β-TRCP regulates PTC cell migration via regulating VEGFR2 protein levels and VEGF-A secretion in vitro. (A and B) The media from various cultured human thyroid cancer cell lines were collected for ELISA analysis to determine the concentration of secreted VEGF-A. Data are representative of three independent experiments. The error bars represent mean ± SD. **, P < 0.01; ***, P < 0.001. (C) Immunoblot analysis of BCPAP cells infected with EV or HA–β-TRCP1–encoding lentiviral vectors. Where indicated, VEGF-A was added for 15 min before harvesting. Data are representative of two independent experiments. (D) EV or β-TRCP–expressing BCPAP cells were exposed to 200 ng/ml VEGF-A where indicated. Cells were photographed after 18 h. Bars, 5 µm. Data are representative of three independent experiments. (E) Quantitative measurement of migrated BCPAP cells shown in D. The error bars represent mean ± SD. ***, P < 0.001 (n = 3).