The importance of N6-methyladenosine modification in tumor immunity and immunotherapy

Manipulating the tumour immune microenvironment by N6-methyladenosine RNA modification

N6-methyladenosine (m6A), a posttranscriptional regulatory mechanism, is the most common epigenetic modification in mammalian mRNA. M6A modifications play a crucial role in the developmental network of immune cells. The expression of m6A-related regulators often affects carcinogenesis and tumour suppression networks. In the tumour microenvironment, m6A-modified enzymes can affect the occurrence and progression of tumours by regulating the activation and invasion of tumour-associated immune cells. Immunotherapy, which utilises immune cells, has been demonstrated to be a powerful weapon in tumour treatment and is increasingly being used in the clinic. Here, we provide an updated and comprehensive overview of how m6A modifications affect invasive immune cells and their potential role in immune regulation. In addition, we summarise the regulation of epigenetic regulators associated with m6A modifications in tumour cells on the antitumour response of immune cells in the tumour immune microenvironment. These findings provide new insights into the role of m6A modifications in the immune response and tumour development, leading to the development of novel immunotherapies for cancer treatment.

Identifying subtypes and developing prognostic models based on N6-methyladenosine and immune microenvironment related genes in breast cancer

Breast cancer (BC) is the most prevalent cancer in women globally. The tumor microenvironment (TME), comprising epithelial tumor cells and stromal elements, is vital for breast tumor development. N6-methyladenosine (m6A) modification plays a key role in RNA metabolism, influencing its various aspects such as stability and translation. There is a notable link between m6A methylation and immune cells in the TME, although this relationship is complex and not fully deciphered. In this research, BC expression and clinicopathological data from TCGA were scrutinized to assess expression profiles, mutations, and CNVs of 31 m6A genes and immune microenvironment-related genes, examining their correlations, functions, and prognostic impacts. Lasso and Cox regression identified prognostic genes for constructing a nomogram. Single-cell analyses mapped the distribution and patterns of these genes in BC cell development. We investigated associations between gene-derived risk scores and factors like immune infiltration, TME, checkpoints, TMB, CSC indices, and drug response. As a complement to computational analyses, in vitro experiments were conducted to confirm these expression patterns. We included 31 m6A regulatory genes and discovered a correlation between these genes and the extent of immune cell infiltration. Subsequently, a 7-gene risk score was generated, encompassing HSPA2, TAP1, ULBP2, CXCL1, RBP1, STC2, and FLT3. It was observed that the low-risk group exhibited better overall survival (OS) in BC, with higher immune scores but lower tumor mutational burden (TMB) and cancer stem cell (CSC) indices, as well as lower IC50 values for commonly used drugs. To enhance clinical applicability, age and stage were incorporated into the risk score, and a more comprehensive nomogram was constructed to predict OS. This nomogram was validated and demonstrated good predictive performance, with area under the curve (AUC) values for 1-year, 3-year, and 5-year OS being 0.848, 0.807, and 0.759, respectively. Our findings highlight the profound impact of prognostic-related genes on BC immune response and prognostic outcomes, suggesting that modulation of the m6A-immune pathway could offer new avenues for personalized BC treatment and potentially improve clinical outcomes.

Crosstalk between colorectal CSCs and immune cells in tumorigenesis, and strategies for targeting colorectal CSCs

Cancer immunotherapy has emerged as a promising strategy in the treatment of colorectal cancer, and relapse after tumor immunotherapy has attracted increasing attention. Cancer stem cells (CSCs), a small subset of tumor cells with self-renewal and differentiation capacities, are resistant to traditional therapies such as radiotherapy and chemotherapy. Recently, CSCs have been proven to be the cells driving tumor relapse after immunotherapy. However, the mutual interactions between CSCs and cancer niche immune cells are largely uncharacterized. In this review, we focus on colorectal CSCs, CSC-immune cell interactions and CSC-based immunotherapy. Colorectal CSCs are characterized by robust expression of surface markers such as CD44, CD133 and Lgr5; hyperactivation of stemness-related signaling pathways, such as the Wnt/β-catenin, Hippo/Yap1, Jak/Stat and Notch pathways; and disordered epigenetic modifications, including DNA methylation, histone modification, chromatin remodeling, and noncoding RNA action. Moreover, colorectal CSCs express abnormal levels of immune-related genes such as MHC and immune checkpoint molecules and mutually interact with cancer niche cells in multiple tumorigenesis-related processes, including tumor initiation, maintenance, metastasis and drug resistance. To date, many therapies targeting CSCs have been evaluated, including monoclonal antibodies, antibody‒drug conjugates, bispecific antibodies, tumor vaccines adoptive cell therapy, and small molecule inhibitors. With the development of CSC-/niche-targeting technology, as well as the integration of multidisciplinary studies, novel therapies that eliminate CSCs and reverse their immunosuppressive microenvironment are expected to be developed for the treatment of solid tumors, including colorectal cancer.

Emerging roles of m6A RNA modification in cancer therapeutic resistance

Marvelous advancements have been made in cancer therapies to improve clinical outcomes over the years. However, therapeutic resistance has always been a major difficulty in cancer therapy, with extremely complicated mechanisms remain elusive. N6-methyladenosine (m6A) RNA modification, a hotspot in epigenetics, has gained growing attention as a potential determinant of therapeutic resistance. As the most prevalent RNA modification, m6A is involved in every links of RNA metabolism, including RNA splicing, nuclear export, translation and stability. Three kinds of regulators, "writer" (methyltransferase), "eraser" (demethylase) and "reader" (m6A binding proteins), together orchestrate the dynamic and reversible process of m6A modification. Herein, we primarily reviewed the regulatory mechanisms of m6A in therapeutic resistance, including chemotherapy, targeted therapy, radiotherapy and immunotherapy. Then we discussed the clinical potential of m6A modification to overcome resistance and optimize cancer therapy. Additionally, we proposed existing problems in current research and prospects for future research.

ALKBH5 prevents hepatocellular carcinoma progression by post-transcriptional inhibition of PAQR4 in an m6A dependent manner

BACKGROUND

N6-methyladenosine (m6A) is a prevalent modification of mRNA and is known to play important roles in tumorigenesis in many types of cancer. The function of N6-methyladenosine (m6A) RNA methylation depends on a variety of methyltransferases and demethylases. AlkB homolog 5 (ALKBH5) is a demethylase, and its biological function has not been completely explored in HCC.

RESULTS

ALKBH5 is downregulated and has antitumor effects in HCC cells. In addition, Progestin and AdipoQ Receptor 4 (PAQR4) was identified as a downstream target of ALKBH5 based on transcriptome sequencing and validation studies. We found that ALKBH5 decreases PAQR4 mRNA and protein expression in an N6-methyladenosine (m6A)-dependent manner. The study also showed that ALKBH5 changes PAQR4 expression via the m6A reader IGF2BP1. In both in vivo and in vitro experiments, PAQR4 showed a strong association with the development of HCC. Finally, we found that PAQR4 interacts with AKT and enhances PI3K/AKT pathway activation.

CONCLUSIONS

ALKBH5 inhibits HCC growth by downregulating PAQR4 expression in an m6A-dependent manner, therefore suppressing PI3K/AKT pathway activation.

The novel m6A writer METTL5 as prognostic biomarker probably associating with the regulation of immune microenvironment in kidney cancer

Nowadays, among all urinary system cancers, the mortality of kidney cancer (KC) has risen to the first, and the incidence has been keeping on the third. Many recent studies have demonstrated that m6A modification regulated by the methyltransferases (writers) is closely related to the tumorigenesis of multiple cancers. In our previous study, we found that the methyltransferase METTL5 had a stronger association with the hazard ratio of KC more than most tumors, indicating its special function in carcinogenesis of KC. Until now, the expression, functions and mechanism of METTL5 in KC are still unclear. In this study, we analyzed the mRNA expression of METTL5 using the data sets from public databases, and revealed that the METTL5 expression was significantly up-regulated in tumor tissues of kidney renal clear cell carcinoma (KIRC) and kidney renal papillary cell carcinoma (KIRP) compared to normal tissues. Also, the METTL5 expression was correlated with the tumor stage and grade, indicating the potential involvement of METTL5 in tumor progression. Additionally, the higher expression of METTL5 predicted poorer prognosis of KIRC and KIRP patients. Subsequently, we revealed that the functions of METTL5 in KIRC might be related to immune modulation, because its co-expressed gene were enriched in immune-relevant pathways including Th17 cell differentiation, Th1 and Th2 cell differentiation, and phosphatidylinositol 3-kinase activity. Next, we disclosed that the METTL5 expression was correlated to the microenvironment score and immune score of KIRC and KIRP, and associated with the infiltration ratios of 25 types of immune cells. Besides, we demonstrated a wide difference of the METTL5's effect on the survival of patients with high and low immune infiltration, further suggesting METTL5 might affect tumor development via modulating the immune microenvironment. The findings of our study provide a novel potential prognostic biomarker and immune drug target for KC.

Identification of macrophage correlated biomarkers to predict the prognosis in patients with intrahepatic cholangiocarcinoma

Background

It has been shown that tumor-associated immune cells, particularly macrophages, play a fundamental role in the development and treatment response of intrahepatic cholangiocarcinoma (ICC). However, little is known about macrophages at the single cellular level of ICC patients.

Methods

ScRNA-seq from Zhang et al. was used in the present study to identify the genes differentially expressed in ICCs. Furthermore, transcriptomic data from TCGA datasets, IHC and flowcytometry from our cohort were used to confirm the findings. Kaplan-Meier and TIDE scores were also used for prognostic analysis and ICB responses.

Results

A significant number of macrophages were found in ICCs as compared to adjacent tissues. We then extracted, processed, and classified the macrophages from the ICCs and adjacent tissues into 12 clusters. Significantly, the macrophages from the ICC exhibited an immunosuppressed state in terms of both signature gene expression and functional enrichment. Furthermore, our results indicate that, of the 10 selective tumor-promoting genes of macrophages, only MMP19 and SIRPα can predict ICB responses in ICCs. Although a higher expression of MMP19 and SIRPα predict a poor prognosis for ICCs without immunotherapy after surgery, patients with high SIRPα expression were more sensitive to immunotherapy, whereas those with high MMP19 expression were not sensitive to immunotherapy. To define the mechanisms, we found that SIRPα^hi ICCs exhibited an increased enrichment KEGG pathway of leukocyte transendothelial migration and neutrophil extracellular trap formation. The increased immune cell infiltration will increase sensitivity to immunotherapy.

Conclusion

Collectively, macrophages are critical to the immune status of ICCs, and MMP19 and SIRPα can predict prognosis and ICB responses for ICCs.