Oral Presentation ESA-SRB Conference 2015

Surveying the epigenome landscape of the prostate cancer microenvironment: identification of estrogen receptor α as a key differentially methylated gene (#159)

Mitchell Lawrence 1 , Ruth Pidsley 2 , Stuart Ellem 1 , Luc Furic 1 , Shalima Nair 2 , Hugh French 2 , Aaron Statham 2 , Ola Larsson 3 , Mark Frydenberg 1 , John Pedersen 4 , Grant Buchanan 5 , Renea Taylor 1 , Susan Clark 2 , Gail Risbridger 1
  1. Monash University, Clayton, Vic, Australia
  2. Garvan Institute of Medical Research, Sydney, NSW, Australia
  3. Karolinska Institutet,, Stockholm, Sweden
  4. TissuPath Pathology, Melbourne
  5. Basil Hetzel Institute, Adelaide, SA, Australia

The stroma acquires molecular and functional changes in prostate cancer. This was once assumed to be a transient reaction to aberrant signalling from nearby cancer cells. Yet, there is increasing evidence that stroma undergoes more permanent changes, because non-malignant prostate fibroblasts (NPFs) and cancer-associated fibroblasts (CAFs) maintain their differences in the absence of epithelium. For example, steroid hormone receptors in tumour stroma, including estrogen receptor α (ERα), are differentially expressed between NPFs and CAFs. Therefore, we hypothesised that tumor stroma acquires epigenetic modifications that alter the expression of steroid hormone receptors and promote tumour progression.

Primary cultures of NPFs and CAFs were established from radical prostatectomy specimens from 15 patients. In vivo tissue recombination assays were used to verify the functional differences between cells and show that CAFs, but not NPFs, induced prostate epithelial cells to form tumours. Whole genome bisulphite sequencing was used to construct the first complete epigenome map of human tumour stroma.

Our data demonstrated that NPFs and CAFs have distinct epigneome profiles with locus-specific rather than genome-wide differences. We identified ~7000 differentially methylated regions (DMRs) between CAFs and NPFs; many were at key regulatory loci and correlated with differential gene expression profiled with RNAseq. Targeted bisulfite sequencing showed that changes in DNA methylation were highly consistent between patients and could accurately discriminate between CAFs and NPFs. Of note, ESR1 which encodes ERα, was hypomethylated in CAFs. Accordingly, CAFs exhibited increased ERa expression and enrichment of an estrogen-regulated gene signature, of which CXCL12 was the most highly over-expressed gene. CXCL12 secreted by CAFs recruited CXCR4+ mast cells, activating a pro-tumourigenic loop in the tumour microenvironment.

This study shows that epigenomic changes are an underlying mechanism for the enduring differences between NPFs and CAFs. Furthermore, key epigenetically-regulated genes in CAFs, like ESR1, promote the progression of prostate cancer.