Gene expression profiles and biomarker identification for KMT5A identifies novel potential therapeutic targets in prostate cancer

Abstract

Prostate cancer (PC), is initially androgen dependent due to the androgenic nature of the organ. Hence, initial therapy comprises androgen depletion via chemical castration in conjunction with an anti-androgen therapeutic. However, patients relapse and the tumours aggressively re-grow in a castrate resistant (CRPC) manner. In CRPC, androgen receptor (AR) signaling remains functional via numerous mechanisms hence the AR remains a viable therapeutic target. However, treatment with current AR targeting therapeutics also results in relapse indicating the potential of targeting AR signaling indirectly by targeting AR co-factors. Recently, KMT5A, a lysine methyltransferase, has been identified as an AR co-activator exclusively in models of CRPC. A number of KMT5A inhibitors have been identified recent years, which would enhance the possibility of targeting KMT5A in PC. This thesis aims to determine the signature of genes that are regulated directly by KMT5A or by combined activities of AR and KMT5A in PC cell lines and to further identify biomarkers for KMT5A activity. These aims were approached using Illumina Human HT-12 arrays to detect KMT5A gene expression profiles in an in vitro cell line model of androgen independent PC (LNCaP-AI cells). Microarray data analysis revealed a number of androgenregulated genes to be modulated by KMT5A concurrently, and other genes that were found to be regulated by KMT5A activity, and a further cohort of genes that were found to be regulated solely by KMT5A. CDC20 was selected for further study from the identified KMT5A regulated genes as a possible biomarker for KMT5A activity in aggressive PC. KMT5A was found to regulate CDC20 mRNA and protein expression. The enzymatic activity of KMT5A was demonstrated to affect CDC20 expression through the enrichment of the H4K20me1 mark at the CDC20 promoter in androgen-sensitive (LNCaP) and androgen-independent (LNCaP-AI) cells. The regulation of CDC20 by KMT5A expression, therefore identifies CDC20 as putative biomarker for KMT5A activity. KMT5A was also shown to influence CDC20 expression via p53. Knockdown of KMT5A inhibited the mono-methylation of p53 at K382 to enhance p53 activity, demonstrated by increased p21 expression which negatively regulated CDC20 ii expression. These findings were confirmed using commercially available KMT5A inhibitors Ryuvidine and UNC0379. In summary, KMT5A inhibition in PC cells using small molecule inhibitors may provide benefit to patients that have relapsed on AR- targeting therapeutics and as such requires further investigation as a potential therapeutic target. CDC20 was identified as a putative biomarker for KMT5A activity which may prove useful to detect effective KMT5A inhibition in these studies.