Regulating MYC translation in cancer
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Reversible downregulation of MYC in a spheroid model of metastatic epithelial ovarian cancer
Upon detachment from the primary tumour, epithelial ovarian cancer cells can form multicellular aggregates, also referred to as spheroids, that have the capacity to establish metastases at distant sites. These structures exhibit numerous adaptations that may facilitate metastatic transit and promote tumorigenic potential. One such adaptation is the acquisition of dormancy, characterized by decreased proliferation and molecular features of quiescence. One of the most frequently dysregulated genes in cancer is MYC, which encodes a transcription factor that promotes cell proliferation. In this study, we demonstrate that MYC protein abundance and associated gene expression is significantly decreased in EOC spheroids compared to adherent cells. This downregulation occurs rapidly upon cell detachment and is proteasome-dependent. Moreover, MYC protein abundance and associated gene expression is restored upon spheroid reattachment to an adherent culture surface. Overall, our findings suggest that suppression of MYC activity is a common feature of EOC spheroids and may contribute to the reversible acquisition of dormancy.
A critical role of N4-acetylation of cytidine in mRNA by NAT10 in T cell expansion and antiviral immunity
Following activation, naive T cells exit quiescence and require global translation for rapid expansion, yet the underlying mechanisms remain unclear. Here, we show that during T cell activation, cells upregulate the expression of N-acetyltransferase 10 (NAT10), an enzyme responsible for N4-acetylcytidine (ac4C) modification of mRNAs. ac4C-modified Myc mRNAs show higher translation efficiency, enabling rapid synthesis of MYC protein and supporting robust T cell expansion. Conditional deletion of Nat10 in mouse T cells causes severe cell cycle arrest and limitation of cell expansion due to MYC deficiency, ultimately exacerbating infection in an acute lymphocytic choriomeningitis virus model. Additionally, T cells from older individuals with lower NAT10 levels show proliferative defects, which may partially account for impaired antiviral responses in older individuals. This study reveals a mechanism governing T cell expansion, signal-dependent mRNA degradation induction and the potential in vivo biological significance of ac4C modification in T cell-mediated immune responses.
Enhancer reprogramming: critical roles in cancer and promising therapeutic strategies
Transcriptional dysregulation is a hallmark of cancer initiation and progression, driven by genetic and epigenetic alterations. Enhancer reprogramming has emerged as a pivotal driver of carcinogenesis, with cancer cells often relying on aberrant transcriptional programs. The advent of high-throughput sequencing technologies has provided critical insights into enhancer reprogramming events and their role in malignancy. While targeting enhancers presents a promising therapeutic strategy, significant challenges remain. These include the off-target effects of enhancer-targeting technologies, the complexity and redundancy of enhancer networks, and the dynamic nature of enhancer reprogramming, which may contribute to therapeutic resistance. This review comprehensively encapsulates the structural attributes of enhancers, delineates the mechanisms underlying their dysregulation in malignant transformation, and evaluates the therapeutic opportunities and limitations associated with targeting enhancers in cancer.
RBPMS inhibits bladder cancer metastasis by downregulating MYC pathway through alternative splicing of ANKRD10
RNA-binding proteins (RBPs) are pivotal mediators of the alternative splicing (AS) machinery of pre-mRNA. Research has demonstrated that the AS process is significantly dysregulated and plays a crucial role in bladder cancer (BLCA). We conducted comprehensive screening and analysis of the TCGA-BLCA cohort, specifically focusing on genes with significant differences in expression levels between carcinoma and adjacent non-cancerous tissues. Among the 500 differentially expressed genes, 5 RNA-binding proteins were identified. Only the RNA-binding protein with multiple splicing (RBPMS) demonstrated a consistent downregulation in BLCA and was correlated with an unfavorable prognosis for affected patients. Subsequent experiments revealed that RBPMS exerted inhibitory effects on the epithelial-mesenchymal transition (EMT) pathway and the migratory potential of BLCA cells. RNA-Seq analysis identified ANKRD10 as a key target mRNA regulated by RBPMS in BLCA. RBPMS depletion in BLCA cells resulted in AS of ANKRD10 and increased ANKRD10-2 expression. ANKRD10-2 functioned as a transcriptional co-activator of MYC proteins, thereby augmenting their transcriptional activity. Furthermore, ANKRD10-2 knockdown significantly rescued the migration enhancement induced by RBPMS depletion in BLCA cells. Taken together, this study revealed a mechanism whereby RBPMS suppresses the migration and invasion of BLCA cells by attenuating MYC pathway activity via the AS of ANKRD10.
Cancer-intrinsic Cxcl5 orchestrates a global metabolic reprogramming for resistance to oxidative cell death in 3D
Pancreatic ductal adenocarcinoma is characterized by a three-dimensional (3D) tumor microenvironment devoid of oxygen and nutrients but enriched in extracellular matrix, which acts as a physical and chemical barrier. In 3D, cancer cells reprogram their metabolic pathways in ways that help them survive hostile conditions. However, little is known about the metabolic phenotypes of cancer cells in 3D and the intrinsic cues that modulate them. We found that Cxcl5 deletion restricted pancreatic tumor growth in a 3D spheroid-in-Matrigel culture system without affecting cancer cell growth in 2D culture. Cxcl5 deletion impaired 3D-specific global metabolic reprogramming, resistance to hypoxia-induced cell death, and upregulation of Hif1α and Myc. Overexpression of Hif1α and Myc, however, effectively restored 3D culture-induced metabolic reconfiguration, growth, redox homeostasis, and mitochondrial function in Cxcl5−/− cells, reducing ferroptosis. We also found that pancreatic cancer patients with higher expression of hypoxia and metabolism-related genes whose expression is well-correlated with CXCL5 generally have poorer prognosis. Together, our findings identify an unanticipated role of Cxcl5 in orchestrating the cancer metabolic reprogramming in 3D culture that is required for energy and biomass maintenance and that restricts oxidative cell death. Thus, our results provide a rationale for targeting CXCL5 as a promising therapeutic strategy.
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