Endocrine Abstracts

Circulating oestrogen concentrations affect the incidence of and outcomes for patients with colorectal cancer (CRC). We have previously shown that steroid sulphatase (STS), the fundamental enzyme that liberates conjugated oestrogens into their active forms, is significantly elevated in human CRC tissue. Here we demonstrate that elevated STS activity correlates to increased CRC proliferation, and that these effects are mediated through G-protein coupled oestrogen receptor (GPER) signalling via connective tissue growth factor (CTGF), yes-associated protein 1 (YAP1), and the Hippo-signalling pathway.

We developed a novel in vivo CRC mouse model using HCT116 xenografts stably over-expressing STS cDNA (HCT116_STS), with vector-only over-expressing xenografts (HCT116_VO) acting as controls. Animals were treated orally with the specific STS inhibitor, STX64 (20 mg/kg per thrice weekly), or vehicle control. At the end of the experiment, tumour wet weight and STS activity was measured. To investigate GPER effects in CRC, we determined how oestrogens and G1, a GPER agonist, and G15, a GPER antagonist, impacted proliferation in CRC cell lines. Using immunoblotting in CRC cell lines and human CRC samples we further examined whether GPER signalling increases CTGF and activates YAP1 and its transcriptional co-activator TAZ, key effectors of the Hippo pathway.

After 21 days, HCT116_STS xenografts in vivo exhibited significantly (P<0.01) greater proliferation (426±81 mm³) compared to controls (273±42 mm³). This increased growth was significantly (P<0.001) inhibited by STX64. G1 and oestrogen treatment increased CRC proliferation in a dose-dependent manner. GPER-stimulation increased CTGF expression and deactivated the Hippo pathway with these effects inhibited by G15. Furthermore, GPER and CTGF expression significantly correlates (P<0.001) in human CRC tissue with expression elevated in malignancy compared to tissue matched controls.

These results define a new oestrogen-driven pro-proliferative GPER-stimulated pathway through Hippo signalling in CRC.