title: The combined immunodetection of AP-2alpha and YY1 transcription factors is associated with ERBB2 gene overexpression in primary breast tumors.
abstract: BACKGROUND
  Overexpression of the ERBB2 oncogene is observed in about 20% of human breast tumors and is the consequence of increased transcription rates frequently associated with gene amplification. Several studies have shown a link between activator protein 2 (AP-2) transcription factors and ERBB2 gene expression in breast cancer cell lines. Moreover, the Yin Yang 1 (YY1) transcription factor has been shown to stimulate AP-2 transcriptional activity on the ERBB2 promoter in vitro. In this report, we examined the relationships between ERBB2, AP-2alpha, and YY1 both in breast cancer tissue specimens and in a mammary cancer cell line.
  
  
  METHODS
  ERBB2, AP-2alpha, and YY1 protein levels were analyzed by immunohistochemistry in a panel of 55 primary breast tumors. ERBB2 gene amplification status was determined by fluorescent in situ hybridization. Correlations were evaluated by a chi2 test at a p value of less than 0.05. The functional role of AP-2alpha and YY1 on ERBB2 gene expression was analyzed by small interfering RNA (siRNA) transfection in the BT-474 mammary cancer cell line followed by real-time reverse transcription-polymerase chain reaction and Western blotting.
  
  
  RESULTS
  We observed a statistically significant correlation between ERBB2 and AP-2alpha levels in the tumors (p < 0.01). Moreover, associations were found between ERBB2 protein level and the combined high expression of AP-2alpha and YY1 (p < 0.02) as well as between the expression of AP-2alpha and YY1 (p < 0.001). Furthermore, the levels of both AP-2alpha and YY1 proteins were inversely correlated to ERBB2 gene amplification status in the tumors (p < 0.01). Transfection of siRNAs targeting AP-2alpha and AP-2gamma mRNAs in the BT-474 breast cancer cell line repressed the expression of the endogenous ERBB2 gene at both the mRNA and protein levels. Moreover, the additional transfection of an siRNA directed against the YY1 transcript further reduced the ERBB2 protein level, suggesting that AP-2 and YY1 transcription factors cooperate to stimulate the transcription of the ERBB2 gene.
  
  
  CONCLUSIONS
  This study highlights the role of both AP-2alpha and YY1 transcription factors in ERBB2 oncogene overexpression in breast tumors. Our results also suggest that high ERBB2 expression may result either from gene amplification or from increased transcription factor levels.
authors.affiliation: Department of Pathology, GIGA-Research, CRCE, University of Liege and CHU of Liege, B23, Avenue de l'Hopital, 3, 4000 Liege, Belgium.
authors.forename: Abdelkader
authors.initials: A
authors.lastname: Allouche
authors.forename: Gregory
authors.initials: G
authors.lastname: Nolens
authors.forename: Annalisa
authors.initials: A
authors.lastname: Tancredi
authors.forename: Laurence
authors.initials: L
authors.lastname: Delacroix
authors.forename: Julie
authors.initials: J
authors.lastname: Mardaga
authors.forename: Viviana
authors.initials: V
authors.lastname: Fridman
authors.forename: Rosita
authors.initials: R
authors.lastname: Winkler
authors.forename: Jacques
authors.initials: J
authors.lastname: Boniver
authors.forename: Philippe
authors.initials: P
authors.lastname: Delvenne
authors.forename: Dominique Y
authors.initials: DY
authors.lastname: Begon
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D005260:Female; D018734:Genes, erbB-2 / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D008875:Middle Aged; D050656:Transcription Factor AP-2 / Q000096:biosynthesis* / Q000235:genetics; D050986:YY1 Transcription Factor / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D050656:Transcription Factor AP-2; D050986:YY1 Transcription Factor; C494698:YY1 protein, human