RNA polymerase III transcription deregulation: a study on Brf1 overexpression in prostate cancer

Nam, Noor Akmar (2013) RNA polymerase III transcription deregulation: a study on Brf1 overexpression in prostate cancer. PhD thesis, University of Glasgow.

Abstract

RNA Polymerase III (Poll III) contributes to about 10% of nuclear transcription and is essential for the synthesis of short untranslated transcripts, including tRNA and 5S rRNA. Pol III deregulation has been implicated in driving cellular proliferation and transformation, along with increased expression of a number of Pol III specific transcription factors and transcripts. The significance of Pol III in clinical pathology, including that of human malignancies, remains to be formally tested. Using prostate cancer as a model, two key components of the Pol III complex, namely Brf1 and tRNAiMet, were investigated. The expression patterns of Brf1 and tRNAiMet were studied in this thesis using immunohistochemistry (IHC) and in situ hybridisation (ISH) respectively. Brf1, a subunit of transcription factor IIIB (TFIIIB), was detected predominantly in the nucleus with heterogenous staining intensity, its presence ranging from weak to strong. Examination across a wide range of tissue types and organs, both normal and tumour tissues revealed high levels of Brf1 expression in the epithelium. In addition, Brf1 expression could also be detected in connective tissues and, to a lesser extent, in muscular and nervous tissues. A number of tumour types exhibited elevated expression of Brf1 protein relative to their normal control tissues. These included prostate adenocarcinoma, B-cell lymphoma and, interestingly, tumours arising from connective tissues (sarcoma, fibrosarcoma and chondrosarcoma). As expected, tRNAiMet expression, as revealed by ISH analysis, was mostly observed in the cytoplasm, although some nuclear staining was also present. Similar to Brf1, tRNAiMet expression was detected predominantly in epithelial tissues such as the skin epidermis, prostate gland and epithelial lining of the cervix. A number of tumours were found to overexpress tRNAiMet. These included breast ductal carcinoma, oesophageal carcinoma and melanoma.
The clinical impact of Brf1 and tRNAiMet overexpression was examined using tissue microarrays (TMA) containing tissue samples obtained from patients with prostate cancer (PCa) and benign prostate hyperplasia (BPH). Collectively, data from two independent patient cohorts, Glasgow TMA: BPH (n=21), PCa (n=151) and Newcastle TMA: BPH (n=113), PCa (n=365), showed that Brf1 expression was upregulated in prostate cancer relative to BPH (p=0.0034). Brf1 expression was not found to be associated with the following clinical and biologic parameters: Gleason sum score (indicative of tumour differentiation and morphology, p=0.653); prostate specific antigen (PSA level, indicative of tumour bulk or volume, p=0.381) and Ki-67 expression (signifying cellular proliferation, p=0.034). However, and importantly, within the prostate cancer patient cohorts studied, high Brf1 expression was associated with a significantly less favourable survival outcome (Kaplan Meier analysis, p<0.001). Together, the data presented in this study support the relevance of Brf1 and tRNAiMet overexpression as part of Pol III deregulation in tumours, especially of epithelial origin. This study also suggests the potential application of Brf1 as a prognostic marker in cancer, however, this warrants a further study.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Due to copyright restrictions the full text of this thesis cannot be made available online. Access to the printed version is available.
• Keywords: RNA polymerase III, cancer, Brf1, tRNAiMet, prostate cancer.
• Subjects: Q Science > Q Science (General); R Medicine > RB Pathology; R Medicine > RZ Other systems of medicine
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cancer Sciences > Beatson Institute of Cancer Research
• Supervisor's Name: Leung, Prof. Hing Y. and White, Prof. Robert J.
• Date of Award: 2013
• Embargo Date: 15 July 2016
• Depositing User: Dr Noor Akmar Nam
• Unique ID: glathesis:2013-4458
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 22 Jul 2013 13:14
• Last Modified: 15 Jul 2016 08:07
• URI: https://theses.gla.ac.uk/id/eprint/4458