PCNA and neoplasm: Moreover, CHIP-WT-expressing tumor tissues treated with IFN-α exhibited much lower level of proliferating cell nuclear antigen (PCNA; estimated approximately 10-fold lower) compared with CHIP-WT-expressing tumors without IFN-α, implying that IFN-α-mediated CHIP ISGylation and its activation can efficiently suppress tumor cell proliferation and promote necrosis of lung tumors (Fig. 7d).