Mutant p53 Gains Its Function via c-Myc Activation upon CDK4 Phosphorylation at Serine 249 and Consequent PIN1 Binding.

TP53 missense mutations significantly influence the development and progression of various human cancers via their gain of new functions (GOF) through different mechanisms. Here we report a unique mechanism underlying the GOF of p53-R249S (p53-RS), a p53 mutant frequently detected in human hepatocellular carcinoma (HCC) that is highly related to hepatitis B infection and aflatoxin B1. A CDK inhibitor blocks p53-RS's nuclear translocation in HCC, whereas CDK4 interacts with p53-RS in the G1/S phase of the cells, phosphorylates it, and enhances its nuclear localization. This is coupled with binding of a peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) to p53-RS, but not the p53 form with mutations of four serines/threonines previously shown to be crucial for PIN1 binding. As a result, p53-RS interacts with c-Myc and enhances c-Myc-dependent rDNA transcription key for ribosomal biogenesis. These results unveil a CDK4-PIN1-p53-RS-c-Myc pathway as a novel mechanism for the GOF of p53-RS in HCC.

Loss of the E6AP Ubiquitin Ligase Induces p53-Dependent Phosphorylation of Human Papillomavirus 18 E6 in Cells Derived from Cervical Cancer.

Cancer-causing human papillomavirus (HPV) E6 oncoproteins contain a well-characterized phosphoacceptor site within the PDZ (PSD-95/Dlg/ZO-1) binding motif (PBM) at the C terminus of the protein. Previous studies have shown that the threonine or serine residue in the E6 PBM is subject to phosphorylation by several stress-responsive cellular kinases upon the induction of DNA damage in cervical cancer-derived cells. However, there is little information about the regulation of E6 phosphorylation in the absence of DNA damage and whether there may be other pathways by which E6 is phosphorylated. In this study, we demonstrate that loss of E6AP results in a dramatic increase in the levels of phosphorylated E6 (pE6) despite the expected overall reduction in total E6 protein levels. Furthermore, phosphorylation of E6 requires transcriptionally active p53 and occurs in a manner that is dependent upon DNA-dependent protein kinase (DNA PK). These results identify a novel feedback loop, where loss of E6AP results in upregulation of p53, leading to increased levels of E6 phosphorylation, which in turn correlates with increased association with 14-3-3 and inhibition of p53 transcriptional activity. IMPORTANCE This study demonstrates that the knockdown of E6AP from cervical cancer-derived cells leads to an increase in phosphorylation of the E6 oncoprotein. We show that this phosphorylation of E6 requires p53 transcriptional activity and the enzyme DNA PK. This study therefore defines a feedback loop whereby activation of p53 can induce phosphorylation of E6 and which in turn can inhibit p53 transcriptional activity independently of E6's ability to target p53 for degradation.

Dynamic landscape and regulation of RNA editing in mammals.

Adenosine-to-inosine (A-to-I) RNA editing is a conserved post-transcriptional mechanism mediated by ADAR enzymes that diversifies the transcriptome by altering selected nucleotides in RNA molecules. Although many editing sites have recently been discovered, the extent to which most sites are edited and how the editing is regulated in different biological contexts are not fully understood. Here we report dynamic spatiotemporal patterns and new regulators of RNA editing, discovered through an extensive profiling of A-to-I RNA editing in 8,551 human samples (representing 53 body sites from 552 individuals) from the Genotype-Tissue Expression (GTEx) project and in hundreds of other primate and mouse samples. We show that editing levels in non-repetitive coding regions vary more between tissues than editing levels in repetitive regions. Globally, ADAR1 is the primary editor of repetitive sites and ADAR2 is the primary editor of non-repetitive coding sites, whereas the catalytically inactive ADAR3 predominantly acts as an inhibitor of editing. Cross-species analysis of RNA editing in several tissues revealed that species, rather than tissue type, is the primary determinant of editing levels, suggesting stronger cis-directed regulation of RNA editing for most sites, although the small set of conserved coding sites is under stronger trans-regulation. In addition, we curated an extensive set of ADAR1 and ADAR2 targets and showed that many editing sites display distinct tissue-specific regulation by the ADAR enzymes in vivo. Further analysis of the GTEx data revealed several potential regulators of editing, such as AIMP2, which reduces editing in muscles by enhancing the degradation of the ADAR proteins. Collectively, our work provides insights into the complex cis- and trans-regulation of A-to-I editing.

Mutant p53 reprograms TNF signaling in cancer cells through interaction with the tumor suppressor DAB2IP.

Inflammation is a significant factor in cancer development, and a molecular understanding of the parameters dictating the impact of inflammation on cancers could significantly improve treatment. The tumor suppressor p53 is frequently mutated in cancer, and p53 missense mutants (mutp53) can acquire oncogenic properties. We report that cancer cells with mutp53 respond to inflammatory cytokines increasing their invasive behavior. Notably, this action is coupled to expression of chemokines that can expose the tumor to host immunity, potentially affecting response to therapy. Mechanistically, mutp53 fuels NF-κB activation while it dampens activation of ASK1/JNK by TNFα, and this action depends on mutp53 binding and inhibiting the tumor suppressor DAB2IP in the cytoplasm. Interfering with such interaction reduced aggressiveness of cancer cells in xenografts. This interaction is an unexplored mechanism by which mutant p53 can influence tumor evolution, with implications for our understanding of the complex role of inflammation in cancer.

Prolyl isomerase PIN1 regulates DNA double-strand break repair by counteracting DNA end resection.

The regulation of DNA double-strand break (DSB) repair by phosphorylation-dependent signaling pathways is crucial for the maintenance of genome stability; however, remarkably little is known about the molecular mechanisms by which phosphorylation controls DSB repair. Here, we show that PIN1, a phosphorylation-specific prolyl isomerase, interacts with key DSB repair factors and affects the relative contributions of homologous recombination (HR) and nonhomologous end-joining (NHEJ) to DSB repair. We find that PIN1-deficient cells display reduced NHEJ due to increased DNA end resection, whereas resection and HR are compromised in PIN1-overexpressing cells. Moreover, we identify CtIP as a substrate of PIN1 and show that DSBs become hyperresected in cells expressing a CtIP mutant refractory to PIN1 recognition. Mechanistically, we provide evidence that PIN1 impinges on CtIP stability by promoting its ubiquitylation and subsequent proteasomal degradation. Collectively, these data uncover PIN1-mediated isomerization as a regulatory mechanism coordinating DSB repair.

Isoprenylcysteine carboxy methyltransferase (ICMT) is associated with tumor aggressiveness and its expression is controlled by the p53 tumor suppressor.

Isoprenyl cysteine carboxyl methyltransferase (ICMT) plays a key role in post-translational regulation of prenylated proteins. On the basis of previous results, we hypothesized that the p53 pathway and ICMT expression may be linked in cancer cells. Here, we studied whether WT p53 and cancer-associated p53 point mutants regulate ICMT levels and whether ICMT overexpression affects tumor progression. Studying the effect of p53 variants on ICMT mRNA and protein levels in cancer cells, we found that WT p53 and p53 mutants differentially affect ICMT expression, indicating that p53 status influences ICMT levels in tumors. To investigate the underlying mechanisms, we constructed ICMT-luciferase reporters and found that WT p53 represses ICMT transcription. In contrast, p53 mutants showed a positive effect on ICMT expression. Promoter truncation analyses pinpointed the repressive effect of WT p53 to the -209 and -14 region on the ICMT promoter, and ChIP assays indicated that WT p53 is recruited to this region. Instead, a different promoter region was identified as responsible for the mutant p53 effect. Studying the effect of ICMT overexpression on tumor-associated phenotypes in vitro and in vivo, and analyzing breast and lung cancer databases, we identified a correlation between p53 status and ICMT expression in breast and lung cancers. Moreover, we observed that ICMT overexpression is correlated with negative clinical outcomes. Our work unveils a link between postprenylation protein processing and the p53 pathway, indicating that the functional interplay between WT and mutant p53 alters ICMT levels, thereby affecting tumor aggressiveness.

Expression and subcellular localization of the bromodomain-containing protein 7 is a prognostic biomarker in breast cancer.

Bromodomain-containing protein 7 (BRD7) is a member of the bromodomain-containing protein family. Previous studies suggest that BRD7 is predominantly localized in the nucleus, wherein it functions as a transcriptional regulator. Several lines of evidence imply a tumour suppressor function for BRD7. However, the importance of BRD7 in the pathogenesis of breast cancer is not well understood. We have investigated the expression, CpG island methylation and subcellular localization of BRD7 in breast cancer cell lines and clinical cases and thereby assessed its prognostic significance by correlating with clinical-pathological features and time-dependent clinical outcomes. We show that nuclear exclusion of BRD7 occurs commonly in breast cancer and is strongly associated with cases expressing wild-type p53. Moreover, clinical outcomes are significantly less favourable in cases with nuclear exclusion or loss of expression than those in which there is nuclear expression of BRD7. Methylation of the CpG island of BRD7 increases in breast cancer relative to normal breast tissue, but there is not an obvious correlation between methylation and reduced expression or between methylation and clinical outcomes. Overall, our results suggest that nuclear exclusion, rather than transcriptional silencing, is a common mechanism by which the tumour suppressor function of wild-type p53 is inhibited in breast cancer, and show that BRD7 is a promising candidate biomarker in breast cancer.

GDA, a web-based tool for Genomics and Drugs integrated analysis.

Several major screenings of genetic profiling and drug testing in cancer cell lines proved that the integration of genomic portraits and compound activities is effective in discovering new genetic markers of drug sensitivity and clinically relevant anticancer compounds. Despite most genetic and drug response data are publicly available, the availability of user-friendly tools for their integrative analysis remains limited, thus hampering an effective exploitation of this information. Here, we present GDA, a web-based tool for Genomics and Drugs integrated Analysis that combines drug response data for >50 800 compounds with mutations and gene expression profiles across 73 cancer cell lines. Genomic and pharmacological data are integrated through a modular architecture that allows users to identify compounds active towards cancer cell lines bearing a specific genomic background and, conversely, the mutational or transcriptional status of cells responding or not-responding to a specific compound. Results are presented through intuitive graphical representations and supplemented with information obtained from public repositories. As both personalized targeted therapies and drug-repurposing are gaining increasing attention, GDA represents a resource to formulate hypotheses on the interplay between genomic traits and drug response in cancer. GDA is freely available at http://gda.unimore.it/.

Mutant p53 potentiates the oncogenic effects of insulin by inhibiting the tumor suppressor DAB2IP.

Obesity and type 2 diabetes are significant risk factors for malignancies, being associated with chronic inflammation and hyperinsulinemia. In this context, insulin can synergize with inflammation to promote proliferation, survival, and dissemination of cancer cells. Point mutation of p53 is a frequent event and a significant factor in cancer development and progression. Mutant p53 protein(s) (mutp53) can acquire oncogenic properties that increase metastasis, proliferation, and cell survival. We report that breast and prostate cancer cells with mutant p53 respond to insulin stimulation by increasing cell proliferation and invasivity, and that such a response depends on the presence of mutp53. Mechanistically, we find that mutp53 augments insulin-induced AKT1 activation by binding and inhibiting the tumor suppressor DAB2IP (DAB2-interacting protein) in the cytoplasm. This molecular axis reveals a specific gain of function for mutant p53 in the response to insulin stimulation, offering an additional perspective to understand the relationship between hyperinsulinemia and cancer evolution.

MiR-181 family-specific behavior in different cancers: a meta-analysis view.

The involvement of microRNAs in malignant transformation and cancer progression was previously grounded. The observations made by multiple published studies led to the conclusion that some of these small sequences could be eventually used as biomarkers for diagnosis/prognosis. This meta-analysis investigated whether microRNA-181 family members could predict the outcome of patients carrying different types of cancer. We searched the PubMed and Embase databases for studies evaluating the expression levels of miR-181a/b/c/d in patients with cancer, selecting the publications that assessed the relation between low and high levels of one of these four microRNAs and patients' outcome. Hazard ratios (HRs) or risk ratios (RRs) were extracted from the studies, and random-effect model was performed to investigate the role of miR-181 in the outcome of these patients. The meta-analysis comprised 26 studies including 2653 cancer patients from 6 countries. The results showed significant association between the expression of miR-181 family members and colorectal cancer. Considering the heterogeneity of the pathologies, the analysis, including all types of cancer and the expression of all the miR-181 family members together, showed no association with distinct outcome (HR = 1.099, p = 0.435). When the analysis was performed on each microRNA separately, the expression of miR-181c was significantly associated with the outcome of patients with cancer (HR = 2.356, p = 0.011) and miR-181a expression levels significantly correlated with survival in patients with non-small-cell lung cancer (HR = 0.177, p < 0.05). This meta-analysis revealed evidence regarding the involvement of miR-181 family members in the outcome of patients with some types of cancer, according to their expression level.

YAP enhances the pro-proliferative transcriptional activity of mutant p53 proteins.

Mutant p53 proteins are present in more than half of human cancers. Yes-associated protein (YAP) is a key transcriptional regulator controlling organ growth, tissue homeostasis, and cancer. Here, we report that these two determinants of human malignancy share common transcriptional signatures. YAP physically interacts with mutant p53 proteins in breast cancer cells and potentiates their pro-proliferative transcriptional activity. We found YAP as well as mutant p53 and the transcription factor NF-Y onto the regulatory regions of cyclin A, cyclin B, and CDK1 genes. Either mutant p53 or YAP depletion down-regulates cyclin A, cyclin B, and CDK1 gene expression and markedly slows the growth of diverse breast cancer cell lines. Pharmacologically induced cytoplasmic re-localization of YAP reduces the expression levels of cyclin A, cyclin B, and CDK1 genes both in vitro and in vivo. Interestingly, primary breast cancers carrying p53 mutations and displaying high YAP activity exhibit higher expression levels of cyclin A, cyclin B, and CDK1 genes when compared to wt-p53 tumors.

p53 at the endoplasmic reticulum regulates apoptosis in a Ca2+-dependent manner.

The tumor suppressor p53 is a key protein in preventing cell transformation and tumor progression. Activated by a variety of stimuli, p53 regulates cell-cycle arrest and apoptosis. Along with its well-documented transcriptional control over cell-death programs within the nucleus, p53 exerts crucial although still poorly understood functions in the cytoplasm, directly modulating the apoptotic response at the mitochondrial level. Calcium (Ca(2+)) transfer between the endoplasmic reticulum (ER) and mitochondria represents a critical signal in the induction of apoptosis. However, the mechanism controlling this flux in response to stress stimuli remains largely unknown. Here we show that, in the cytoplasm, WT p53 localizes at the ER and at specialized contact domains between the ER and mitochondria (mitochondria-associated membranes). We demonstrate that, upon stress stimuli, WT p53 accumulates at these sites and modulates Ca(2+) homeostasis. Mechanistically, upon activation, WT p53 directly binds to the sarco/ER Ca(2+)-ATPase (SERCA) pump at the ER, changing its oxidative state and thus leading to an increased Ca(2+) load, followed by an enhanced transfer to mitochondria. The consequent mitochondrial Ca(2+) overload causes in turn alterations in the morphology of this organelle and induction of apoptosis. Pharmacological inactivation of WT p53 or naturally occurring p53 missense mutants inhibits SERCA pump activity at the ER, leading to a reduction of the Ca(2+) signaling from the ER to mitochondria. These findings define a critical nonnuclear function of p53 in regulating Ca(2+) signal-dependent apoptosis.

MCM7 and its hosted miR-25, 93 and 106b cluster elicit YAP/TAZ oncogenic activity in lung cancer.

Lung cancer is the first cause of cancer death worldwide and the Hippo pathway transcriptional coactivators YAP/TAZ have a pro-oncogenic role in this context. In order to understand the mechanisms through which YAP/TAZ elicit their oncogenic role in different systems, many studies are focused on YAP/TAZ target genes involved in the regulation of cell proliferation/survival and migration. However, there is scarce evidence on the role of YAP/TAZ in microRNA regulation while there is increasing evidence supporting the role of microRNAs in the main oncogenic processes. Here, we showed that YAP/TAZ were able to regulate several microRNAs in non-small cell lung cancer (NSCLC) cell lines. In detail, we focused on a cluster of three oncogenic microRNAs (miR-25, 93 and 106b) hosted in the MCM7 gene that were overexpressed in lung tumors compared to normal tissues. In addition, similar behavior was observed in breast cancer and head and neck tumor casuistries, where they showed a prognostic role. In NSCLC cells, YAP/TAZ induced the transcription of the MCM7 gene and its hosted miRs, thereby promoting cell proliferation through the post-transcriptional inhibition of the p21 cell cycle regulator. Accordingly, p21 was maintained at low levels in lung tumors compared to normal tissues. Conversely, its expression was restored in NSCLC cells upon YAP/TAZ interference or upon treatment with the statin cerivastatin. In summary, we provide evidence for a novel mechanism of modulation supporting the protumorigenic functions of the YAP/TAZ factors through the modulation of a bioncogenic locus consisting of one gene and three hosted microRNAs.

Interaction of p53 with prolyl isomerases: Healthy and unhealthy relationships.

BACKGROUND: The p53 protein family, comprising p53, p63 and p73, is primarily involved in preserving genome integrity and preventing tumor onset, and also affects a range of physiological processes. Signal-dependent modifications of its members and of other pathway components provide cells with a sophisticated code to transduce a variety of stress signaling into appropriate responses. TP53 mutations are highly frequent in cancer and lead to the expression of mutant p53 proteins that are endowed with oncogenic activities and sensitive to stress signaling. SCOPE OF REVIEW: p53 family proteins have unique structural and functional plasticity, and here we discuss the relevance of prolyl-isomerization to actively shape these features. MAJOR CONCLUSIONS: The anti-proliferative functions of the p53 family are carefully activated upon severe stress and this involves the interaction with prolyl-isomerases. In particular, stress-induced stabilization of p53, activation of its transcriptional control over arrest- and cell death-related target genes and of its mitochondrial apoptotic function, as well as certain p63 and p73 functions, all require phosphorylation of specific S/T-P motifs and their subsequent isomerization by the prolyl-isomerase Pin1. While these functions of p53 counteract tumorigenesis, under some circumstances their activation by prolyl-isomerases may have negative repercussions (e.g. tissue damage induced by anticancer therapies and ischemia-reperfusion, neurodegeneration). Moreover, elevated Pin1 levels in tumor cells may transduce deregulated phosphorylation signaling into activation of mutant p53 oncogenic functions. GENERAL SIGNIFICANCE: The complex repertoire of biological outcomes induced by p53 finds mechanistic explanations, at least in part, in the association between prolyl-isomerases and the p53 pathway. This article is part of a Special Issue entitled Proline-directed foldases: Cell signaling catalysts and drug targets.

DLX5, FGF8 and the Pin1 isomerase control ΔNp63α protein stability during limb development: a regulatory loop at the basis of the SHFM and EEC congenital malformations.

Ectrodactyly, or Split-Hand/Foot Malformation (SHFM), is a congenital condition characterized by the loss of central rays of hands and feet. The p63 and the DLX5;DLX6 transcription factors, expressed in the embryonic limb buds and ectoderm, are disease genes for these conditions. Mutations of p63 also cause the ectodermal dysplasia-ectrodactyly-cleft lip/palate (EEC) syndrome, comprising SHFM. Ectrodactyly is linked to defects of the apical ectodermal ridge (AER) of the developing limb buds. FGF8 is the key signaling molecule in this process, able to direct proximo-distal growth and patterning of the skeletal primordial of the limbs. In the limb buds of both p63 and Dlx5;Dlx6 murine models of SHFM, the AER is poorly stratified and FGF8 expression is severely reduced. We show here that the FGF8 locus is a downstream target of DLX5 and that FGF8 counteracts Pin1-ΔNp63α interaction. In vivo, lack of Pin1 leads to accumulation of the p63 protein in the embryonic limbs and ectoderm. We show also that ΔNp63α protein stability is negatively regulated by the interaction with the prolyl-isomerase Pin1, via proteasome-mediated degradation; p63 mutant proteins associated with SHFM or EEC syndromes are resistant to Pin1 action. Thus, DLX5, p63, Pin1 and FGF8 participate to the same time- and location-restricted regulatory loop essential for AER stratification, hence for normal patterning and skeletal morphogenesis of the limb buds. These results shed new light on the molecular mechanisms at the basis of the SHFM and EEC limb malformations.

Autophosphorylation and Pin1 binding coordinate DNA damage-induced HIPK2 activation and cell death.

Excessive genome damage activates the apoptosis response. Protein kinase HIPK2 is a key regulator of DNA damage-induced apoptosis. Here, we deciphered the molecular mechanism of HIPK2 activation and show its relevance for DNA damage-induced apoptosis in cellulo and in vivo. HIPK2 autointeracts and site-specifically autophosphorylates upon DNA damage at Thr880/Ser882. Autophosphorylation regulates HIPK2 activity and mutation of the phosphorylation-acceptor sites deregulates p53 Ser46 phosphorylation and apoptosis in cellulo. Moreover, HIPK2 autophosphorylation is conserved between human and zebrafish and is important for DNA damage-induced apoptosis in vivo. Mechanistically, autophosphorylation creates a binding signal for the phospho-specific isomerase Pin1. Pin1 links HIPK2 activation to its stabilization by inhibiting HIPK2 polyubiquitination and modulating Siah-1-HIPK2 interaction. Concordantly, Pin1 is required for DNA damage-induced HIPK2 stabilization and p53 Ser46 phosphorylation and is essential for induction of apotosis both in cellulo and in zebrafish. Our results identify an evolutionary conserved mechanism regulating DNA damage-induced apoptosis.

Targeting prolyl-isomerase Pin1 prevents mitochondrial oxidative stress and vascular dysfunction: insights in patients with diabetes.

AIM: Diabetes is a major driver of cardiovascular disease, but the underlying mechanisms remain elusive. Prolyl-isomerase Pin1 recognizes specific peptide bonds and modulates function of proteins altering cellular homoeostasis. The present study investigates Pin1 role in diabetes-induced vascular disease. METHODS AND RESULTS: In human aortic endothelial cells (HAECs) exposed to high glucose, up-regulation of Pin1-induced mitochondrial translocation of pro-oxidant adaptor p66(Shc) and subsequent organelle disruption. In this setting, Pin1 recognizes Ser-116 inhibitory phosphorylation of endothelial nitric oxide synthase (eNOS) leading to eNOS-caveolin-1 interaction and reduced NO availability. Pin1 also mediates hyperglycaemia-induced nuclear translocation of NF-κB p65, triggering VCAM-1, ICAM-1, and MCP-1 expression. Indeed, gene silencing of Pin1 in HAECs suppressed p66(Shc)-dependent ROS production, restored NO release and blunted NF-kB p65 nuclear translocation. Consistently, diabetic Pin1(-/-) mice were protected against mitochondrial oxidative stress, endothelial dysfunction, and vascular inflammation. Increased expression and activity of Pin1 were also found in peripheral blood monocytes isolated from diabetic patients when compared with age-matched healthy controls. Interestingly, enough, Pin1 up-regulation was associated with impaired flow-mediated dilation, increased urinary 8-iso-prostaglandin F2α and plasma levels of adhesion molecules. CONCLUSIONS: Pin1 drives diabetic vascular disease by causing mitochondrial oxidative stress, eNOS dysregulation as well as NF-kB-induced inflammation. These findings provide molecular insights for novel mechanism-based therapeutic strategies in patients with diabetes.

Pin1 and WWP2 regulate GluR2 Q/R site RNA editing by ADAR2 with opposing effects.

ADAR2 catalyses the deamination of adenosine to inosine at the GluR2 Q/R site in the pre-mRNA encoding the critical subunit of AMPA receptors. Among ADAR2 substrates this is the vital one as editing at this position is indispensable for normal brain function. However, the regulation of ADAR2 post-translationally remains to be elucidated. We demonstrate that the phosphorylation-dependent prolyl-isomerase Pin1 interacts with ADAR2 and is a positive regulator required for the nuclear localization and stability of ADAR2. Pin1(-/-) mouse embryonic fibroblasts show mislocalization of ADAR2 in the cytoplasm and reduced editing at the GluR2 Q/R and R/G sites. The E3 ubiquitin ligase WWP2 plays a negative role by binding to ADAR2 and catalysing its ubiquitination and subsequent degradation. Therefore, ADAR2 protein levels and catalytic activity are coordinately regulated in a positive manner by Pin1 and negatively by WWP2 and this may have downstream effects on the function of GluR2. Pin1 and WWP2 also regulate the large subunit of RNA Pol II, so these proteins may also coordinately regulate other key cellular proteins.

Cooperation of p53 mutations with other oncogenic alterations in cancer.

Following the initial findings suggesting a pro-oncogenic role for p53 point mutants, more than 30 years of research have unveiled the critical role exerted by these mutants in human cancer. A growing body of evidence, including mouse models and clinical data, has clearly demonstrated a connection between mutant p53 and the development of aggressive and metastatic tumors. Even if the molecular mechanisms underlying mutant p53 activities are still the object of intense scrutiny, it seems evident that full activation of its oncogenic role requires the functional interaction with other oncogenic alterations. p53 point mutants, with their pleiotropic effects, simultaneously activating several mechanisms of aggressiveness, are engaged in multiple cross-talk with a variety of other cancer-related processes, thus depicting a complex molecular landscape for the mutant p53 network. In this chapter revealing evidence illustrating different ways through which this cooperation may be achieved will be discussed. Considering the proposed role for mutant p53 as a driver of cancer aggressiveness, disarming mutant p53 function by uncoupling the cooperation with other oncogenic alterations, stands out as an exciting possibility for the development of novel anti-cancer therapies.

iASPP preferentially binds p53 proline-rich region and modulates apoptotic function of codon 72-polymorphic p53.

iASPP is one of the most evolutionarily conserved inhibitors of p53, whereas ASPP1 and ASPP2 are activators of p53. We show here that, in addition to the DNA-binding domain, the ASPP family members also bind to the proline-rich region of p53, which contains the most common p53 polymorphism at codon 72. Furthermore, the ASPP family members, particularly iASPP, bind to and regulate the activity of p53Pro72 more efficiently than that of p53Arg72. Hence, escape from negative regulation by iASPP is a newly identified mechanism by which p53Arg72 activates apoptosis more efficiently than p53Pro72.