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

Abstract

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. We recently identified two HOXA10 estrogen response elements (EREs). Here we demonstrate that estrogen-responsive HOXA10 expression is cell type specific. We conducted an in vitro study at an academic medical center. Reporter assay, gel shift assays (electrophoretic mobility shift assay), and immunohistochemistry were done. 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-alpha and -beta 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. Tissue specificity inherent to a regulatory element as well as differential cellular expression of transcription factors imparts differential tissue-specific estrogen responsiveness.