published_or_final_version / abstract / Obstetrics and Gynaecology / Master / Master of Philosophy

published_or_final_version / abstract / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / Pathology / Doctoral / Doctor of Philosophy

published_or_final_version / Clinical Oncology / Master / Master of Philosophy

University of Macau / Institute of Chinese Medical Sciences

published_or_final_version / Biological Sciences / Master / Master of Philosophy

published_or_final_version / Obstetrics and Gynaecology / Master / Master of Philosophy

Emerging evidences have documented that aberrant expression of FOXM1 is closely associated with human cancers. A recent comprehensive genome analysis has revealed that FOXM1 signaling is one of the major pathways involved in ovarian cancer oncogenesis. However, the regulatory network of FOXM1 in exerting the metastatic phenotypes remains unknown. Therefore, the identification of FOXM1 downstream targets will assist in understanding of its molecular mechanism in ovarian cancer oncogenesis. In this study, by bioinformatics and a series of functional analyses, we identified DLX1 as a novel target of FOXM1. Our results clearly demonstrated that enforced expression of FOXM1 (FOXM1B and FOXM1C) could increase DLX1 in mRNA and protein levels. Conversely, depletion of FOXM1 by Thiostrepton (FOXM1 specific inhibitor) or RNAi knockdown could reduce DLX1 expression. Importantly, we demonstrated that the changes of DLX1 expression were in concomitant with the expression of a positive control gene, Cyclin-D1. Additionally, the luciferase promoter assay further showed that there are two conserved FOXM1 binding sites TFBS1 and TFBS2 which located at -61~-52bp upstream and -737~727bp upstream of the transcription factor binding sites (TSS) of DLX1 promoter respectively. In comparison of two binding sites, the more conserved binding site, TFBS1, seems have higher importance of FOXM1 binding in DLX1 transcriptional activation. Furthermore, our study using immunohistochemical and Q-PCR analyses showed that DLX1 was frequently up-regulated in ovarian cancer samples. Noticeably, clinicopathological analysis revealed that the upregulated DLX1 was significantly associated with not only the overexpressed FOXM1 (P=0.001) but also high grade ovarian cancer (P<0.001). Previous studies have reported that DLX1 is a homeobox transcription factor controlling neuron migration and proliferation in embryogenesis. However, the oncogenic functions of DLX1 are rarely reported. In this study, we revealed that DLX1 could promote ovarian cancer cell proliferation and cell migration which are the main phenomena found in high grade tumors. To the best of our knowledge, this is the first report showing the regulation of FOXM1 on DLX1 and the metastatic functions exerted by DLX1 in ovarian cancer cells. Although ovarian cancer cells are epithelial cell type which is different from neurons, the similar cell functions derived from DLX1 reflecting that both cell types share the similar signaling pathway of DLX1. However, further investigation on the downstream network of DLX1 and the in vivo tumorigenic capacities in ovarian cancer cells are warranted. To conclude, we have identified DLX1 as a novel target of FOXM1 and frequently up-regulated in high grade ovarian cancer. The in vitro tumorigenic assay demonstrated DLX1 could promote cell proliferation and cell migration which are the metastatic properties usually found in high grade ovarian cancer. Therefore, these data highlight the possibilities of using DLX1 as a biomarker and therapeutic target in combating ovarian cancer in the future. / published_or_final_version / Obstetrics and Gynaecology / Master / Master of Philosophy

Ovarian cancer is a leading cause of death among of gynecological cancers. Current therapies are ineffective with a poor 5-year survival of only ~25%. p70 S6 kinase (p70 S6K) is a downstream target of the phosphatidylinositol 3-kinase pathway and is frequently activated in human ovarian cancer. However, the molecular targets and signaling pathways by which p70 S6K may affect tumor development and progression are poorly understood. Interestingly, in the laboratory, Mdm2, an important negative regulator of the p53 tumor suppressor, was identified in a yeast two hybrid screening of potential interacting partners for p70 S6K. In this study, I aimed to investigate the specific interaction of p70 S6K and Mdm2 and determine how this may contribute to ovarian tumorigenesis. Using a co-immunoprecipitation assay, the in vivo interaction of p70 S6K and Mdm2 in human ovarian cancer cells was confirmed. Upon UV-induced genotoxic stress, p70 S6K activation was associated with Mdm2 phosphorylation on S166 and subsequent p53 accumulation. This could be reversed by the use of rapamycin and p70 S6K siRNA to inhibit its kinase activity and expression respectively, confirming that the effect was p70 S6K specific. Conversely, ectopic expression of wildtype p70 S6K or a constitutively active mutant of p70 S6K, D3E-E389 (D3E) was sufficient to induce phosphorylation of Mdm2. Moreover, the p70 S6K mediated activation of Mdm2 was independent of p53 mutations. Similar results were observed upon other stress challenges such as hypoxia using hypoxia mimicking agent desferrioxamine (DFX). These findings identify Mdm2 as a new target of p70 S6K and reveal that p70 S6K intervenes the Mdm2-p53 regulatory loop in ovarian cancer, which may provide a survival advantage to cancer cells under stress conditions. / published_or_final_version / Biological Sciences / Master / Master of Philosophy

published_or_final_version / abstract / toc / Medicine / Master / Doctor of Medicine