Breast cancer anti-estrogen resistance 3 inhibits transforming growth factor β/Smad signaling and associates with favorable breast cancer disease outcomes

Abstract

IntroductionThis study helps to define the implications of breast cancer anti-estrogen resistance 3 (BCAR3) in breast cancer and extends the current understanding of its molecular mechanism of action. BCAR3 has been shown to promote cell proliferation, migration and attachment to extracellular matrix components. However, in a cohort of metastatic breast cancer patients who received tamoxifen treatment, high BCAR3 mRNA levels were associated with favorable progression-free survival outcome. These results suggest that, besides its established roles, BCAR3 may have additional mechanisms of action that regulate breast cancer aggressive phenotype. In this study, we investigated whether BCAR3 is a novel antagonist of the canonical transforming growth factor β (TGFβ) pathway, which induces potent migration and invasion responses in breast cancer cells.MethodsWe surveyed functional genomics databases for correlations between BCAR3 expression and disease outcomes of breast cancer patients. We also studied how BCAR3 could regulate the TGFβ/Smad signaling axis using Western blot analysis, coimmunoprecipitation and luciferase assays. In addition, we examined whether BCAR3 could modulate TGFβ-induced cell migration and invasion by using an automated imaging system and a confocal microscopy imaging–based matrix degradation assay, respectively.ResultsRelatively low levels of BCAR3 expression in primary breast tumors correlate with poor distant metastasis-free survival and relapse-free survival outcomes. We also found a strong correlation between the loss of heterozygosity at BCAR3 gene alleles and lymph node invasion in human breast cancer, further suggesting a role for BCAR3 in preventing disease progression. In addition, we found BCAR3 to inhibit Smad activation, Smad-mediated gene transcription, Smad-dependent cell migration and matrix digestion in breast cancer cells. Furthermore, we found BCAR3 to be downregulated by TGFβ through proteasome degradation, thus defining a novel positive feedback loop mechanism downstream of the TGFβ/Smad signaling pathway.ConclusionBCAR3 is considered to be associated with aggressive breast cancer phenotypes. However, our results indicate that BCAR3 acts as a putative suppressor of breast cancer progression by inhibiting the prometastatic TGFβ/Smad signaling pathway in invasive breast tumors. These data provide new insights into BCAR3’s molecular mechanism of action and highlight BCAR3 as a novel TGFβ/Smad antagonist in breast cancer.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-014-0476-9) contains supplementary material, which is available to authorized users.

Breast Cancer Antiestrogen Resistance-3 (BCAR3) in Mammary Gland Development and Breast Cancer

“…This can be determined by analyzing the correlation between BCAR3 expression and tumor subtype, tumor grade, metastasis, and overall survival in breast cancer patients. As mentioned previously, high levels of BCAR3 mRNA in patients treated with tamoxifen were found to correlate with increased progressionfree survival (Guo et al, 2014)…”

“…BCAR3 was originally identified as a gene that, when overexpressed in cell lines, conferred resistance to antiestrogens (VanAgthoven et al, 1998). However, one study reported that high BCAR3 mRNA levels associated with increased progressionfree survival in a cohort of ER+ breast cancer patients receiving tamoxifen treatment (Guo et al, 2014). This is potentially contradictory to what we know about BCAR3 function in vitro.…”

“…There is only one published study analyzing the relationship between BCAR3 expression and progressionfree survival in breast cancer patients. This study reported that high BCAR3 mRNA levels correlated with increased progressionfree survival in patients with ER+ breast cancer who received tamoxifen treatment (Guo et al, 2014). This is surprising considering BCAR3 was first identified in a screen for genes whose overexpression BCAR3 is composed of an amino-terminal SH2 domain, a serine/proline-rich linker, and a carboxy-terminal guanine-nucleotide exchange factor (GEF)-like domain with sequence homology to the CDC25 family of GEFs.…”

“…In addition to the role BCAR3 plays in cancer cell motility, BCAR3 has been reported to regulate proliferation through increased cyclin D1 expression (Near et al, 2007). The ability of BCAR3 to promote these phenotypes is dependent on its direct binding with Cas (Wallez et al, 2014) Despite in vitro data suggesting BCAR3 may control tumor growth or progression, high BCAR3 mRNA expression in ER+ breast tumors has been reported to be associated with increased progressionfree survival (Guo et al, 2014). It is important to note, however, that this relationship between BCAR3 mRNA and survival was only present in ER+ tumors.…”

“…Signaling through the TGFβ receptor II in macrophages promotes expression of genes characteristic of M2 polarization . As BCAR3 expression has been shown to inhibit TGF/Smad signaling in breast cancer cell lines (Guo et al, 2014), BCAR3 loss may augment TGF signaling in these cells and promote polarization of M2 macrophages. Future experiments could employ doublelabeling immunohistochemistry to characterize the polarization state of macrophages in situ.…”