Expression of different-sized placental alkaline phosphatase mRNAs in placenta and choriocarcinoma cells

The expression of human placental-type alkaline phosphatase (ALPase) in the placenta and in three choriocarcinoma cell lines was examined by translation in vitro and RNA blot analysis using a cDNA for placental ALPase. Placental RNA directed the synthesis of two polypeptides that could be immunoprecipitated with antiserum to placental ALPase. Translation of RNA from the choriocarcinoma cell lines, with or without sodium butyrate treatment, yielded a single immunoprecipitable product of molecular weight intermediate between those of the products from the placenta mRNA. Two cDNA clones for placental ALPase were isolated by antibody screening of a placental cDNA library constructed in lambda gt11. The overlapping cDNAs include 462 nucleotides of coding sequence. RNA blot analysis has confirmed that induction of placental-type ALPase levels during placental development is accompanied by an increase in steady-state placental ALPase mRNA concentrations. Examination of the mRNAs revealed a placental ALPase mRNA of 3.0 kilobases (kb) and a distinct choriocarcinoma placental-type ALPase mRNA of 2.6 kb, implying that transformation of normal to malignant trophoblast is associated with the expression of a distinct placental-type ALPase gene transcript and its protein product.