title: Reduced association of anti-apoptotic protein Mcl-1 with E3 ligase Mule increases the stability of Mcl-1 in breast cancer cells.
abstract: BACKGROUND
  Mechanisms that increase resistance to apoptosis help promote cellular transformation. Cancer cells have deregulated apoptotic pathways, where increased expression and stability of anti-apoptotic proteins Mcl-1 and Bcl-2 increases resistance to apoptosis. Pathways that increase the stability of proteins in cancer cells remain poorly understood.
  
  
  METHODS
  Using human mammary epithelial and established breast cancer cell lines, we assessed the mechanisms that increase the stability of anti-apoptotic proteins in breast cancer cells by caspase assay, western blot, small-inhibitory RNA treatment and immunoprecipitation.
  
  
  RESULTS
  While breast cancer cells were resistant to de novo inhibition of protein synthesis, a rapid proteosome-mediated degradation of Mcl-1 and Bcl-2 induced apoptosis in mammary epithelial cells. Although Mule, an E3 ligase that targets Mcl-1 for degradation was expressed in mammary epithelial and breast cancer cell lines, rapid increase of polyubiquitinated Mcl-1 and Bcl-2 was detected only in mammary epithelial cells. Only transient formation of the Mule-Mcl-1 complex was detected in breast cancer cells. Downregulation of pERK1/2 in breast cancer cells reduced Mcl-1 levels and increased Mcl-1/Mule complex.
  
  
  CONCLUSIONS
  Our findings suggest that reduced Mule/Mcl-1 complex has a significant role in increasing the stability of Mcl-1 in breast cancer cells and increased resistance to apoptosis.
authors: Department of Internal Medicine, Charles Drew University of Medicine and Science, 3084 Hawkins Building, 1731 East 120th Street, Los Angeles, CA 90059, USA. shehlapervin@cdrewu.edu
authors: S
authors: S
authors: Pervin
authors: A
authors: A
authors: Tran
authors: L
authors: L
authors: Tran
authors: R
authors: R
authors: Urman
authors: M
authors: M
authors: Braga
authors: G
authors: G
authors: Chaudhuri
authors: R
authors: R
authors: Singh
mesh_terms: D051017:Apoptosis Regulatory Proteins / Q000737:chemistry* / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004847:Epithelial Cells / Q000378:metabolism; D006801:Humans; D046911:Macromolecular Substances / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D055550:Protein Stability; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry* / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D051017:Apoptosis Regulatory Proteins; D046911:Macromolecular Substances; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; D025521:Tumor Suppressor Proteins; C502830:HUWE1 protein, human; D044767:Ubiquitin-Protein Ligases; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3