Abstract C226: Phosphorylation of ser63/73 in c-jun is required to respond to docetaxel treatment in prostate cancer cells.

Abstract

Abstract Background: Docetaxel (doc) is currently used as first-line therapy in castration-resistant prostate cancer (CRPC). However, a significant number of patients are irresponsive to the drug. To better understand this inter-individual variability, we studied the impact of c-jun phosphorylation, a major pathway of doc-induced apoptosis, in prostate cancer (PCa) cells. Furthermore, we validated the effect of doc treatment on the androgen receptor (AR) and c-jun gene alteration. Methods: All in vitro experiments were performed on human PCa cell lines- PC-3, LNCaP and LNCaP cells cultured in bicalutamide for 4 weeks (LNb4). To examine the role of c-jun in doc therapy, AR-negative PC-3 cells were transfected with c-jun or c-jun, mutated at serine 63/73 (c-junA) or co-transfected with AR and c-jun or c-junA. Quantitative real time PCR (qPCR) of c-jun, AR, PSA, KLK2, NKX3.1 and c-Myc mRNA was used to determine the impact of doc treatment on gene expression. Proliferation and Western blotting assays were performed to analyze the treatment efficacy and protein expression, respectively. Results: A pronounced increase in cell proliferation, in c-junA-transfected cells, in presence or absence of doc was observed, suggesting that phosphorylation of c-jun at Ser63/73 might be necessary to respond to doc treatment. Moreover, cells that were co-transfected with AR seemed to be more responsive to doc treatment compared to cells transfected with c-junA or c-jun alone. Western blot analysis revealed that cells which were co-transfected with AR and c-jun exhibit a strong band for AR compared to other transfection groups. Time-dependent gene expression alterations after exposure to doc were observed in LNCaP and LNb4 cells. In LNCaP cells, doc treatment lead to a decreased in AR, but an increased in PSA mRNA. In contrast, a significant increase in AR mRNA was observed in LNb4 cells, whereas PSA mRNA levels gradually decreased after an initial flare. Expression pattern of KLK2 mRNA was similar to that of PSA in both cell types. NKX3.1 mRNA expression in LNCaP cells showed a significant increase after 48h, whereas in LNb4 cells, NKX3.1 expression significantly increased already after 6h but then gradually decreased throughout 48h of exposure to doc. No significant changes in the mRNA expression of c-jun or c-Myc were observed. Conclusions: Our results indicate functional significance of phosphorylated c-jun and AR in doc treated PCa cells. Moreover, we also provide further evidence of AR role in treatment resistance mechanisms. Conclusively, our study shows promising results that merits further in-depth investigation. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C226. Citation Format: Nishtman Dizeyi, Martina Viktoria Tinzl, Shao-yong Chen, Julius Semenas, Per-Anders Abrahamsson. Phosphorylation of ser63/73 in c-jun is required to respond to docetaxel treatment in prostate cancer cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C226.