PCNA and gastric cancer: Kato et al. [102] showed that metformin induces cell cycle arrest in the G1/S phase, increases the expression of GADD45 (a stress sensor and a cell cycle regulator), increases the expression of P21 (a cyclin-dependent kinase inhibitor), decreases the expression of E2F1 (a pro-proliferating transcription factor), and decreases proliferating cell nuclear antigen (PCNA) in gastric cancer cells.