PT  - JOURNAL ARTICLE
AU  - Robertson, Kent A.
AU  - Bullock, Heather A.
AU  - Xu, Yi
AU  - Tritt, Renee
AU  - Zimmerman, Erika
AU  - Ulbright, Thomas M.
AU  - Foster, Richard S.
AU  - Einhorn, Lawrence H.
AU  - Kelley, Mark R.
TI  - Altered Expression of Ape1/ref-1 in Germ Cell Tumors and Overexpression in NT2 Cells Confers Resistance to Bleomycin and Radiation
DP  - 2001 Mar 03
TA  - Cancer Research
PG  - 2220--2225
VI  - 61
IP  - 5
4099  - http://cancerres.aacrjournals.org/content/61/5/2220.short
4100  - http://cancerres.aacrjournals.org/content/61/5/2220.full
SO  - Cancer Res2001 Mar 03; 61
AB  - The human AP endonuclease (Ape1 or ref-1) DNA base excision repair (BER) enzyme is a multifunctional protein that has an impact on a wide variety of important cellular functions including oxidative signaling, transcription factor regulation, and cell cycle control. It acts on mutagenic AP (baseless) sites in DNA as a critical member of the DNA BER repair pathway. Moreover, Ape1/ref-1 stimulates the DNA-binding activity of transcription factors (Fos-Jun, nuclear factor-κB, Myb, ATF/cyclic AMP-responsive element binding protein family, HIF-1α, HLF, PAX, and p53) through a redox mechanism and thus represents a novel component of signal transduction processes that regulate eukaryotic gene expression. Ape1/ref-1 has also been shown to be closely linked to apoptosis associated with thioredoxin, and altered levels of Ape1/ref-1 have been found in some cancers. In a pilot study, we have examined Ape1/ref-1 expression by immunohistochemistry in sections of germ cell tumors (GCTs) from 10 patients with testicular cancer of various histologies including seminomas, yolk sac tumors, and malignant teratomas. Ape1/ref-1 was expressed at relatively high levels in the tumor cells of nearly all sections. We hypothesized that elevated expression of Ape1/ref-1 is responsible in part for the resistance to therapeutic agents. To answer this hypothesis, we overexpressed the Ape1/ref-1 cDNA in the GCT cell line NT2/D1 using retroviral gene transduction with the vector LAPESN. Using an oligonucleotide cleavage assay and immunohistochemistry to assess Ape1/ref-1 repair activity and expression, respectively, we found that the repair activity and relative Ape1/ref-1 expression in GCT cell lines are directly related. NT2/D1 cells transduced with Ape1/ref-1 exhibited 2-fold higher AP endonuclease activity in the oligonucleotide cleavage assay, and this was reflected in a 2–3-fold increase in protection against bleomycin. Lesser protection was observed with γ-irradiation. We conclude that: (a) Ape1/ref-1 is expressed at relatively high levels in some GCTs; (b) elevated expression of Ape1/ref-1 in testicular cancer cell lines results in resistance to certain therapeutic agents; and (c) Ape1/ref-1 expression in GCT cell lines determined by immunohistochemistry and repair activity assays parallels the level of protection from bleomycin. We further hypothesize that elevated Ape1/ref-1 levels observed in human testicular cancer may be related to their relative resistance to therapy and may serve as a diagnostic marker for refractory disease. To our knowledge, this is the first example of overexpressing Ape1/ref-1 in a mammalian system resulting in enhanced protection to DNA-damaging agents. ©2001 American Association for Cancer Research.