A novel role for the AAA ATPase spastin as a HOXA10 transcriptional corepressor in Ishikawa endometrial cells.

Homeobox A10 (HOXA10), a transcription factor required for uterine development and embryo receptivity, functions downstream of estrogen and progesterone in uterine endometrium. HOXA10 represses endometrial expression of empty spiracles homeobox 2 (EMX2), the human ortholog of Drosophila empty spiracles. The ATPases associated with various cellular activities (AAA) ATPase spastin has a well-characterized role in neurotransmitter trafficking. In this study, we characterize a novel role of spastin in transcriptional regulation. We identified spastin as a novel component of the HOXA10 transcriptional complex in Ishikawa nuclear extracts by immunoprecipitation and mass spectrophotometry. Using EMX2 as a model endometrial HOXA10 target gene, we show that the HOXA10-spastin corepressor complex bound the EMX2 promoter in chromatin immunoprecipitation assays. HOXA10 has been previously shown to repress endometrial EMX2 expression. We further observed that, although cotransfection of HOXA10 and spastin continued to repress endometrial EMX2-luciferase expression, the repression was reversed when spastin small interfering RNA was cotransfected with HOXA10. Mutations in the nuclear localization signal sequences of spastin abrogated not only its nuclear translocation but also its colocalization with HOXA10 as well as reversed EMX2-luciferase repression. Here, we describe a novel role for the AAA ATPase spastin in Ishikawa cells as a HOXA10 corepressor of EMX2. Uterine EMX2 levels are inversely related to embryo implantation rates. HOXA10 acts downstream of progesterone and has been shown to facilitate embryo implantation through regulation of endometrial EMX2 expression. Endometrial spastin, therefore, likely has a novel function downstream of estrogen and progesterone in implantation biology as a cofactor of HOXA10.

Decreased endometrial HOXA10 expression associated with use of the copper intrauterine device.

OBJECTIVE: To characterize human endometrial HOXA10 expression in patients using a copper intrauterine device (IUD). DESIGN: Case-control study. SETTING: Academic medical center. PATIENT(S): Women using copper IUDs. INTERVENTION(S): Immunohistochemical analysis of endometrial HOXA10 expression in biopsy samples obtained from 24 women using a copper Paraguard T380A as well as in samples obtained from 10 normal cycling women who were not using an IUD or hormonal contraceptives. MAIN OUTCOME MEASURE(S): Endometrial HOXA10 expression. RESULT(S): Endometrial HOXA10 expression was markedly decreased in the biopsy samples obtained from women using the IUD contraceptive when compared with controls. The mean H score for endometrial stromal cell HOXA10 expression in samples obtained from women using the Paraguard IUD was 0.21 compared with 2.2 in the control endometrial biopsy samples. Endometrial glandular expression of HOXA10 was absent in all IUD users. CONCLUSION(S): Decreased endometrial HOXA10 expression was apparent in women who use a copper IUD. Expression of HOXA10 is essential for endometrial receptivity. A novel mechanism of copper IUD action involves suppression of genes required for endometrial receptivity. The dramatic decrease of endometrial HOXA10 in response to IUD use may contribute to contraceptive efficacy.