PACT is a negative regulator of p53 and essential for cell growth and embryonic development

Abstract

The tumor suppressor p53 regulates cell cycle progression and apoptosis in response to various types of stress, whereas excess p53 activity creates unwanted effects. Tight regulation of p53 is essential for maintaining normal cell growth. p53-associated cellular protein-testes derived (PACT, also known as P2P-R, RBBP6) is a 250-kDa Ring finger-containing protein that can directly bind to p53. PACT is highly up-regulated in esophageal cancer and may be a promising target for immunotherapy. However, the physiological role of the PACT-p53 interaction remains largely unclear. Here, we demonstrate that the disruption of PACT in mice leads to early embryonic lethality before embryonic day 7.5 (E7.5), accompanied by an accumulation of p53 and widespread apoptosis. p53-null mutation partially rescues the lethality phenotype and prolonged survival to E11.5. Endogenous PACT can interact with Hdm2 and enhance Hdm2-mediated ubiquitination and degradation of p53 as a result of the increase of the p53-Hdm2 affinity. Consequently, PACT represses p53-dependent gene transcription. Knockdown of PACT significantly attenuates the p53-Hdm2 interaction, reduces p53 polyubiquitination, and enhances p53 accumulation, leading to both apoptosis and cell growth retardation. Taken together, our data demonstrate that the PACT-p53 interaction plays a critical role in embryonic development and tumorigenesis and identify PACT as a member of negative regulators of p53.apoptosis ͉ embryonic lethality ͉ ubiquitination

Breast Cancer Amplified Sequence 2, a Novel Negative Regulator of the p53 Tumor Suppressor

“…Transcriptional activation of p53 is also repressed by p202 via binding to the PXXP motifs of p53 (39) and by LSD1 through demethylated p53 protein (31). Notably, HSP27 and PFTm function as small-sized protein inhibitors of p53 by promoting the assembly of p53 into complexes (6,15,40). Here, we describe the novel functioning of BCAS2 as a smallsized p53 binding protein, not previously known to be a p53 inhibitor.…”

“…It is interesting to examine whether BCAS2 plays as a scaffold or adaptor molecule to mediate MDM2 or other E3 ligase-related proteins for p53 protein degradation. Various negative apoptotic regulators of p53 were recently identified that reduce p53 protein activity through different mechanisms (6,8,14,15,21,(36)(37)(38)(39)(40)(41)(42). For example, MDM2, PACT, aurora kinase A, and E6 function by causing p53 protein ubiquitination and degradation (6,13,33,43).…”

The end of the message: multiple protein–RNA interactions define the mRNA polyadenylation site

“…For example, Mpe1 has been implicated in regulating ubiquitination of PAP and potentially other factors (Lee and Moore 2014). Rbbp6 has also been shown to possess E3 ligase activity and function as an activator of Mdm2-mediated ubiquitination of p53 (Li et al 2007;Miotto et al 2014). Finally, a splice isoform of Rbbp6, called iso3 and consisting solely of the DWNN, competes with the full-length protein to modulate cleavage efficiency (Di Giammartino et al 2014).…”

RBBP6 isoforms regulate the human polyadenylation machinery and modulate expression of mRNAs with AU-rich 3′ UTRs

“…RBBP6 interferes with binding of p53 to DNA and also facilitates interaction between p53 and its negative regulator, Mdm2, leading to enhanced p53 ubiquitination and degradation. Moreover, disruption of RBBP6 in mice leads to early embryonic lethality, but a p53-null mutation partially rescues viability (Li et al 2007). The RBBP6 C-terminal region contains domains responsible for interaction with both tumor suppressors.…”