Sijun Sun

Abstract Cuproptosis, caused by excessively high copper concentrations, is urgently exploited as a potential cancer therapeutic. However, the mechanisms underlying the initiation, propagation, and ultimate execution of cuproptosis in tumors remain unknown. Here, we show that copper content is significantly elevated in gastric cancer (GC), especially in malignant tumors. Screening reveals that METTL16, an atypical methyltransferase, is a critical mediator of cuproptosis through the m 6 A modification on FDX1 mRNA. Furthermore, copper stress promotes METTL16 lactylation at site K229 followed by cuproptosis. The process of METTL16 lactylation is inhibited by SIRT2. Elevated METTL16 lactylation significantly improves the therapeutic efficacy of the copper ionophore– elesclomol. Combining elesclomol with AGK2, a SIRT2-specific inhibitor, induce cuproptosis in gastric tumors in vitro and in vivo. These results reveal the significance of non-histone protein METTL16 lactylation on cuproptosis in tumors. Given the high copper and lactate concentrations in GC, cuproptosis induction becomes a promising therapeutic strategy for GC.

Mitochondria are cellular powerhouses that generate energy through the electron transport chain (ETC). The mitochondrial genome (mtDNA) encodes essential ETC proteins in a compartmentalized manner, however, the mechanism underlying metabolic regulation of mtDNA function remains unknown. Here, we report that expression of tricarboxylic acid cycle enzyme succinate-CoA ligase SUCLG1 strongly correlates with ETC genes across various TCGA cancer transcriptomes. Mechanistically, SUCLG1 restricts succinyl-CoA levels to suppress the succinylation of mitochondrial RNA polymerase (POLRMT). Lysine 622 succinylation disrupts the interaction of POLRMT with mtDNA and mitochondrial transcription factors. SUCLG1-mediated POLRMT hyposuccinylation maintains mtDNA transcription, mitochondrial biogenesis, and leukemia cell proliferation. Specifically, leukemia-promoting FMS-like tyrosine kinase 3 (FLT3) mutations modulate nuclear transcription and upregulate SUCLG1 expression to reduce succinyl-CoA and POLRMT succinylation, resulting in enhanced mitobiogenesis. In line, genetic depletion of POLRMT or SUCLG1 significantly delays disease progression in mouse and humanized leukemia models. Importantly, succinyl-CoA level and POLRMT succinylation are downregulated in FLT3-mutated clinical leukemia samples, linking enhanced mitobiogenesis to cancer progression. Together, SUCLG1 connects succinyl-CoA with POLRMT succinylation to modulate mitochondrial function and cancer development.

Purpose: To investigate how branched-chain amino acid (BCAA) metabolism is remodeled and to determine its contribution to diabetic retinopathy progression. Methods: We analyzed Bcat1 and Bcat2 expression in the retina using single-cell sequencing data and immunofluorescence. Bcat1-mediated remodeling of BCAA metabolism was assessed via targeted metabolomics in Müller cells. We performed chromatin immunoprecipitation (ChIP) to examine histone methylation at inflammatory gene promoters. Additionally, we utilized RNA sequencing and kinase screening assays to delineate phosphorylation regulation of Bcat1 activity. In vivo, we established diabetic mouse models and treated them with Bcat1-specific inhibitor to evaluate retinal inflammation and vascular leakage. Results: Bcat1 was predominantly expressed in Müller cells and exhibited increased activity under diabetic conditions, leading to a remodeling of BCAA catabolism and upregulation of inflammatory genes (interleukin 6 [Il6] and tumor necrosis factor-α [Tnf-α]). Bcat1 activity was negatively regulated by polo-like kinase 4 (Plk4)-mediated phosphorylation at threonine 333. In high glucose-treated Müller cells, elevated Bcat1 activity reduced α-ketoglutarate (α-KG), a critical substrate for histone demethylation reactions, resulting in higher histone H3 lysine 4 trimethylation (H3K4me3) levels at inflammatory gene promoters, and further boosted retinal inflammation. Treatment with chemical Bcat1 inhibitors (BAY-069 and ERG240) significantly reduced inflammatory gene expression and vascular leakage in diabetic retinas in vivo. Conclusions: Bcat1 activation mediates BCAA metabolism remodeling in Müller cells and epigenetically induces retinal inflammation, which offers a potential therapeutic target for diabetic retinopathy. Diabetes and diabetic retinopathy are potentially driven not only by hyperglycemia but also by dysregulated amino acid metabolism.

Mitochondria harbor the oxidative phosphorylation (OXPHOS) system to sustain cellular respiration. However, the transcriptional regulation of OXPHOS remains largely unexplored. Through the cancer genome atlas (TCGA) transcriptome analysis, transcription factor THAP domain-containing 3 (THAP3) was found to be strongly associated with OXPHOS gene expression. Mechanistically, THAP3 recruited the histone methyltransferase SET and MYND domain-containing protein 3 (SMYD3) to upregulate H3K4me3 and promote OXPHOS gene expression. The levels of THAP3 and SMYD3 were altered by metabolic cues. They collaboratively supported liver cancer cell proliferation and colony formation. In clinical human liver cancer, both of them were overexpressed. THAP3 positively correlated with OXPHOS gene expression. Together, THAP3 cooperates with SMYD3 to epigenetically upregulate cellular respiration and liver cancer cell proliferation.