AP-2γ promotes proliferation in breast tumour cells by direct repression of the CDKN1A gene

Overexpression of the activator protein (AP)-2 gamma transcription factor in breast tumours has been identified as an independent predictor of poor outcome and failure of hormone therapy. To understand further the function of AP-2 gamma in breast carcinoma, we have used an RNA interference and gene expression profiling strategy with the MCF-7 cell line as a model. Gene expression changes between control and silenced cells implicate AP-2 gamma in the control of cell cycle progression and developmental signalling. A function for AP-2 gamma in cell cycle control was verified using flow cytometry: AP-2 gamma silencing led to a partial G1/S arrest and induction of the cyclin-dependent kinase inhibitor, p21cip/CDKN1A. Reporter and chromatin immunoprecipitation assays demonstrated a direct, functional interaction by AP-2 gamma at the CDKN1A proximal promoter. AP-2 gamma silencing coincided with acquisition of an active chromatin conformation at the CDKN1A locus and increased gene expression. These data provide a mechanism whereby AP-2 gamma overexpression can promote breast epithelial proliferation and, coupled with previously published data, suggest how loss of oestrogen regulation of AP-2 gamma may contribute to the failure of hormone therapy in patients. The EMBO Journal (2009) 28, 3591-3601. doi:10.1038/emboj.2009.290; Published online 1 October 2009