Effect of sodium butyrate on alkaline phosphatase in HRT-18, a human rectal cancer cell line.

Treatment of the human rectal cancer cell line HRT-18 with sodium butyrate caused a reversible elevation of alkaline phosphatase activity which was inhibited by cycloheximide and actinomycin D. The alkaline phosphatase in untreated cells was heat stable at neutral pH and inhibited by phenylalanine but not by homoarginine, and 80% of the enzyme activity was precipitated by antibody against human term-placental enzyme. Following butyrate treatment, the enzyme became more sensitive to all the inhibitors tested and more heat stable, compared to the enzyme in control cells. In addition, the butyrate-induced enzyme could be completely precipitated by anti-placental alkaline phosphatase antibody. The electrophoretic pattern of the butyrate-induced enzyme was different from that of control cells. Control HRT-18 cells contained a butyrate-insensitive heat-labile alkaline phosphatase component with an electrophoretic mobility similar to the enzyme from human colon cancer tissues. The alkaline phosphatase from four human colon cancer tissues was of the early placental form, while the enzyme from human normal mucosa was of the intestinal type.