This Article Full Text 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 Sun, X.-L. Articles by Antony, A. C. Search for Related Content PubMed PubMed Citation Articles by Sun, X.-L. Articles by Antony, A. C.

Modulation of the Cytotoxicity of 3'-Azido-3'-deoxythymidine and Methotrexate after Transduction of Folate Receptor cDNA into Human Cervical Carcinoma

Identification of a Correlation between Folate Receptor Expression and Thymidine Kinase Activity¹

Xin-Lai Sun, Hiremagalur N. Jayaram, Kamran Gharehbaghi, Qing-Jun Li, Xiangli Xiao and Aok C. Antony²

Division of Hematology-Oncology, Department of Medicine [X-L. S., Q-J. L., X. X., A. C. A.], Laboratory for Experimental Oncology [H. N. J., K. G.], and Department of Biochemistry and Molecular Biology [H. N. J.], Indiana University School of Medicine, and the Richard L. Roudebush Veterans Affairs Medical Center [A. C. A.], Indianapolis, Indiana 46202

Cervical carcinoma is an AIDS-defining illness. The expression of folate receptors (FRs) in cervical carcinoma (HeLa-IU₁) cells was modulated by stable transduction of FR cDNA encapsidated in recombinant adeno-associated virus-2 in the sense and antisense orientation (sense and antisense cells, respectively). Although sense cells proliferated slower than antisense or untransduced cells in vivo and in vitro in 2% (but not 10%) FCS, [methyl-³H]thymidine incorporation into DNA was significantly increased in sense cells in 10% serum; therefore, the basis for this discrepancy was investigated. The activity of thymidine kinase (TK) was subsequently directly correlated with the extent of FR expression in single cell-derived clones of transduced cells. This elevated TK activity was not a result of recruitment of the salvage pathway based on the presence of adequate dTTP pools, normal thymidylate synthase (TS) activity, persistence of increased thymidine incorporation despite the exogenous provision of excess 5,10-methylene-tetrahydrofolate, and documentation of adequate folates in sense cells.

The increase in TK activity conferred significant biological properties to sense cells (but not antisense or untransduced cells) as demonstrated by augmented phosphorylation of 3'-azido-3'-deoxythymidine (AZT) and concomitantly greater sensitivity to the cytotoxic effects of AZT. Conversely, sense cells were highly resistant to methotrexate, but this was reversed by the addition of AZT. The direct correlation of FR expression and TK activity indicates a previously unrecognized consequence of FR overexpression.