This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Roberts, D. Articles by Loehr, E. V. Search for Related Content PubMed PubMed Citation Articles by Roberts, D. Articles by Loehr, E. V.

Elevation of Thymidylate Synthetase Activity in CCRF-CEM Cells¹

St. Jude Children's Research Hospital, Memphis, Tennessee 38101 [D. R. E. V. L.], and Department of Pharmacology, University of Tennessee Medical Units, Memphis, Tennessee 38103 [D. R.]

The basis for an elevation of thymidylate synthetase activity by methotrexate has been studied with CCRF-CEM cell cultures. In a comparison of oncolytic drug effects on three enzymes from these cells, methotrexate elevated both thymidylate synthetase and thymidine kinase activity but not alanine transaminase activity. The pattern of response by these three enzymes to cytosine arabinoside and hydroxyurea varied from the observations with methotrexate. Cytosine arabinoside and actinomycin D depressed thymidylate synthetase activity. A small but variable response to hydroxyurea was observed. The combination of actinomycin D with methotrexate resulted in a level of thymidylate synthetase activity intermediate between those observed with the individual drugs.

An elevation of thymidylate synthetase activity also occurred in cells from cultures to which substrate or product precursors of the thymidylate synthetase reaction were added. The combination of thymidine or deoxyuridine with methotrexate elevated thymidylate synthetase activity above the level observed with the individual compounds. An in vitro binding of methotrexate to thymidylate synthetase was expressed by an inhibition of enzyme activity.

Folinic acid elevated thymidylate synthetase activity and reversed methotrexate inhibition of growth and of deoxyuridine incorporation into DNA. The methotrexate-induced elevation of thymidylate synthetase activity could be modulated by high concentrations of folinic acid. The elevation of thymidylate synthetase activity by methotrexate, deoxyuridine, thymidine, and folinic acid was attributed to a stabilization of thymidylate synthetase by the formation of enzyme complexes. The predominant phase of the growth cycle of the culture presumably controls the potential for enzyme synthesis, and the action of other drugs on protein synthesis modifies thymidylate synthetase response to methotrexate.

¹ Supported by Research Grants CA-11148 and CA-08480 from the National Cancer Institute, NIH, and by American Lebanese Syrian Associated Charities.

Received 2/ 3/71. Accepted 4/20/71.