USP4 and liver cancer: For instance, USP22 promotes liver cancer progression by directly binding and deubiquitinating PPARγ, while USP28 regulates myocardial mitochondrial homeostasis in diabetic mice by directly binding and deubiquitinating PPARα, thereby alleviating cardiac dysfunction.[26] Here, we identified another deubiquitinase, USP4, that can bind and stabilize PPARα.