Characterization of insulin-like growth factor-II binding sites in the microvillous membrane of the trophoblast of human placenta

Abstract

CHARACTERIZATION OF INSULIN-LIKE GROWTH FACTOR-II BINDING SITES IN THE MICROVILLOUS MEMBRANE OF THE TROPHOBLAST OF HUMAN PLACENTA. R. Rebourcet, *J. Willeput, *F. De Ceuninck, F. Mondon and F. Ferrt, U. 361 INSERM, Maternit6 Baudelocque, *U. 30 INSERM, HSpital Necker, Pads, France. Insulin-like growth factors (IGF-I and IGF-II) and its receptors are considered as important regulatory factors in trophoblastic functions such as growth, differenciation and stero'fdogenesis. Very high affinity and specific binding sites for [125I]IGF-II (Kdl = 6.10-15M, Kd2 = 3.10-14M) have been detected in purified microvillous membrane prepared from human term placentae obtained by elective cesarean section. The relative order of competition of [125I]IGF-II binding was IGF-II > IGF-I >> insulin. By contrast a single class of sites was found for the variant Ser29 IGF-II with a Kd value in the range of 1.10-14M. The human placental syncytiotrophoblast is a polarized epithelium with the microvillous membrane facing maternal blood space.In placenta IGF-II is predominantly synthetized within cytotrophoblasts (1). The fact that IGF-II could also derive from maternal blood argues for the existence of paracrine and/or autocrine interactions for the peptide at the feto-matemal interface. (1) R. Ohlsson et al. (1989) EMBO. J., 8, 1993-9. This study was supported by grants for GERP and INSERM. A.61 EVIDENCE FOR INSULIN-LIKE GROWTH FACTOR-II BINDING SITES IN SMOOTH MUSCLE OF STEM VILLI VESSELS OF HUMAN TERM PLACENTA. R. Rebourcet, *J. Willeput, *F. De Ceuninck, F. Mondon and F. Ferrt, U. 361 INSERM, Maternit6 Baudelocque, *U. 30 INSERM, HSpital Necker, Pads, France. Insulin-like growth factor-II (IGF-II) is a polypeptide structurally related to IGF-I and insulin. IGFs and their relative mRNA have been detected in most fetal tissues since the second trimester of pregnancy and these peptides were found in the feto-placental circulation. Consequently, it has been suggested that IGF-II is a fetal growth hormone involved in the complex but well-coordinated relationships between fetal and placental growths. Specific and high affinity binding sites for [I25I]IGF-II have been characterized on membranes of smooth muscle cells of stem villi vessels. Specific binding of increasing concentrations of [1251]IGF-II or [1251] Ser29 IGF-II variant (10 to 250.1012M and 10 to 125 1012M respectively) to stem villi vessel membranes was saturable. Scatchard analysis revealed for IGF-II a single class of binding sites (Kd = 38 FM) and a maximal binding capacity (Bmax) of 0.4 pmol/mg protein. The preferential competitors of [125I]IGF-II binding are in order : IGF-II > IGF-I ; insulin is not a competitor. The same analysis achieved with the variant Ser29 IGF-II exhibited similar Kd value but a less important binding capacity (Bmax -0.1 pmol/mg protein). These interactions of IGF-IIs with the placental vasculature via specific binding sites suggest IGF-IIs are candidates for a role in stimulating angiogenesis required for the optimal development of the feto-placental vascular bed during pregnancy. This study was supported by grants for GERP and INSERM.