Identification of HTF (HER2 transcription factor) as an AP-2 (activator protein-2) transcription factor and contribution of the HTF binding site to ERBB2 gene overexpression

• Published in: Biochemical journal 2003-02, Vol.370 (Pt 1), p.323-329
• Main Authors: Vernimmen, Douglas, Begon, Dominique, Salvador, Christophe, Gofflot, Stéphanie, Grooteclaes, Madeleine, Winkler, Rosita
• Format: Article
• Language: English
• Subjects: AP-2 binding site; Base Sequence; Binding Sites; Biochemistry, biophysics & molecular biology; Biochimie, biophysique & biologie moléculaire; BT-474; DNA Primers; DNA-Binding Proteins - metabolism; DNase I footprint; EMSA; ERBB2 promoter; HER2 transcription factor; HTF; human; Humans; Life sciences; luciferase; Mutagenesis, Site-Directed; oncogene; Promoter Regions, Genetic; Receptor, ErbB-2 - genetics; Receptor, ErbB-2 - metabolism; Sciences du vivant; Sequence Homology, Nucleic Acid; Transcription Factor AP-2; Transcription Factors - metabolism; transcription regulation; transfection; Tumor Cells, Cultured; Western blotting
• ISSN: 0264-6021; 1470-8728; 1470-8728
• DOI: 10.1042/BJ20021238

The ERBB2 gene is overexpressed in 30% of human breast cancers and this is correlated with poor prognosis. Overexpression of the ERBB2 gene is due to increased transcription and gene amplification. Our previous studies have identified a new cis element in the ERBB2 promoter which is involved in the gene's overexpression. This cis element, located 501 bp upstream from the main ERBB2 transcription initiation site, binds a transcription factor called HTF (HER2 transcription factor). We report here the identification of HTF as an AP-2 (activator protein-2) transcription factor. The new cis element is bound by AP-2 with high affinity, compared with a previously described AP-2 binding site located 284 bp downstream. Co-transfection of an AP-2alpha expression vector with a reporter vector containing the newly identified AP-2 binding site in front of a minimal ERBB2 promoter induced a dose-dependent increase in transcriptional activity. We examined the contribution of the new AP-2 binding site to ERBB2 overexpression. For this purpose we abolished the new and/or the previously described AP-2 binding sequence by site-directed mutagenesis. The results show that the two functional AP-2 sites in the first 700 bp of the ERBB2 promoter co-operate to achieve maximal transcriptional activity.