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|Title:||Analyzing the biological role of the Transcription Factor Kaiso in Breast Tumourigenesis|
|Abstract:||<p>Kaiso is a member of the BTB/POZ-ZF (hereafter POZ-ZFL), family of transcription factors that have significant roles in development and cancer. Kaiso was identified as a p120<sup>ctn</sup> interaction partner, and has a highly conserved protein-protein interaction POZ domain at its N-terminus and three DNA binding C<sub>2</sub>H<sub>2</sub> zinc fingers (ZF) at its C-terminus. Kaiso is a bi-modal transcriptional regulator; it recognizes and binds both a sequence specific Kaiso binding site (KBS), TCCTGCNA, and methylated CpG-dinucleotides. Since Kaiso was initially identified, several tumourigenesis-associated Wnt signalling target genes such as <em>matrilysin</em>, <em>cyclin D1, metastasin, MTA2, Wnt11</em> and <em>siamois</em> have been found to be negatively regulated by Kaiso. These data implicated Kaiso in Wnt signalling and in fact, the rescue of the β-catenin induced double-headed phenotype in Xenopus laevis by Kaiso overexpression provided the first strong experimental evidence that Kaiso was linked to Wnt signalling. Since then, Kaiso has been implicated in tumourigenesis both as a potential tumour suppressor (decreased Kaiso expression in 30% of human breast tumours and 50% of human ovarian tumours) and as an oncoprotein (Kaiso-null mice being viable, fertile and displaying delayed tumour onset when crossed with APC<sup>Min/+</sup> tumour susceptible mice). Interestingly, Kaiso protein expression varies in human tumour tissue and Kaiso's subcellular localization varied according to the tissue microenvironment.</p> <p>The goal of this research project was to elucidate the biological role of Kaiso in breast tumourigenic processes, and to correlate the expression patterns of <em>kaiso</em> and its target genes (<em>cyclinD1</em>, <em>matrilysin and mta2</em>) in human breast normal and tumour tissue. Focus formation =assays, showed that Kaiso over-expression increased focus formation in Rat-l rodent non-transformed cells, suggesting that Kaiso promotes oncogenic transformation. Kaiso misexpression tumourigenesis-associated processes of cell proliferation, motility and invasion were also examined on MCF7 human breast adenocarcinoma cells. Kaiso misexpression did not have a significant effect on cell proliferation but Kaiso depletion appeared to hinder cell motility and invasion in breast tumour cells, thus suggesting that Kaiso displays tumour promoting properties.</p> <p>We also examined the expression patterns of Kaiso's target genes in matched pairs of breast lobular and ductal carcinoma tissues, and detected increased <em>matrilysin</em> levels relative to <em>kaiso</em> in all patient samples analyzed by qRT-PCR. There was no noticeable trend in <em>mta2</em> levels relative to Kaiso in the ductal carcinomas, but there was a positive correlation between <em>mta2</em> and <em>kaiso</em> in the lobular carcinomas. In contrast, <em>cyclinD1</em> levels were varied across all tissues examined.</p> <p>This trend continued in the immunohistochemical analysis performed on the ductal and lobular breast carcinomas, with variable CyclinDl staining occurring in all tissues examined. However, there was an increase in nuclear and cytoplasmic Kaiso in the lobular breast carcinomas, coinciding with decreased, cytoplasmic p120<sup> ctn</sup> and significantly decreased E-cadherin in the tumour tissue relative to normal. Our ductal carcinomas displayed negligible Kaiso staining, along with decreased p120<sup> ctn</sup> and increased cytoplasmic E-cadherin in the tumour tissue relative to normal, although p120<sup> ctn</sup> and E-cadherin did not display the expected localization in normal tissue. The expression and sub-cellular localization of these proteins are heavily dependent on the tumour microenvironment and external factors such as patient age, disease progression and type of carcinoma. In conclusion, data suggests that Kaiso plays a tumour promoting role in the processes of transformation, cell motility and migration in MCF7 breast tumour cells.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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