Identification and characterisation of novel mechanisms affecting prostate cancer cell growth

Abstract

Prostate cancer development and progression to lethal metastatic castration-resistant prostate cancer (CRPCa) is driven by the androgen receptor. Androgen deprivation therapy (ADT) is the first line of treatment used to control cancer growth. Although ADT is usually effective, the recurrence of castration-resistant prostate cancer is common and ultimately lethal. Progression to CRPCa is thought to involve persistence of AR signalling and reprogramming of the AR transcriptional landscape, allowing tumour cells to continue to grow despite low levels of circulating androgens. The overall aim of this study was to identify and characterise mechanisms affecting prostate cancer cell growth. To do this I used RNA-sequencing in the androgenresponsive LNCaP cell line, coupled with previously published RNA-sequencing of advanced prostate cancer treated with ADT and clinical prostate cancer expression data to identify androgen-regulated genes, alternative isoforms and pathways. A set of 660 genes showed reciprocal changes in expression in response to acute androgen stimulation in culture, and androgen deprivation in patients with prostate cancer. A multiple dataset meta-analysis strategy coupled with gene ontology analysis has identified glycosylation as a novel androgen regulated pathway. Although patterns of glycosylation are known to change in prostate cancer the mechanisms underlying these changes are not well understood. The data in this study suggest androgens may increase the aggressiveness and metastatic potential of PCa cells through mediating changes in glycosylation patterns. Further investigation into the sialyltransferase enzyme ST6Gal1 has shown that high levels alter the expression of key epithelial to mesenchymal transition (EMT) makers and increase the invasion potential of prostate cancer cells, whilst reduction significantly decreased cell proliferation, cell to matrix adhesion, migration and invasion capability. Together with the androgen regulated transcriptional changes, the RNA sequencing data also identified a number of androgen regulated alternative mRNA isoforms, including promoter switches for the RLN1 and RLN2 genes. In summary correlation of gene expression changes in prostate cancer cells in response to acute androgen stimulation with those repressed in patients by ADT has revealed a new panel of clinically relevant androgen regulated genes. Analysis of this panel has demonstrated important androgen control over glycosylation modifications has important implications for prostate cancer biology, and also suggests further targets for future analysis.