Stable knockdown of TβRIII in MSL TNBC cells reduces xenograft tumor growth . A) Immunoblot analysis of TβRIII protein expression in lysates harvested from SUM159 cells stably expressing control and four different TβRIII shRNA vectors (TβRIII-KD, KD2-4). B) Flow cytometry analysis of TβRIII protein levels in SUM159 controls, TβRIII-KD and TβRIII-KD4. C) Immunoblot analysis of TβRIII protein expression in lysates harvested from MDA-MB-231 and MDA-MB-157 cells stably expressing control and TβRIII-KD. D-E) Tumors in nude mice were palpable three weeks post implantation of the MSL cell line (D, SUM159 and E, MDA-MB-231). Serial tumor volumes (mm3) were measured weekly for five weeks post palpation for both controls and TβRIII-KD. Each data bar represents the mean tumor volume of 10 tumors; error bar represents SEM (**P ≤0.005, ***P <0.0001 for a two-tailed Student’s t-test). MSL, mesenchymal stem-like; SEM, standard error of the mean; TNBC, triple negative breast cancer; TβRIII, type III transforming growth factor-beta receptor.