Abstract
Hormone replacement therapy (HRT) affects the incidence and potential progression of colorectal cancer (CRC). As HRT primarily consists of estrone sulfate (E1S), understanding whether this conjugated estrogen is transported and metabolized in CRC will define its potential effect in this malignancy. Here, we show that a panel of CRC cell lines (Colo205, Caco2, HCT116, HT-29) have steroid sulfatase (STS) activity, and thus can hydrolyze E1S. STS activity is significantly higher in CRC cell lysate, suggesting the importance of E1S transport in intracellular STS substrate availability. As E1S transport is regulated by the expression pattern of certain solute carrier organic anion transporter polypeptides, we show that in CRC OATP4A1 is the most abundantly expressed transporter. All four CRC cell lines rapidly transported E1S into cells, with this effect significantly inhibited by the competitive OATP inhibitor BSP. Transient knockdown of OATP4A1 significantly disrupted E1S uptake. Examination of estrogen receptor status showed ERα was present in Colo205 and Caco2 cells. None of the cells expressed ERβ. Intriguingly, HCT116 and HT29 cells strongly expressed the G protein coupled estrogen receptor (GPER), and that stimulation of this receptor with estradiol (E2) and G1, a GPER agonist, significantly (p < 0.01) increased STS activity. Furthermore, tamoxifen and fulvestrant, known GPER agonist, also increased CRC STS activity, with this effect inhibited by the GPER antagonist G15. These results suggest that CRC can take up and hydrolyze E1S, and that subsequent GPER stimulation increases STS activity in a potentially novel positive feedback loop. As elevated STS expression is associated with poor prognosis in CRC, these results suggest HRT, tamoxifen and fulvestrant may negatively impact CRC patient outcomes.
Highlights
Estrogens play an important role in the etiology of colorectal cancer (CRC) (Foster, 2013)
These results demonstrate that estrone sulfate (E1S) uptake kinetics most likely dictate the ability of CRC to hydrolyze E1
As E1S is transported through the cell membrane by organic anion transporter polypeptides (OATP) the expression of these transporters was determined
Summary
Pre-menopausal women are protected against CRC compared to age-matched men (Farquhar et al, 2005), and data from the Women’s Health Initiative suggests post-menopausal women on HRT, a combination of estrone sulfate (E1S) and progestins, have a 40% reduced incidence of developing CRC compared to women not on HRT (Chlebowski et al, 2004). Despite this epidemiological evidence suggesting HRT as protective against CRC, evidence exists showing estrogens influence CRC proliferation. The ability of CRC to take up and metabolize E1S will define local concentrations of active estrogens and subsequent action
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