Pin1 modulates p63α protein stability in regulation of cell survival, proliferation and tumor formation

Abstract

The homolog of p53 gene, p63, encodes multiple p63 protein isoforms. TAp63 proteins contain an N-terminal transactivation domain similar to that of p53 and function as tumor suppressors; whereas ΔNp63 isoforms, which lack the intact N-terminal transactivation domain, are associated with human tumorigenesis. Accumulating evidence demonstrating the important roles of p63 in development and cancer development, the regulation of p63 proteins, however, is not fully understood. In this study, we show that peptidyl-prolyl isomerase Pin1 directly binds to and stabilizes TAp63α and ΔNp63α via inhibiting the proteasomal degradation mediated by E3 ligase WWP1. We further show that Pin1 specifically interacts with T538P which is adjacent to the P550PxY543 motif, and disrupts p63α–WWP1 interaction. In addition, while Pin1 enhances TAp63α-mediated apoptosis, it promotes ΔNp63α-induced cell proliferation. Furthermore, knockdown of Pin1 in FaDu cells inhibits tumor formation in nude mice, which is rescued by simultaneous knockdown of WWP1 or ectopic expression of ΔNp63α. Moreover, overexpression of Pin1 correlates with increased expression of ΔNp63α in human oral squamous cell carcinoma samples. Together, these results suggest that Pin1-mediated modulation of ΔNp63α may have a causative role in tumorigenesis.

p63 threonine phosphorylation signals the interaction with the WW domain of the E3 ligase Itch

“…Therefore, in keeping with very recent studies, 99 the Thr phosphorylation and the action of Pin1 on p63 directly regulates the physical recognition and interaction of Itch, similar to what has been described in the case of WWP1, 98,99,110 affecting the steady-state levels of the p63 protein. This could be also explained with a proline trans to cis isomerization of the p(T/S)P motif by Pin1.…”

“…[94][95][96][97] In order to understand the biochemical properties of the interaction between these 2 proteins, the interaction between the Itch-WW2 and the synthetic peptide pep63, including the PPxY recognition motif, has been monitored using spectroscopic techniques; the apparent dissociation constant value of the Itch-WW2-pep63 complex has been reported previously. 96 The presence of the consensus TP motif, close to the PPxY recognition motif, and also the recent studies on the Pin1/p63 interaction 98,99 led us to evaluate the effect of the threonine phosphorylation of the (T/S)PPPxY motif on the binding of the Itch-WW domains to the pep63 peptide. The measured apparent dissociation constants of Itch-WW2 with both pep63 and the phosphorylated Thr form Ppep63 were obtained from the intrinsic fluorescence of the domain upon addition of increasing amounts of the peptides, resulting in a value of 42.09 § 7.45 mM (for the WW2-pep63), which is in keeping with our previously reported value, 96 and 10.97 § 1.45 mM for the Itch-WW2-Ppep63 (Fig.…”

“…107 As reported above, p(T/ S)P motif is a characteristic recognition binding motif of the WW domain of Pin1 proline isomerase and recent data have shown a catalytic action of Pin1 on p63. 99 Therefore we have investigated the effect of the cis/trans isomerization of the first proline on the binding of the Itch-WW-p(T/S)PPPxY motif. Firstly, the binding between Itch-WW2 and Ppep63, following a previous incubation of the Ppep63 with Pin1 aimed at creating a proline cis/trans isomerization, has been analyzed by fluorescence spectroscopy (Fig.…”

P63 in health and cancer

“…These sites are absent in the p63g isoforms. Recent evidence shows that Pin1 stabilizes the a isoforms, but not the g variants (Li et al, 2013). This supports that the six Pin1-binding sites in the C-terminal region may play a critical role in p63a stability.…”

“…The peptidyl-prolyl isomerase Pin1 may modulate p63 activity. This in turn affects cell survival/proliferation and tumorigenesis (Li et al, 2013). Pin1 consists of an N-terminal WW domain and a C-terminal peptidyl-prolyl cis/trans isomerase (PPIase) domain.…”