LoVo, a continuous cell line derived from a human colon
carcinoma produces two alkaline
phosphatases: the heat-labile, L-
homoarginine-insensitive, intestinal form, characteristic of its tissue of origin and the heat-stable, term-placental form, ectopically produced by a variety of
tumors. Under basal conditions the activity levels of both
enzymes are similar. Hyperosmolality and
sodium butyrate induce increased levels of activity of the two alkaline
phosphatases in a disparate fashion; whereas hyperosmolality augments the activity of both to the same extent, the effect of
butyrate is more pronounced on the activity of the intestinal
enzyme. When the two inducers are combined, induction of term-
placental alkaline phosphatase is additive and that of the intestinal
enzyme is synergistic. The effect of hyperosmolality is blocked by
cycloheximide, and induction by
sodium butyrate is inhibited by
thymidine,
cordycepin and
cycloheximide. The known
alkaline phosphatase inducer,
prednisolone, has no effect on the
enzymes of LoVo cells. Our results suggest that in these
tumor cells the activity levels of the closely homologous term-placental and intestinal alkaline
phosphatases appear to be independently controlled.