Characterization of the role of Pin1 as a regulator of p53 family function and dysfunction

MANTOVANI F.; GIRARDINI J.E.; TOCCO F.; GUIDA E.; BISSO A.; NAPOLI M.; DEL SAL G.

Lyon, Francia

Workshop; 3rd International workshop on mutant p53; 2007

Characterization of the role of Pin1 as a regulator of p53 family function and dysfunction Mantovani, F., Girardini, J., Tocco, F., Guida, E., Bisso A., Napoli, M. and Del Sal, G. Laboratorio Nazionale Consorzio Interuniversitario Biotecnologie (LNCIB), Area Science Park, and Dipartimento di Biochimica Biofisica e Chimica delle Macromolecole, Università di Trieste, Trieste, 34100, Italy.   Coordinated cell signaling is crucial for normal cell behaviour and tissue homeostasis. In order to cope with the overwhelming complexity of signaling events, cells have evolved efficient mechanisms that allow proper regulation of signal transduction. These mechanisms relay substantially on post-translational modifications in order to transfer information within signaling pathways. Recently, a crucial role has emerged for phosphorylation-dependent conformational changes caused by the prolyl-isomerase Pin1 on several highly interconnected substrates. Pin1 binds and catalyzes cis/trans isomerization of prolines on S/P or T/P motifs in many proteins involved in different processes. Our previous work has established a crucial role for Pin1 in the regulation of the p53 and p73 apoptotic response, supporting the idea that Pin1 contributes to checkpoint mechanisms essential for normal cell physiology. However, Pin1 is over-expressed in several human tumors, suggesting that the presence of other alterations may subvert the contribution of Pin1 to mechanisms that restrain uncontrolled proliferation. We have further characterized the mechanisms underlying p53 functional activation showing that Pin1 is able to enhance p53 function by modulating different events that prelude its full activation. We found that Pin1 is required for efficient loading of both p53 and p300 on p53-target promoters upon stress, and, being recruited on chromatin by p53, stimulates acetylation of DNA-bound p53. In addition, Pin1 mediates its dissociation from the apoptosis inhibitor iASPP, leading to cell death. However, mutations in the p53 gene frequently result in expression of p53 point mutants that accumulate in human tumors, which may actively collaborate with tumor progression through the acquisition of gain of function properties. We found that Pin1 interacts with several cancer-associated p53 mutants, and that this interaction is relevant for mutant p53 function. Therefore, Pin1 could be part of a checkpoint system that surveys cell proliferation in normal cells, but it may also contribute to the amplification of proliferative signals in a pathological context. Accordingly, the design of anti-cancer therapies should take into account cancer-specific alterations that may condition tumor progression and clinical outcome. Our results would predict that inhibition of Pin1 may counteract the cytotoxicity and hence the clinical activity of drugs that induce p53-dependent apoptosis. Conversely, Pin1 inhibition could be beneficial at later stages in tumors that may have also acquired mutant p53. Interfering with mutant p53 function may represent a valid alternative to block tumor growth and development of aggressive phenotypes. We have isolated peptide aptamers (PAs) able to interact with p53R175H using a two-hybrid strategy. These PAs are able to efficiently recognize several different p53 point mutants and p73, but not wt p53. Transient expression of PAs blocks mutant p53 transactivation activity and induces apoptosis in cells expressing mutant p53.