β-TRCP regulates VEGFR2 protein levels in human PTC-derived cells, and thereby influences sensitivity to the VEGFR2 inhibitor sorafenib. (A and B) HMVECs were co-cultured with EV or β-TRCP–expressing BCPAP cells in the presence or absence of VEGF-A antibody. (B) Cells were photographed after 44 h. Bars, 5 µm. Data are representative of three independent experiments. (C) Quantitative measurement of migrated BCPAP cells shown in B. The error bars represent mean ± SD. ***, P < 0.001 (n = 3). (D) Immunoblot analysis of the BCPAP cells infected with the indicated shRNA lentiviral vectors. Data shown is representative of two independent experiments. (E) BCPAP cells shown in D were exposed to 200 ng/ml VEGF-A where indicated. Recruited cells were photographed after 5 h. Bars, 5 µm. Data shown is representative of two independent experiments. (F) Various PTC cell lines were treated with the indicated concentrations of sorafenib. Cell viability was measured at 48 h. Data shown is representative of three independent experiments. The error bars represent mean ± SD. *, P < 0.05; ***, P < 0.001 (n = 3). (G) EV or HA–β-TRCP1–expressing BCPAP cells were treated with the indicated concentrations of sorafenib. Cell viability was measured at 48 h. The error bars represent mean ± SD. **, P < 0.01; ***, P < 0.001 (n = 3).