METTL1-mediated m7G modification of valine tRNAs drives pancreatic ductal adenocarcinoma progression

Background: Transfer RNA (tRNA) modifications play a critical role in regulating codon-specific mRNA translation and supporting tumor cell adaptation. The RNA methyltransferase METTL1 installs N7-methylguanosine (m7G) modifications on tRNAs, shaping their codon usage landscape and influencing protein synthesis. However, the function and mechanism of the METTL1/tRNA axis in pancreatic ductal adenocarcinoma (PDAC) remain poorly understood. This study examines the role of METTL1-mediated m7G tRNA modification in the progression of PDAC and its associated metabolic reprogramming. Methods: METTL1 expression was analyzed using transcriptomic data from The Cancer Genome Atlas (TCGA) and validated in an independent PDAC tissue cohort by qRT-PCR. METTL1-knockout PDAC cell lines were generated via CRISPR/Cas9. Cellular proliferation and migration were assessed through MTT, colony formation, and wound-healing assays, while tumor growth was evaluated in xenograft models. Global tRNA m7G levels were measured using dot blot, and qRT-PCR was used to quantify specific tRNA abundances. Polysome profiling identified METTL1-dependent translational targets, and mitochondrial function was assessed by Seahorse Mito Stress testing. Results: METTL1 was significantly upregulated in PDAC (p < 0.001) and correlated with poor patient survival (p < 0.05). METTL1 knockout suppressed PDAC cell proliferation, migration, and tumor growth (p < 0.001) in vitro and in vivo. Mechanistically, METTL1 loss decreased the abundance of m7G-modified valine tRNAs, particularly Val-AAC, Val-CAC, and Val-TAC (all p < 0.001), leading to reduced translation of valine codon-enriched oxidative phosphorylation genes. Consequently, METTL1 deficiency impaired mitochondrial respiration and energy production. Consistently, valine tRNA expression was elevated in PDAC tissues (p < 0.01), and selective knockdown of these tRNAs inhibited proliferation and migration (p < 0.001) by disrupting mitochondrial function. Reintroduction of Val-AAC, Val-CAC, and Val-TAC restored growth (p < 0.001) and migratory capacity (p < 0.01) in METTL1-deficient cells. Conclusions: METTL1-mediated m7G modification of valine tRNAs promotes PDAC progression by reprogramming the translational landscape to support mitochondrial metabolism. This METTL1-tRNA-mitochondrial axis represents a novel metabolic vulnerability and a promising therapeutic target in pancreatic cancer.