Sec62 Protein Level is Crucial for the ER Stress Tolerance of Prostate Cancer

BACKGROUND. We previously reported that over-expression of the SEC62 gene is a widespread phenomenon in prostate cancer. Since the use of endoplasmic reticulum (ER) stress-inducing substances such as thapsigargin in prostate cancer therapy is widely discussed in the literature, we investigated the influence of Sec62 protein content on the cellular response to these drugs. METHODS. Growth effects were analyzed by real-time cell analysis and viability tests in DU145-cells representing an increased SEC62 expression or PC3- and LNCaP-cells representing a similar SEC62 expression compared to non-tumor cells. Ca2+-imaging in an established HeLa-system with fluorescent dye was used to study molecular effects of Sec62 depletion. RESULTS. We found a lower propensity toward apoptotic cell death after thapsigargin treatment for DU145 cells compared to PC3 or LNCaP and siRNA-mediated silencing of SEC62 resulted in a reduced viability of thapsigargin-treated PC3 cells, indicating that Sec62 functions in cellular stress response. Measurement of cytosolic [Ca2+] demonstrated the influence of Sec62 on the cellular response to thapsigargin on a molecular level. Using real-time cell analysis, we observed the loss of androgen stimulation of LNCaP cells in the presence of thapsigargin, and an additional negative effect on cell growth of Sec62 depletion. Also, for PC3- and DU145-cells Sec62 depletion inhibited growth after thapsigargin treatment. CONCLUSIONS. Our data indicate a crucial function of Sec62 in the response to thapsigargin-induced ER stress. This will be of great significance on the background of elevated Sec62 protein levels in prostate cancer cells when treatment with thapsigargin analogs is considered. Prostate 71: 1074-1083, 2011. (C) 2011 Wiley-Liss, Inc.