O-GlcNAcylation has been implicated in the tumorigenesis of various tissue origins, but its function in liver tumorigenesis is not clear. Here, we demonstrate that O-GlcNAcylation can enhance the expression, stability and function of Yes-associated protein (YAP), the downstream transcriptional regulator of the Hippo pathway and a potent oncogenic factor in liver cancer. O-GlcNAcylation induces transformative phenotypes of liver cancer cells in a YAP-dependent manner. An O-GlcNAc site of YAP was identified at Thr241, and mutating this site decreased the O-GlcNAcylation, stability, and pro-tumorigenic capacities of YAP, while increasing YAP phosphorylation. Importantly, we found via in vitro cell-based and in vivo mouse model experiments that O-GlcNAcylation of YAP was required for high-glucose-induced liver tumorigenesis. Interestingly, a positive feedback between YAP and global cellular O-GlcNAcylation is also uncovered. We conclude that YAP O-GlcNAcylation is a potential therapeutic intervention point for treating liver cancer associated with high blood glucose levels and possibly diabetes.

Distinctive from their normal counterparts, cancer cells exhibit unique metabolic dependencies on glutamine to fuel anabolic processes. Specifically, pancreatic ductal adenocarcinoma (PDAC) cells rely on an unconventional metabolic pathway catalyzed by aspartate aminotransferase, malate dehydrogenase 1 (MDH1), and malic enzyme 1 to rewire glutamine metabolism and support nicotinamide adenine dinucleotide phosphate (NADPH) production. Here, we report that methylation on arginine 248 (R248) negatively regulates MDH1. Protein arginine methyltransferase 4 (PRMT4/CARM1) methylates and inhibits MDH1 by disrupting its dimerization. Knockdown of MDH1 represses mitochondria respiration and inhibits glutamine metabolism, which sensitizes PDAC cells to oxidative stress and suppresses cell proliferation. Meanwhile, re-expression of wild-type MDH1, but not its methylation-mimetic mutant, protects cells from oxidative injury and restores cell growth and clonogenic activity. Importantly, MDH1 is hypomethylated at R248 in clinical PDAC samples. Our study reveals that arginine methylation of MDH1 by CARM1 regulates cellular redox homeostasis and suppresses glutamine metabolism of pancreatic cancer.

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Increased aerobic glycolysis is a hallmark of cancer metabolism. How cancer cells coordinate glucose metabolism with extracellular glucose levels remains largely unknown. Here, we report that coactivator-associated arginine methyltransferase 1 (CARM1 or PRMT4) signals glucose availability to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and suppresses glycolysis in liver cancer cells. CARM1 methylates GAPDH at arginine 234 (R234), inhibiting its catalytic activity. Glucose starvation leads to CARM1 upregulation, further inducing R234 hypermethylation and GAPDH inhibition. The re-expression of wild-type GAPDH, but not of its methylation-mimetic mutant, sustains glycolytic levels. CARM1 inhibition increases glycolytic flux and glycolysis. R234 methylation delays tumor cell proliferation in vitro and in vivo. Compared with normal tissues, R234 is hypomethylated in malignant clinical hepatocellular carcinoma samples. Notably, R234 methylation positively correlates with CARM1 expression in these liver cancer samples. Our findings thus reveal that CARM1-mediated GAPDH methylation is a key regulatory mechanism of glucose metabolism in liver cancer.