Colorectal cancer (CRC) is the 2nd most commonly diagnosed cancer in Europe. Previously, we have shown steroid sulphatase (STS), the enzyme that converts conjugated oestrogens to their active forms, is significantly upregulated in human CRC tissue. Furthermore, increased STS activity substantiates greater CRC tumour burden in mouse models. Here we demonstrate that this oestrogen-induced increase of CRC proliferation is mediated by G-protein coupled oestrogen receptor (GPER) via Hippo pathway signalling through the yes-associated protein 1 (YAP1), transcriptional coactivator with PDZ-binding motif (TAZ), and connective tissue growth factor (CTGF).
To examine how GPER effects CRC proliferation we employed in vitro BrdU proliferation assays and in vivo mouse models of CRC treated with G1, a GPER agonist, oestrogens and G15, a GPER antagonist. To investigate whether YAP1, its target gene CTGF, and its transcriptional co-activator TAZ, were altered by oestrogen-induced GPER signalling, we used immunoblotting and immunohistochemistry. YAP1 knockdown cells were also examined by treating them with G1, oestrogens and verteporfin, a YAP1 inhibitor, to assess the role of YAP1 on proliferation.
GPER-stimulation by G1 and oestrogen increased CRC proliferation in a dose-dependent manner, with this effect inhibited by G15 in vitro and in vivo CRC xenografts. YAP1 mediated this pro-proliferative response in CRC cells in contrast to colon adenoma cells. These findings were underpinned by increased phosphorylation of YAP1 and increased protein expression of TAZ and CTGF after oestrogen and G1 treatment. Intriguingly, CTGF up-regulation correlated with elevated GPER in human CRC tissue. In line with the above results, pharmacological inhibition of YAP1 and YAP1 knockdown blocked G1-induced cellular proliferation supporting the functional pro-proliferative role of YAP1 in CRC.
Taken together, our results propose a new oestrogen-driven pro-proliferative GPER-stimulated pathway through Hippo signalling in CRC. Further studies are required to establish whether this early metabolic response translates into increased cellular viability and cancer development.
20 May 2017 - 23 May 2017