Characterization of 17β-hydroxysteroid dehydrogenase type 1 in choriocarcinoma cells: regulation by basic fibroblast growth factor

Abstract

17β-Hydroxysteroid dehydrogenase type 1 (17-HSD type 1) is a steroidogenic enzyme catalyzing reversible interconversion of estradiol and estrone. 17-HSD type 1 is actively expressed in human placenta. We characterized 17-HSD type 1 expression and its regulation by basic fibroblast growth factor (bFGF) in JAR, JEG-3 and BeWo choriocarcinoma cell lines. Based on Southern and Northern analysis, as well as measurement of catalytic activity and immunoreactive protein, all the choriocarcinoma cell lines contained and expressed the gene coding for 17-HSD type 1, identical to that of normal human cells. However, the cell lines showed marked quantitative differences in the levels of expression of the enzyme, being lowest in JAR cells and highest in BeWo cells, as measured by immunofluorometric assay, Northern analysis and catalytic activity. These differences in the basal level of expression were most probably not based on any sequence differences in the putative proximal promoter area of the gene in different cell lines, since no dissimilarities were observed in the 806 bp region upstream from the transcription start site of 1.3 kb mRNA coding for 17-HSD type 1 except for frequent polymorphism characteristic of normal human cells using polymerase chain reaction/single-strand conformation polymorphism (PCR-SSCP) analysis. The reductive (estrone → estradiol) activity was about 4–7 times higher compared with the oxidative activity (estradiol → estrone) in all the cell lines studied, indicating that in these choriocarcinoma cell lines, 17-HSD activity favours estradiol formation. Treatment with 30 ng/ml of basic fibroblast growth factor (bFGF) for 5 days stimulated irnmunoreactive 17-HSD type 1 concentrations 4.5-fold and 3.5-fold above the control level in JAR and JEG-3 cells, respectively, whereas no stimulatory effects were seen in BeWo cells. Similarly, concentrations of 17-HSD type 1 1.3 kb mRNA and 17-HSD catalytic activity increased in JAR and JEG-3 cells after stimulation with bFGF, whereas no effects were seen in BeWo cells. We suggest that bFGF may have a regulatory role in placental estrogen metabolism via its effects on 17-HSD type 1. Keywords: Fibroblast growth factor; Placenta; Choriocarcinoma; Steroidogenesis; Estradiol