The biological function of protein arginine methyltransferase 3 (PRMT3) is not well known because very few physiological substrates of this methyltransferase have been identified to date. The clinical significance of PRMT3 in pancreatic cancer was studied by database analysis. The PRMT3 protein level of human pancreatic tumors was detected by immunoblotting and immunohistochemical staining. PRMT3-associated proteins and the methylation sites on the proteins were investigated using mass spectrometry. Seahorse Bioscience analyzed the metabolic reprogramming. Combination index analysis and xenograft animal model were conducted to explore the effects of combination of inhibitors of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and oxidative phosphorylation on tumor growth. We found that the expression of PRMT3 is upregulated in pancreatic cancer, and its expression is associated with poor survival. We identified GAPDH as a PRMT3-binding protein and demonstrated that GAPDH is methylated at R248 by PRMT3 in vivo. The methylation of GAPDH by PRMT3 enhanced its catalytic activity while the mutation of R248 abolished the effect. In cells, PRMT3 overexpression triggered metabolic reprogramming and enhanced glycolysis and mitochondrial respiration simultaneously in a GAPDH-dependent manner. PRMT3-overexpressing cancer cells were addicted to GAPDH-mediated metabolism and sensitive to the inhibition of GAPDH and mitochondrial respiration. The combination of inhibitors of GAPDH and oxidative phosphorylation induced a synergistic inhibition on cellular growth in vitro and in vivo. Our results suggest that PRMT3 mediates metabolic reprogramming and cellular proliferation through methylating R248 of GAPDH, and double blockade of GAPDH and mitochondrial respiration could be a novel strategy for the treatment of PRMT3-overexpressing pancreatic cancer.

中文翻译：

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蛋白质精氨酸甲基转移酶3诱导的代谢重编程是胰腺癌的脆弱目标。

蛋白质精氨酸甲基转移酶3（PRMT3）的生物学功能尚不为人所知，因为迄今为止，这种甲基转移酶的生理底物很少。通过数据库分析研究PRMT​​3在胰腺癌中的临床意义。通过免疫印迹和免疫组织化学染色检测人胰腺肿瘤的PRMT3蛋白水平。使用质谱法研究了PRMT3相关的蛋白质和蛋白质上的甲基化位点。Seahorse Bioscience分析了代谢重编程。结合指标分析和异种移植动物模型，探讨了3-磷酸甘油醛脱氢酶（GAPDH）抑制剂和氧化磷酸化抑制剂对肿瘤生长的影响。我们发现PRMT3的表达在胰腺癌中上调，其表达与生存能力差有关。我们将GAPDH鉴定为PRMT3结合蛋白，并证明GAPDH在体内通过PRMT3在R248处被甲基化。PRMT3对GAPDH的甲基化增强了其催化活性，而R248的突变消除了该作用。在细胞中，PRMT3的过表达同时以GAPDH依赖性方式触发了代谢重编程，并增强了糖酵解和线粒体呼吸作用。过度表达PRMT3的癌细胞沉迷于GAPDH介导的代谢，并对GAPDH和线粒体呼吸的抑制敏感。GAPDH抑制剂和氧化磷酸化的组合在体外和体内对细胞生长产生协同抑制作用。