Objectives: The majority of endometrial cancers arise as a result of estrogen stimulation, the molecular targets of which remain incompletely defined. We hypothesize that the granulin-epithelin precursor (GEP) may be one such target. In this study, we examined the frequency of GEP and estrogen receptor (ER) co-expression in human endometrial cancers. Once we established the co-expression of GEP with the estrogen receptor we examined the potential estrogen regulation of GEP expression, as well as the functional significance of GEP expression in vitro.
Methods: Double immunofluorescence and confocal microscopy were used to compare GEP and ER expression among 41 endometrial cancers. The effects of estradiol and tamoxifen treatment on GEP expression in two endometrial cancer cell lines, KLE and HEC-1-A, were assessed through reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis. The antiproliferative effect of GEP silencing by short hairpin (sh)RNA, was evaluated in HEC-1-A cells using an MTT assay.
Results: GEP co-expression with ER was observed in 63% of the cancers examined. A two- to fivefold increase in GEP expression with estradiol and/or tamoxifen treatment was observed in KLE cells. Silencing of GEP in HEC-1-A cells using shRNA resulted in a decrease in proliferation among transfected cells.
Conclusions: Co-expression of GEP and ER in endometrial cancer cells, and the regulation of GEP by estrogen, suggests a role for GEP in steroid-mediated endometrial cancer cell growth. Further characterization of GEP as a steroid-mediated growth factor in these cells may broaden our understanding of endometrial cancer biology and also provide guidance in the development of novel therapeutic targets.