TP53 (p53) forms a complex with PPP1R13B (ASPP1) or TP53BP2 (ASPP2). This interaction involves the DNA binding domain of TP53 and the C-terminus of ASSP proteins (Samuels-Lev et al. 2001, Patel et al. 2008). ASPP proteins can also form a complex with p53 family members TP63 (p63) and TP73 (p73) (Robinson et al. 2008, Patel et al. 2008). ASPP proteins enhance the binding of p53 family members to promoters of pro-apoptotic genes and promote their transcription, but do not affect the transcription of cell cycle regulators. ASPP proteins are frequently down-regulated in breast cancers that express wild-type TP53 (Samuels-Lev et al. 2001, Bergamaschi et al. 2004).