Activator protein-2gamma (AP-2gamma) expression is specifically induced by oestrogens through binding of the oestrogen receptor to a canonical element within the 5'-untranslated region.
The activator protein 2 (AP-2) transcription factors are essential proteins for oestrogenic repression of the ERBB2 proto-oncogene in breast cancer cells. In the present study, we have examined the possible oestrogenic regulation of AP-2 genes themselves in breast-tumour-derived lines. As early as 1 h after oestrogen treatment, AP-2gamma mRNA was markedly increased, whereas AP-2alpha was down-regulated, but with slower kinetics, and AP-2beta was not affected at all. Addition of anti-oestrogens ablated these effects. Modulation of the protein levels corresponded to changes in the transcript levels, thus suggesting that in oestrogen-treated cells, an inversion of the balance between AP-2alpha and AP-2gamma isoforms occurs. The 5'-untranslated region (5'-UTR) of the human AP-2gamma gene contains one consensus and one degenerate oestrogen-responsive element (ERE). Reporter constructs carrying the AP-2gamma promoter and the 5'-UTR were up-regulated by oestrogens in transient transfection assays. Deletion of the most conserved (but not of the degenerate) ERE from reporter constructs abrogated the oestrogenic response, although both ERE-containing segments were footprinted in DNaseI protection assays. In vitro binding assays demonstrated the ability of oestrogen receptor alpha (ERalpha) to bind to this site, and chromatin immunoprecipitation analysis of the endogenous gene showed that ERalpha occupies this region in response to oestrogens. We conclude that AP-2gamma is a primary oestrogen-responsive gene and suggest that AP-2 proteins may mediate some oestrogenic responses.
Orso
Francesca
F
Institute for Cancer Research and Treatment, University of Turin, 10060 Candiolo, Turin, Italy.
Cottone
Erika
E
Hasleton
Mark D
MD
Ibbitt
J Claire
JC
Sismondi
Piero
P
Hurst
Helen C
HC
De Bortoli
Michele
M
D020121:5' Untranslated Regions; D001483:Base Sequence; D001665:Binding Sites; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D004958:Estradiol / Q000494:pharmacology*; D047628:Estrogen Receptor alpha; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008969:Molecular Sequence Data; D000090063:Proto-Oncogene Mas; D011960:Receptors, Estrogen / Q000378:metabolism*; D020218:Response Elements; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D015533:Transcriptional Activation
D020121:5' Untranslated Regions; D004268:DNA-Binding Proteins; D047628:Estrogen Receptor alpha; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011960:Receptors, Estrogen; C493673:TFAP2A protein, human; C493677:TFAP2B protein, human; C493679:TFAP2C protein, human; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D004958:Estradiol