Modulation Studies of Alkaline Phosphatase in Human Choriocarcinoma Cells

The BeWo line of human choriocarcinoma has been studied in an attempt to understand the phased expression of AP in normal placenta and genome derepression in certain cancers. Be Wo contains at least two species of AP. The major activity is heat‐stable and has amino acid inhibition characteristics similar to the D‐variant isoenzyme of normal term placenta. The other activity is heat‐labile and has characteristics which suggest it may be the same as the AP isoenzyme recently found in first trimester placenta. In Be Wo, AP is not influenced by cAMP. Both AP activities can be increased by butyrate. Halogenated pyrimidines are known to increase AP activity in cell lines with low constitutive activity. In BeWo, IdU results in increased activity of both heat‐stable AP and heat‐labile AP. The time course of increased activity as well as the ability to prevent the increase with excess TdR suggest that IdU must be incorporated into DNA to have an effect.