Inhibition by Deoxycytidine, Cytidine, and β-Cytosine Arabinoside of the Induction of Alkaline Phosphatase Activity in Hela Cells

Abstract

The main objective of these experiments was the further examination of whether the induction of alkaline phosphatase activity in HeLa cells by 5-iodo-2′-deoxyuridine (IdUrd) depends on the incorporation of IdUrd into DNA. Thymidine (dThd), deoxycytidine (dCyd), cytidine, and β-cytosine arabinoside (Are-C) inhibited in a dose-dependent manner the induction of alkaline phosphatase activity by IdUrd in HeLa cells, and 5-iodo-2′-deoxycytidine induced activity in a dose-dependent manner at concentrations similar to those of IdUrd. Three of these compounds, dThd, dCyd, and Ara-C, were studied with regard to degree of inhibition of induction and IdUrd incorporation into DNA. Although the various doses of these three compounds decreased the incorporation of IdUrd into DNA, there was no apparent linear correlation between the extent of inhibition of IdUrd incorporation and the degree of inhibition of the induction of alkaline phosphatase activity. dCyd also inhibited in a dose-dependent manner the induction of alkaline phosphatase by hydrocortisone, sodium butyrate, and choline chloride. These results, although not unequivocal, support the idea that IdUrd induction of alkaline phosphatase activity in HeLa cells does not require IdUrd incorporation into DNA. The dCyd altered the thermostabillty for alkaline phosphatase activity from control or IdUrd-treated cells, and for control cells the change in thermostability occurred without a change in the enzyme specific activity.