Induction of placental alkaline phosphatase biosynthesis by sodium butyrate

Placental alkaline phosphatase activity was induced in choriocarcinoma cells by sodium butyrate. Butyrate stimulated de novo synthesis of the enzyme and the increase in phosphatase activity could be completely accounted for by the increase in phosphatase protein: the increases in placental alkaline phosphatase immunoactivity and placental alkaline phosphatase biosynthesis as measured by incorporation of the radioactive precursors, L-[35S]methionine, [3H]mannose, and [3H] glucosamine were similar to the increase in phosphatase activity. Sodium butyrate increased the rates of placental alkaline phosphatase biosynthesis but had no effect on the rate of placental alkaline phosphatase degradation or processing. Both control and butyrate-induced cells contained polypeptides of 61,500 and 64,500 apparent molecular weights that were identified as the precursor and fully processed forms of the placental alkaline phosphatase monomer, respectively. Further, processing of the 61,500-dalton polypeptide to the 64,500-dalton polypeptide involved the incorporation of additional glucosamine and N-acetylneuraminic acid moieties. Gel electrophoresis of anti-placental alkaline phosphatase-precipitable polypeptides from an in vitro protein-synthesizing system directed by RNA isolated from control or butyrate-induced cells demonstrated that sodium butyrate induced the synthesis of placental alkaline phosphatase mRNA. Our data indicate that sodium butyrate induces the specific transcription of the placental alkaline phosphatase gene.