Coordinated regulation of two TRAIL-R2/KILLER/DR5 mRNA isoforms by DNA damaging agents, serum and 17 beta-estradiol in human breast cancer cells

A search of the Genebank database revealed that there are two distinct gene sequences with the common name of TRAIL-R2/Killer/DR5. Using reverse trans cription-polymerase chain reaction (RT-PCR), we confirmed the existence of two isoforms of TRAIL-R2/Killer/DR5 mRNA, which we have designated the long and short isoforms based on their electrophoretic mobility. We found that both the long and short mRNA isoforms are ubiquitously expressed in human t issues and cell lines. The long form generally predominates, but the propor tion of the two isoforms varies depending on the tissue type. Treatment of MCF-7 human breast cancer cells with the DNA damaging drugs adriamycin, cam pthothecin, or etoposide causes a coordinated up-regulation of both isoform s. Treatment of the p53-mutant T-47D breast cancer cell line with adriamyci n also results in up-regulation of both isoforms, suggesting that adriamyci n up-regulates TRAIL-R2/Killer/DR5 expression independent of functional p53 . The expression of both mRNA isoforms are increased in MCF-7 cells culture d in charcoal-stripped fetal bovine serum compared to normal serum, suggest ing that sex steroid hormones may play a role in the negative regulation of their expression. This was confirmed in MCF-7 cells cultured in stripped s erum supplemented with 17 beta-estradiol, which also resulted in a decrease in the mRNA expression of both isoforms. These results demonstrate that th e TRAIL-R2/Killer/DR5 gene gives rise to two distinct forms of mRNA, and th at these two forms are coordinately regulated by DNA damage and 17 beta-est radiol in human breast cancer cells. The functional significance of the two isoforms remains to be determined.