TIP60 represses transcriptional activity of p73 beta via an MDM2-bridged ternary complex

Abstract

TIP60, a histone acetyl transferase, acts as a p53 coactivator by interfering with MDM2-mediated degradation of p53. However, little is known about its functional regulation of p73, which has structural features similar to p53. In this study we found that TIP60 represses apoptosis, which is induced by exogenous and endogenous p73 beta. TIP60 also negatively regulated the expression of p73 beta downstream target genes such as p21 and Bax. Moreover, the specific repression of p73 beta-mediated transactivation by TIP60 was independent of p53 expression and not due to histone deacetylase recruiting transcriptional machinery. Transcriptional activities of both p73splicing variants, p73 alpha and p73 beta, were also repressed by TIP60. Furthermore, TIP60 markedly enhanced p73 beta binding affinity to MDM2 and physically associated with MDM2 through its zinc finger domain, which is specifically localized in the nucleus. Therefore, we demonstrate that TIP60 forms a ternary complex with p73 beta, which is directly bridged by MDM2. It is important to note that our findings contribute to a functional linkage between TIP60 and p73 beta through MDM2 in the transcriptional regulation of cellular apoptosis.