Differential Expression of DNA Double-Strand Break Repair Proteins in Breast Cells

摘要

Two mechanisms that repair DNA double-strand breaks in mammalian cells are homologous recombination and non-homologous DNA end-joining (NHEJ). Previous studies showed that a critical component of the NHEJ pathway, the DNA- activated protein kinase (DNA-PK), was poorly expressed in non-lactating (resting) breast tissue. Therefore, we proposed to identify the mechanisms responsible for regulating levels of non-homologous end-joining DNA repair components in human breast tissue and to measure the DNA double-strand break repair capacity of breast epithelial cells. We reexamined the expression of DNA- PK in human breast tissues by immuno-histochemistry and extended these studies to two other components of the NHEJ repair pathway, XRCC4 and DNA ligase IV, as well as other DNA repair components including NBSl and MRE11. In contrast to the original report, 90% of the epithelial cells in normal resting breast tissues from 10 different patients expressed both components of DNA-PK, DNAPKcs and Ku. In contrast, stromal cells failed to express NHEJ proteins, but a cell line derived from breast stromal tissue did. No polymorphisms were detected in the Ku7O gene of 14 breast cancer patients, but a high frequency fragment length polymorhism was identified in the promoter region of the Ku8O gene from breast cancer patients. We also showed that 11.3% of breast cancer patients amplified the gene for the Wip1 phosphatase that regulates p53 activity. Furthermore, mouse cells lacking the Wip1 gene were resistant to cell transformation, and mice lacking the Wip1 gene were resistant to tumor formation, suggesting that Wip1 is a potential target for anti-cancer drugs.