Abstract
BackgroundThe tetraspan protein epithelial membrane protein-2 (EMP2), which mediates surface display of diverse proteins, is required for endometrial competence in blastocyst implantation, and is uniquely correlated with poor survival from endometrial adenocarcinoma tumors. Because EMP2 is differentially expressed in the various stages of the murine and human estrous cycle, we tested the hypothesis that the steroid hormones progesterone and estrogen influence EMP2 expression and localization.MethodsFrozen human proliferative and secretory endometrium were collected and analyzed for EMP2 expression using SDS-PAGE/Western blot analysis. The response of EMP2 to progesterone and estradiol was determined using a combination of real-time PCR, SDS-PAGE/Western blot analysis, and confocal immunofluorescence in the human endometrial carcinoma cell line RL95-2. To confirm the in vitro results, ovariectomized mice were treated with progesterone or estradiol, and EMP2 expression was analyzed using immunohistochemistry.ResultsWithin normal human endometrium, EMP2 expression is upregulated in the secretory phase relative to the proliferative phase. To understand the role of steroid hormones on EMP2 expression, we utilized RL95-2 cells, which express both estrogen and progesterone receptors. In RL95-2 cells, both estradiol and progesterone induced EMP2 mRNA expression, but only progesterone induced EMP2 protein expression. To compare steroid hormone regulation of EMP2 between humans and mice, we analyzed EMP2 expression in ovarectomized mice. Similar to results observed in humans, progesterone upregulated endometrial EMP2 expression and induced EMP2 translocation to the plasma membrane. Estradiol did not promote translocation to the cell surface, but moderately induced EMP2 expression in cytoplasmic compartments in vivo.ConclusionThese findings suggest that targeting of EMP2 to specific locations under the influence of these steroid hormones may be important for integrating the molecular responses required for implantation competence.
Highlights
The tetraspan protein epithelial membrane protein-2 (EMP2), which mediates surface display of diverse proteins, is required for endometrial competence in blastocyst implantation, and is uniquely correlated with poor survival from endometrial adenocarcinoma tumors
EMP2 is necessary for blastocyst implantation in mice [1], and aberrant EMP2 expression correlated with poor survival in endometrial adenocarcinoma patients [2]
EMP2 expression in human tissue EMP2 expression varies both temporally and spatially during the murine estrous and human menstrual cycles, suggesting that it is regulated by the steroid hormones progesterone and estradiol
Summary
The tetraspan protein epithelial membrane protein-2 (EMP2), which mediates surface display of diverse proteins, is required for endometrial competence in blastocyst implantation, and is uniquely correlated with poor survival from endometrial adenocarcinoma tumors. EMP2 has been shown to play a role in trafficking of molecules, which include integrins, major histocompatibility complex (MHC) class I molecules, and glycosylphosphatidyl inositol (GPI)-anchored proteins, to noncaveolar glycolipid-enriched lipid rafts [3,4,5]. These plasma membrane microdomains are important in the formation of receptor-protein complexes required for efficient signal transduction. Through this mechanism, EMP2 plays a role in the regulation of cell adhesion and invasion [3,6,7]. In the native human endometrium EMP2 expression is minimally detectable during the proliferative phase, but is much more highly expressed during the secretory phase [1,2]
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