Differential Cell-Specific Modulation of HOXA10 by Estrogen and Specificity Protein 1 Response Elements

Context: HOX genes are highly evolutionarily conserved regulators of embryonic development. HOXA10 also regulates differentiation of the adult reproductive tract and mammary gland in response to sex steroids. Objective: We recently identified two HOXA10 estrogen response elements (EREs). Here we demonstrate that estrogen-responsive HOXA10 expression is cell type specific. Design and Setting: We conducted an in vitro study at an academic medical center. Main Outcome Measure: Reporter assay, gel shift assays (electrophoretic mobility shift assay), and immunohistochemistry were done. Results: The HOXA10 EREs and a specificity protein 1 (Sp1) binding site differentially drive the cell-type-specific E2 response. In electrophoretic mobility shift assays, both estrogen receptor-α and -β bound both EREs but not the Sp1 site. In reporter assays, both EREs and the Sp1 site demonstrated estrogen responsiveness and tissue specificity; transiently transfected uterine Ishikawa cells or breast MCF-7 cells showed differential responses to E2 treatment. Each response element (Sp1, ERE1, and ERE2) drove distinct differential expression in each cell type. Sp1 protein was expressed in a menstrual-cycle stage-specific expression pattern in endometrium, first expressed in perivascular cells. Conclusions: Tissue specificity inherent to a regulatory element as well as differential cellular expression of transcription factors imparts differential tissue-specific estrogen responsiveness.