Cells exposed to antifolates show increased cellular levels of proteins fused to dihydrofolate reductase: A method to modulate gene expression

Philipp Mayer-Kuckuk, Debabrata Banerjee, Sundeep Malhotra, Mikhail Doubrovin, Marian Iwamoto, Tim Akhurst, Julius Balatoni, William Bornmann, Ronald Finn, Steven Larson, Yuman Fong, Juri Gelovani Tjuvajev, Ronald Blasberg, Joseph R. Bertino

Research output: Contribution to journalArticlepeer-review

55 Scopus citations

Abstract

Human cells exposed to antifolates show a rapid increase in the levels of the enzyme dihydrofolate reductase (DHFR). We hypothesized that this adaptive response mechanism can be used to elevate cellular levels of proteins fused to DHFR. In this study, mouse cells transfected to express a green fluorescent protein-DHFR fusion protein and subsequently exposed to the antifolate trimetrexate (TMTX) showed a specific and time-dependent increase in cellular levels of the fusion protein. Next, human HCT-8 and HCT-116 colon cancer cells retrovirally transduced to express a DHFR-herpes simplex virus 1 thymidine kinase (HSV1 TK) fusion protein and treated with the DHFR inhibitor TMTX exhibited increased levels of the DHFR-HSV1 TK fusion protein and an increase in ganciclovir sensitivity by 250-fold. The level of fusion protein in antifolate-treated human tumor cells was increased in response to a 24-h exposure of methotrexate, trimetrexate, as well as dihydrofolate. This effect depended on the antifolate concentration and was independent of the fusion-protein mRNA levels, consistent with this increase occurring at a translational level. In a xenograft model, nude rats bearing DHFR-HSV1 TK-transduced HCT-8 tumors and treated with TMTX showed, after 24 h, a 2- to 4-fold increase of fusion-protein levels in tumor tissue from treated animals compared with controls, as determined by Western blotting. The fusion-protein increase was imaged with positron-emission tomography, where a substantially enhanced signal of the transduced tumor was detected in animals after antifolate administration. Drugmediated elevation of cellular DHFR-fused proteins is a very useful method to modulate gene expression in vivo for imaging as well as therapeutic purposes.

Original languageEnglish (US)
Pages (from-to)3400-3405
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume99
Issue number6
DOIs
StatePublished - Mar 19 2002

All Science Journal Classification (ASJC) codes

  • General

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