The mechanism by which prostate cancer progresses from androgen dependence (AD) to androgen independence/castration resistance (AI/CR) is currently a major focus of prostate cancer-related research. Prostate cancers that progress to a state of AI/CR are typically resistant to most standard types of treatments. Due to its primary role in driving normal prostate cell growth and proliferation, the androgen receptor (AR) is believed to play a key role in progression. Coregulators, or any proteins which may either enhance or abrogate AR activity, are considered to be one of the potential mechanisms by which AR function may become impaired. Cyclin G-associated kinase (GAK) was initially identified as a potential coregulator of AR in a Tup 1 repressed transactivation system. A LNCaP cDNA library was screened for proteins which interacted with the NH2-terminus of AR. GAK was isolated from three independent library clones using two different AR baits (AR 1-549 and AR 1-646). This interaction was confirmed via GST pulldown and coimmunoprecipitation experiments, and preliminary luciferase assays suggested that GAK activates AR in a hormone dependent manner. In this study, my objectives were to validate GAK’s role as a coregulator of AR and to determine if overexpressing GAK affects progression to AI. In vitro luciferase assays whereby GAK was either overexpressed or knocked down in both LNCaP and PC3 cells did not significantly affect AR activity. Xenograft experiments utilizing a doxycycline (DOX) inducible lentiviral LNCaP-GAK overexpressing stable cell line demonstrated that while GAK may not play a significant role in modulating AR activity, it may adopt a more subtle role enhancing tumour take and tumour volume growth rate in vivo. While these results could not confirm GAK to be a direct coregulator of AR, it is entirely possible that GAK may influence prostate cancer progression, albeit indirectly. Recent publications report a growing amount of evidence suggesting GAK’s involvement in the critical cellular process of clathrin coated vesicle endocytosis, the dysregulation of which could potentially indirectly affect AR regulated genes. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate

Prostate cancer is one of the most frequently diagnosed cancers and the second leading cause of cancer-related deaths in male population. While localized prostate cancer can be successfully treated with surgery or radiation therapy, the metastatic disease has no curable options. Metastasis can be developed as a result of failed therapy of localized cancer or present at initial diagnosis. As metastasis is the most common cause of prostate cancer-related death, developing novel approaches and improving the efficiency of existing therapies for the metastatic prostate cancer treatment will significantly improve patients’ survival. <div><br><div>The first-line treatment option for metastatic prostate cancer and localized prostate cancer with high risk of recurrence is androgen deprivation therapy (ADT) that decreases androgen receptor (AR) signaling. However, targeting AR signaling inevitably leads to AR reactivation and cancer progression to the castration-resistant prostate cancer (CRPC) that has no curable treatment options. Moreover, about 30% of CRPC cases progress to neuroendocrine prostate cancer (NEPC), highly aggressive and lethal type of prostate cancer. </div><div><br></div><div>Recently my group has shown that protein arginine methyltransferase 5 (PRMT5) functions as an activator of AR expression in hormone-naïve prostate cancer (HNPC). In this dissertation, I demonstrate that PRMT5 also functions as an epigenetic activator of AR transcription in CRPC via symmetric dimethylation of H4R3 at the AR promoter. This epigenetic activation is dependent on pICln, a PRMT5 interaction partner involved in spliceosome assembly, and independent of MEP50, the canonical cofactor of PRMT5. PRMT5 and pICln, but not MEP50, were required for the expression of AR signaling pathway genes. In clinical samples of both HNPC and CRPC, nuclear PRMT5 and pICln protein expressions were highly positively correlated with nuclear AR protein expression. In xenograft tumors, targeting PRMT5 or pICln significantly decreased tumor growth and AR expression. </div><div><br></div><div>Overall, this work identifies PRMT5/pICln as a therapeutic target for HNPC and CRPC treatment that needs to be further evaluated in clinical setting. </div></div>

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20970号 / 医博第4316号 / 新制||医||1026(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 小川 修, 教授 戸井 雅和, 教授 万代 昌紀 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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