PCNA and cancer: MSI2 deficiency suppresses the growth and survival of CRC cells to promote ferroptosis through inactivating the MAPK signaling pathway to inhibit HSPB1 phosphorylation, which leads to downregulation of PCNA and Ki67 and upregulation of ACSL4 in cancer cells and subsequently induces redox imbalance, iron accumulation and mitochondrial shrinkage, ultimately triggering ferroptosis (Fig. 9).