Abstract B83: Sulfiredoxin is an AP-1 target gene that is required for transformation and shows elevated expression in human skin tumors

B83

Previous studies from others and our lab have shown that activator protein 1 (AP-1) plays a pivotal role in tumorigenesis in vitro and in vivo. Expression of a dominant negative form c-Jun, TAM67, dramatically inhibits tumor promoter induced skin carcinogenesis. In this study, our goals are to identify target genes that are specifically induced by tumor promoter and inhibited by TAM67, and to investigate their functional significances in tumor promotion and progression. First, we demonstrated that Sulfiredoxin (Srx) is a novel target of AP-1 activation and TAM67 inhibition. In mouse epidermis, expression of Srx was upregulated by tumor promoter and inhibited by TAM67 as revealed by DNA microarray. This was further confirmed in mouse epithelial-derived JB6 cells by RT-PCR, Western blotting, luciferase reporter and chromatin immunoprecipitation assays at transcript and protein levels. Next, we demonstrated that Srx is important for maintaining of cellular redox homeostasis through reduction of overoxidized Peroxiredoxins (Prxs). Knockdown of Srx led to a much slower reduction rate of overoxidized Prxs, whereas overexpression of Srx resulted in an increased reduction rate of overoxidized Prxs. Then we found that knockdown of Srx dramatically inhibited tumor promoter induced neoplastic transformation as indicated by anchorage-independent growth in soft agar. This effect was not due to the inhibition of cell proliferation as depletion of Srx stimulated cell proliferation under adherent conditions. Depletion of Srx also led to impaired AP-1 activation and increased cell death under oxidative conditions, which indicated that Srx might be involved in the regulation of AP-1 activity through a novel positive feedback loop. Finally, we examined the expression profiling of Srx in normal skin and tissues from patients with various skin diseases by tissue microarray. We found strong positive expression of Srx in skin malignant tumors. In summary, we identified Srx as a novel target of tumor promoter induced AP-1 activation and is inhibited by TAM67. We demonstrated that Srx is important for maintaining of cellular redox balance and is required for tumor promoter induced neoplastic transformation. We also found strong expression of Srx in human skin malignant tumors. Therefore, we propose that Srx can be used as a marker for skin malignancy, and manipulation of Srx expression may be of interest in cancer prevention and treatment.

Citation Information: Cancer Prev Res 2008;1(7 Suppl):B83.