YTHDF1 Facilitates the Progression of Hepatocellular Carcinoma by Promoting FZD5 mRNA Translation in an m6A-Dependent Manner

Main N6-Methyladenosine Readers: YTH Family Proteins in Cancers

Among the over 150 RNA modifications, N6-methyladenosine (m6A) is the most abundant internal modification in eukaryotic RNAs, not only in messenger RNAs, but also in microRNAs and long non-coding RNAs. It is a dynamic and reversible process in mammalian cells, which is installed by “writers,” consisting of METTL3, METTL14, WTAP, RBM15/15B, and KIAA1429 and removed by “erasers,” including FTO and ALKBH5. Moreover, m6A modification is recognized by “readers,” which play the key role in executing m6A functions. IYT521-B homology (YTH) family proteins are the first identified m6A reader proteins. They were reported to participate in cancer tumorigenesis and development through regulating the metabolism of targeted RNAs, including RNA splicing, RNA export, translation, and degradation. There are many reviews about function of m6A and its role in various diseases. However, reviews only focusing on m6A readers, especially YTH family proteins are few. In this review, we systematically summarize the recent advances in structure and biological function of YTH family proteins, and their roles in human cancer and potential application in cancer therapy.

The m6A Reader YTHDF1 Facilitates the Tumorigenesis and Metastasis of Gastric Cancer via USP14 Translation in an m6A-Dependent Manner

Objectives

N⁶-methyladenosine (m⁶A) RNA methylation is implicated in the progression of multiple cancers via influencing mRNA modification. YTHDF1 can act as an oncogene in gastric cancer (GC), while the biological mechanisms via which YTHDF1 regulates gastric tumorigenesis through m⁶A modification remain largely unknown.

Methods

GEO and TCGA cohorts were analyzed for differentially expressed m⁶A modification components in GC clinical specimens and their association with clinical prognosis. Transwell and flow cytometry assays as well as subcutaneous xenograft and lung metastasis models were used to evaluate the phenotype of YTHDF1 in GC. Intersection of RNA/MeRIP-seq, luciferase assay, RIP-PCR, RNA pull-down and MeRIP-PCR was used to identify YTHDF1- modified USP14 and its m⁶A levels in GC cells.

Results

High-expressed YTHDF1 was found in GC tissues and was related to poor prognosis, acting as an independent prognostic factor of poor survival in GC patients. YTHDF1 deficiency inhibited cell proliferation and invasion (in vitro), and gastric tumorigenesis and lung metastasis (in vivo) and also induced cell apoptosis. Intersection assays revealed that YTHDF1 promoted USP14 protein translation in an m⁶A-dependent manner. USP14 upregulation was positively correlated with YTHDF1 expression and indicated a poor prognosis in GC.

Conclusion

Our data suggested that m⁶A reader YTHDF1 facilitated tumorigenesis and metastasis of GC by promoting USP14 protein translation in an m⁶A-dependent manner and might provide a potential target for GC treatment.

Analysis and Validation of circRNA-miRNA Network in Regulating m6A RNA Methylation Modulators Reveals CircMAP2K4/miR-139-5p/YTHDF1 Axis Involving the Proliferation of Hepatocellular Carcinoma

The m⁶A RNA methylation modulators play a crucial role in regulating hepatocellular carcinoma (HCC) progression. The circular RNA (circRNA) regulatory network in regulating m⁶A RNA methylation modulators in HCC remains largely unknown. In this study, 5 prognostic m⁶A RNA methylation modulators in HCC were identified from The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) projects. The differentially expressed microRNAs (DEmiRNAs) and circRNAs (DEcircRNAs) between paired tumor and normal tissues were screened out from TCGA and or Gene Expression Omnibus (GEO) database to construct the circRNA-miRNA- m⁶A RNA methylation modulator regulatory network, which included three m⁶A RNA methylation modulators (HNRNPC, YTHDF1, and YTHDF2), 11 DEmiRNAs, and eight DEcircRNAs. Among the network, hsa-miR-139-5p expression was negatively correlated with YTHDF1. Hsa-miR-139-5p low or YTHDF1 high expression was correlated with high pathological grade, advanced stage and poor survival of HCC. Additionally, cell cycle, base excision repair, and homologous recombination were enriched in YTHDF1 high expression group by GSEA. A hub circRNA regulatory network was constructed based on hsa-miR-139-5p/YTHDF1 axis. Furthermore, hsa_circ_0007456(circMAP2K4) was validated to promote HCC cell proliferation by binding with hsa-miR-139-5p to promote YTHDF1 expression. Taken together, we identified certain circRNA regulatory network related to m⁶A RNA methylation modulators and provided clues for mechanism study and therapeutic targets for HCC.

Dynamic Expression of m6A Regulators During Multiple Human Tissue Development and Cancers

N6-methyladenosine (m⁶A) plays critical roles in human development and cancer progression. However, our knowledge regarding the dynamic expression of m⁶A regulators during human tissue development is still lacking. Here, we comprehensively analyzed the dynamic expression alterations of m⁶A regulators during seven tissue development and eight cancer types. We found that m⁶A regulators globally exhibited decreased expression during development. In addition, IGF2BP1/2/3 (insulinlike growth factor 2 MRNA-binding protein 1/2/3) exhibited reverse expression pattern in cancer progression, suggesting an oncofetal reprogramming in cancer. The expressions of IGF2BP1/2/3 were regulated by genome alterations, particularly copy number amplification in cancer. Clinical association analysis revealed that higher expressions of IGF2BP1/2/3 were associated with worse survival of cancer patients. Finally, we found that genes significantly correlated with IGF2BP1/2/3 were significantly enriched in cancer hallmark-related pathways. In summary, dynamic expression analysis will guide both mechanistic and therapeutic roles of m⁶A regulators during tissue development and cancer progression.

Wnt/β-Catenin Signaling as a Driver of Hepatocellular Carcinoma Progression: An Emphasis on Molecular Pathways

Liver cancers cause a high rate of death worldwide and hepatocellular carcinoma (HCC) is considered as the most common primary liver cancer. HCC remains a challenging disease to treat. Wnt/β-catenin signaling pathway is considered a tumor-promoting factor in various cancers; hence, the present review focused on the role of Wnt signaling in HCC, and its association with progression and therapy response based on pre-clinical and clinical evidence. The nuclear translocation of β-catenin enhances expression level of genes such as c-Myc and MMPs in increasing cancer progression. The mutation of CTNNB1 gene encoding β-catenin and its overexpression can lead to HCC progression. β-catenin signaling enhances cancer stem cell features of HCC and promotes their growth rate. Furthermore, β-catenin prevents apoptosis in HCC cells and increases their migration via triggering EMT and upregulating MMP levels. It is suggested that β-catenin signaling participates in mediating drug resistance and immuno-resistance in HCC. Upstream mediators including ncRNAs can regulate β-catenin signaling in HCC. Anti-cancer agents inhibit β-catenin signaling and mediate its proteasomal degradation in HCC therapy. Furthermore, clinical studies have revealed the role of β-catenin and its gene mutation (CTNBB1) in HCC progression. Based on these subjects, future experiments can focus on developing novel therapeutics targeting Wnt/β-catenin signaling in HCC therapy.