Hypoxia induces hepatocellular carcinoma metastasis via the HIF-1α/METTL16/lnc-CSMD1-7/RBFOX2 axis

RNA methyltransferase METTL16: from molecular mechanisms to therapeutic prospects in cancers

Methyltransferase-like 16 (METTL16) plays a critical role in epigenetic regulation, particularly through RNA methylation. As a key RNA methyltransferase, METTL16 catalyzes the addition of N6-methyladenosine modifications to RNA molecules, which are essential for the regulation of RNA stability, post-transcriptional modifications, and translation efficiency. This, in turn, links METTL16-mediated gene expression to various diseases. Notably, METTL16 has dual regulatory effects on tumors, with its influence varying according to the specific cancer type. Furthermore, METTL16 expression and activity are tightly controlled through multiple layers, including transcriptional regulation, epigenetic modifications (such as DNA methylation and histone modifications), and signaling pathways associated with hypoxia, particularly hypoxia-inducible factors. These regulatory networks collectively govern METTL16's function, impacting tumor progression, development, and drug resistance. Targeting METTL16 with small molecule inhibitors or activators offers a promising therapeutic strategy for cancer treatment. The potential of METTL16 as a therapeutic target is further enhanced when combined with other treatment modalities. Future research should aim to elucidate the specific pathophysiological mechanisms of METTL16 across various cancer types, evaluate its therapeutic potential, and develop compounds capable of inhibiting or activating METTL16. This review consolidates the current understanding of METTL16, emphasizing its expression patterns, functional roles, regulatory mechanisms, and therapeutic prospects in cancers.

Emerging importance of m6A modification in liver cancer and its potential therapeutic role

Liver cancer refers to malignant tumors that form in the liver and is usually divided into several types, the most common of which is hepatocellular carcinoma (HCC), which originates in liver cells. Other rare types of liver cancer include intrahepatic cholangiocarcinoma (iCCA). m6A modification is a chemical modification of RNA that usually manifests as the addition of a methyl group to adenine in the RNA molecule to form N6-methyladenosine. This modification exerts a critical role in various biological processes by regulating the metabolism of RNA, affecting gene expression. Recent studies have shown that m6A modification is closely related to the occurrence and development of liver cancer, and m6A regulators can further participate in the pathogenesis of liver cancer by regulating the expression of key genes and the function of specific cells. In this review, we provided an overview of the latest advances in m6A modification in liver cancer research and explored in detail the specific functions of different m6A regulators. Meanwhile, we deeply analyzed the mechanisms and roles of m6A modification in liver cancer, aiming to provide novel insights and references for the search for potential therapeutic targets. Finally, we discussed the prospects and challenges of targeting m6A regulators in liver cancer therapy.

The Mechanism and Latest Progress of m6A Methylation in the Progression of Pancreatic Cancer

Pancreatic cancer (PC), known as the "king of cancers," is characterized by an exceptionally low five-year survival rate, posing a formidable challenge to global public health. N6-methyladenosine (m6A) methylation is prevalent across various stages of eukaryotic RNA expression, including splicing, maturation, stability, translation, and localization, and represents a pivotal mechanism of epigenetic regulation. m6A methylation influences tumor initiation and progression by modulating post-transcriptional processes, playing a critical role in sustaining cancer cell stemness, promoting cell proliferation, and mediating drug resistance. Extensive research underscores the substantial contribution of m6A modifications to PC development. However, the multiplicity of m6A regulators and their intricate mechanisms of action complicate the landscape. This review aims to deepen the understanding of m6A's role in PC by delineating its involvement in four key areas of tumorigenesis: the hypoxic tumor microenvironment, metabolic reprogramming, immune microenvironment, and resistance mechanisms. Additionally, the review addresses the emerging frontier of m6A interactions with non-coding RNAs (ncRNAs), offering insights into the potential therapeutic and prognostic applications of m6A in the treatment and prognosis prediction of PC.

The promoting effect of the POU3F2/METTL16/PFKM cascade on glycolysis and tumorigenesis of hepatocellular carcinoma

INTRODUCTION AND OBJECTIVES

Deregulation of m6A methylation, the most prevailing RNA modification, participates in cancer pathogenesis. METTL16, an atypical methyltransferase, functions as a pro-tumorigenic factor in hepatocellular carcinoma (HCC). Here, we explored the action of METTL16 on HCC glycolysis and the associated mechanism.

MATERIALS AND METHODS

Expression analysis was done by quantitative PCR, immunoblotting, or immunohistochemistry. Cell sphere formation, invasiveness, apoptosis, proliferation and viability were detected by sphere formation, transwell, flow cytometry, EdU and CCK-8 assays, respectively. Xenograft studies were performed to analyze the role in vivo. Methylated RNA immunoprecipitation (MeRIP) and RIP assays were used to verify the METTL16/PFKM relationship. PFKM mRNA stability was tested by actinomycin D treatment. Chromatin immunoprecipitation (ChIP) and luciferase assays were performed to analyze the POU3F2/METTL16 relationship.

RESULTS

In HCC, METTL16 expression was elevated, and increased levels of METTL16 transcript predicted poor HCC prognosis. METTL16 deficiency resulted in suppressed HCC cell growth, invasiveness and sphere formation. Moreover, METTL16 depletion diminished HCC cell glycolysis. Mechanistically, PFKM expression was positively associated with METTL16 expression. METTL16 mediated m6A methylation to stabilize PFKM mRNA via an IGF2BP3-dependent manner. Restored PFKM expression exerted a counteracting effect on METTL16 deficiency-mediated in vitro cell phenotype alterations and in vivo xenograft growth suppression. Furthermore, POU3F2 promoted the transcription of METTL16 in HCC cells.

CONCLUSIONS

Our findings define the crucial role of the POU3F2/METTL16/PFKM axis in HCC pathogenesis, offering the potential opportunity to combat HCC.

RBFOX2 as a regulatory linchpin in cancer: insights from a comprehensive review of its roles in tumorigenesis

RNA-binding proteins (RBPs) are essential regulators of RNA expression during both transcriptional and post-transcriptional processes. Recent evidence indicates that dysregulation of RBPs is associated with cancer initiation and progression. Among these, RBFOX2 has been identified as exhibiting variable expression patterns across different cancers and is implicated in various malignant processes, including tumor growth, metastasis, ferroptosis, stemness, and chemoresistance. Despite these findings, the precise mechanisms by which RBFOX2 contributes to carcinogenesis remain largely unexplored. In this comprehensive review, we systematically examine the multifaceted functions of RBFOX2 in tumorigenesis, with a particular focus on its roles in alternative splicing, mRNA stability, and microRNA processing. Upon elucidating the specific roles of RBFOX2 in various cancers, targeted drugs can be devised to inhibit cancer development. Furthermore, we evaluate the specific roles of RBFOX2 in various cancer types, including pancreatic ductal adenocarcinoma, myeloid leukemia, and nasopharyngeal carcinoma. By providing an in-depth analysis, we aim to establish RBFOX2 as a potential diagnostic and therapeutic target in cancer biology and treatment, thereby offering new insights for future research.

METTL16-SENP3-LTF axis confers ferroptosis resistance and facilitates tumorigenesis in hepatocellular carcinoma

BACKGROUND

Ferroptosis, characterized by iron-dependent lipid peroxidation, emerges as a promising avenue for hepatocellular carcinoma (HCC) intervention due to its tumor susceptibility. RNA N6-methyladenosine (m6A) modification has been involved in several types of regulated cell death. However, the roles and molecular mechanisms of m6A-related regulators in HCC cell ferroptosis remain unclear.

METHODS

By examining a series of m6A modification enzymes upon ferroptosis induction or inhibition, we identified METTL16 as a novel ferroptotic repressor in HCC cells. The roles of METTL16 on ferroptosis and HCC development were investigated in multiple cell lines, human HCC organoids, subcutaneous xenografts and MYC/Trp53-/- HCC model in hepatocyte-specific Mettl16 knockout and overexpression mice. The underlying mechanism was elucidated with MeRIP/RIP-qPCR, luciferase assay, Co-IP assay and Mass Spectrometry. The clinical significance and relevance were evaluated in human samples.

RESULTS

High METTL16 expression confers ferroptosis resistance in HCC cells and mouse models, and promotes cell viability and tumor progression. Mechanistically, METTL16 collaborates with IGF2BP2 to modulate SENP3 mRNA stability in an m6A-dependent manner, and the latter impedes the proteasome-mediated ubiquitination degradation of Lactotransferrin (LTF) via de-SUMOylation. Elevated LTF expression facilitates the chelation of free iron and reduces liable iron pool level. SENP3 and LTF are implicated in METTL16-mediated HCC progression and anti-ferroptotic effects both in vivo and in vitro. Clinically, METTL16 and SENP3 expression were positively correlated, and high METTL16 and SENP3 expression predicts poor prognosis in human HCC samples.

CONCLUSIONS

Our study reveals a new METTL16-SENP3-LTF signaling axis regulating ferroptosis and driving HCC development. Targeting this axis is a promising strategy for sensitizing ferroptosis and against HCC.

Hypoxia as a Target for Combination with Transarterial Chemoembolization in Hepatocellular Carcinoma

Hypoxia is a hallmark of solid tumors, including hepatocellular carcinoma (HCC). Hypoxia has proven to be involved in multiple tumor biological processes and associated with malignant progression and resistance to therapy. Transarterial chemoembolization (TACE) is a well-established locoregional therapy for patients with unresectable HCC. However, TACE-induced hypoxia regulates tumor angiogenesis, energy metabolism, epithelial-mesenchymal transition (EMT), and immune processes through hypoxia-inducible factor 1 (HIF-1), which may have adverse effects on the therapeutic efficacy of TACE. Hypoxia has emerged as a promising target for combination with TACE in the treatment of HCC. This review summarizes the impact of hypoxia on HCC tumor biology and the adverse effects of TACE-induced hypoxia on its therapeutic efficacy, highlighting the therapeutic potential of hypoxia-targeted therapy in combination with TACE for HCC.

The crosstalk between cellular survival pressures and N6-methyladenosine modification in hepatocellular carcinoma

BACKGROUND

Within the tumor microenvironment, survival pressures are prevalent with potent drivers of tumor progression, angiogenesis, and therapeutic resistance. N6-methyladenosine (m6A) methylation has been recognized as a critical post-transcriptional mechanism regulating various aspects of mRNA metabolism. Understanding the intricate interplay between survival pressures and m6A modification provides new insights into the molecular mechanisms underlying hepatocellular carcinoma (HCC) progression and highlights the potential for targeting the survival pressures-m6A axis in HCC diagnosis and treatment.

DATA SOURCES

A literature search was conducted in PubMed, MEDLINE, and Web of Science for relevant articles published up to April 2024. The keywords used for the search included hepatocellular carcinoma, cellular survival, survival pressure, N6-methyladenosine, tumor microenvironment, stress response, and hypoxia.

RESULTS

This review delves into the multifaceted roles of survival pressures and m6A RNA methylation in HCC, highlighting how survival pressures modulate the m6A landscape, the impact of m6A modification on survival pressure-responsive gene expression, and the consequent effects on HCC cell survival, proliferation, metastasis, and resistance to treatment. Furthermore, we explored the therapeutic potential of targeting this crosstalk, proposing strategies that leverage the understanding of survival pressures and m6A RNA methylation mechanisms to develop novel, and more effective treatments for HCC.

CONCLUSIONS

The interplay between survival pressures and m6A RNA methylation emerges as a complex regulatory network that influences HCC pathogenesis and progression.

CX3CL1 (Fractalkine)-CX3CR1 Axis in Inflammation-Induced Angiogenesis and Tumorigenesis

The chemotactic cytokine fractalkine (FKN, chemokine CX3CL1) has unique properties resulting from the combination of chemoattractants and adhesion molecules. The soluble form (sFKN) has chemotactic properties and strongly attracts T cells and monocytes. The membrane-bound form (mFKN) facilitates diapedesis and is responsible for cell-to-cell adhesion, especially by promoting the strong adhesion of leukocytes (monocytes) to activated endothelial cells with the subsequent formation of an extracellular matrix and angiogenesis. FKN signaling occurs via CX3CR1, which is the only known member of the CX3C chemokine receptor subfamily. Signaling within the FKN-CX3CR1 axis plays an important role in many processes related to inflammation and the immune response, which often occur simultaneously and overlap. FKN is strongly upregulated by hypoxia and/or inflammation-induced inflammatory cytokine release, and it may act locally as a key angiogenic factor in the highly hypoxic tumor microenvironment. The importance of the FKN/CX3CR1 signaling pathway in tumorigenesis and cancer metastasis results from its influence on cell adhesion, apoptosis, and cell migration. This review presents the role of the FKN signaling pathway in the context of angiogenesis in inflammation and cancer. The mechanisms determining the pro- or anti-tumor effects are presented, which are the cause of the seemingly contradictory results that create confusion regarding the therapeutic goals.