Background: Cancer cells selectively promote the translation of oncogenic transcripts to stimulate cancer progression. Although growing evidence has revealed that tRNA modifications and related genes participate in this process, their roles in head and neck squamous cell carcinoma (HNSCC) remain largely uncharacterized. Here, we sought to investigate the function and mechanisms of the transfer RNA (tRNA) N7‐methylguanosine (m ⁷ G) modification in regulating the occurrence and development of HNSCC. Methods: Cell lost‐of‐function and gain‐of‐function assays, xenograft models, conditional knockout and knockin mouse models were used to study the physiological functions of tRNA m ⁷ G modification in HNSCC tumorigenesis. tRNA modification and expression profiling, mRNA translation profiling and rescue assays were performed to uncover the underlying molecular mechanisms. Single‐cell RNA sequencing (scRNA‐seq) was conducted to explore the tumor microenvironment changes. Results: The tRNA m ⁷ G methyltransferase complex components Methyltransferase‐like 1 (METTL1)/WD repeat domain 4 (WDR4) were upregulated in HNSCC and associated with a poor prognosis. Functionally, METTL1/WDR4 promoted HNSCC progression and metastasis in cell‐based and transgenic mouse models. Mechanistically, ablation of METTL1 reduced the m ⁷ G levels of 16 tRNAs, inhibiting the translation of a subset of oncogenic transcripts, including genes related to the phosphatidylinositol‐3‐kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) signaling pathway. In addition, chemical modulators of the PI3K/Akt/mTOR signaling pathway reversed the effects of Mettl1 in mouse HNSCC. Furthermore, scRNA‐seq results revealed that Mettl1 knockout in mouse tumor cells altered the immune landscape and cell‐cell interaction between the tumor and stromal compartment. Conclusions: The tRNA m ⁷ G methyltransferase METTL1 was found to promote the development and malignancy of HNSCC through regulating global mRNA translation, including the PI3K/AKT/mTOR signaling pathway, and found to alter immune landscape. METTL1 could be a promising treatment target for HNSCC patients.

RNA modification plays an essential function in regulating gene expression and diverse biological processes. RNA modification enzyme methyltransferase-like 3 (METTL3) affects tumor progression by regulating the N6-methyladenosine (m6A) modification in the mRNAs of critical oncogenes or tumor suppressors, but its effect in oral squamous cell carcinoma (OSCC) remains unknown. In this study, we revealed that METTL3 was consistently upregulated in two OSCC cohorts, and high METTL3 expression was associated with poor prognosis. Functionally, cell proliferation, self-renewal, migration, and invasion ability in vitro and tumor growth and metastasis in vivo were decreased after METTL3 knockdown in OSCC cells. In contrast, the opposite results were obtained after METTL3 overexpression. In addition, the results obtained with the Mettl3 genetically modified mouse model validated the essential role of Mettl3 in chemical-induced oral carcinogenesis. In mechanism, methylated RNA immunoprecipitation sequencing (MeRIP-seq), MeRIP-quantitative real-time PCR, and luciferase reporter and mutagenesis assays identified that METTL3 mediates the m6A modification in the 3' UTR of BMI1 mRNA. METTL3 promotes BMI1 translation in OSCC under the cooperation with m6A reader IGF2BP1. Our findings revealed that METTL3 promotes OSCC proliferation and metastasis through BMI1 m6A methylation, suggesting that the METTL3-m6A-BMI1 axis may serve as a prognostic biomarker or therapeutic target in patients with OSCC.

The tumor microenvironment has been recently reported to play a pivotal role in sustaining tumor cells survival and protecting them from immunotherapy and chemotherapy-induced death. It remains largely unknown how the specific signaling pathway exerts the tumor microenvironment in head and neck squamous cell carcinoma though previous studies have elucidated the regulatory mechanisms involve in tumor immune microenvironment, stromal cells, tumor angiogenesis and cancer stem cell. These components are responsible for tumor progression as well as anti-cancer therapy resistance, leading to rapid tumor growth and treatment failure. In this review, we focus on discussing the interaction between tumor cells and the surrounding components for better understanding of anti-cancer treatment ineffectiveness and its underlying molecular mechanisms.

Interplay between innate and adaptive immune cells is important for the antitumor immune response. However, the tumor microenvironment may turn immune suppressive, and tumor associated macrophages are playing a role in this transition. Here, we show that CD276, expressed on tumor-associated macrophages (TAM), play a role in diminishing the immune response against tumors. Using a model of tumors induced by N-butyl-N-(4-hydroxybutyl) nitrosamine in BLCA male mice we show that genetic ablation of CD276 in TAMs blocks efferocytosis and enhances the expression of the major histocompatibility complex class II (MHCII) of TAMs. This in turn increases CD4 + and cytotoxic CD8 + T cell infiltration of the tumor. Combined single cell RNA sequencing and functional experiments reveal that CD276 activates the lysosomal signaling pathway and the transcription factor JUN to regulate the expression of AXL and MerTK, resulting in enhanced efferocytosis in TAMs. Proving the principle, we show that simultaneous blockade of CD276 and PD-1 restrain tumor growth better than any of the components as a single intervention. Taken together, our study supports a role for CD276 in efferocytosis by TAMs, which is potentially targetable for combination immune therapy.

Background: CD276 (B7-H3), a pivotal immune checkpoint, facilitates tumorigenicity, invasiveness, and metastasis by escaping immune surveillance in a variety of tumors; however, the underlying mechanisms facilitating immune escape in esophageal squamous cell carcinoma (ESCC) remain enigmatic. Methods: We investigated the expression of CD276 in ESCC tissues from patients by using immunohistochemistry (IHC) assays. In vivo, we established a 4-nitroquinoline 1-oxide (4NQO)-induced CD276 knockout (CD276^wKO) and K14cre; CD276 conditional knockout (CD276^cKO) mouse model of ESCC to study the functional role of CD276 in ESCC. Furthermore, we used the 4NQO-induced mouse model to evaluate the effects of anti-CXCL1 antibodies, anti-Ly6G antibodies, anti-NK1.1 antibodies, and GSK484 inhibitors on tumor growth. Moreover, IHC, flow cytometry, and immunofluorescence techniques were employed to measure immune cell proportions in ESCC. In addition, we conducted single-cell RNA sequencing analysis to examine the alterations in tumor microenvironment following CD276 depletion. Results: In this study, we elucidate that CD276 is markedly upregulated in ESCC, correlating with poor prognosis. In vivo, our results indicate that depletion of CD276 inhibits tumorigenesis and progression of ESCC. Furthermore, conditional knockout of CD276 in epithelial cells engenders a significant downregulation of CXCL1, consequently reducing the formation of neutrophil extracellular trap networks (NETs) via the CXCL1–CXCR2 signaling axis, while simultaneously augmenting natural killer (NK) cells. In addition, overexpression of CD276 promotes tumorigenesis via increasing NETs’ formation and reducing NK cells in vivo. Conclusions: This study successfully elucidates the functional role of CD276 in ESCC. Our comprehensive analysis uncovers the significant role of CD276 in modulating immune surveillance mechanisms in ESCC, thereby suggesting that targeting CD276 might serve as a potential therapeutic approach for ESCC treatment.

Head and neck squamous cell carcinoma (HNSCC) is a highly aggressive tumor and the sixth most common cancer worldwide. Current treatment strategies for HNSCC are surgery, radiotherapy, chemotherapy, immunotherapy or combinatorial therapies. However, the overall 5-year survival rate of HNSCC patients remains at about 50%. Cancer stem cells (CSCs), a small population among tumor cells, are able to self-renew and differentiate into different tumor cell types in a hierarchical manner, similar to normal tissue. In HNSCC, CSCs are proposed to be responsible for tumor initiation, progression, metastasis, drug resistance, and recurrence. In this review, we discuss the molecular and cellular characteristics of CSCs in HNSCC. We summarize current approaches used in the literature for identification of HNSCC CSCs, and mechanisms required for CSC regulation. We also highlight the role of CSCs in treatment failure and therapeutic targeting options for eliminating CSCs in HNSCC.