DNA methylation variations are required for reversible EMT induced by cancer-associated fibroblasts in PCa cells

Epithelial-to-mesenchymal transition (EMT) and cancer stem cells play relevant roles in metastasis and drug resistance in castration-resistant PCa. Conditioned-media from Cancer-Associated Fibroblasts from two patients with aggressive PCa induce EMT, reversible DNA methylation and transcriptional variations in androgen independent PC3, but not in androgen dependent LN-CaP cells. Focal CpG islands hyper-methylation associated to transcriptional repression of epithelial markers occurs together with widespread hypo-methylation, including promoters of EMT and stemness regulating genes resulting in their transcriptional activation. Remarkably, DNA methylation and transcription patterns are entirely reverted upon exposure to serum-free medium (mesenchymal-to-epithelial transition). DNMT3A is required for de novo methylation and silencing of CDH1 and GRHL2, the ZEB1 direct repressor, while its knock-down prevents EMT entry. These unprecedented results highlight that CAF-released factors induce reversible DNA methylation patterns required for transcriptional variations essential for EMT and stemness in androgen independent PCa cells, suggesting that similar plasticity might occur in tumour microenvironment.