published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Medicine / Master / Master of Medical Sciences

Colorectal cancer (CRC) is the second most common cancer in Hong Kong. While high-penetrance germline mutations account for up to 6% of cases, much of the variation in genetic risk may be attributable to multiple low-penetrance variants. Previous genome wide association studies (GWAS) have identified a number of CRC susceptibility alleles in Caucasian populations. Our GWAS investigated the association between genetic variants with CRC risk in the Han Chinese population in Hong Kong. In Stage I, genomic DNA samples from 455 female Chinese CRC subjects were genotyped using the Illumina 610 Quad SNP chip. Association analysis was performed on 439 cases and 771 general population female controls recruited for a study on bone mineral density. Population stratification was examined through principal components analysis using EIGENSTRAT version 2.0. From the association results, 46 SNPs (Group 1) were selected for follow-up replication (Stage II), together with 10 SNPs (Group 2) from previous GWAS studies. Genomic DNA samples from 3,571 Chinese subjects were genotyped using Sequenom MassARRAY system. Association analysis was performed on 1,505 cases and 1,452 controls. 5 SNPs (rs835378, rs2652007, rs2139273, rs2139273 and rs9286410) exceeded the genome-wide significance level in stage I, although none replicated in Stage 2, suggesting genotyping error. Results from stage II showed that the three most significant SNP were among those selected from the previous studies, yet their significance levels in Stage I were very weak . None of the SNPs selected from Stage I was significant at p<0.01 in Stage 2. Two composite scores of genetic susceptibility, one for each group of SNPs, were calculated in stage II genotype data, as the total number of high-risk alleles (according to the direction of effect in Stage I results or previous GWAS) present in an individual. Both composite scores were significantly associated with CRC risk in Stage 2 (Group 1, p=2.38 x 10-5, beta=0.046, SE=0.012; Group 2 p=1.06 x 10-7, beta=0.10, SE=0.019), suggesting that while we had insufficient power to confirm individual SNPs identified in our GWAS and the previous GWAS, these findings indicate that the SNP sets selected from Stage I results, as well as those selected from previous GWAS, contain SNPs with genuine effects on CRC risk. One SNP, rs10795668 (OR = 0.79 [CI] 95%:0.71 – 0.87 p=3.78 x 10-6), was significantly associated with CRC risk in Stage II after adjustment for multiple testing. Two further SNPs, rs6983267 and rs4939827, also achieved suggestive p-values in Stage II. All these SNPs were selected from previous GWAS in the Caucasian population, demonstrating that shared genetic factors operate for CRC in diverse populations. / published_or_final_version / Psychiatry / 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

Colorectal cancer has been a major health issue worldwide. Not only it affects the patients but it also carries physical and psychological influences to their caregivers. Despite the concerns of the psychological needs of caregivers of colorectal cancer patients, there has been a lack of a good understanding of their needs, and how to intervene in order to alleviate their psychological problems and burdens. Therefore, this thesis aimed at designing and evaluating a nurse-led telephone based psychosocial education program for improving the psychological conditions and quality of life among Chinese caregivers of patients with colorectal cancer. The nurse-led telephone based psycho-educational program was designed based on the transactional model of stress and copying. It was piloted on 6 caregivers and refined. Its efficacy over the patients discharged under the ‘usual routine hospital standard discharge care procedure’ was assessed in a randomized controlled trial on 140 Chinese caregivers of colorectal cancer patients. Caregivers in the intervention group received three telephone calls from an experienced Nurse Interventionist at 1, 3 and 5 weeks after the patients’ discharge. Each call addressed any unmet needs of the caregivers with the provision of education and psychological support. At baseline, 2 weeks, 4 weeks and 8 weeks, all caregivers were assessed for the primary outcome of depression measured by the Depression Anxiety Stress Scale (DASS), and for the secondary outcomes of anxiety, stress, burden of care and quality of life. The mixed effects model, which takes into account the extra-covariance among repeated measurements, and which is consistent with the intention-to-treat principle, was used in the efficacy analysis. Of the 140 caregivers recruited in the randomized controlled study, 5 dropped out before the end of the study. However, all the caregivers were included in the analysis. There was no significant baseline difference between the intervention and ‘usual care’ groups. The psycho-education program reduced depression more than the ‘usual care’ group by2.7 (95% CI = 0.6 to 4.8, p=0.013) units in DASS at 2 weeks, and even more by 3.5 (95% CI = 1.7 to 5.24, p<0.001) at 4 weeks. However, the ‘usual care’ group caught up at 8 weeks, and no significant effect of the psycho-education program was found (p=0.144). Moreover, the program also reduced anxiety and stress more than the ‘usual care’ group by1.83 (95% CI = 0.61 to 3.50, p=0.004) and 3.50 (95% CI = 1.74 to 5.25, p<0.001) respectively at follow-up. In addition, the burden of care and quality of life were also generally improved more in the psycho-education program group. Furthermore, strong positive associations among depression, stress, anxiety, and burden of care were found. Caregivers perceived to have a high burden of care would be associated with more depression, stress or anxiety(r = 0.53, p<0.001). Moreover, depression, anxiety, and stress had a strong negative association with the physical, psychological, social relationship and environmental well-being but not with social relationships(r = -0.16, p = 0.550). In conclusion, this thesis has developed the first nurse-led telephone based psycho-education program for caregivers of colorectal cancer patients. The program can effectively help caregivers in reducing their feelings of stress from depression, anxiety, stress and the burden of care, as well as improving their quality of life. It paves the way for a new direction for a comprehensive colorectal cancer care service in addressing the caregivers’ needs. / published_or_final_version / Nursing Studies / Doctoral / Doctor of Nursing

published_or_final_version / Pathology / Master / Master of Philosophy

The current study examined the impact of plant sterols, stanols, sterol esters, and stanol esters on (i) cholesterol-lowering efficiency, (ii) gene expression of ABCG5 and ABCG8 sterol transporters in the liver and small intestine, and (iii) colon mucosal cell proliferation in hamsters. After 5 weeks on experimental diets, plasma total cholesterol levels were reduced ( P<0.05) by stanols, sterol esters and stanol esters compared to cholesterol-control diet. Different PS analogs did not alter ABCG5 and ABCG8 mRNA levels in small intestine and liver as compared to cholesterol control. In addition, colon mucosal cell proliferation was 21.4% lower (P<0.01) in group fed 0.7% stanol esters relative to cholesterol control. Results suggest that hypocholesterolemic effects of PS analogs are not associated with changes of liver and small intestine ABCG5 and ABCG8 sterol transporters. Data also indicated that plant stanol ester may possess anticarcinogenic properties.

The IGF system is a crucial regulator of normal growth and development, however dysregulation of the system on multiple levels is associated with the incidence of a wide variety of malignancies including the breast, thyroid, lung, and colon, making the IGF system an important anti-cancer therapeutic target. Due to its role in mediating cellular proliferation, protection from apoptosis, and metastasis, traditional focus has been set on examining the role of the type 1 IGF receptor [IGF1R] in cancer. However there is mounting evidence to suggest the insulin receptor [IR] may also be involved in the potentiation and pathogenesis of cancers. The observation that IGF-II is overexpressed, compared to normal tissues, by cancers suggests signaling via target receptors by this ligand has important implications on cancer pathogenesis. Indeed, both the IGF1R and IR have been demonstrated to be up-regulated in a variety of malignancies. In regards to IR isoform, the IGF-II binding IR-A is preferentially expressed by a number of cancer cell types. Together with the observation that an autocrine proliferative loop exists between IGF-II and the IR-A in malignant thyrocytes and cultured breast cancer cells, suggests signaling via the IR-A may play a role in cancer cell growth and survival. However, very few studies on the IR-A have been conducted in cells co-expressing the IGF1R. This is mainly due to the difficulties associated with discrimination between signaling arising from IGF1R homodimers, IR-A homodimers, and IGF1R/IR-A hybrid receptors. It is not known how the IR-A interacts, and functions in conjunction with the other receptors of the IGF system to signal biologically relevant outcomes, especially in terms of anti-cancer therapeutics that aim to block and down-regulate the IGF1R. Current anti-cancer therapies targeting the IGF system have concentrated on blocking IGF signaling via the IGF1R, due mostly to the functional properties of the receptor, but also in part due to the metabolic consequences associated with blockade and inhibition of the IR. This individual targeting of the IGF1R potentially leaves a pathway by which IGF-II secreted by the tumour can circumvent current IGF1R based therapies. Consequently, this thesis investigated whether the IR-A could compensate for the targeted loss of the IGF1R and how the IR-A interacts with the IGF1R in cells co-expressing these two receptors. In addition, the individual ability of the IR isoforms to signal biological outcomes in response to IGF stimulation was assessed. The main experimental techniques used throughout this body of work included; assessment of protein expression and activation by Western blot, siRNA mediated gene silencing, and measures of cell proliferation, survival, and migration. The key areas of investigation included: 1. Investigation of the individual ability of the IR isoforms to signal biological outcomes in response to IGF stimulation 2. Identification of an appropriate cell line model in which to investigate the interactions between the IR-A and IGF1R 3. Optimisation of siRNA mediated knock-down of the IR-A and IGF1R in SW480 colorectal adenocarcinoma cells 4. Determination of the biological role of the IR-A in SW480 cells co-expressing the IGF1R The key findings from this work included: 1. The IR-A could not compensate for IGF1R depletion in SW480 cells 2. Dual silencing of the IR-A and IGF1R indicated signaling via the IGF1R was dominant to signaling via the IR-A in SW480 cells 3. Signaling via IR-A/IGF1R hybrid receptors may not be as potent as signaling via IGF1R homodimers 4. IGF-I at physiological concentrations can stimulate biological responses via both isoforms of the IR. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337339 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2008

Bibliography: leaves 214-236. / xviii, 238 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physiology, 1999

The IGF system is a crucial regulator of normal growth and development, however dysregulation of the system on multiple levels is associated with the incidence of a wide variety of malignancies including the breast, thyroid, lung, and colon, making the IGF system an important anti-cancer therapeutic target. Due to its role in mediating cellular proliferation, protection from apoptosis, and metastasis, traditional focus has been set on examining the role of the type 1 IGF receptor [IGF1R] in cancer. However there is mounting evidence to suggest the insulin receptor [IR] may also be involved in the potentiation and pathogenesis of cancers. The observation that IGF-II is overexpressed, compared to normal tissues, by cancers suggests signaling via target receptors by this ligand has important implications on cancer pathogenesis. Indeed, both the IGF1R and IR have been demonstrated to be up-regulated in a variety of malignancies. In regards to IR isoform, the IGF-II binding IR-A is preferentially expressed by a number of cancer cell types. Together with the observation that an autocrine proliferative loop exists between IGF-II and the IR-A in malignant thyrocytes and cultured breast cancer cells, suggests signaling via the IR-A may play a role in cancer cell growth and survival. However, very few studies on the IR-A have been conducted in cells co-expressing the IGF1R. This is mainly due to the difficulties associated with discrimination between signaling arising from IGF1R homodimers, IR-A homodimers, and IGF1R/IR-A hybrid receptors. It is not known how the IR-A interacts, and functions in conjunction with the other receptors of the IGF system to signal biologically relevant outcomes, especially in terms of anti-cancer therapeutics that aim to block and down-regulate the IGF1R. Current anti-cancer therapies targeting the IGF system have concentrated on blocking IGF signaling via the IGF1R, due mostly to the functional properties of the receptor, but also in part due to the metabolic consequences associated with blockade and inhibition of the IR. This individual targeting of the IGF1R potentially leaves a pathway by which IGF-II secreted by the tumour can circumvent current IGF1R based therapies. Consequently, this thesis investigated whether the IR-A could compensate for the targeted loss of the IGF1R and how the IR-A interacts with the IGF1R in cells co-expressing these two receptors. In addition, the individual ability of the IR isoforms to signal biological outcomes in response to IGF stimulation was assessed. The main experimental techniques used throughout this body of work included; assessment of protein expression and activation by Western blot, siRNA mediated gene silencing, and measures of cell proliferation, survival, and migration. The key areas of investigation included: 1. Investigation of the individual ability of the IR isoforms to signal biological outcomes in response to IGF stimulation 2. Identification of an appropriate cell line model in which to investigate the interactions between the IR-A and IGF1R 3. Optimisation of siRNA mediated knock-down of the IR-A and IGF1R in SW480 colorectal adenocarcinoma cells 4. Determination of the biological role of the IR-A in SW480 cells co-expressing the IGF1R The key findings from this work included: 1. The IR-A could not compensate for IGF1R depletion in SW480 cells 2. Dual silencing of the IR-A and IGF1R indicated signaling via the IGF1R was dominant to signaling via the IR-A in SW480 cells 3. Signaling via IR-A/IGF1R hybrid receptors may not be as potent as signaling via IGF1R homodimers 4. IGF-I at physiological concentrations can stimulate biological responses via both isoforms of the IR. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337339 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2008