Marco Napoli

A Pin1/Mutant p53 Axis Promotes Aggressiveness in Breast Cancer

TP53 missense mutations dramatically influence tumor progression, however, their mechanism of action is still poorly understood. Here we demonstrate the fundamental role of the prolyl isomerase Pin1 in mutant p53 oncogenic functions. Pin1 enhances tumorigenesis in a Li-Fraumeni mouse model and cooperates with mutant p53 in Ras-dependent transformation. In breast cancer cells, Pin1 promotes mutant p53 dependent inhibition of the antimetastatic factor p63 and induction of a mutant p53 transcriptional program to increase aggressiveness. Furthermore, we identified a transcriptional signature associated with poor prognosis in breast cancer and, in a cohort of patients, Pin1 overexpression influenced the prognostic value of p53 mutation. These results define a Pin1/mutant p53 axis that conveys oncogenic signals to promote aggressiveness in human cancers.

The rebel angel: mutant p53 as the driving oncogene in breast cancer

Breast cancer is the most frequent invasive tumor diagnosed in women, causing over 400 000 deaths yearly worldwide. Like other tumors, it is a disease with a complex, heterogeneous genetic and biochemical background. No single genomic or metabolic condition can be regarded as decisive for its formation and progression. However, a few key players can be pointed out and among them is the TP53 tumor suppressor gene, commonly mutated in breast cancer. In particular, TP53 mutations are exceptionally frequent and apparently among the key driving factors in triple negative breast cancer —the most aggressive breast cancer subgroup—whose management still represents a clinical challenge. The majority of TP53 mutations result in the substitution of single aminoacids in the central region of the p53 protein, generating a spectrum of variants (’mutant p53s’, for short). These mutants lose the normal p53 oncosuppressive functions to various extents but can also acquire oncogenic properties by gain-of-function mechanisms. This review discusses the molecular processes translating gene mutations to the pathologic consequences of mutant p53 tumorigenic activity, reconciling cell and animal models with clinical outcomes in breast cancer. Existing and speculative therapeutic methods targeting mutant p53 are also discussed, taking into account the overlap of mutant and wild-type p53 regulatory mechanisms and the crosstalk between mutant p53 and other oncogenic pathways in breast cancer. The studies described here concern breast cancer models and patients—unless it is indicated otherwise and justified by the importance of data obtained in other models.

The prolyl-isomerase Pin1 is a Notch1 target that enhances Notch1 activation in cancer

Signalling through Notch receptors requires ligand-induced cleavage to release the intracellular domain, which acts as a transcriptional activator in the nucleus. Deregulated Notch1 signalling has been implicated in mammary tumorigenesis; however the mechanisms underlying Notch activation in breast cancer remain unclear. Here, we demonstrate that the prolyl-isomerase Pin1 interacts with Notch1 and affects Notch1 activation. Pin1 potentiates Notch1 cleavage by γ-secretase, leading to an increased release of the active intracellular domain and ultimately enhancing Notch1 transcriptional and tumorigenic activity. We found that Notch1 directly induces transcription of Pin1, thereby generating a positive loop. In human breast cancers, we observed a strong correlation between Pin1 overexpression and high levels of activated Notch1. Thus, the molecular circuitry established by Notch1 and Pin1 may have a key role in cancer.

Peptide aptamers targeting mutant p53 induce apoptosis in tumor cells.

Mutations in the p53 tumor suppressor gene frequently result in expression of p53 point mutants that accumulate in cancer cells and actively collaborate with tumor progression through the acquisition of novel properties. Interfering with mutant p53 functions may represent a valid alternative for blocking tumor growth and development of aggressive phenotypes. The interactions and activities of selected proteins can be specifically modulated by the binding of peptide aptamers (PA). In the present work, we isolated PAs able to interact more efficiently with p53 conformational mutants compared with wild-type p53. The interaction between mutant p53 and PAs was further characterized using molecular modeling. Transient expression of PAs was able to reduce the transactivation activity of mutant p53 and to induce apoptosis specifically in cells expressing mutant p53. These PAs could provide a potential strategy to inhibit the oncogenic functions of mutant p53 and improve mutant p53-targeted cancer therapies.

Stathmin regulates mutant p53 stability and transcriptional activity in ovarian cancer

Stathmin is a p53‐target gene, frequently overexpressed in late stages of human cancer progression. Type II High Grade Epithelial Ovarian Carcinomas (HG‐EOC) represents the only clear exception to this observation. Here, we show that stathmin expression is necessary for the survival of HG‐EOC cells carrying a p53 mutant (p53MUT) gene. At molecular level, stathmin favours the binding and the phosphorylation of p53MUT by DNA‐PKCS, eventually modulating p53MUT stability and transcriptional activity. Inhibition of stathmin or DNA‐PKCS impaired p53MUT–dependent transcription of several M phase regulators, resulting in M phase failure and EOC cell death, both in vitro and in vivo. In primary human EOC a strong correlation exists between stathmin, DNA‐PKCS, p53MUT overexpression and its transcriptional targets, further strengthening the relevance of the new pathway here described. Overall our data support the hypothesis that the expression of stathmin and p53 could be useful for the identification of high risk patients that will benefit from a therapy specifically acting on mitotic cancer cells.

The p53 family orchestrates the regulation of metabolism: physiological regulation and implications for cancer therapy

The p53 family of transcription factors is essential to counteract tumour formation and progression. Although previously this was exclusively associated with the ability of the p53 family to induce cell cycle arrest and apoptosis, an increasing number of reports have now indisputably demonstrated that the tumour suppressive functions of the p53 family members also rely on their ability to control and regulate cellular metabolism and maintain cellular oxidative homeostasis. Here, we review how each p53 family member, including p63 and p73, controls metabolic pathways in physiological conditions, and how these mechanisms could be exploited to provide anticancer therapeutic opportunities.

The family that eats together stays together: new p53 family transcriptional targets in autophagy

Autophagy is a biological process that is crucial to maintain cellular homeostasis and is regulated by several metabolic pathways, including the p53 tumor suppressor pathway. In this issue of Genes & Development, Kenzelmann Broz and colleagues (pp. 1016-1031) show how the p53 family as a whole, including p63 and p73, collaborate in controlling autophagy to support tumor suppression.

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.

Unifying the p73 knockout phenotypes: TAp73 orchestrates multiciliogenesis

Multiciliogenesis is essential for the function of different epithelia, and its failure results in brain defects, respiratory diseases, and infertility. In this issue of Genes & Development, Nemajerova and colleagues (pp. 1300-1312) reveal the p53 family member and p73 isoform TAp73 as a transcription factor dictating the differentiation of multiciliated cells. Their findings provide the long-awaited unifying explanation for the diverse phenotypes of the p73 knockout mice.

MEK Is a Therapeutic and Chemopreventative Target in Squamous Cell Carcinoma

ACKNOWLEDGMENTS The Italian Melanoma Intergroup (IMI) includes the following additional members who participated as investigators in this study and should be considered as co-authors: Nicola Mozzillo (Istituto Nazionale Tumori, Napoli, Italy), Panagiotis Paliogiannis (Chirurgia, Microchirurgia e Scienze Mediche, Universita di Sassari, Italy), PaolaQueirolo (Oncologia, Azienda Ospedaliera, Genoa, Italy), Corrado Rubino (Chirurgia Plastica, Universita di Salerno, Italy), MariaCristina Sini (IstitutodiChimicaBiomolecolare,CNR, Sassari, Italy), Ignazio Stanganelli (Dermatologia, Universita di Parma—Skin Cancer Unit, IRST, Meldola, Italy), Francesco Tanda (Anatomia Patologica, Universita di Sassari, Italy). The authors are grateful to patients for their important contribution to this study. The work was supported by Ricerca Finalizzata Ministero Salute andSardinianRegionalGovernment (Regione Autonoma della Sardegna).