PCNA and hepatocellular carcinoma: Moreover, Liu et al.34 reported a feedback mechanism and described that the HIF-2α increase positively regulates β-catenin/Myc proto-oncogene protein (c-Myc) expression and that c-Myc directly upregulates proliferating cell nuclear antigen (PCNA) expression under hypoxic conditions in HCC cells, thus increasing the proliferation involved in sorafenib resistance.