DNA damaging agents MMC and Taxol inhibit YY1 expression but induce FEN1 expression. A. and B. YY1 and FEN1 expression in MDA-MB-231 breast cancer cell line in response to the MMC and Taxol treatment. The mRNA level (A) and protein level (B) were measured by quantitative PCR and Western blot. The left panel in B showed the quantification of Western blot results. All experiments were independent carried out at least three times. C. Analysis of YY1 binding to the FEN1 promoter in response to the MMC treatment. Cells were treated with MMC, and the level of YY1-bound FEN1 promoter was evaluated by the ChIP assay. The lowest DNA staining density is arbitrarily set as 1. D. western blot confirmed the overexpression of Flag-tagged YY1 in 293 T cells. The β-actin(ACTB) was used as control. E. and F. The survivorship of 293 T cell and 293 T cell harboring a YY1 expression plasmid, pCMV-Flag-YY1, or the empty vector, under treatment of mytomycine C (MMC) (Panel E) or taxol (Panel F). In both panels, the cells were treated with indicated concentrations of MMC or taxol for 48 hours. The number of survival cells was counted. The survival rate of the untreated cells with or without YY1 overexpression was arbitrarily set as 1.