Inhibition of Specificity Protein 1 Is Involved in Phloretin-Induced Suppression of Prostate Cancer

Figure 6

Phloretin induced the degradation of Sp1 protein in PCa cells. (a) Cells were treated with 10 μg/ml CHX alone or cotreated with 10 μg/ml CHX and 50 μM phloretin (CHX pretreated for 30 min) for western blot assays to detect the protein levels of Sp1 and Sp3/4. The quantification: first, the densities of bands of Sp1 and β-actin were quantified using ImageJ software, and the ratios of Sp1/β-actin (the Sp1 and β-actin with no treatment of phloretin and CHX as control) were calculated; second, the ratios of Sp1/β-actin vs. Con were obtained by using the values of Sp1/β-actin vs. the value of control Sp1/β-actin (control Sp1/β-actin vs. control Sp1/β-actin as 1). (b) Cells were treated with phloretin (50 μM) and/or MG132 (10 μM), and then cells were harvested for western blotting assay to detect the protein levels of Sp1 and Sp3/4. All western blotting assays used β-actin as loading control. (c) PC-3 cells were transfected with the various luciferase constructs and treated with phloretin (50 μM) or MG132 (10 μM) alone, or cotreated with phloretin (50 μM) and MG132 (10 μM), and then dual-luciferase activities (Firefly and Renilla) were measured. The fold inductions of luciferases were calculated by using relative luciferases (the relative luciferase of control as 1). ; . Con: control.

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