Inhibition of ubiquitin conjugating enzyme UBE2C reduces proliferation and sensitizes breast cancer cells to radiation, doxorubicin, tamoxifen and letrozole.

Purpose: The objective of this study was to determine radiation, doxorubicin, tamoxifen and letrozole sensitivity of breast cancer cells in response to functional inhibition of the ubiquitin conjugating enzyme UBE2C.

Methods: Taqman Real time PCR was performed to measure UBE2C levels in breast cancer cell lines and control HBL100 and HEK293T cells. A dominant negative form of UBE2C (DN-UBE2C) was used to functionally inhibit wild type UBE2C. Cell proliferation and anchorage independent growth were measured by colorimetric and soft agar assays, respectively. Radiation, doxorubicin, tamoxifen and letrozole responses of the cell lines were assessed by colorimetric and clonogenic assays.

Results: Overexpression of UBE2C was observed in all breast cancer cell lines tested using quantitative real time PCR. UBE2C expression was found to be highest in MDAMB231 and relatively lowest in MCF7 cells, compared to control cells. Both the growth rate and the anchorage independent growth of MCF7 and MDAMB231 cells transfected with DN-UBE2C were significantly reduced compared to cells transfected with vector alone. MCF7 and MDAMB231 cells expressing DN-UBE2C were significantly more sensitive to different doses of radiation and doxorubicin compared to both wild type and vector alone transfected cells. In addition, DN-UBE2C transfected MCF7 cells were more sensitive to inhibition by tamoxifen and letrozole compared to wild type and vector alone transfected cells.

Conclusions: Our results show that inhibition of UBE2C sensitizes breast cancer cells to radiation, doxorubicin and hormone blocking agents. UBE2C may, therefore, serve as a potential therapeutic target aimed at inducing radiation and chemo sensitization.