Human term placenta releases placental protein 10 (PP10) in tissue culture

Placenta, decidua, chorion and amnion were studied to determine the tissue concentration of placental protein 10 (PP10). As measured by radio-immunoassay, all tissues studied were found to contain approximately the same concentration of PP10, in both early and late pregnancy. The release of PP10 was studied in tissue culture, first by using explants of placenta, decidua, amnion and chorion in four preliminary studies. Only the placenta released significant amounts of PP10 into the culture medium and, therefore, further studies were carried out with placental explants. In gel filtration, the bulk of PP10 in the culture medium eluted in the same position as purified PP10, and the dose-response curves of the two materials were parallel. The total secretion of PP10 into the culture medium was studied throughout 96 hours of incubation. Cycloheximide, a protein synthesis inhibitor, reduced the release of PP10 into medium by 31.3 +/- 12.5%. In cycloheximide-treated tissue cultures, the secretion of PP10 recovered when cycloheximide was replaced by original culture medium without cycloheximide. There results show that placenta is a major source of PP10.