published_or_final_version / Biological Sciences / Master / Master of Philosophy

Polycomb group (PcG) proteins governs the regulation of diverse cellular functions, such as cell fate decision, cell cycle progression, maintenance of embryonic stem cell pluripotency, and DNA damage repair. Although aberrant expression of PcG proteins has been frequently reported in different cancer types, CBX8 is one of the least studied PcG family members in cancer. Recently, a study showed that forced expression of CBX8 in normal human and mouse fibroblasts demonstrated that cells could bypass senescence via INK4a-ARF repression; while another report demonstrated that CBX8 was involved in MLL-AF9-linked leukemogenesis. Despite accumulating evidence on CBX8-related carcinogenic functions, the role of CBX8 in solid cancers has not been investigated thus far. This study is therefore initiated to investigate and establish the functional role of CBX8 in colorectal cancer. In this study, expression of CBX8 in 121 pairs of human CRC samples was analyzed by immunohistochemistry; and data were correlated with different clinicopathological parameters. To evaluate the functional effects of CBX8, CBX8 overexpressed and downregulated clones were established from three CRC cell lines. The in vitro effects of CBX8 on cell proliferation, cell cycle progression and apoptosis profiles were investigated; and the effects of CBX8 on tumorigenicity in vivo were further demonstrated in mice xenograft models. The results showed that CBX8 expression was downregulated or loss in approximately 48.8% of human colorectal tumors, and downregulated or loss of CBX8 expression were mainly observed in tumors with intermediate to later stages (stage II to IV). Moreover, expression of CBX8 showed a significant inverse correlation with colorectal tumor sizes (P < 0.0001). Ectopic expression of CBX8 in CRC cell lines resulted in inhibition of cell proliferation, clonogenic ability and anchorage-independent growth, which are hallmarks of tumorigenesis. Conversely, downregulation of CBX8 promoted proliferation and clonogenic ability. Moreover, it was found that restoring CBX8 expression could induce G0/G1 arrest of cell cycle. The tumor suppressive role of CBX8 in colorectal cells was further demonstrated in vivo through subcutaneous and orthotropic mice tumor models; followed by immuno-staining of the proliferation marker Ki-67. To unveil the possible mechanisms behind the tumor suppressing effects of CBX8, two signalling pathways commonly engaged in CRC were evaluated. At least part of the effects could be attributed to the mediation of MAPK signaling pathway; whereas the Wnt signalling was not affected by CBX8. This study demonstrated for the first time the loss of CBX8 expression in intermediate and late stage tumors, and was the first to report the tumor suppressing ability of CBX8 in solid cancers. The effects of CBX8 in this study were different to the functional implications reported in the current literature. This functional divergence in distinct cell types suggested a dynamic role of CBX8 depending on specific cellular context. / published_or_final_version / Surgery / Master / Master of Philosophy

Uveal Melanoma (UM) is the most common malignant intra-ocular tumor in adults. Forty-five percent of UM patients develop metastasis within fifteen years of the initial diagnosis. Cutaneous Melanoma (CM) is a highly metastatic cancer that accounts for the majority of skin cancer deaths. Current treatments are not especially effective for the metastatic phase of the disease. Therefore, the identification of new molecular targets that can be exploited in the clinic are needed. / KISS1 is a putative human metastasis suppressor gene. The purpose of this study was to investigate the expression of KISS1 in melanoma and its potential value as a prognostic marker. / From results in vitro and in vivo we were able to characterize KISS1 in UM for the first time as well as its expression at the protein level, in CM. The correlation between KISS1 expression and UM survival rate suggests an important role for KISS1 as a prognostic marker in this tumor.

[Truncated abstract] Erythropoietin (Epo) is a glycoprotein hormone involved in the formation of erythrocytes, by controlling survival, differentiation and proliferation. The technique of cDNA Representational Difference Analysis was utilized to investigate J2E-NR cells that demonstrate a viability response to Epo, but not differentiation or proliferation. The aim of this project was to identify genes that may be upregulated in response to Epo-induced survival; however, no change in gene expression was detected. This was most probably because any changes were below the limit of detectability for the cDNA RDA technique, or the viability effect was mediated post-transcriptionally. Next, it was decided to investigate HLS5, a putative tumour suppressor that was identified in a myeloid variant of the J2E cell line and had been shown to cause apoptosis. A number of HeLa cell lines inducible for Hls5 expression using the tet-off system were produced; despite extremely low expression, Hls5 was shown to produce marked suppression of growth and proliferation, particularly in colony assays colony size and numbers were halved for one induced clone. … A number of haemopoiesis-associated genes were downregulated (viz. globin genes and the Epo receptor gene), which suggested Hls5s role in the myeloid variant of J2E cells, may be to suppress genes expressed in the erythroid lineage. In addition, several interferon-responsive genes were decreased in cells with elevated HLS5, suggesting it may play a role in negatively regulating interferon signaling. Online databases were also searched for information on HLS5, and showed that it is significantly downregulated in liver, lung and uterine cancers, supporting the proposition that HLS5 is a tumour suppressor gene. In summary, a number of approaches were taken to identify the effects of the Hls5 protein. It appears that it strongly suppresses proliferation and that this is likely mediated through an effect on mitosis. This may also result in apoptosis of overexpressing cells. It is possible that this is the mechanism through which HLS5 exerts its potential tumour suppressor function, as a number of tumour suppressors appear to be associated with mitosis/apoptosis control. Hls5 is also likely to have other functions in haemopoietic cells, which includes downregulation of erythroid-specific genes and suppression of interferon responses.

Thesis (M.S.)--State University of New York at Binghamton, Department of Biological Sciences, 2007. / Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 99-110) Also available in print.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2006. / Title from first page of PDF file (viewed Feb. 19, 2009). Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 116-125).

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 192-203). Also available in print.