Characterization of an insulin-like growth factor binding protein, analogous to human pregnancy-associated secreted endometrial alpha 1-globulin, in decidua of the baboon (Papio anubis) placenta.
The major secreted protein of the human decidua (pregnancy-associated endometrial alpha 1-globulin [alpha 1-PEG]), is an insulin-like growth factor-binding protein (IGF-BP) that is immunologically and biochemically similar to placental protein 12 (PP12) extracted from term human placenta. Since previous studies have demonstrated that the baboon and human endometrium synthesize and release a number of biochemically and immunologically related polypeptides in culture, this study was undertaken to further characterize a related IGF-BP in baboon placental tissues. Decidua, chorio-amniotic membranes with adhering decidua (CAM-D), and placental villi were obtained from pregnant baboons between Days 134 and 160 of gestation by Cesarean sections. Portions of tissue were either cultured in the presence of 35S-methionine, fixed for immunocytochemistry, or frozen in liquid nitrogen for cytosol extraction. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) of tissue culture media (TCM) revealed that the major secretory product of the decidua and CAM-D was an acidic polypeptide (Mr 33,000). Western blot analysis and immunoprecipitation of TCM with murine monoclonal antibody (B2H10) against human alpha 1-PEG demonstrated that this molecule, secreted by the baboon decidua and CAM-D, but not the placental villi, was immunologically identical to the human IGF-BP. Immunocytochemical localization of IGF-BP was intense in the cytoplasm of stromal cells in decidua and CAM-D and absent in the placenta. Gel filtration of TCM and cytosol followed by screening of eluates for 125I-IGF-I binding resolved two peaks (Mr greater than 100,000 and 35,000) of specific IGF-BP in decidua and CAM-D. The 35,000 peak had 100-200 times the binding capacity of the Mr greater than 100,000 peak and a Kd of 1.14-1.83 nM. The eluates contained in the Mr 35,000 peak were also immunoreactive to alpha 1-PEG, as accessed by a polyclonal radioimmunoassay. Affinity cross-linking with 125I-IGF-I followed by sodium dodecyl sulfate-PAGE revealed an immunoreactive complex of Mr 36,000, confirming that the baboon protein represents a high affinity IGF-BP. These studies indicate that the hypertrophied stromal cells of the baboon decidua and CAM-D synthesize and release an IGF-BP as their major secretory product, analogous to the situation in humans. The results of this study suggest that this protein may play a role in the regulation of IGF action during pregnancy.
Fazleabas
A T
AT
Department of Obstetrics and Gynecology, University of Illinois College of Medicine, Chicago 60680.
Verhage
H G
HG
Waites
G
G
Bell
S C
SC
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000032:analysis*; D002850:Chromatography, Gel; D046508:Culture Techniques; D003600:Cytosol / Q000032:analysis; D003656:Decidua / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D000071816:Glycodelin; D006801:Humans; D007150:Immunohistochemistry; D007163:Immunosorbent Techniques; D018969:Insulin-Like Growth Factor Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008970:Molecular Weight; D010215:Papio; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000032:analysis*
D002352:Carrier Proteins; D000071816:Glycodelin; D018969:Insulin-Like Growth Factor Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; C045246:PAEP protein, human; D011257:Pregnancy Proteins