<p> Kaiso is a unique member of the BTB/POZ (Broad complex, Tramtrak, Bric à brac,/Pox virus and zinc finger) zinc finger family of transcription factors with established roles in development and tumourigenesis. Kaiso was originally identified as a novel binding partner of the Armadillo catenin p120^ctn, a cytosolic co-factor and regulator of the cell-cell adhesion molecule and tumor suppressor E-cadherin. In addition to their roles in cell adhesion, the multifunctional Armadillo catenins also regulate gene expression, thus providing at least two mechanisms for their contribution to tumourigenesis. The discovery of a novel interaction between p120^ctn and the transcription factor Kaiso was therefore consistent with gene regulatory roles for Armadillo catenins. Interestingly, Kaiso represses transcription via a sequence-specific DNA binding site (TCCTGCnA) as well as through methylated CpG di-nucleotides, and one role of nuclear p120^ctn is to inhibit Kaiso DNA-binding and transcriptional repression. We recently identified sequence-specific Kaiso binding sites in a subset of Wnt/β-catenin/TCF tumour-associated target genes, and here we present data characterizing cyclin D1 as a putative Kaiso target gene.</p> <p> Kaiso binds the cyclin D1 promoter in vitro and in vivo, and artificial promoter assays revealed that Kaiso overexpression results in the repression of a cyclin D1 promoter luciferase reporter. Since cyclin D1 is highly amplified in ~50% of human breast tumours, and a cancer profiling array demonstrated that Kaiso is misexpressed in ~40% of human breast tumours, we hypothesized that Kaiso represses and regulates cyclin D1 expression to inhibit breast tumourigenesis. In fact, examination of Kaiso expression in human breast cell lines demonstrated that cyclin D1 mRNA levels were upregulated in Kaiso-depleted cells. My studies further revealed that methylation-dependent Kaiso-DNA binding may contribute to Kaiso's transcriptional repression of the cyclin D1 promoter. We also determined that Kaiso inhibits, while p120^ctn activates, β-catenin-mediated activation of the cyclin D1 promoter. These findings further support a role for Kaiso and p120^ctn in breast tumourigenesis via their modulation of the canonical Wnt signaling pathway which is highly implicated in human tumourigenesis. Together these findings support our hypothesis that Kaiso regulates cyclin D1 expression. However, further studies are required to elucidate the mechanism employed by Kaiso to elicit cyclin D1 repression and to examine how this activity may contribute to breast tumourigenesis.</p> / Thesis / Master of Science (MSc)

Breast cancer (BCa) is a leading cause of cancer-related female deaths worldwide and is a complex disease consisting of many different subtypes with varying clinical course and outcomes. Triple negative breast cancer (TNBC), an aggressive and highly metastatic subtype, is most prevalent in women of African ancestry (WAA) but the causes of this disparity are not fully understood. The goal of this study was to investigate the epidemiological and genetic profiles in ancestrally-related WAA in Barbados and Nigeria to advance knowledge and lay the foundation for development of improved or novel BCa therapeutics. To gain insight about TNBC across the African continent, a systematic review and meta-analysis was conducted. TNBC frequencies on average across Africa were estimated at 26.8% but were highest in West African countries (46.0%). We also sought to identify the epidemiological profile of BCa in Barbados—a Caribbean island with significant West African ancestry. We reviewed pathological reports for BCa from the sole public hospital in Barbados and compared those data with USA population-based data. We found a high prevalence of high prevalence of TNBC amongst women diagnosed with breast cancer in Barbados (25%), compared to 21% in non-Hispanic Black and 10% in non-Hispanic White women in the USA for the 2010-2016 period. We also investigated the somatic mutational profile of WAA with TNBC in Barbados and Nigeria using whole exome sequencing (WES) of formalin-fixed paraffinembedded TNBC tissues. This investigation revealed novel and pathogenic variants in well-known cancer-associated genes such as TP53, BRCA1 and MDC1. The somatic mutation signature in Nigerian tissues correlated with aflatoxin signature, implying a role for environmental factors influencing the genomics profile in this cohort. Copy number variants were revealed at high frequencies for PIK3CA, FGFR2 and HIF1AN genes. Collectively, these findings uncovered novel epidemiological and genetic trends in WAA with high prevalence of the aggressive TNBC subtype / Thesis / Doctor of Philosophy (PhD) / Breast cancer (BCa) is a leading cause of cancer-related death in women worldwide. Although Caucasian women are diagnosed with BCa more than women of African ancestry (WAA), more WAA unfortunately die from BCa. The reasons for this disparity are currently unknown, however, a higher proportion of WAA are diagnosed with an aggressive type of BCa called triple negative breast cancer (TNBC). This might partially explain the high cancer death rate in WAA. To understand this disparity in BCa incidence and outcomes, we investigated TNBC disease trends across the African continent and in Barbados (a Caribbean island with predominantly African ancestry) and found a high proportion of TNBC diagnoses in Barbados and West African countries. We also discovered a novel genetic profile within these groups that may be useful to develop new cancer therapies that would decrease TNBC aggressiveness and death in these populations.