N5 endometrial stromal cell line: A model system to study decidual prolactin gene expression

Prolactin gene expression in extrapituitary tissues, such as decidua and ly mphocytes, is regulated by a distinct promoter approximately 6 kb upstream of the pituitary prolactin gene transcription start site. Here ne describe studies in a human endometrial stromal cell line, N5, that was immortalized by transfection with an SV40 mutant and which expresses the prolactin gene driven by the extrapituitary: promoter. The N5 cells have phenotypic featu res of primary cultures of decidualized human endometrial stromal cells and secrete low levels of prolactin and insulin-like growth factor binding pro tein-1 (IGFBP-1), bath of which are markers of decidualized endometrial str omal cells. As in primary cultures of endometrial stromal cells, treatment of N5 cells with progesterone and estradiol alone or in combination with pr ostaglandin E-2 stimulated the synthesis and release of prolactin. Transien t transfection of the N5 cells with an expression vector containing -2927/66 bp of the decidual prolactin promoter coupled to a luciferase reporter g ene resulted in a 20 to 25-fold increase in luciferase activity, a magnitud e similar to that which occurs in primary cultures of endometrial stromal c ells decidualized in vitro by treatment with progesterone and estradiol. Lu ciferase expression levels were similar in untreated N5 cells and N5 cells treated with progesterone and estradiol. Taken together, these results indi cate that the N5 human endometrial stromal cell line has phenotypic charact eristics of normal decidualized stromal cells and is a useful model to stud y regulation of decidual prolactin gene expression.