As carcinosarcoma tumors are considered biphasic (i.e., defined by having malignant epithelial and stromal compartments) [37, 74], we evaluated both epithelial and stromal cell staining for GPER expression and observed that both components were strongly positive for GPER.
Interestingly, within our endometrial cancer repository, we identified six patients who received tamoxifen-based therapy for recurrent endometrial cancer, and of these only one patient (case 1, above, with low GPER expression) experienced a complete response; in contrast, all nonresponders displayed increased GPER expression (defined as expression above the mean ) by immunohistochemistry of paraffin-embedded tumor samples (Fisher's P = 0.03), suggesting that a lack of or low GPER expression may be a predictor of tamoxifen responsiveness in endometrial cancer.
Whereas survival is high among women with type I endometrial cancers, the opposite is true for type II cancers, which express high levels of GPER .
Although GPCRs are traditionally thought of as cell surface receptors, mediating transmembrane signaling of membrane-impermeable ligands (e.g., ionic small molecules, peptides, and proteins), we originally described GPER localization as being predominantly intracellular .
Whereas the classical estrogen receptors (ER[alpha] and ER[beta]) are traditionally thought to mediate primarily genomic responses , GPER has become recognized as an estrogen receptor thatmediates rapid cellular signaling.
In this study, we demonstrated that an endometrial cell line representative of [ER.sup.-] type II tumors maintains the ability to signal in response to estrogen via GPER. In Hec50 cells, estrogen signaling via GPER results in a metalloproteinase/EGFR-dependent activation of downstream kinase pathways, including PI3K and ERK, both important players in cancer cell survival and growth.
The pharmacopeia of estrogen receptor ligands has been developed in the absence of consideration for their interaction with GPER. For example, the development of SERMs and SERDs was largely based on the development of compounds with high binding affinity to ER[alpha] and the effects of these compounds on transcriptional regulation (through estrogen response elements) and overall tissue-specific activities (breast cancer cell growth versus uterine effects such as imbibition).
In our current study, we found that PPT (at 100 nM, with a weak response at 10 nM, unpublished observation) also acts as an agonist for GPER. The three estrogen receptor selective compounds PPT, DPN, and G-1 have recently been used to evaluate the estrogen receptor involved in a number of physiological or cellular responses [105-107].
GPER stimulation has been demonstrated to increase cell proliferation in a broad array of cell lines, including some endometrial cancer cell lines, suggesting a potential importance in one or more aspects of carcinogenesis [15, 20, 24, 26, 27].
To examine the role of GPER in endometrial tumor growth, we sought to establish and investigate xenograft tumors in mice.
To determine if estrogen itself and GPER in particular contributes to tumor growth of ER[[alpha].sup.-] Hec50 cells, we established subcutaneous Hec50 tumors in ovariectomized athymic mice.
In this paper, we have demonstrated that GPER plays an important role in the estrogen-mediated signaling of a representative type II endometrial cancer cell line.