PARENT SESSION
3:45 PM to 5:15 AM
Sunday, April 21, 2002
Mini-Symposium 5
Oxygenation and Stress Response
Room: Nevada 1-2
, Co-Chair: Koch, Cameron¹; Mason, Kathy²¹University of Pennsylvania, Philadelphia, PA²MD Anderson Cancer Center, Houston, TX

(MS05-8) AP-1 activation of DNA methyltransferase contributes to a unique multi-modality resistant phenotype via cellular oxidative stress responses.

Sieck, Leah^*,1, Bisht, Kheem¹, Bradbury, C. Matthew¹, Gius, David¹, ¹ National Cancer Institute, Bethesda, MD

ABSTRACT-
Previous results in our laboratory demonstrated that: (1) OC-14 hamster peroxide-resistant cells are resistant to cytotoxicity induced by Cisplatin, Etoposide, and H₂O₂, referred to as multi-modality resistant phenotype (MMRP), (2) OC-14 cells overexpress c-Fos and c-Jun and exhibit elevated AP-1 DNA binding activity, (3) the inhibition of AP-1 activity reverses the MMRP in OC-14 cells, and (4) OC-14 cells overexpress DNA methyltransferase (dnmt1). Therefore, we hypothesize that the consitutive activation of the AP-1 complex resulting in the induction of dnmt1 is one mechanism whereby tumor cells gain resistance to specific anti-cancer agents. DNA binding was established in nuclear extracts by EMSA with a P₃₂-labeled AP-1 oligonucleotide. Cells treated with Cisplatin (CDDP), 5-aza-deoxycytidine (5adC), Etoposide, or H₂O₂ were assayed for survival by clonogenic assay. Permanent cell lines constitutively overexpress c-Fos (CMVc-Fos) and demonstrate a correspondiing elevated level of AP-1 activity. In addition, the cell lines contain a similar MMRP to CDDP, Etoposide, and H₂O₂, as seen in OC-14 cells. Also, the MMRP in OC-14 and CMVc-Fos cells were reversed by inhibition of dnmt1 with 5adC. Finally, permanent cell lines that overexpress dmnt1 also demonstrated a similar MMRP as OC-14 cells to the cytotoxicity of CDDP, Etoposide, and H₂O₂. These results suggest that dnmt1 may be a downstream target of the constitutive activation of the AP-1 complex. Our results also suggest that the AP-1 complex contributes to the regulation of cellular oxidative stress responses that may contribute to the MMRP demonstrated by tumors treated with systemic cytotoxic agents thought to induce oxidative stress.

KEYWORDS: AP-1, DNA methyltransferase, multi-modality resistant phenotype, oxidative stress