Prostate cancer is a major cause of cancer-related mortality in Australia men. Mortality is primarily due to metastasis and the development of resistance to therapy. While prostate cancer is primarily driven by the androgen receptor signalling, a number of other factors play important roles in its growth and progression. In particular, small non-coding RNA molecules called microRNAs (miRNAs) are known to be key regulators of progression in prostate cancer. Our group previously identified one specific miRNA, miR-194-5p (miR-194), as an important driver of prostate cancer metastasis; however, the molecular mechanisms by miR-194 mediates these effects is not fully understood. My PhD project aimed to identify target genes and pathways that miR-194 regulates in order to better understand its role in prostate cancer. I used cutting-edge genomic techniques and bioinformatics to identify 163 miR-194 target genes in prostate cancer. In Chapter 3, I used this data to identify a new role for miR-194 in prostate cancer. More specifically, I found that miR-194 activity was inversely correlated with androgen receptor (AR) activity in clinical samples, an observation explained mechanistically by AR-mediated repression of miR-194 expression. In concordance with these findings, miR-194 activity was significantly elevated in treatment-induced neuroendocrine prostate cancer (NEPC), an aggressive AR-independent subtype of prostate cancer. Furthermore, miR-194 can enhance transdifferentiation of epithelial LNCaP cells to neuroendocrine-like cells, a function mediated at least in part by its ability to target the FOXA1 transcription factor. Importantly, targeting miR-194 effectively inhibited the growth of aggressive models of NEPC, including patient-derived organoids. By integrating the miR-194 “targetome” with transcriptomic data, my work has provided important insights into miRNA function in cancer cells (Chapter 4). Specifically, I have found that miR-194 functions potently through canonical interactions and can mediate co-operative repression through targeting multiple sites in the same mRNA transcript. Further, I have demonstrated that miR-194 is associated with widespread non-canonical interactions that can regulate gene expression, albeit to a lesser extent than canonical sites. Finally, in Chapter 5 I have demonstrated that miR-194 has dichotomous effects on proliferation and invasion in breast and prostate cancer despite both cancers having several underlying biological similarities. Furthermore, in breast cancer I have found that miR-194 inhibits estrogen receptor expression, potentially by targeting FOXA1. Overall, my work has provided unique insights into the pathobiology of miR-194, demonstrated its role as a potential therapeutic target in aggressive AR-independent prostate cancer subtypes, and identified novel functions for miR-194 in breast cancer.Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 202
