Identification and analysis of novel radiation response genes using a gene trapped library of human mammary epithelial cells

Abstract

Breast cancer is one of the most common cancers among women and is the second leading cause of cancer-associated death in women in the United States. Ionizing radiation is a known carcinogen of the female breast. The female breast is one of the most sensitive tissues to radiation induced cancer and ionizing radiation is one of the few agents identified as a cause of breast cancer in women. Enhanced mutation rates at all levels of radiation exposure were found to cause an increase in transformation. It is believed that the expression of several unknown genes is directly affected by gamma radiation. Radiation exposure results in altered expression of a wide variety of genes and gene pathways. Many radiation response genes have only recently been identified and more remain to be identified. Abnormal expression of these genes may be involved in the early steps in breast carcinogenesis induced by radiation. An assay has been developed to screen breast cells for a single gene mutation using a technique called gene trapping, which allows changes to be detected in the expression of a specific gene upon treatment with different doses of radiation. These radiation-response genes can then be identified through the rapid amplification of cDNA ends (RACE) procedure and sequenced. Clones affected by radiation exposure were isolated and further analyzed to see if could lead to malignant transformation of the normal breast epithelial cell into a neoplastic cell and effect survival. Five candidate radiation response genes were identified and their relative mRNA expression levels were analyzed in the MCF10A parental cells both with and without ionizing ionizing radiation treatment. The five genes are as follows: human androgen receptor, human creatine kinase, human DORA reverse strand protein 1, human eukaryotic elongation translation factor 1 beta 2, and human ribosomal protein L27. They were found to be significantly downregulated relative to the parental at doses of radiation ranging from 0.10 Gy to 4.0 Gy. A radiation dose response was clearly seen for all these genes and that was not cell-type specific. The importance of these genes in radiation-induced cell killing, mutagenesis, clastogenesis and cancer remains to be determined.