YY1 and breast carcinoma: Among positive regulators, members of the AP-2 and Ets families of transcription factors are required for maximal ERBB2 promoter activity and have been associated with the overexpression of the gene in breast cancer (for a review, see [35]); in addition, the multifunctional transcription factor YY1 has been shown to cooperate with AP-2 to stimulate ERBB2 promoter activity through the AP-2 binding sites [36].