PO-385 DNA methylation profile of castration-resistant prostate cancer cells

Introduction Androgen deprivation (AD) therapy is the principle treatment for high-risk locally advanced or metastatic prostate cancer. A significant number of patients develop resistance to this therapy leading to castration resistant prostate cancer (CRPC). A proposed mechanism for CRPC progression imply androgen receptor (AR) activation in the absence of its natural ligand. Epigenetics modifications are crucial events in AR-mediated gene expression regulation. For this reason, the main objective of the present study was to determine the role of DNA methylation in the progression to CRPC. Material and methods We used the Infinium 450K BeadChip methylation array to compare the DNA methylation profile of the prostate cancer cell lines LNCaP, the canonical androgen-dependent prostate cancer cell line, and the LNCaP abl, an androgen-independent derivative of LNCaP cells. CLDN3 silencing of LNCaP cells were performed by siRNA. The expression data of these cell lines were downloaded from GEO (GSE11428). Chromatin immunoprecipitation (ChIP) assay was performed with antibodies for AcH3, H3K4me3 and H3K27me3. Results and discussions The comparison of the data from the methylation array and the expression array provided a list of genes with deregulated expression in LNCaP abl cells by changes in promoter methylation: EGF, ELF5 and HYI were upregulated by promoter hypomethylation, and CLDN3, MARKS and THBS1 were downregulated by promoter hypermethylation among others. We selected CLDN3 for further study because codify for a protein implicated in tight junctions between cells. The loss of expression of CLDN3 in LNCaP abl cells were also related with the presence of the repressive histone mark H3K27me3 at the promoter region while in LNCaP cells, that express CLDN3, the active histone marks AcH3 and H3K4me3 were present. Finally, we wanted to analyse the functional relevance of the expression changes of CLDN3 in our cellular system. We observed an increase of the invasion in LNCaP abl cells. To verify that this phenotype is due, at least in part, to the loss of CLDN3, we inhibited its expression in LNCaP cells by siRNA and observed that the lack of CLDN3 expression increases the invasion recapitulating the phenotype of the abl cells. Conclusion We have identified a panel of genes deregulated in prostate cancer cell lines resistant to hormonal treatment by changes in DNA promoter methylation. In particular the epigenetic silencing of CLDN3 may have a relevant role in the development of CRPC.