The C-terminus of p63 contains multiple regulatory elements with different functions

The transcription factor p63 is expressed as at least six different isoforms, of which two have been assigned critical biological roles within ectodermal development and skin stem cell biology on the one hand and supervision of the genetic stability of oocytes on the other hand. These two isoforms contain a C-terminal inhibitory domain that negatively regulates their transcriptional activity. This inhibitory domain contains two individual components: one that uses an internal binding mechanism to interact with and mask the transactivation domain and one that is based on sumoylation. We have carried out an extensive alanine scanning study to identify critical regions within the inhibitory domain. These experiments show that a stretch of ~13 amino acids is crucial for the binding function. Further, investigation of transcriptional activity and the intracellular level of mutants that cannot be sumoylated suggests that sumoylation reduces the concentration of p63. We therefore propose that the inhibitory function of the C-terminal domain is in part due to direct inhibition of the transcriptional activity of the protein and in part due to indirect inhibition by controlling the concentration of p63. Keywords: p63, transcriptional regulation, auto-inhibition, sumoylatio

The p53 Family in Brain Disease

Significance: The p53 family of transcription factors, including p53, p63, and p73, plays key roles in both biological and pathological processes, including cancer and neural development.Recent Advances: In recent years, a growing body of evidence has indicated that the entire p53 family is involved in the regulation of the central nervous system (CNS) functions as well as in the pathogenesis of several neurological disorders. Mechanistically, the p53 proteins control neuronal cell fate, terminal differentiation, and survival, via a complex interplay among the family members.Critical Issues: In this article, we discuss the involvement of the p53 family in neurobiology and in pathological conditions affecting the CNS, including neuroinflammation.Future Directions: Understanding the molecular mechanism(s) underlying the function of the p53 family could improve our general knowledge of the pathogenesis of brain disorders and potentially pave the road for new therapeutic intervention

NRF2 and p53: Januses in cancer?

The transcription factor nuclear factor (erythroid-derived 2)-like 2, also known as NFE2L2 or NRF2, is a master regulator of the anti-oxidative stress response and positively controls the expression of a battery of anti-oxidative stress response proteins and enzymes implicated in detoxification and glutathione generation. Although its detoxifying activity is important in cancer prevention, it has recently been shown that cancer cells also exploit its protective functions to thrive and resist chemotherapy. NRF2 was also shown to the pentose phosphate pathway and glutaminolysis, which promotes purine synthesis for supporting rapid proliferation and glutathione for providing anti-oxidative stress protection. Evidence obtained from cancer patients and cell lines suggest that NRF2 is highly active in a variety of human cancers and is associated with aggressiveness. p53 is a tumor suppressor that also promotes an anti-oxidative stress metabolic program and glutaminolysis. Here we will discuss the similarities between NRF2 and p53 and review evidence that p53 might be exploited by cancer cells to gain protection against oxidative stress, as is the case for NRF2. We discuss findings of co-regulation between these transcription factors and propose possible therapeutic strategies that can be used for treatment of cancers that harbor WT p53 and express high levels of NRF2

Screening for E3-Ubiquitin ligase inhibitors: challenges and opportunities.

The ubiquitin proteasome system (UPS) plays a role in the regulation of most cellular pathways, and its deregulation has been implicated in a wide range of human pathologies that include cancer, neurodegenerative and immunological disorders and viral infections. Targeting the UPS by small molecular regulators thus provides an opportunity for the development of therapeutics for the treatment of several diseases. The proteasome inhibitor Bortezomib was approved for treatment of hematologic malignancies by the FDA in 2003, becoming the first drug targeting the ubiquitin proteasome system in the clinic. Development of drugs targeting specific components of the ubiquitin proteasome system, however, has lagged behind, mainly due to the complexity of the ubiquitination reaction and its outcomes. However, significant advances have been made in recent years in understanding the molecular nature of the ubiquitination system and the vast variety of cellular signals that it produces. Additionally, improvement of screening methods, both in vitro and in silico, have led to the discovery of a number of compounds targeting components of the ubiquitin proteasome system, and some of these have now entered clinical trials. Here, we discuss the current state of drug discovery targeting E3 ligases and the opportunities and challenges that it provides

MOLECULAR RECOGNITION MECHANISM OF p63 BY ITCH-E3 LIGASE: ADVANCES AND EFFECTS OF A p63 MUTATION RELATED TO ECTODERMAL DYSPLASIAS.

Recently, it has been shown that Itch mediates the degradation of TAp63 and ΔNp63 proteins1. Itch E3–ligase contains four WW domains important in the recognized process. Several signalling complexes, that these domains mediate, have been implicated in human diseases (Muscular Dystrophy, Alzheimer's Disease, Huntington Disease etc.). WW domains are highly compact protein-protein binding modules that interact with short proline-rich sequences. Based on their ligand-binding specificity they have been categorized into four groups. WW domains fold into stable three-stranded antiparallel b-sheet structures, and their primary sequence share two conserved tryptophan residues spaced 20-22 amino acids apart. The four WW domains of Itch are considered belonging to the Group I, which binds polypeptides with a PY motif characterized by a PPXY consensus sequence, where X can be any residue. It is likely that the Itch-p63 interaction results from a direct interaction of Itch-WW2 domain with the PY motif of p63. Here, we present a structural characterization of the interaction by fluorescence, CD and NMR spectroscopy of the Itch-WW2 domain. Interaction studies in vitro between Itch-WW2 domain and pep63, which correspond to the fragment of the p63 protein including the PY motif, were performed. Moreover, the effects of a site specific mutation of p63, that has been reported in both Hay–Wells syndrome and Rapp–Hodgkin syndrome, was also evaluated both on the conformation of pep63 and on the WW-pep63 interaction. 1Rossi M., Aqeilan I., Neale M., Candi E., Salomoni P., Knight R.A., Croce C.M., Melino G. PNAS (2006) 103: 12753-5

Lysine-specific modifications of p53: a matter of life and death?

Post-translational modifications provide a fine-tuned control of protein function(s) in the cell. The well-known tumour suppressor p53 is subject to many post-translational modifications, which alter its activity, localization and stability, thus ultimately modulating its response to various forms of genotoxic stress. In this review, we focus on the role of recently discovered lysine-specific modifications of p53, methylation and acetylation in particular, and their effects on p53 activity in damaged cells. We also discuss a possibility of mutual influence of covalent modifications in the p53 and histone proteins located in the vicinity of p53 binding sites in chromatin and propose important ramifications stemming from this hypothesis

Cell Death-based therapy

Apoptosis plays a centrale role in regulating tissue homeostasis. The balance between cell death and proliferation in favour of cell survival can result in tumor formation. The understanding of the molecular mechanisms regulating apoptosis has provided the basis for novel targeted therapies that can induce death in cancer cells or sensitize them to cytotoxic agents and radiation therapy. These novel agents include those targeting either the extrinsic or the intrinsic pathway of apoptosis. Failure to undergo in response to anticancer therapy can result in resistance. Thus, insights into the ways in wich cancer cells evade apoptosis might provide new opportunities for drug development