Robert McDonald III , Gen Sheng Wu , Todd Waldman , et al . - / - Human Cancer CellsWAF 1 / CIP 1 Repair Defect in p 21

p53 induction and cell cycle arrest occur following DNA damage, possibly to allow repair prior to replication. p21WAFI/CIP11a cyclin-cyclindependent kinase inhibitor and proliferating cell nuclear antigen-inter acting protein, is induced by p53 and mediates the cell cycle arrest. To investigate a role for p21 in DNA repair in vivo, we studied the expression of in vitro damaged reporter DNA transfected into p21 +/+ or -/— HCII l(. human colon cancer cells. Introduction of UV-damaged or a'.vplatinum-damaged cytomegalovirus-driven ß-galactosidase reporter DNA into tumor cells revealed a significant decrease (2-5-fold) in reporter expression in p21 —¿ /— versus +/+ cells. In the absence of DNA damage, there was a significant increase (2—3-fold)in the number of 6-TG-resistant colonies derived from p21 -/versus +/+ cells. Reintroduction of wildtype p21, but not a p21 C-terminal truncation mutant which lacks the proliferating cell nuclear antigen interaction domain, stimulated (2-3fold) the repair capacity of the p21-deficient cells. We conclude that p21 deficiency is associated with a defect in DNA repair, which could lead to an increased sensitivity of tumor cells to DNA damage.