Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

Investigation of The Roles of Polyamines in Epibrassinolide-induced

Apoptosis in Various Prostate Cancer Cell Lines
Prostate cancer is the second leading cause of cancer-related death among men, in the worldwide. Prostate gland has the highest polyamine concentrations of any tissue in human body. Their levels were found increased in blood flow during prostate cancer, therefore they have been indicated as biomarkers for prostate cancer development. Polyamines (PAs), amine-derived organic compounds, are known for their role in cell proliferation and growth. Therefore reducing polyamine contents in tumor cells is one of the recent theurapeutic approaches. Recently many chemotherapeutic agents have been demonstrated to induce polyamine catabolism with the generation of reactive oxygen species (ROS) as by-products, deplete intracellular PA levels and cause apoptosis in different tumor models. Epibrassinolide (EBR) a biologically active member of the brassinosteroids, plant growth regulator family, has been recently indicated as an apoptotic inducer in various cancer cells without affecting non-tumor cell growth. However, the precise molecular mechanism of EBR is not entirely understood.
In this study, the apoptotic effect of EBR was investigated in androgen receptor (AR) positive LNCaP and AR negative DU145 prostate cancer cell lines by relative cell viability, mitochondria membrane potential loss determinations and the formation of DNA fragmentation. In addition, the changes in the expression profiles of caspases and Bcl-2 family members were detected by immunoblotting method. The cell cycle profile changes in response to EBR treatment were investigated by fluorescence-activated cell sorter and immunoblotting methods. The polyamine biosynthetic catabolic enzymes alterations following EBR treatment were determined by immunoblotting quantitative real-time polymerase chain reaction methods. Additionally, the roles of polyamines and AR in EBR-induced apoptosis were shown by cell viability determination and DNA fragmentation profiles by ELİSA method after the gene silencing procedure using specific siRNAs.
We aimed to determine the potential apoptotic effect of EBR related with PA metabolism in androgen-dependent LNCaP, androgen-independent DU145 prostate cancer cells in this study. EBR treatment induced cell viability loss, mitochondria-mediated and caspase-dependent apoptosis in both prostate cancer cell lines. EBR also affected the expression levels of cell cycle regulatory proteins and caused cell cycle arrest in prostate cancer cells. However, LNCaP cells were found more sensitive to EBR than DU145 cells. The reason of the different responses against EBR was investigated by targeting polyamine biosynthetic and catabolic enzymes. We concluded that the changes of protein expression levels of polyamine metabolic enzymes are critical in EBR-induced apoptosis in LNCaP cells.
We determined that in the presence of polyamine catabolic enzymes inhibitor or siRNAs, the apoptotic response against EBR was prevented in LNCaP prostate cancer cells. Since EBR is a steroid-derived molecule, its ability to induce apoptosis in relation with the androgen receptor was investigated due to the different genomic characterization of two cell lines in terms of active AR status. AR silencing method showed that AR is functional in EBR-induced apoptosis in LNCaP prostate cancer cell line. All these results highlighted the therapeutic efficiency of EBR as well as constituted an introduction to enlight the relation of EBR with other molecular pathways.