Synthesis of Placental Protein 12 by Decidua from Early Pregnancy*

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Abstract
The synthesis and secretion of placental protein 12 (PP12) by early pregnancy decidua and trophoblast were studied in vitro from tissues obtained by curettage during elective termination of pregnancy (weeks 8–14). The tissue explarits were incubated in Ham’s F–10 medium for a 27–h period, and the PP12 levels in media and tissue homogenates were measured by RIA. De nouo synthesis of PP12 was assessed by measuring the incorporation of radioactivity into PP12 after 20 h of incubation of tissues with 20⁄iCi⁄ml [35S]methionine. PP12 from the culture medium wasimmunoprecipitated with anti–PPl2(A) antiserum, and the immunoprecipitate was analyzed by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. The initial tissue content of PP12 was 10–to 72–fold higher in decidua than in trophoblast. The total amount of radioimmunoassayable PP12 released into medium by decidual explants during the 27–h incubation period together with that present in the tissues at the end of incubation exceeded the initial tissue content by 242.7 ± 63.7% (mean± SE). Only small amounts of PP12 were detected in media from trophoblast cultures. During the first 7 h of incubation, inclusion of cycloheximide had no effect on PP12 release by decidual explants in three of four experiments. Between 7 and 27 h, the amount of PP12 released by cycloheximidetreated tissues was 20.0 ± 7% of that released by control tissues (P < 0.01). Cycloheximide had no effect on PP12 release by trophoblasts. Decidual explants incorporated [35S[ methionine into PP12, but trophoblasts did not. In sodium dodecyl sulfategel electrophoresis, the newly synthesized PP12 comigrated with the major band of purified PP12 corresponding to mol wt 29,000. These data clearly confirm that PP12 is a protein of decidual rather than trophoblastic origin, and indicate that decidua from early pregnancy has the ability to synthesize it.