Role of Clusterin in Estrogen Deprivation-Mediated Cell Death in Breast Cancer Cells

摘要

During the first year of work on this Proposal, we determined that the nCLU protein in human breast cancer cells is translated starting at an AUG- 34 start site from within its 'IRNA. This start site meant that this protein is translated at an unique site from that of sCLU. Furthermore, we showed that nCLU mRNA is created by alternative splicing, exon II is omitted and exons I and II are spliced together. The loss of estrogen receptor in C4:2W cells correlated with a higher level of nCLU protein, and concomitant low levels of Ku70 when compared to the parental estrogen-dependent T47D breast cancer cell line. Our previous data indicated that the N-terminal coiled-coil (Nterm) and C-terminal coiled-coil domains of nCLU interact with each other. Here, we demonstrated that conditional over- expression of the Nterm in MCF7 breast cancer cells results in radioresistance at clinically-relevant doses of IR (0.5 and 1 Gy). This finding, in combination with our data that nCLU is a pro-apoptotic protein, leads us to conclude that Nterm acts as a dominant-negative deletion mutant of nCLU. These data are consistent with our original hypothesis. In conclusion, our data indicate that the nCLU protein plays an important role in breast cancer cell radiation survival, and that the efficiency of radiation therapy of breast cancer may be a function of the estrogen dependency of the particular cancer.