CHEK2 and hepatocellular carcinoma: In particular, USP39 de-ubiquitinates and stabilizes CHK2 to regulate the DNA damage response and chemical radiation resistance [43], de-ubiquitinates and stabilizes the SP1 protein to promote hepatocellular carcinoma progression [44], and inhibits VEGF-A165b-selective splicing by regulating SRSF1 and SRPK1 to promote malignant proliferation and angiogenesis of renal cell carcinoma [45].