Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M.Sc.(Physiology)--Faculty of Health Sciences))--University of Pretoria, 2003. / Includes bibliographical references (p. 92-107). Also available online.

Thesis (Ph. D.)--University of Hong Kong, 1985.

published_or_final_version / Anatomy / Master / Master of Philosophy

Background: Esophageal squamous cell carcinoma (ESCC) has been increasing in incidence, but knowledge of the genetic basis of this disease remains limited. In general, esophageal carcinoma can be divided into two main types: Esophageal Squamous Cell Carcinoma (ESCC) and Esophageal Adenocarcinoma (EAC). The pathogenesis of esophageal carcinoma still remains unclear, although some risk factors like chronic irritation, or chronic inflammation which may be caused by diseases such as gastroesophageal reflux disease (GERD) or unhealthy lifestyles like smoking have been proved to be related to the carcinogenic process. Diagnosis and treatment for this kind of cancer have continue to develop and evolve, but the 5-year overall survival rate is still relatively low. Therefore, it is clinically important to identify any potential genetic changes which may help us to discover some useful biomarker targets for the further development of more direct and harmless targeted therapy for our esophageal cancer patients. Objectives: In this study, I aimed to identify some potential oncogenic microRNA (miRNA) and to study their clinical meaning in ESCC patients. Methods: Microarray was applied to identify differentially expressed miRNAs in ESCC tumour tissue, compared with corresponding adjacent non-tumour esophageal tissue. One candidate oncogenic miRNA, miR-665, was investigated in the present study. After testing the expression level of miR-665 in ESCC cell lines and patients’ samples with RT-PCR, miR-665 stably expressing cells was established using two ESCC cell lines (KYSE30 and KYSE510). Functional characterization was then conducted using in vitro and in vivo assays to examine the effect of miR-665 towards the development of ESCC. Bioinformatic software such as Target Scan was used to generate a list of predicted target genes that may be modulated by miR-665. Results: The high expression of miR-665 has been confirmed in ESCC tissues and cell lines, showing the potential carcinogenic function of miR-665. Ectopic expression of miR-665 also demonstrates its ability to enhance tumour growth and invasion in vitro and in vivo. Bioinformatic analysis of miR-665 predicted targets showed putative binding sites for miR-665 within the 3’UTR region of NLK. Conclusions: This study has identified a novel miRNA and a related gene which might play an important role in the pathogenesis of ESCC, affecting the cancer process and tumour growth. This may help to find potential new biomarker for the future improvement and development of new treatment of ESCC patients. / published_or_final_version / Clinical Oncology / Master / Master of Philosophy

Esophageal squamous cell carcinoma (ESCC), the major histological subtype of esophageal cancer, is one of the most common malignancies with poor prognosis in the world. Despite continued development of diagnosis and treatment, ESCC remains the sixth leading cause of cancer death worldwide. Current treatment regimens in ESCC are often characterized by ineffectiveness and poor selectivity. Therapeutic methods directed at cancer-associated genes or cancer stem cells (CSCs) may be effective approaches to cure this deadly cancer. Therefore, this study aims to identify specific ESCC-related genes and cancer stemness genes which help us to develop new targeted agents to achieving objective, long-lasting therapeutic responses in ESCC. To obtain an accurate overview of genetic changes occurring in ESCC patients, our group performed microarray-based mRNA expression profiling and high-throughout transcriptome sequencing (RNA-Seq) to compare differentially expressed genes between ESCC tumors and their corresponding non-tumorous tissues. Prostate stem cell antigen (PSCA) was considered to be a candidate of primary interest due to significantly reduced expression in both microarray and RNA-Seq data. In this study, we examined the role of PSCA on the pathogenesis of esophageal cancer. Our results showed that PSCA was frequently down-regulated in ESCC. Its expression was negatively regulated by transcription factor SOX5. Also, we provided evidence that down-regulation of PSCA was associated with poor clinical outcomes of patients with ESCC. Both in vitro and in vivo assays revealed that PSCA could arrest cell cycle progression and promote differentiation. To further elucidate the mechanism involved in biological function of PSCA, we performed co-immunoprecipitation and mass spectroscopy to identify proteins that associate with PSCA. This study found that RB1CC1, a key signaling node to regulate cellular proliferation and differentiation, interacted specifically with PSCA both in vitro and in vivo. Binding of PSCA and RB1CC1 in cytoplasm resulted in stabilization and translocation of RB1CC1 into nucleus and then further regulates the crucial cell cycle and differentiation genes. Furthermore, in order to identify the cancer stemness genes specifically expressed in CSCs of ESCC, we utilized gene expression analysis to profile 34 stemness-associated genes in ESCC specimens. Developmental pluripotency associated 4 (DPPA4), a well known pluripotent marker of stem cell, was considered as the best candidate. Our following histopathological study demonstrated that DPPA4 rigorously marked the rare CSCs, in contrast to core stemness factors (OCT4 and SOX2) and previous reported CSC markers (CD90 and CD44), which expressed in a large population of cancer cells. Moreover, the expression of DPPA4 was also found to have prognostic value in ESCC, as the appearance of DPPA4+ cells was significantly associated with poor differentiation, advanced stage and higher incidences of lymph node metastasis. Finally, our functional studies showed that ESCC cells expressing exogenous DPPA4 conferred an enhanced ability to initiate tumor, self-renew, resist chemotherapy and metastasize through lymphatic system. In summary, this study provide evidence indicating that novel tumor suppressor gene PSCA and cancer stemness gene DPPA4 may contribute to the development and progression of ESCC. Additionally, they may serve as potential targets for development of effective therapeutic strategies. / published_or_final_version / Clinical Oncology / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / toc / Diagnostic Radiology / Master / Master of Philosophy

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

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