published_or_final_version / Medicine / Master / Master of Philosophy

published_or_final_version / Pathology / Master / Master of Philosophy

published_or_final_version / Pathology / Master / Master of Medical Sciences

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Obstetrics and Gynaecology / Doctoral / Doctor of Philosophy

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

Hepatocellular carcinoma (HCC) is the major type of primary liver cancer which is well-known for its high heterogenicity and metastatic potential. Despite of the current advancement in surgical resection and the availability of targeted therapy, HCC remains a barely curable and fatal disease. We previously demonstrated that deregulation of epigenetic regulators is a common event in human HCC. Herein, we identified the frequent up-regulation of the prototype of H3K9 tri-methyltransferase SUV39H1 in clinical HCCs. SUV39H1 over-expression was also significantly associated with increased Ki67 expression and the presence of venous invasion. By using both SUV39H1 over-expression and knockdown model, we consistently demonstrated that SUV39H1 contributed to HCC tumor growth and migration. Most importantly, SUV39H1 knockdown drastically suppressed in vivo tumorigenicity and extra-hepatic metastasis of HCC cells in nude mice model. These findings evidently demonstrated the oncogenic role of SUV39H1 in HCC and implied potential therapeutic targeting of SUV39H1 for HCC treatment. Molecularly, SUV39H1 knockdown HCC cell underwent morphological changes and accompanied with increased lysosomal β-galactosidase activity and elevated p21 protein and γH2AX level. This data suggested senescence induction in SUV39H1 knockdown HCC cells. SUV39H1 has been implicated in telomere regulation and transcriptional control. However, neither telomere length nor expression of tumor suppressor genes was altered in SUV39H1 knockdown HCC cells. Interestingly, we demonstrated a novel observation that SUV39H1 may potentially methylate non-histone substrates that are yet to be identified, which may contribute to the pro-tumorigenic function of SUV39H1 in HCC. We also investigated the upstream regulation of SUV39H1 and identified miR-125b as the negative post-transcriptional regulator of SUV39H1. Ectopic expression of miR-125b abolished SUV39H1 3’UTR-coupled luciferase activity and suppressed endogenous SUV39H1 at both mRNA and protein level. Clinically, miR-125b level was found inversely correlated with SUV39H1 expression. We have previously reported the frequent under-expression of miR-125b in HCC. Collectively, our data suggested that SUV39H1 up-regulation in HCC may be the sequential outcome of miR-125b down-regulation. In conclusion, we demonstrated for the first time that SUV39H1 up-regulation contributed to HCC development and metastasis, potentially via senescence evasion. SUV39H1 elevation in HCC was attributed to the loss of its negative regulator, the tumor suppressive miR-125b. / published_or_final_version / Pathology / Doctoral / Doctor of Philosophy

Breast cancer is the most common cancer in females worldwide. RIP140 was one of the first proteins recognized as nuclear receptor transcriptional cofactor which interacts with several nuclear receptors. RIP140 plays a central role in metabolic tissues with multifunctional co-regulation. It is an essential protein required for energy homeostasis and mammary gland development. RIP140 has been found to be involved in development of breast cancer in response to estrogen. RIP140 is recruited by estrogen receptors in the presence of estrogen. Increasing levels of estrogen and RIP140 stimulate their transcription and regulate proliferation and differentiation of mammary glands. We hypothesize that RIP140 may be over expressed in breast cancer and may be correlated with clinicopathological features and may thus serve as a possible new prognostic marker in breast cancer. In our study, the correlation between the RIP140 expression and survival was investigated by immunohistochemistry (IHC), and analyzed by Pearson’s chi-square and Kaplan Meier analysis. Cox regression analysis was performed to examine the relationship between clinic-pathological parameters and the survival. Total of one hundred and eighteen breast cancer samples were examined for the RIP140 staining localization in breast cancer cells. Our results showed that the IHC staining of RIP140 was observed in both cytoplasm and nucleus of breast cancer cells. The ER positive staining was significantly correlated with high nuclear expression of RIP140, but not RIP140 cytoplasmic expression. Thus nuclear RIP140 expression was examined for correlation with other clinic-pathological features and patient survival. The correlation between nuclear RIP140 expression and clinic-pathological features by Pearson’s chi-square test showed that high RIP140 nuclear staining score is associated with ER positive status (p-value=0.041) and tumor stage (p-value=0.008). Kaplan Meier test shown that nuclear RIP140 expression is not significant associated with either overall survival or disease-specific survival. However, a trend of high nuclear RIP140 score was observed with poorer overall and disease-specific survival though not statistically significant. To conclude, our results suggest RIP140 is not a useful prognostic marker for breast cancer. Further investigation with larger sample size is necessary to improve the statistical significance of the test. / published_or_final_version / Pathology / Master / Master of Medical Sciences

Esophageal cancer (EC), which is geographically diverse, has only a 10.7% five-year survival rate. One of the histologic forms, esophageal squamous cell carcinoma (ESCC), in Hong Kong accounts for 81.5% of the total EC cases and its five-year survival rate is only ~14%, due to its high frequency of metastasis. In our previous studies, functional complementation study of chromosome 9 defects led to the discovery of a novel tumor suppressor gene, Deleted in Esophageal Cancer 1 (DEC1), mapping to 9q32. DEC1 was shown to reduce tumorigenicity in a mouse model and its expression was shown to be associated with lymph node metastasis, early onset of ESCC, and familial ESCC development in a tissue microarray (TMA) study. Moreover, DNAJ (Hsp40) homologue subfamily B member 6 (DNAJB6), a molecular co-chaperone protein and the focus of the current study, was identified as a DEC1-interacting protein through a yeast two-hybrid screening. The interaction was further confirmed by the GST pull-down assay and co-localization studies. Using a TMA constructed with ESCC tissues from Hong Kong, the clinical relevance of DNAJB6 expression was demonstrated. In the present study, the role of DNAJB6 in ESCC was investigated using cell line-based in vivo and in vitro studies. DNAJB6 was shown to be down-regulated in ESCC cell lines. The two isoforms of DNAJB6 have distinct subcellular localizations, with DNAJB6a mainly localized to the nucleus and DNAJB6b diffused throughout the cell. Existence of a functional nuclear localization signal peptide and a functional nuclear export signal peptide was verified in DNAJB6a and DNAJB6b, respectively. In vitro evidence of possible DNAJB6a truncation was found. In vivo subcutaneous nude mice tumorigenicity assays showed that over-expression of DNAJB6a, but not DNAJB6b, suppresses tumor growth at the primary site, while DNAJB6a silencing enhances tumor growth. The suppressive effect of DNAJB6a depends on nuclear localization of the protein and the HPD tripeptide motif in the N-terminal J domain. In vitro function studies show that DNAJB6a over-expression impairs cell proliferation by suppressing G1/S transition. AKT1 phosphorylation is down-regulated in DNAJB6a over-expressed cells, leading to up-regulation of p27KIP1 protein expression and down-regulation of cyclin E1 protein expression, the G1/S transition promoter, in an AKT1-dependent manner. DNAJB6a silencing results in the opposite effect. Over-expression of DNAJB6b, but not DNAJB6a, instead suppresses lung colonization in an experimental metastasis assay, and prolongs survival of the mice. Silencing of DNAJB6a in immortalized normal esophageal epithelial cells initially induces a senescence-like phenotype with greatly reduced proliferation possibly due to oncogenic stress from up-regulation of AKT1 phosphorylation and cyclin E1 protein expression, but promotes EMT-like molecular alterations by up-regulating STAT3 phosphorylation and TWIST1 protein expression and resumes proliferation after prolonged culture. In summary, these results suggest that DNAJB6 plays a critical role in ESCC initiation, development, and metastasis and provides valuable insight into the understanding of ESCC tumorigenesis and metastasis. This suggests its usefulness as a biomarker candidate for detecting early ESCC tumor initiation. / published_or_final_version / Clinical Oncology / Doctoral / Doctor of Philosophy