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ABSTRACT
Cytochrome P450 1B1 (CYP1B1), a well-known oncogene, has garnered wide attention because of its tumor-specific expression pattern and actions as a carcinogenic factor. Although CYP1B1 might play a crucial role in carcinogenesis, the detailed molecular mechanisms underlying oncogenic involvement in cancer development remain unclear. The present study investigated the manner in which CYP1B1 promotes survival of various cancer cells. Treatment with 2,2ˊ,4,6ˊ-tetramethoxystilbene (TMS), a specific CYP1B1 inhibitor, significantly inhibited cell viability in human breast cancer and leukemia cell lines, including MCF-7, MDA-MB-231, HL-60, and U937 cells. In order to characterize the cellular functions of CYP1B1 associated with cancer cell survival, the relationship between this oncogene and death receptor 4 (DR4) was determined. Following induction or inhibition of CYP1B1, mRNA and protein expression levels of DR4 were measured, and this oncogene was found to significantly repress DR4 mRNA and protein expression. Further, the suppression of DR4 by CYP1B1 was restored with 5-aza-2ˊ-deoxycytidine (5-aza-dC), a DNA methyltransferase inhibitor, indicating that DNA methylation may be involved in CYP1B1-mediated DR4 inhibition. Methylation-specific polymerase chain reaction (PCR) in CYP1B1-overexpressed HL-60 cells revealed that this oncogene induced hypermethylation on DR4 promoter. Interestingly, data showed that DR4 suppression of CYP1B1 is mediated by the DNA-binding ability of specificity protein 1 (Sp1). These findings suggest that CYP1B1 promotes cancer cell survival through involvement of DNA methylation-mediated DR4 inhibition and that Sp1 may act as key mediator required for oncogenic action.