title: Knockdown of the Inhibitor of Apoptosis BRUCE Sensitizes Resistant Breast Cancer Cells to Chemotherapeutic Agents.
abstract: OBJECTIVE
  Management of patients with breast cancer often fails because of inherent or acquired resistance to chemotherapy. BRUCE (BIR repeat containing ubiquitin-conjugating enzyme) is a member of the inhibitor of apoptosis protein (IAP) family. It has various cellular functions including suppression of apoptosis and promotion of cytokinesis. Furthermore, it pays a critical role in promotion of DNA damage repair and preservation of genome stability, a new function recently reported by our group. Although BRUCE is expressed in breast cancer cell lines, its expression in human primary breast tumors and its contribution to chemoresistance in breast cancers has not been explored. Chemotherapeutic drugs are used in the treatment of breast cancer patients. However, they are not effective to all patients and patients often develop resistance. Consequently we explored if BRUCE protein level, as judged by immunohistochemistry (IHC), is higher in primary breast tumors than normal breast tissue. We also examined if depletion of BRUCE, using a lentiviral shRNA approach, enhances cell sensitivity to multiple chemotherapeutic agents, including cisplatin, an agent that induces DNA damage by generating DNA cross-links, and taxol, a microtubule stabilizer and mitotic inhibitor. The reason for including these two chemotherapeutic agents in this study is that they hit two essential cellular processes of DNA repair and cytokinesis in which BRUCE plays critical roles.
  
  
  RESULTS
  IHC analysis of BRUCE revealed significantly higher levels of BRUCE in primary breast tumors than normal breast tissue. Knockdown of BRUCE protein expression by lentiviral shRNA resulted in increased sensitivity to cisplatin in the resistant breast cancer MDB-MD-231 cell line. Moreover, depletion of BRUCE in this cell line achieved a more profound level of cell killing when coupled to low doses of cisplatin and taxol combined, rather than either drug used alone.
  
  
  CONCLUSIONS
  Our data suggest that elevated protein levels of BRUCE in breast tumors may contribute to chemoresistance in breast cancer patients. In support of this suggestion, our data demonstrate that a reduction in BRUCE expression in breast cancer cell lines increases the toxicity of several chemotherapeutic agents. In all likelihood, the contribution of increased BRUCE levels to chemoresistance are likely due to its roles in suppression of apoptosis, promotion of cytokinesis and facilitation of DNA damage repair. These observations suggest that therapeutic suppression of BRUCE could improve chemosensitivity in chemo-resistant breast cancer patients. Therefore, future development of effective inhibitors of BRUCE could benefit patients with high BRUCE expression and chemoresistance.
authors.affiliation: Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, USA.
authors.forename: Jason B
authors.initials: JB
authors.lastname: Garrison
authors.affiliation: Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, USA.
authors.forename: Chunmin
authors.initials: C
authors.lastname: Ge
authors.affiliation: Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, USA.
authors.forename: Lixiao
authors.initials: L
authors.lastname: Che
authors.affiliation: Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, USA.
authors.forename: Derek A
authors.initials: DA
authors.lastname: Pullum
authors.affiliation: Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, Houston, USA.
authors.forename: Guang
authors.initials: G
authors.lastname: Peng
authors.affiliation: Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, USA.
authors.forename: Sohaib
authors.initials: S
authors.lastname: Khan
authors.affiliation: Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, USA.
authors.forename: Nira
authors.initials: N
authors.lastname: Ben-Jonathan
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, USA.
authors.forename: Jiang
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Cancer Biology, University of Cincinnati College of Medicine, Cincinnati, USA.
authors.forename: Chunying
authors.initials: C
authors.lastname: Du
keywords: Breast cancer cells; Breast tumors; Cell death; Chemotherapy; DNA damage repair and signaling; Inhibitor of apoptosis protein (IAP)