TI - A novel variant of ER-alpha , ER-alpha36 mediates testosterone-stimulated ERK and Akt activation in endometrial cancer Hec1A cells . AB - Background Endometrial cancer is one of the most common gynecologic malignancies and its incidence has recently increased . Experimental and epidemiological data support that testosterone plays an important role in the pathogenesis of endometrial cancer , but the underlying mechanism has not been fully understood . Recently , we identified and cloned a variant of estrogen receptor ( ER ) alpha , ER-alpha36 . The aim of the present study was to investigate the role of ER-alpha36 in testosterone carcinogenesis . Methods The cellular localization of ER-alpha36 was determined by immunofluorescence . Hec1A endometrial cancer cells ( Hec1A/V ) and Hec1A cells with siRNA knockdown of ER-alpha36 ( Hec1A/RNAi ) were treated with testosterone , ERK and Akt PHOSphorylation was assessed by Western blot analysis . Furthermore , the kinase inhibitors U0126 and LY294002 and the aromatase inhibitor letrozole were used to elucidate the pathway underlying testosterone-induced activities . Results Immunofluorescence shows that ER-alpha36 was localized on the plasma membrane of the both ER-alpha - and androgen receptor -negative endometrial cancer Hec1A cells . Testosterone induced ERK and Akt PHOSphorylation , which could be abrogated by ER-alpha 36 shRNA knockdown or the kinase inhibitors , U0126 and LY294002 , and the aromatase inhibitor letrozole . Conclusion Testosterone induces ERK and Akt PHOSphorylation via the membrane-initiated signaling pathways mediated by ER-alpha36 , suggesting a possible involvement of ER-alpha 36 in testosterone carcinogenesis .