Fig 2: CDK8 enhances MDA-MB-231 breast cancer cell viability and migration. The infection efficiency of CDK8 knockdown was (A) determined by western blotting and (B) semi-quantified. (C) Infection efficiency of CDK8 knockdown was further assessed via reverse transcription-quantitative PCR. (D) Effect of CDK8 knockdown on cell viability, as determined by MTT assay. The effect of CDK8 knockdown on cell migration was (E) assessed by performing a wound healing assay (magnification, ×400) and (F) the rate of migration was quantified. *P<0.05, **P<0.01 and ***P<0.001 vs. LV-NC-shRNA (one-way ANOVA). CDK8, cyclin-dependent kinase 8; LV, lentiviral vector; NC, negative control; shRNA, short hairpin RNA; OD, optical density.

Fig 3: CDK8 mRNA and protein expression levels are significantly increased in MDA-MB-231 breast cancer cells. CDK8 (A) protein and (B) mRNA expression levels in MDA-MB-231 and MCF10A cells were detected by western blotting and reverse transcription-quantitative PCR, respectively. **P<0.01 and ***P<0.001 vs. MCF10A (one-way ANOVA). CDK8, cyclin-dependent kinase 8.

Fig 4: Capsaicin inhibits breast cancer cell viability by downregulating the CDK8/PI3K/Akt signaling pathway. MDA-MB-231 cells were treated with capsaicin (10, 50, 100 and 200 µM), PI3K inhibitor (LY294002; 25 µM) or CDK8 inhibitor (Senexin A; 2.5 µM) for 24 h. Protein expression levels were (A) determined via western blotting, and (B) p-PI3K/PI3K and (C) p-Akt/Akt were semi-quantified. (D) Effect of Senexin on cell viability, as determined by MTT assay. The effect of Senexin on cell migration was (E) assessed by performing a wound healing assay (magnification, ×400) and (F) the rate of migration was quantified. *P<0.05, **P<0.01 and ***P<0.001 vs. control (one-way ANOVA). CDK8, cyclin-dependent kinase 8; p, phosphorylated.

Fig 5: Capsaicin inhibits breast cancer cell viability by downregulating CDK8. (A) Effect of capsaicin on cell viability, as determined by MTT assay. The effect of capsaicin on cell migration was (B) determined by performing a wound healing assay (magnification, ×400) and (C) rate of migration was quantified. CDK8 protein expression levels were (D) determined via western blotting and (E) semi-quantified (n=3). *P<0.05, **P<0.01 and ***P<0.001 vs. 0 µM capsaicin (one-way ANOVA). CDK8, cyclin-dependent kinase 8.