Alteration of Nucleoside Transport of Chinese Hamster Cells by Dibutyryl Adenosine 3′:5′-Cyclic Monophosphate

Abstract

Cultured Chinese hamster ovary cells showed no significant change in generation time or fraction in the S-phase in the presence of 1 mM N(6),O(2')-dibutyryl adenosine 3':5'-cyclic monophosphate. Growth continued for at least two generations after expression of the morphological transformation induced by this cyclic AMP analog. Despite identical growth rates, apparent rates of DNA and RNA synthesis (incorporation of [(3)H]-thymidine or [(3)H]uridine) were reduced up to 15-fold in log phase by 1 mM cyclic nucleotide. [(3)H]Deoxycytidine incorporation was much less sensitive to dibutyryl cyclic AMP. Uptake studies with [(3)H]thymidine demonstrated an inhibition of transport rate dependent on the concentration of dibutyryl cyclic AMP in the growth medium. The rate of thymidine uptake at 1 degrees was decreased 21-fold by 1 mM cyclic nucleotide; half-maximal inhibition occurred at 6 muM. At 37 degrees , the pool size of acid-soluble thymidylate was strongly reduced by 1 mM cyclic nucleotide, and synergistic reduction of the pool size was found with 0.5 mM aminophylline. Phosphorylation of the acid-soluble intracellular label was unaffected by dibutyryl cyclic AMP. Inhibition of thymidine uptake is attributed to an observed decrease in thymidine kinase activity caused by growth in 1 mM dibutyryl cyclic AMP, and possibly to a simultaneous alteration in membrane permeability. Kinase-facilitated uptake of other metabolites may be regulated in a similar fashion by cyclic AMP.