Fig 2: Model.As ERα (+) breast tumors acquire resistance to tamoxifen, a group of nuclear transport proteins including XPO1 will be up-regulated, increasing ERK5 export from nucleus. Thus, 1) ERα, which is in the nucleus, will not have the partners to elicit proper transcriptional responses to tamoxifen and 2) ERK5, which partners with other cytoplasmic proteins, will now contribute to increased tumorigenicity and tamoxifen resistance.

Fig 3: XPO1 is increased in luminal B subtype patient tumor samples and human breast cancer cell lines, and increased XPO1 levels increase cell proliferation of tamoxifen-resistant cell lines in the presence of 4-OH-TAM.A, Verification of XPO-1 levels in patient tumor samples. mRNA from tumor FFPE samples were isolated. After the quality of RNA was verified, qPCR was run for XPO1 and 36B4 as control. A one-way ANOVA model was fitted to assess the contribution of subtype to expression of XPO1 mRNA. When the main effects were statistically significant at α = .05, pairwise t tests with a Newman-Keuls correction were used to identify the subtype that had the highest level of XPO1 expression. ***, P < .01. B, Impact of XPO1 inhibitor on cell cycle progression. Cells were treated with Veh or 1 μM 4-OH-TAM in the presence or absence of 10−7 M SXR. Cell numbers were examined using the FACS analysis. C, Anchorage-independent growth of tamoxifen-resistant BT474 cells treated or nontreated with XPO1 inhibitor (SXR). Colony formation was visualized with Giemsa staining. On the right are representative pictures of spheroid, single colonies formed by BT474 cells. A two-way ANOVA model was fitted to assess the contribution of ligand (Veh, E2, or tamoxifen) and inhibitor (Ctrl and SXR) treatment on anchorage-dependent growth of BT474 cells. When the main effects were statistically significant at α = .05, pairwise t tests with a Bonferroni correction were used to identify whether treatment were statistically different from each other. **, P < .01; ****, P < .0001. D, XPO1 overexpression in MCF-7 and BT474 cell increase ERK5 activation. MCF7 cells (left panel) or BT474 cells (right panel) were infected with AdCMV as control or AdXPO1. XPO1mRNA overexpression was detected by qPCR. XPO1 protein overexpression was assessed by Western blot of immunofluorescence analysis. A t test was applied to assess whether AdXPO1 virus infection resulted in statistically significant overexpression of XPO1 in each cell line. *, P < .05 E, XPO1 overexpression in MCF-7 and BT474 cells increase cell proliferation. MCF-7 cells (left panel) and BT474 cells (right panel) were infected with AdCMV as control or AdXPO1, and then cells were treated with increasing doses of 4-OH-TAM in the presence or absence of 100 nM SXR. Ctrl, control; FACS, fluorescence-activated cell sorter.