Physical interaction with YES-associated protein (YAP) enhances p73 transcriptional activity

ROSSI M, STRANO S, MUNARRIZ E, CASTAGNOLI L, SHAUL Y, SACCHI A, OREN M, CESARENI G, BLANDINO G.

Congreso; EMBO/FEBS advanced lecture course: “Molecular Mechanisms in Signal Transduction”; 2001

The p53 tumor suppressor gene is the most frequent target for genetic alterations in human cancer and its transcriptional activity is crucial for induced cell cycle arrest as well as programmed cell death. Recently Caput et al. have identified a p53 homologue, p73, that shares a remarkable homology in DNA sequence as well as in protein structure. As expected for p53-like proteins, p73 is a nuclear protein that can binds to canonical p53 DNA binding sites and can activate transcription from p53 responsive promoters in transiently transfected cells. Furthermore, overproduction of p73 can induce apoptosis, cell growth arrest and differentiation in p53+/+ and p53-/- tumor cells. Although these properties make it a good candidate for a tumor suppressor gene its physiological function still remains unclear. In fact, unlike p53-/- mice, p73-/- mice are not tumor prone but instead manifest severe developmental abnormalities, suggesting possible tissue specific function during development. In an attempt to better characterize the function of this gene we tried to identify new proteins interacting with its translation product. As p73 shows several different proline rich motifs in its amino acid sequence, we looked at the ability of various SH3 as well as WW domains to bind to p73 in pull down assays. Although structurally distinct, SH3 and WW domains are functionally related due to their ability to bind to proline-rich ligands. They have been found in a variety of unrelated proteins. Acting as molecular adapters, these domains, determine which proteins can interact in the closely regulated pathways of signal transduction. Here we report a novel interaction between p73 and YAP. YAP was originally identified as a protein binding to the SH3 domain of the Yes proto-oncogene product that belongs to the Src family of protein-tyrosine kinases. The interaction between p73 and YAP occurs in vitro as well as under physiological conditions in the cell, and the over expression of YAP causes an increase of p73 transcriptional activity. It involves the WW domain of YAP and the PPPPY proline rich region of p73. As required for ligands to group I WW domains, the terminal tyrosine (Y) of the PPPPY motif of p73 was shown to be essential for the association with YAP. Furthermore, we documented that YAP interacts only with those members of the p53 family, which have well conserved PPxY motif, a target sequence for WW domains. Differential interaction of YAP with members of the p53 family may provide a molecular explanation for their functional divergence in signaling.