu, Yanlian Yang, Ling Zhu, and co-workers report an extracellular-vesicle-based nanodrug for the targeting delivery of short interfering RNA (siRNA) against N6-methyladenosine (m 6 A) reader YTH N6-methyladenosine RNA binding protein 1 (YTHDF1) for the epigenetic and immune regulation of gastric cancer. This versatile nanoplatform provides an efficient and low toxic strategy to inhibit epigenetic regulators and holds great potential in promoting immunotherapy.