The induction of alkaline phosphatase activity in HeLa cells by 5-iodo-2'-deoxyuridine.

uridine (lUdR) there was an increase in alkaline phosphatase activity after about 24 hr, reaching a maximum usually at about 72 hi. At this concentration, during this time, there was a relatively small inhibition of cell replication. The increment in alkaline phosphatase activity was in large measure prevented by concomitant addition of 10 /¿Mthymidine. Further, lUdR did not increase alkaline phosphatase activity in a mutant line of HeLa cells lacking thymidine kinase. These data indicate that lUdR must be phosphorylated and incorporated into DNA to increase alkaline phosphatase activity. lUdR also usually increased alkaline phosphatase activity of HeLa71 which has a high constitutive level of the enzyme. lUdR did not affect the alkaline phosphatase activity elevated by prior treatment with 1 n\l hydrocortisone. On the other hand, 1 ¿iM hydrocortisone further increased the already elevated alkaline phosphatase activity in cells pretreated with 5 ¿iMlUdR, although after hydrocortisone addition the final level of enzyme activity attained in lUdR-treated and untreated cells was the same.