PCNA and type 2 diabetes mellitus: Compounding these issues, islets from T2DM patients exhibit elevated proliferating cell nuclear antigen (PCNA) expression with concomitant downregulation of cyclin dependent kinase 2 (CDK2) and p27-kip1, suggesting that diabetic islets from T2DM patients are able to enter the cell cycle but are unable to proliferate due to G1/S phase arrest [57].