Insulin-Like Growth Factor Binding Proteins in Human Endometrium: Steroid-Dependent Messenger Ribonucleic Acid Expression and Protein Synthesis*

Abstract

The insulin-like growth factor (IGF) autocrine/paracrine system is believed to play a role in endometrial differentiation and trophoblast growth. The IGFs bind with high affinity to a family of binding proteins (IGFBPs) that regulate the actions of the IGFs at their target cells. IGFBP-1, one of three well-characterized IGFBPs in humans, has been shown by numerous investigators to be present in secretory but not proliferative endometrium; however, no information is available with regard to two other human IGFBPs, IGFBP-2 and IGFBP-3, in normal human endometrium. We have examined expression of the messenger RNAs (mRNAs) encoding IGFBP-2 and IGFBP-3 in human proliferative endometrium [under the influence of estradiol (E2)] compared to secretory endometrium (under the influence of E2 and progesterone). Using a complementary DNA probe specific for IGFBP-2, by Northern analysis, expression of a 1.4 kilobase mRNA was found to be differentially expressed in secretory compared to proliferative phase endometrium. Using a complementary DNA probe encoding IGFBP-3, a 2.4 kilobase mRNA was found in endometrium and was also found to be differentially expressed in secretory compared to proliferative phase endometrium. Endometrial stromal cells were established in culture and revealed constitutive synthesis and secretion of IGFBP-2 and IGFBP-3 into the conditioned medium (CM), as detected by Western ligand blot analysis of the CM. Identification of the IGFBPs in the CM was made using IGFBP-2 and IGFBP-3 specific antiserum. In the presence of E2 and progesterone, there was an enhancement in the amount of IGFBP-3 and a marked enhancement of IGFBP-2 in the conditioned media, suggesting sex steroid-dependence of IGFBP-2 and, to a lesser extent, IGFBP-3 protein synthesis. Western ligand blot analysis of IGFBPs in serum throughout the menstrual cycle revealed no hormonal dependence in the serum IGFBPs, suggesting local action of the IGFBPs in endometrium. These data thus show that mRNAs encoding IGFBP-2 and IGFBP-3 are expressed in human endometrium, that their expression is differentially regulated in secretory compared to proliferative phase endometrium (different steroidogenic environments), and that the synthesis of both IGFBP-2 and IGFBP-3 proteins is regulated by steroid hormones.

Complex mediation of uterine endometrial epithelial cell growth by insulin-like growth factor-II (IGF-II) and IGF-binding protein-2

“…Significant uterine endometrial IGFBP-2 expression has been demonstrated for a number of mammals (Giudice et al 1991, Rechler 1993 et , Cerro & Pintar 1997. In porcine uterus, this expression is induced during the periimplantation period and reaches maximal levels by mid-pregnancy.…”

“…Although the complete mechanism(s) of action has not been fully defined for any of the IGFBPs, these proteins can augment or inhibit IGF action, depending upon the nature of the IGFBP, the cell context and the experimental conditions. Uterine endometrial expression of IGFBP-2 has been demonstrated in the human (Giudice et al 1991), pig (Simmen et al 1992, Song et al 1996, and rat (Cerro & Pintar 1997), in addition to other species. In pregnant pig uterus, the abundance of IGFBP-2 mRNA and protein is induced during late pre-implantation (around day 15, postestrus) and reaches maximal levels by mid-pregnancy (day 60) (Simmen et al 1992, Song et al 1996.…”

IGFs and IGF-binding proteins in the regulation of human ovarian and endometrial function

“…Furthermore, IGFBP-2, -4, -5 and -6 mRNAs demonstrate a diffuse stromal pattern of expression, whereas IGFBP-1 and -3 are more concentrated in selected subpopulations of endometrial cells , Zhou et al 1994. IGFBP-2 and IGFBP-3 mRNAs are significantly increased in the late secretory phase of the endometrium (Giudice et al 1991). Moreover, IGFBP-3 mRNA is primarily concentrated in endometrial capillaries, largely due to the intensive vascularization of endometrial glands during the secretory phase (Zhou et al 1994).…”

Insulin-like growth factor binding proteins in the rat uterus and their regulation by oestradiol and growth hormone

“…Expression of mRNA encoding IGFBP-2 and -3 in human endometrium (Giudice et al, 1991) and secretion of multiple forms of IGFBPs by decidual cells (Clemmons et al, 1990) Insulin-like growth factor binding proteins in the uterine extracts and serum were analysed by western ligand blotting (Fig. 1).…”