Medicine (St Vincent's) - Theses

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    The contribution of genetic variations in the region of the parathyroid hormone-like hormone, PTHLH, gene to breast cancer susceptibility
    Freeman, Adam Noel ( 2016)
    Aims: • Analyse the evidence for PTHLH and PTHrP, its protein product, playing a role in breast cancer and update the empirical definition of the gene. • Describe the 3-Dimensional structure of the PTHLH region and determine its system of regulatory interactions, including remote regulatory elements affecting PTHLH. • Integrate existing tools in addition to the novel perspectives generated above to enable a comprehensive annotation and analysis of genetic variants identified through molecular epidemiological techniques including Genome-Wide Association Studies (GWAS) and somatic DNA sequencing of tumour tissue to derive putative molecular mechanisms for the region’s involvement in breast cancer susceptibility. Methodology: • Review published studies and databases, integrating findings from diverse sources. • Acquire and analyse DNA and RNA sequencing, regulatory, expression, algorithm-inferred, and proximity-ligation data from multiple public data sources including ENCODE, ROADMAP, dbGAP, COSMIC and other to update the definition of PTHLH, and advance concepts of structure and regulatory function in the region. • Acquire and analyse primary GWAS data, performing imputation with multiple algorithms and references, and annotating associated variants with a suite of tools. • Use genome browsers including UCSC, WUSTL, and Golden Helix SVS, and their associated databases and tools, to analyse and visually integrate findings. Results: • PTHrP has multiple discretely functional segments active throughout the cell. It likely plays a bivalent and context-dependent role in cancer biology. Analysis of somatic variation in cancer suggests PTHrP may have a tumourigenic role within the nucleus. • PTHLH sits within a 1.3Mb TAD featuring multiple sub-structures that are integrated with the region’s regulatory function. There are activated chromatin hubs (ACHs) at protein-coding genes with evidence of extensive interaction between them. This is facilitated by the TAD’s structure, collocating them at the neck of the TAD. • The ACHs at MRPS35, KLHL42, and CCDC91 each monopolise a subordinate regulatory sub-net with a hierarchical structure. They each appear to act as important remote regulatory elements that integrate regulatory signals generated within their respective sub-nets, transferring them to PTHLH, and other genes, via ACH-ACH interactions. • There appear to be multiple discrete GWAS breast cancer association signals in the PTHLH region. Annotation of the associated variants suggests three particular regulatory elements may be its key drivers. In the context of the regulatory concepts developed in this thesis, the variants may affect a particular regulatory signal at multiple points in its assembly. PTHLH is the likely downstream target of this signal. • There are multiple poorly-describe coding, and non-coding, genes in the region that are also potential actors in breast cancer and should be investigated. Conclusion: • The PTHLH region is likely involved in the pathogenesis of breast cancer through the modification of PTHLH expression. There are likely to be other mechanisms in parallel that are yet to be fully described.