In Vitro Biosynthesis and Comparative Posttranslational Processing of Immunoreactive Precursor Corticotropin/β-Endorphin by Human Placental and Pituitary Cells*

Abstract

Normal human pituitary cells and human placental cells derived from the trophoblastic shell and adhering decidua incorporate [³H]lysine and [35S]methionine during a 30- min incubation period into high molecular weight glycoproteins containing the antigenic determinants of both ACTH and β- endorphin, demonstrating for the first time actual placental synthesis of such material and synthesis by the human pituitary. Such high molecular weight ACTH/β-endorphin was resolved into at least two molecular species upon sodium dodecyl sulfate polyacrylamide gel electrophoresis, with apparent molecular weights of 34,000 ± 2,600 and 46,000 ± 3,900. These high molecular weight glycoproteins were retained on a Concanavalin-A column and were eluted with excess D-mannose but not with synthetic ACTH or β-endorphin. Partial tryptic mapping of high molecular weight material revealed two fragments physicochemically similar to ACTH-(9-15) and β-endorphin-(l–9) [Mipotropin-(61–69)]. Additional immunoreactive species of lower molecular weight containing only single antigenic determinants (either ACTH or β-endorphin) were detected when cells were incubated with labeled amino acids for 6 h. For placental cell extracts, immunoreactive β-endorphin coeluted with human β-lipotropin and human β-endorphin markers in approximately equimolar amounts upon gel filtration, and immunoreactive ACTH coeluted with human ACTH-(1–39) and aMSH markers in approximately equimolar amounts, whereas for the pituitary, these activities eluted almost exclusively with the human β-lipotropin and human ACTH-(1–39) markers. Thus, while the high molecular weight human placental and pituitary-derived materials are physicochemically similar (and larger than the reported mouse pituitary forms) and appear to serve a precursor function, posttranslational processing of this material differs in the two tissues. (Endocrinology106: 1504, 1980)