title: Growth factor regulation of a 26S proteasomal subunit in breast cancer.
abstract: OBJECTIVE
  We sought to gain insight into the mechanisms of heregulin-beta1 (HRG) action on breast epithelial cells by identifying and characterizing HRG-regulated proteins.
  
  
  METHODS
  Differential display mRNA screening of human breast cancer cells grown in the presence or absence of HRG was used to identify HRG-regulated genes. Biochemical and functional studies were undertaken to examine the impact of HRG and the therapeutic antibody herceptin on protein expression, localization, and function.
  
  
  RESULTS
  We identified the ATPase subunit 4 (S4) of the 26S proteasome as a HRG-regulated target. Both S4 mRNA and protein levels were increased by HRG; however, this HRG-stimulated increase was blocked by the therapeutic antibody herceptin. S4 expression was significantly increased in primary human breast tumors and in estrogen receptor-negative tumors. Coimmunoprecipitation, immunofluorescence, and ATPase activity assays suggested that HRG also induced S4 activity and formation of a functional proteasome complex.
  
  
  CONCLUSIONS
  This is the first demonstration of growth factor-regulated expression, localization, and activity of the S4 subunit of the 26S proteasome in human breast cancer cells. These findings now provide a potential mechanistic rationale for the use of proteasome inhibitors in breast cancers with active HRG signaling.
authors.affiliation: Department of Molecular and Cellular Oncology, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Barnes
authors.forename: Feng
authors.initials: F
authors.lastname: Li
authors.forename: Amjad H
authors.initials: AH
authors.lastname: Talukder
authors.forename: Rakesh
authors.initials: R
authors.lastname: Kumar
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D004815:Epidermal Growth Factor / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006133:Growth Substances / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D020890:Neuregulin-1 / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic / Q000235:genetics; D014162:Transfection
chemical_list: D006133:Growth Substances; D020890:Neuregulin-1; D012333:RNA, Messenger; C087230:heregulin beta1; D004815:Epidermal Growth Factor; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C109306:S4 ATPase, proteasome