The role of PROM-1/CD/AC133 in colorectal cancer.
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Background: Colorectal cancer is the result of dysregulation within classic regulatory pathways in epithelial stem-cell(s): the precursors giving rise to all other intestinal lineages. The resulting cancer stem-cell (CSC) generates tumours utilising its innate properties, e.g. self-renewal and lineage plasticity. CSCs appear to persist within a tumour as a distinct subtype responsible for local recurrence/metastasis. Therefore, therapies targeting colorectal CSCs may lead to improved cancer-specific outcome measures. The PROM-1/CD/AC133 cell surface marker has been associated with colorectal CSCs and its expression is reported as an independent negative prognostic marker. Therefore, this thesis sought to investigate the role of PROM-1/CD/AC133 in colorectal cancer. Methods: Tissue-culture, RT-qPCR, IHC, Western blotting, siRNA, PCR-array and FACS analyses were used to quantify and profile mRNA/protein expression patterns. Results: PROM-1/CD/AC133 was widely expressed in patient-matched colorectal tumour, adjacent normal epithelium, vascular invasion, lymph node metastases with significantly decreased expression in liver metastases. Furthermore, PROM- 1/CD/AC133 expression was not found to enrich colorectal cancer cell line populations for additional stem cell phenotypes (expression of ABCB1/ABCG2/BMIJ Murphy 1/CD44/LGR5/MSI-1). The data confirm the presence of alternative splice variants of PROM-1, and show that transcripts specifying PDZ binding predominate in colorectal cancer cell lines. Concomitantly, siPROM-1 was shown to modulate the expression of several key transcripts in colorectal tumourigenesis as well as regulate signal transduction pathways including the central cancer, colorectal cancer, NF-kB and p53 signalling cascades. Conclusions: PROM-1/CD/AC133 does not identify rare colorectal cancer cells responsible for tumourigenesis. However, it is associated with the regulation of signalling networks associated with cell growth, differentiation and apoptosis suggesting a potential role for this marker in colorectal tumourigenesis. The identification of specific target genes and signalling pathways in this thesis provides a springboard for further investigations into the functional role of this marker in colorectal cancer, with the potential for better treatments for this disease.
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