Abstract 4094: Accumulation of hepatoma up-regulated protein in prostate cancer cells inhibits bortezomib-induced apoptosis

Abstract

Abstract The increased understanding of cellular signaling pathways in the regulation of tumor progression and resistance, together with the identification of key molecular markers has allowed for considerable advances in the establishment of therapies for therapy-resistant Prostate cancer (PCa). Hepatoma Up-Regulated Protein (HURP), is overexpressed in several tumors, and has been identified as a multifunctional protein with tumorigenic capacity. We previously reported on HURP as an essential modulator of PCa resistance to radiation therapy. Bortezomib, a proteasome inhibitor used clinically for multiple myeloma, has been shown to induce apoptosis in PCa cells. In the present study, we evaluate HURP’s role in PCa resistance pathways by analyzing its effects on bortezomib-induced apoptosis. LNCaP-TetOn-HURP, DU145-TetOn-HURP, and PC3-TetOn-HURP clones were established for the expression of HURP. HURP expression was induced with doxycycline (Dox) for 48 h. Next, cells were treated with bortezomib (50 nM) for 24h. To assess the effect of HURP on bortezomib-induced apoptosis, the cells were harvested and subjected to flow cytometry (FC) analysis using annexin V/PI staining. Apoptosis was observed in control cells (-Dox) following the treatment with bortezomib. Induction of HURP expression (+Dox), blocked bortezomib-induced apoptosis. This effect was observed only in LNCaP- and DU145-TetOn-HURP cells with a 1.8 and 2.1 fold decrease in apoptosis, respectively; but not in PC3-TetOn-HURP cells. In addition, we performed FC analysis of DHR123 to analyze the effects of HURP on bortezomib-induced accumulation of reactive oxygen species (ROS). HURP blocked bortezomib-induced ROS accumulation in LNCaP- and DU145-TetOn-HURP cells with a 0.3 and 0.15 fold change, respectively. Bortezomib also induced the expression of p53 and Noxa, and enhanced the cleavage of PARP in LNCaP- and DU145-TetOn-HURP control cells (-Dox), but not in (-Dox) PC3-TetOn-HURP cells. Induction of HURP, however blocked effects on apoptosis effectors in LNCaP- and DU145-TetOn-HURP. Western blot analysis also demonstrated that in HURP-expressing cells, bortezomib-inhibited the phosphorylation of ASK1, JNK or p38. Finally, we assessed the effects of HURP expression on the cytoplasmic localization of Noxa, a mediator of bortezomib-induced apoptotic signaling by immunocytochemistry. Noxa staining was weakly detectable or absent in HURP expressing cells, suggesting the ability of HURP overload to block bortezomib-induced Noxa expression.Overall, our results show that HURP-induced resistance of PCa cells to bortezomib is attributed to the effects of this protein on mechanisms related to a non-specific overload response leading to the activation of ubiquitin system. Funding: PCRP W81XWH-14-1-0151 (CRG), UMMC Department of Pathology (MH) Citation Format: Mohamed Hassan, Abdelouahid Elkhattouti, Nasir Butt, Ingrid Espinoza, Christian Gomez. Accumulation of hepatoma up-regulated protein in prostate cancer cells inhibits bortezomib-induced apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4094. doi:10.1158/1538-7445.AM2017-4094