INDUCTION OF GERM-CELL ALKALINE-PHOSPHATASE BY BUTYRATE AND CYCLIC-AMP IN BEWO CHORIOCARCINOMA CELLS

BeWo choriocarcinoma cells synthesize two alkaline phosphatase isoenzy mes: germ-cell alkaline phosphatase and tissue-unspecific alkaline pho sphatase. We have made use of the differential heat-stabilities of the se two isoenzymes to study the induction of germ-cell alkaline phospha tase by sodium butyrate and cyclic AMP (cAMP). Sodium butyrate causes a large induction of germ-cell alkaline phosphatase activity (approx. 35-fold after 96 h) after an initial lag period of 12-24 h. We showed that butyrate increases germ-cell alkaline phosphatase mRNA. Dibutyryl cAMP also induces germ cell alkaline phosphatase (approx. 2.5-fold af ter 96 h). When optimal concentrations of butyrate and dibutyryl cAMP were added simultaneously to cells, they caused a synergistic inductio n of activity. This suggested that these compounds use separate mechan isms to induce germ-cell alkaline phosphatase activity and that it is the cAMP moiety of dibutyryl cAMP that induces enzyme activity. This w as confirmed by the use of two additional cAMP analogues, 8-(4-chlorop henylthio) cAMP and 8-bromo cAMP, and of two compounds, 3-methyl-1-iso butylxanthine and cholera toxin, which raise the endogenous concentrat ion of cAMP. All four compounds caused a 2-fold increase in enzyme act ivity. Treatment of cells with 8-(4-chlorophenylthio) cAMP, 8-bromo cA MP and cholera toxin increased germ-cell alkaline phosphatase mRNA bet ween 2- and 7-fold. These data suggest that this alkaline phosphatase isoenzyme is regulated at the level of its mRNA by cAMP, in a manner d istinct from that of butyrate.