Glucose-dependent GPER1 expression modulates tamoxifen-induced IGFBP-1 accumulation.

Yan Zheng,Kevin D Houston

doi:10.1530/jme-18-0253

Abstract

G protein-coupled estrogen receptor 1 (GPER1) is a seven-transmembrane receptor that mediates rapid cell signaling events stimulated by estrogens. While the role that GPER1 has in the modulation of E2-responsive tissues and cancers is well documented, the molecular mechanisms that regulate GPER1 expression are currently not well defined. The recently identified GPER1-dependent mechanism of tamoxifen action in breast cancer cells underscores the importance of identifying mechanisms that regulate GPER1 expression in this cell type. We hypothesized that GPER1 expression in breast cancer cells is sensitive to [D-glucose] and provide data showing increased GPER1 expression when cells were cultured in low [D-glucose]. To determine if the observed accumulation of GPER1 was AMP-activated protein kinase (AMPK)-dependent, small molecule stimulation or inhibition of AMPK was performed. AMPK inhibition decreased GPER1 accumulation in cells grown in low [D-glucose] while the AMPK-activating compound AICAR increased GPER1 accumulation in cells grown in high [D-glucose] media. Additionally, transfection of cells with a plasmid expressing constitutively active AMPK resulted in increased GPER1 accumulation. To determine if [D-glucose]-dependent GPER1 accumulation altered breast cancer cell response to tamoxifen, cells grown in the presence of decreasing [D-glucose] were co-treated with tamoxifen and IGFBP-1 transcription was measured. The results from these experiments reveal that D-glucose deprivation increased GPER1-mediated and tamoxifen-induced IGFBP-1 transcription suggesting that [D-glucose] may increase breast cancer cell sensitivity to tamoxifen. Taken together, these results identify a previously unknown mechanism that regulates GPER1 expression that modifies one aspect tamoxifen action in breast cancer cells.

Highlights

Estrogen is a critical signaling molecule that modulates many cell signaling pathways and physiological functions
To determine if G protein-coupled estrogen receptor 1 (GPER1) expression is sensitive to [D-glucose] in breast cancer cells, MCF-7 and T-47D cell lines were grown for h in media containing 0, 5.5 or mM D-glucose and the expression of GPER1 was determined by immunoblot
The expression level of GPER1 was compared between MCF-7 and T-47D cells and results indicated that GPER1 expression was similar in these two cell lines when cultured in maintenance media (Supplementary Fig. 1)

Summary

Introduction

Estrogen is a critical signaling molecule that modulates many cell signaling pathways and physiological functions. Beyond the observed dysregulation of adipogenesis, others reported that male GPER1 KO mice developed hyperinsulinemia and hyperglycemia by 18 months of age (Sharma et al 2013) and female GPER1 KO mice developed impaired glucose tolerance within 6 months of age (Martensson et al 2009) Of note, both classical and non-classical estrogen signaling regulates glucose uptake, glucose storage, insulin secretion and has a role in insulin sensitivity (Brown & Clegg 2010, Barton & Prossnitz 2015). Both classical and non-classical estrogen signaling regulates glucose uptake, glucose storage, insulin secretion and has a role in insulin sensitivity (Brown & Clegg 2010, Barton & Prossnitz 2015) Contrary to these findings, observations from one study showed that GPER1 KO mice had increased glucose homeostasis and reduced non-fasting and fasting blood glucose concentrations (Wang et al 2016). Observations from multiple studies indicate a central role for GPER1 in metabolic homeostasis

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Conclusion