Characterization of the steroid-dependence of insulin-like growth factor-binding protein-2 synthesis and mRNA expression in cultured human endometrial stromal cells

Abstract

The insulin-like growth factors (IGF-I and -II) are believed to be important in endometrial differentiation and blastocyst nidation, and proteins that regulate IGF action (IGF-binding proteins, IGFBPs) are hormonally regulated in endometrium during the menstrual cycle. To characterize further steroid-dependence of the IGFBPs, we established endometrial stromal cells in culture in the absence and presence of oestradiol (E2) and progesterone (P) and examined the conditioned medium for IGFBPs by Western ligand blot analysis. Stromal cells constitutively synthesized IGFBP-3, IGFBP-2, a 27 kd, and a 24 kd IGFBP. In the presence of E2 and P, a 10- to 15-fold increase in IGFBP-2 was detected in the conditioned medium beginning after about 7 days in culture, when cells decidualized and steroid-mediated prolactin secretion began. Withdrawal of steroids resulted in a marked decrease in IGFBP-2, comparable to control levels, and cells increased their IGFBP-2 production when rechallenged with E2 and P. Total RNA was isolated from stromal cells, and Northern blot analysis using a cDNA probe specific for IGFBP-2 revealed differential expression of a 1.4 kb mRNA transcript in steroid-treated compared to control cells. The effects of progestational agents alone on IGFBP synthesis was also examined. Progesterone, medroxyprogesterone acetate and norethindrone all stimulated IGFBP-2 synthesis 12- to 15-fold compared to controls, and a progesterone receptor antagonist, RU 486, blocked the stimulatory effect of progesterone. IGFBP-2 synthesis was increased two-fold above controls by 17-alpha-hydroxyprogesterone, and RU 486 alone and hydrocortisone were without effect. Identification of IGFBP-2 in conditioned medium was made using IGFBP-specific antiserum. These data show that (a) endometrial stromal cells synthesize and secrete IGFBP-2, (b) IGFBP-2 protein synthesis is controlled by steroid hormones, (c) P, by interacting with its receptor, modulates IGFBP-2 synthesis and (d) expression of IGFBP-2 mRNA is controlled by sex steroids.