Estrogen Receptor α (ERα) Expression In Telomerase-Immortalized Human Myometrial Cell Line And Its Response To Estrogen

Labor is initiated by a series of biochemical events that promote up-regulation of genes encoding contraction associated proteins (CAPs) within the uterine myometrium. During late gestation, an increase in circulating estradiol-17β (E₂) levels contributes to the induction of CAP gene expression and initiation of myometrial contractility. To begin to define the mechanisms whereby E₂ up-regulates CAP gene expression, we used a telomerase-immortalized human myometrial cell line (hTERT-HM cells). Our first objectives were to assess the presence of estrogen receptor α (ERα) protein in these cells, as well as their responsiveness to E₂. Using immunoblotting with specific antibodies for ERα (H-184, Santa Cruz), the full-length estrogen receptor was detected at relatively low levels as a protein of 66,000 Da. To analyze the functional properties of ERα in the hTERT-HM cells, we analyzed effects of E₂ on phosphorylation of ERK, a component of the mitogen-activated protein kinase pathway. hTERT-HM cells were cultured in the absence or presence of E₂ (10 nM), in the absence or presence of the ERα antagonist, ICI 182 780, and analyzed for expression of phosphorylated ERK by immunoblotting. E₂ caused a modest increase in levels of phosphorylated ERK; this effect was antagonized by ICI. E₂ treatment of these cells also caused down-regulation of ZEB1 and ZEB2, which are transcription factors known to inhibit expression of CAP genes, such as connexin-43 and oxytocin receptor. Based on these findings, hTERT-HM will likely provide an appropriate model to study the mechanisms whereby estrogen increases CAP gene expression in human myometrium.