Overexpression of YY1 inhibits FEN1 promoter-driven protein expression. A. YY1 was overexpressed in 293 T cells and its impact on the FEN1 protein level was evaluated by western blot using the anti-Flag or anti-FEN1 antibody. B. The pCMV-Flag-YY1 expression vector and the pGL4.0-FEN1 promoter-EGFP vector, or pGL4.0 EGFP vector was co-transfected into 293 T cells. The EGFP expression was detected by semi-quantitative PCR (Upper panel) and quantitative PCR (lower panel). C. The overexpression of Flag-tagged YY1 was confirmed by western blot using the anti-Flag antibody. D and E. EGFP protein levels with or without YY1 overexpression was measured by FACS. Panel D shows the representative FACS images. Panel E is the quantification of FACS. Values are means ± s.d. of four independent experiments. p value was calculated by the two-tail student’s t-test. F. Knockdown of YY1 in 293 T (Left Panel) and MCF7 (right panel) cells. The YY1 and FEN1 expression was measured by quantitative PCR. The mRNA level was normalized with corresponding mRNA level of GADPH, and the normalized mRNA level of YY1 or FEN1 in the cells treated with control siRNA was arbitrarily set as 1. Values are means ± s.d. of three independent experiments. p value was calculated by the two-tail student’s t-test.