Decreased Expression of DNA-dependent Protein Kinase, a DNA Repair Protein, during Human Colon Carcinogenesis

DNA-dependent protein kinase (DNA-PK), consisting of a catalytic subunit (DNA-PKcs) and the Ku70 and Ku86 proteins, participates in the repair of DNA double-strand breaks (DSBs). We assessed its expression immunohistochemically in normal human colon tissue, colon adenomas, colon carcinomas, and normal tissue distant from carcinomas. Normal colonocytes expressed all DNA-PK proteins. Compared with the expression in normal tissue [176.62 ± 18.56 (the intensity of expression × the percentage of cells expressing this protein), mean + SE], the expression of Ku70 was significantly reduced in adenomas (36.62 ± 11.09; P P versus 41.66 ± 14.71 in adenomas ( P versus 85.68 ± 15.76 in carcinomas ( P