title: Breast cancer anti-estrogen resistance 3 inhibits transforming growth factor β/Smad signaling and associates with favorable breast cancer disease outcomes.
abstract: BACKGROUND
  This 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.
  
  
  METHODS
  We 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.
  
  
  RESULTS
  Relatively 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.
  
  
  CONCLUSIONS
  BCAR3 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.
authors.affiliation: Division of Medical Oncology, Department of Medicine, McGill University Health Center, H7 Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, H3A 1A1, Canada. jimin.guo@mail.mcgill.ca.
authors.forename: Jimin
authors.initials: J
authors.lastname: Guo
authors.affiliation: Division of Medical Oncology, Department of Medicine, McGill University Health Center, H7 Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, H3A 1A1, Canada. lucie.canaff@mail.mcgill.ca.
authors.forename: Lucie
authors.initials: L
authors.lastname: Canaff
authors.affiliation: Rosalind and Morris Goodman Cancer Center, 1160 Pine Avenue West, Montreal, Quebec, H3A 1A3, Canada. charles.rajadurai@mail.mcgill.ca.
authors.forename: Charles Vincent
authors.initials: CV
authors.lastname: Rajadurai
authors.affiliation: Division of Medical Oncology, Department of Medicine, McGill University Health Center, H7 Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, H3A 1A1, Canada. nadege.fils-aime@mail.mcgill.ca.
authors.forename: Nadège
authors.initials: N
authors.lastname: Fils-Aimé
authors.affiliation: Division of Medical Oncology, Department of Medicine, McGill University Health Center, H7 Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, H3A 1A1, Canada. jun.tian3@mail.mcgill.ca.
authors.forename: Jun
authors.initials: J
authors.lastname: Tian
authors.affiliation: Division of Medical Oncology, Department of Medicine, McGill University Health Center, H7 Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, H3A 1A1, Canada. meiou.dai@mail.mcgill.ca.
authors.forename: Meiou
authors.initials: M
authors.lastname: Dai
authors.affiliation: Division of Medical Oncology, Department of Medicine, McGill University Health Center, H7 Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, H3A 1A1, Canada. juliana.korah@mail.mcgill.ca.
authors.forename: Juliana
authors.initials: J
authors.lastname: Korah
authors.affiliation: Division of Medical Oncology, Department of Medicine, McGill University Health Center, H7 Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, H3A 1A1, Canada. manuel.villatoro@mail.mcgill.ca.
authors.forename: Manuel
authors.initials: M
authors.lastname: Villatoro
authors.affiliation: Rosalind and Morris Goodman Cancer Center, 1160 Pine Avenue West, Montreal, Quebec, H3A 1A3, Canada. morag.park@mcgill.ca.
authors.forename: Morag
authors.initials: M
authors.lastname: Park
authors.affiliation: Division of Hematology, Department of Medicine, McGill University Health Center, H7 Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, H3A 1A1, Canada. suhad.ali@mcgill.ca.
authors.forename: Suhad
authors.initials: S
authors.lastname: Ali
authors.affiliation: Division of Medical Oncology, Department of Medicine, McGill University Health Center, H7 Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Quebec, H3A 1A1, Canada. jj.lebrun@mcgill.ca.
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Lebrun
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000230:Adenocarcinoma / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D018572:Disease-Free Survival; D005260:Female; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D061986:MCF-7 Cells; D011379:Prognosis; D012333:RNA, Messenger / Q000378:metabolism*; D015398:Signal Transduction; D051785:Smad Proteins / Q000378:metabolism*; D013629:Tamoxifen / Q000627:therapeutic use; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018931:Antineoplastic Agents, Hormonal; C118588:BCAR3 protein, human; D020662:Guanine Nucleotide Exchange Factors; D012333:RNA, Messenger; D051785:Smad Proteins; D016212:Transforming Growth Factor beta; D013629:Tamoxifen