Synthesis of α1-Antichymotrypsin and α1-Antitrypsin by Human Trophoblast

Abstract

ABSTRACT: α1-Antichymotrypsin (α1-ACHY) and α1-an-titrypsin (α1-AT) are closely related glycoprotein protease inhibitors, present in plasma and other extracellular fluids, that neutralize proteases released by leukocytes in response to trauma and inflammatory stimuli. Both inhibitors are synthesized primarily by hepatocytes, although lower levels of synthesis by monocytes and breast and intestinal epithelial cells have been demonstrated. Recently, the immunohistochemical localization of α1-AT and α1-ACHY in intrauterine and extrauterine human trophoblastic tissue has been reported. In the present study, we have sought to determine whether human trophoblast is also able to synthesize α1-AT and α1-ACHY. Messenger RNA for both inhibitors was found by Northern blotting in chorionic villi obtained from first trimester and term placenta. Substantial differences in messenger levels for both inhibitors among individual placentas were noted. α1-ACHY and α1-AT messenger was also present in trophoblast cells in primary culture. Synthesis of α1-AT and α1-ACHY protein was demonstrated by SDS-PAGE after immunoprecipitation of [35S]-labeled α1-AT and α1-ACHY from conditioned media of trophoblast cells in culture metabolically labeled with [35SJ-methionine. It is of some interest that the Mr of the α1-AT and α1-ACHY secreted by trophoblast were 50 000 and 49 000, respectively, compared with 54 000 and 68 000 for these proteins in plasma (or secreted by HepG2 human hepatoma and MCF-7 human breast cancer cells). After enzymatic deglycosylation, the Mr of the α1-AT and α1-ACHY secreted by trophoblast and HepG2 cells were all approximately 46 000, suggesting incomplete glycosylation of the inhibitors released by trophoblast.