Study of VAV3 in models of acquired resistance to endocrine therapies. (A) Western blot analysis results for VAV3 (pT173 and total, top panels), signaling components and control tubulin α (TUBA) from MCF7 cells and long-term estrogen deprivation of MCF7 (MCF7-LTED) cells in basal and YC-1 exposure conditions. pERK, phosphorylated extracellular signal-regulated protein kinase. (B) Western blot analysis results for VAV3, PAK1 and RAC1, as well as control TUBA, in MCF7-LCC9 cell extracts from basal and YC-1 exposure conditions. (C) Short hairpin RNA (shRNA)–mediated depletion of VAV3 reduces the viability, in methylthiazol tetrazolium (MTT)–based assays) of MCF-LTED and MCF7-LCC9 cells relative to parental MCF7. The asterisks correspond to significant differences (P < 0.05) in the viability rate (slope of the trends (shown), including three replicas, and relative to the control pLKO.1). The bottom right panel shows the results of short hairpin RNA (shRNA)–mediated depletion of VAV3 relative to the negative control assay. (D) shRNA-mediated depletion of VAV3 reduces the viability (clonogenic assays) of MCF-LTED and MCF7-LCC9 cells. (E) Reconstitution with MYC-Vav3 partially recovers viability of MCF-LTED cells. The asterisk corresponds to a significant difference (P < 0.05) relative to shRNA-mediated depletion of VAV3. (F) No substantial differences in poly(ADP-ribose) (PARP) cleavage were observed between MCF7 and MCF7-LTED cells exposed to YC-1. (G) Top panel, reduction of E2F1 expression in MCF7 and MCF7-LTED cells exposed to YC-1; MCF7-LTED, but not the parental MCF7, show a reduction at 2 μM YC-1. Bottom panel, control TUBA.