Fibroblasts, Androgen Signalling And Oesophageal Adenocarcinoma

Abstract

Fibroblasts and androgen signalling can influence the biology of cancer. In this thesis their role has been explored in oesophageal adenocarcinoma (OAC), and in prostate cancer. In both cancers there is a need for biomarkers to guide patient management, and more effective treatments to reduce patient morbidity and mortality. Oesophageal adenocarcinoma (OAC) has a dismal course, with a five-year survival of around 15%. Its incidence has increased rapidly in Western countries over the last four decades. The cancer cells are embedded in a stroma of cells, predominantly fibroblasts, and extracellular matrix. The cancer-associated (myo)fibroblasts (CAFs) differ phenotypically from normal fibroblasts. This thesis documents differences in the genome-wide DNA methylation profiles of primary fibroblasts derived from normal oesophageal mucosa and from OAC tissue, consistent with a role for DNA methylation in establishing and maintaining the CAF phenotype. Interactions between these fibroblasts and OAC cells were to be investigated in direct or indirect co-culture, to differentiate effects due to juxtacrine (cell-cell or cell-extracellular matrix) or paracrine (soluble factors) signalling. Whilst unsuccessfully attempting to immortalise the oesophageal fibroblasts, proof of concept experiments were undertaken using co-cultures of prostate myofibroblasts and cancer cells. This permitted the investigation of the effect of androgen receptor (AR) expression in the myofibroblasts on their interactions with prostate cancer cells. This study was clinically relevant since a reduction in stromal AR expression is associated with a poorer prognosis in prostate cancer. The results suggest that AR-expressing myofibroblasts inhibit prostate cancer progression through paracrine signals that slow proliferation and induce apoptosis in the cancer cells, and that myofibroblasts lacking AR permit prostate cancer progression by undergoing apoptosis in response to juxtacrine signals from the cancer cells. Around 85% of OAC is diagnosed in males, for reasons unknown. A role for androgens was therefore explored. The AR was expressed in 97% of OAC patients in a large cohort, and appeared functional in the majority of these based on its nuclear localisation and expression of the androgen-responsive gene FK506-binding protein 5 (FKBP5). Nuclear AR and FKBP5 expression were independently associated with decreased survival. Following on from this, the effects of androgen signalling were studied in OAC cell lines stably transduced with AR. Cell proliferation and gene expression were altered, and could be modified by the concentration of the androgen and the presence of fibroblasts in co-culture. This was the first reported study of the effect of androgen signalling in OAC cell lines in vitro, with results consistent with a role for androgen signalling in this disease. This thesis provides new insight into the role of androgens and fibroblasts in the regulation of OAC and prostate cancer. The prognostic significance of AR expression and signalling in both cancers is highlighted, and the in vitro studies suggest novel mechanisms by which the microenvironment may contribute to the biology of these cancers. This research reveals areas of investigation that could lead to the identification of clinically useful biomarkers, and the development of novel treatments.