ΔNp63 regulates select routes of reprogramming via multiple mechanisms

Supercharging BRD4 with NUT in carcinoma

NUT carcinoma (NC) is an extremely aggressive squamous cancer with no effective therapy. NC is driven, most commonly, by the BRD4-NUT fusion oncoprotein. BRD4-NUT combines the chromatin-binding bromo- and extraterminal domain-containing (BET) protein, BRD4, with an unstructured, poorly understood protein, NUT, which recruits and activates the histone acetyltransferase p300. Recruitment of p300 to chromatin by BRD4 is believed to lead to the formation of hyperacetylated nuclear foci, as seen by immunofluorescence. BRD4-NUT nuclear foci correspond with massive contiguous regions of chromatin co-enriched with BRD4-NUT, p300, and acetylated histones, termed "megadomains" (MD). Megadomains stretch for as long as 2 MB. Proteomics has defined a BRD4-NUT chromatin complex in which members that associate with BRD4 also exist as rare NUT-fusion partners. This suggests that the common pathogenic denominator is the presence of both BRD4 and NUT, and that the function of BRD4-NUT may mimic that of wild-type BRD4. If so, then MDs may function as massive super-enhancers, activating transcription in a BET-dependent manner. Common targets of MDs across multiple NCs and tissues are three stem cell-related transcription factors frequently implicated in cancer: MYC, SOX2, and TP63. Recently, MDs were found to form a novel nuclear sub-compartment, called subcompartment M (subM), where MD-MD interactions occur both intra- and inter-chromosomally. Included in subM are MYC, SOX2, and TP63. Here we explore the possibility that if MDs are simply large super-enhancers, subM may exist in other cell systems, with broad implications for how 3D organization of the genome may function in gene regulation and maintenance of cell identity. Finally, we discuss how our knowledge of BRD4-NUT function has been leveraged for the therapeutic development of first-in-class BET inhibitors and other targeted strategies.

Distinct p63 and p73 Protein Interactions Predict Specific Functions in mRNA Splicing and Polyploidy Control in Epithelia

Epithelial organs are the first barrier against microorganisms and genotoxic stress, in which the p53 family members p63 and p73 have both overlapping and distinct functions. Intriguingly, p73 displays a very specific localization to basal epithelial cells in human tissues, while p63 is expressed in both basal and differentiated cells. Here, we analyse systematically the literature describing p63 and p73 protein-protein interactions to reveal distinct functions underlying the aforementioned distribution. We have found that p73 and p63 cooperate in the genome stability surveillance in proliferating cells; p73 specific interactors contribute to the transcriptional repression, anaphase promoting complex and spindle assembly checkpoint, whereas p63 specific interactors play roles in the regulation of mRNA processing and splicing in both proliferating and differentiated cells. Our analysis reveals the diversification of the RNA and DNA specific functions within the p53 family.

Oral Mucosa-Derived Induced Pluripotent Stem Cells from Patients with Ectrodactyly-Ectodermal Dysplasia-Clefting Syndrome

Ectrodactyly-Ectodermal dysplasia-Clefting (EEC) syndrome is a rare monogenic disease with autosomal dominant inheritance caused by mutations in the TP63 gene, leading to progressive corneal keratinocyte loss, limbal stem cell deficiency (LSCD), and eventually blindness. Currently, there is no treatment available to cure or slow down the keratinocyte loss. Human oral mucosal epithelial stem cells (hOMESCs), which are a mixed population of keratinocyte precursor stem cells, are used as source of autologous tissue for treatment of bilateral LSCD. However, hOMESCs from EEC patients have a reduced life span due to TP63 mutations and cannot be used for autologous transplantation. Human induced pluripotent stem cells (hiPSCs) represent a potentially unlimited source of autologous limbal stem cell for EEC patients and can be genetically modified by genome editing technologies to correct the disease ex vivo before transplantation. In this study, we describe for the first time the generation of integration-free EEC-hiPSCs from hOMESCs of EEC patients by Sendai virus vector and episomal vector-based reprogramming. The generated hiPSC clones expressed pluripotency markers and were successfully differentiated into derivatives of the three germ layers, as well as toward corneal epithelium. These cells may be used for EEC disease modeling and open perspectives for applications in cell therapy of LSCD.

Determination of the Culture Time Point to Induce Corneal Epithelial Differentiation in Induced Pluripotent Stem Cells

BACKGROUND

Limbal stem cells (LSC) are progenitor cells in the ocular surface that renew the corneal epithelium. Limbal stem cell deficiency usually induces blindness through the loss of corneal transparency, and bilateral cases do not an accurate treatment because of the lack of an autologous source of stem cells.

METHODS

Induced pluripotent stem cells (iPSC) are promising for use in cell therapy because of their autologous origin and the capability to differentiate into corneal epithelial cells. However, there are not standardized protocols to achieve a complete corneal epithelial differentiation. We examined the expression of several markers in a human episomal iPSC line after an induction period from embryoid bodies.

RESULTS

Progenitor LSC and corneal epithelial differentiation markers, some extracellular matrix protein adhesion molecules, and wingless signaling pathway were studied. Overall, LSC progenitor and corneal epithelium differentiation markers increased after maintaining cell culture in specific conditions for 14 days, whereas pluripotency markers decreased.

CONCLUSIONS

Our approach indicated that the optimal time point to initiate iPSC differentiation into LSC and corneal phenotypes, with the use of specific medium, is from 14 days after initial embryoid bodies treatment induction.

Master regulatory role of p63 in epidermal development and disease

The transcription factor p63 is a master regulator of epidermal development. Mutations in p63 give rise to human developmental diseases that often manifest epidermal defects. In this review, we summarize major p63 isoforms identified so far and p63 mutation-associated human diseases that show epidermal defects. We discuss key roles of p63 in epidermal keratinocyte proliferation and differentiation, emphasizing its master regulatory control of the gene expression pattern and epigenetic landscape that define epidermal fate. We subsequently review the essential function of p63 during epidermal commitment and transdifferentiation towards epithelial lineages, highlighting the notion that p63 is the guardian of the epithelial lineage. Finally, we discuss current therapeutic development strategies for p63 mutation-associated diseases. Our review proposes future directions for dissecting p63-controlled mechanisms in normal and diseased epidermal development and for developing therapeutic options.

Human papillomavirus oncogenic E6 protein regulates human β-defensin 3 (hBD3) expression via the tumor suppressor protein p53

Human β-defensin-3 (hBD3) is an epithelial cell-derived innate immune regulatory molecule overexpressed in oral dysplastic lesions and fosters a tumor-promoting microenvironment. Expression of hBD3 is induced by the epidermal growth factor receptor signaling pathway. Here we describe a novel pathway through which the high-risk human papillomavirus type-16 (HPV-16) oncoprotein E6 induces hBD3 expression in mucosal keratinocytes. Ablation of E6 by siRNA induces the tumor suppressor p53 and diminishes hBD3 in HPV-16 positive CaSki cervical cancer cells and UM-SCC-104 head and neck cancer cells. Malignant cells in HPV-16-associated oropharyngeal cancer overexpress hBD3. HPV-16 E6 induces hBD3 mRNA expression, peptide production and gene promoter activity in mucosal keratinocytes. Reduction of cellular levels of p53 stimulates hBD3 expression, while activation of p53 by doxorubicin inhibits its expression in primary oral keratinocytes and CaSki cells, suggesting that p53 represses hBD3 expression. A p53 binding site in the hBD3 gene promoter has been identified by using electrophoretic mobility shift assays and chromatin immunoprecipitation (ChIP). In addition, the p63 protein isoform ΔNp63α, but not TAp63, stimulated transactivation of the hBD3 gene and was co-expressed with hBD3 in head and neck cancer specimens. Therefore, high-risk HPV E6 oncoproteins may stimulate hBD3 expression in tumor cells to facilitate tumorigenesis of HPV-associated head and neck cancer.

A wound-healing program is hijacked to promote cancer metastasis

In this issue of JEM, Sundaram et al. (https://doi.org/10.1084/jem.20170354) report a mechanism by which the normal epithelial wound healing response is "hijacked" to promote invasion and metastasis in head and neck squamous carcinomas (HNSCCs), a finding that unveils new markers of poor outcomes and potential targets for therapeutic intervention.

TLR5/7-mediated PI3K activation triggers epithelial-mesenchymal transition of ovarian cancer cells through WAVE3-dependent mesothelin or OCT4/SOX2 expression

Toll-like receptor (TLR)-mediated signaling induces cell migration or invasion in several tumors and various stages of cancer. Interactions of mesothelin, a 40-kDa cell surface glycoprotein, with cancer antigen 125 (CA125) is associated with drug resistance, metastasis, and poor clinical outcome of ovarian cancer patients. In this study, we examined the role of TLR5 and TLR7 in the metastasis of ovarian cancer through the induction of mesothelin/CA125 expression and investigated its underlying mechanism. TLR5 agonist (flagellin) and TLR7 agonist (imiquimod) upregulated mesenchymal phenotypes and produced epithelial-mesenchymal transition (EMT)-related cytokines in the SKOV3 cells; however, TLR7 expressing CaOV3 cells had no response to the specific ligand, imiquimod, for enhancing its EMT processes. Stimulation of the SKOV3 cells with flagellin or imiquimod activated Wiskott-Aldrich syndrome protein verprolin-homologous 3 (WAVE3) and mesothelin/CA125, whereas it suppressed the expression of TAp63. Moreover, knockdown of TLR5 or TLR7 in SKOV3 cells profoundly impaired the TLR5- or TLR7-intiated downstream signaling pathway. Loss of WAVE3 in SKOV3 cells led to the inhibition of invasion, suppression of mesenchymal characteristics, prevention of OCT4/SOX2 secretion, and attenuation of mesothelin/CA125 expression after stimulation with flagellin or imiquimod. Although the disruption of mesothelin decreased the migratory activity of the TLR5/7-activated SKOV3 cells, knockdown of mesothelin failed to reduce the expression of mesenchymal markers, OCT4, and SOX2. In addition, targeting OCT4 or SOX2 with siRNA had no effect on the expression of mesothelin and the suppression of transcriptionally active p63 (TAp63) in the TLR5/7-stimulated SKOV3 cells. Our results suggest that TLR5/7-mediated WAVE3 activation not only controls the mesothelin-related EMT processes but also modulates OCT4/SOX2-mediated mesenchymal marker expression. Taken together, both TLR5 and TLR7 expression are critical for the TLR5/7-induced metastasis of ovarian cancer and the inhibition of WAVE3 might be a new therapeutic target to control ovarian cancer metastasis.

p53 switches off pluripotency on differentiation

The role of p53 as “a guardian of the genome” has been well established in somatic cells. However, its role in pluripotent stem cells remains much more elusive. Here, we discuss research progress in understanding the role of p53 in pluripotent stem cells and in pluripotent stem cell-like cancer stem cells. The p53 protein, which plays a key role in embryonic stem cells, was first discovered in 2005. Landmark studies of p53-related reprogramming elucidated this protein’s importance in induced pluripotent stem cells in 2009. The p53-related safety concerns in pluripotent stem cells have been raised in stem cell-based therapy although the use of iPSCs in therapeutic application is promising. Because cancer stem cells have profiles similar to those of pluripotent stem cells, we also describe potential strategies for studies in cancer stem cells and cancer treatments. The new discoveries of p53 family proteins in pluripotent stem cells have made possible stable progress in stem cell transplantation efficiency and safety, as well as treatment strategies targeting cancer stem cells based on pluripotent stem cell technology.

ΔNp63α and microRNAs: leveraging the epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) is a cellular reprogramming mechanism that is an underlying cause of cancer metastasis. Recent investigations have uncovered an intricate network of regulation involving the TGFβ, Wnt, and Notch signaling pathways and small regulatory RNA species called microRNAs (miRNAs). The activity of a transcription factor vital to the maintenance of epithelial stemness, ΔNp63α, has been shown to modulate the activity of these EMT pathways to either repress or promote EMT. Furthermore, ΔNp63α is a known regulator of miRNA, including those directly involved in EMT. This review discusses the evidence of ΔNp63α as a master regulator of EMT components and miRNA, highlighting the need for a deeper understanding of its role in EMT. This expanded knowledge may provide a basis for new developments in the diagnosis and treatment of metastatic cancer.

DNA repair and aging: the impact of the p53 family

Cells are constantly exposed to endogenous and exogenous factors that threaten the integrity of their DNA. The maintenance of genome stability is of paramount importance in the prevention of both cancer and aging processes. To deal with DNA damage, cells put into operation a sophisticated and coordinated mechanism, collectively known as DNA damage response (DDR). The DDR orchestrates different cellular processes, such as DNA repair, senescence and apoptosis. Among the key factors of the DDR, the related proteins p53, p63 and p73, all belonging to the same family of transcription factors, play multiple relevant roles. Indeed, the members of this family are directly involved in the induction of cell cycle arrest that is necessary to allow the cells to repair. Alternatively, they can promote cell death in case of prolonged or irreparable DNA damage. They also take part in a more direct task by modulating the expression of core factors involved in the process of DNA repair or by directly interacting with them. In this review we will analyze the fundamental roles of the p53 family in the aging process through their multifaceted function in DDR.

p73 regulates basal and starvation-induced liver metabolism in vivo

As a member of the p53 gene family, p73 regulates cell cycle arrest, apoptosis, neurogenesis, immunity and inflammation. Recently, p73 has been shown to transcriptionally regulate selective metabolic enzymes, such as cytochrome c oxidase subunit IV isoform 1, glucose 6-phosphate dehydrogenase and glutaminase-2, resulting in significant effects on metabolism, including hepatocellular lipid metabolism, glutathione homeostasis and the pentose phosphate pathway. In order to further investigate the metabolic effect of p73, here, we compared the global metabolic profile of livers from p73 knockout and wild-type mice under both control and starvation conditions. Our results show that the depletion of all p73 isoforms cause altered lysine metabolism and glycolysis, distinct patterns for glutathione synthesis and Krebs cycle, as well as an elevated pentose phosphate pathway and abnormal lipid accumulation. These results indicate that p73 regulates basal and starvation-induced fuel metabolism in the liver, a finding that is likely to be highly relevant for metabolism-associated disorders, such as diabetes and cancer.

ΔNp63 regulates cell proliferation, differentiation, adhesion, and migration in the BL2 subtype of basal-like breast cancer

Triple-negative breast cancers (TNBC) comprise a heterogeneous subgroup of tumors with a generally poor prognosis. Subclassification of TNBC based on genomic analyses shows that basal-like TNBCs, specifically the basal A or BL2 subtype, are characterized by the expression of ΔNp63, a transcription factor that has been attributed a variety of roles in the regulation of proliferation, differentiation, and cell survival. To investigate the role(s) of p63 in basal-like breast cancers, we used HCC1806 cells that are classified as basal A/BL2. We show that these cells endogenously express p63, mainly as the ΔNp63α isoform. TP63 gene knockout by CRISPR resulted in viable cells that proliferate more slowly and adhere less tightly, with an increased rate of migration. Analysis of adhesion-related gene expression revealed a complex set of alterations in p63-depleted cells, with both increased and decreased adhesion molecules and adhesion substrates compared to parental cells expressing p63. Examination of the phenotype of these cells indicated that endogenous p63 is required to suppress the expression of luminal markers and maintain the basal epithelial phenotype, with increased levels of both CK8 and CK18 and a reduction in N-cadherin levels in cells lacking p63. On the other hand, the level of CK5 was not decreased and ER was not increased, indicating that p63 loss is insufficient to induce full luminal-type differentiation. Taken together, these data demonstrate that p63 exerts multiple pro-oncogenic effects on cell differentiation, proliferation and adhesion in basal-like breast cancers.

TAp73 promotes anabolism

Metabolic adaptation has emerged as a hallmark of cancer and a promising therapeutic target, as rapidly proliferating cancer cells adapt their metabolism increasing nutrient uptake and reorganizing metabolic fluxes to support biosynthesis. The transcription factor p73 belongs to the p53-family and regulates tumorigenesis via its two N-terminal isoforms, with (TAp73) or without (ΔNp73) a transactivation domain. TAp73 acts as tumor suppressor, at least partially through induction of cell cycle arrest and apoptosis and through regulation of genomic stability. Here, we sought to investigate whether TAp73 also affects metabolic profiling of cancer cells. Using high throughput metabolomics, we unveil a thorough and unexpected role for TAp73 in promoting Warburg effect and cellular metabolism. TAp73-expressing cells show increased rate of glycolysis, higher amino acid uptake and increased levels and biosynthesis of acetyl-CoA. Moreover, we report an extensive TAp73-mediated upregulation of several anabolic pathways including polyamine and synthesis of membrane phospholipids. TAp73 expression also increases cellular methyl-donor S-adenosylmethionine (SAM), possibly influencing methylation and epigenetics, and promotes arginine metabolism, suggestive of a role in extracellular matrix (ECM) modeling. In summary, our data indicate that TAp73 regulates multiple metabolic pathways that impinge on numerous cellular functions, but that, overall, converge to sustain cell growth and proliferation.

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

Both in epithelial development as well as in epithelial cancers, the p53 family member p63 plays a crucial role acting as a master transcriptional regulator. P63 steady state protein levels are regulated by the E3 ubiquitin ligase Itch, via a physical interaction between the PPxY consensus sequence (PY motif) of p63 and one of the 4 WW domains of Itch; this substrate recognition process leads to protein-ubiquitylation and p63 proteasomal degradation. The interaction of the WW domains, a highly compact protein-protein binding module, with the short proline-rich sequences is therefore a crucial regulatory event that may offer innovative potential therapeutic opportunity. Previous molecular studies on the Itch-p63 recognition have been performed in vitro using the Itch-WW2 domain and the peptide interacting fragment of p63 (pep63), which includes the PY motif. Itch-WW2-pep63 interaction is also stabilized in vitro by the conformational constriction of the S-S cyclization in the p63 peptide. The PY motif of p63, as also for other proteins, is characterized by the nearby presence of a (T/S)P motif, which is a potential recognition site of the WW domain of the IV group present in the prolyl-isomerase Pin1. In this study, we demonstrate, by in silico and spectroscopical studies using both the linear pep63 and its cyclic form, that the threonine phosphorylation of the (T/S)PPPxY motif may represent a crucial regulatory event of the Itch-mediated p63 ubiquitylation, increasing the Itch-WW domains-p63 recognition event and stabilizing in vivo the Itch-WW-p63 complex. Moreover, our studies confirm that the subsequently trans/cis proline isomerization of (T/S)P motif by the Pin1 prolyl-isomerase, could modulate the E3-ligase interaction, and that the (T/S)pPtransPPxY motif represent the best conformer for the ItchWW-(T/S)PPPxY motif recognition.

Bioinformatics analysis of the serine and glycine pathway in cancer cells

Serine and glycine are amino acids that provide the essential precursors for the synthesis of proteins, nucleic acids and lipids. Employing 3 subsequent enzymes, phosphoglycerate dehydrogenase (PHGDH), phosphoserine phosphatase (PSPH), phosphoserine aminotransferase 1 (PSAT1), 3-phosphoglycerate from glycolysis can be converted in serine, which in turn can by converted in glycine by serine methyl transferase (SHMT). Besides proving precursors for macromolecules, serine/glycine biosynthesis is also required for the maintenance of cellular redox state. Therefore, this metabolic pathway has a pivotal role in proliferating cells, including cancer cells. In the last few years an emerging literature provides genetic and functional evidences that hyperactivation of serine/glycine biosynthetic pathway drives tumorigenesis. Here, we extend these observations performing a bioinformatics analysis using public cancer datasets. Our analysis highlighted the relevance of PHGDH and SHMT2 expression as prognostic factor for breast cancer, revealing a substantial ability of these enzymes to predict patient survival outcome. However analyzing patient datasets of lung cancer our analysis reveled that some other enzymes of the pathways, rather than PHGDH, might be associated to prognosis. Although these observations require further investigations they might suggest a selective requirement of some enzymes in specific cancer types, recommending more cautions in the development of novel translational opportunities and biomarker identification of human cancers.

How Does p73 Cause Neuronal Defects?

The p53-family member, p73, plays a key role in the development of the central nervous system (CNS), in senescence, and in tumor formation. The role of p73 in neuronal differentiation is complex and involves several downstream pathways. Indeed, in the last few years, we have learnt that TAp73 directly or indirectly regulates several genes involved in neural biology. In particular, TAp73 is involved in the maintenance of neural stem/progenitor cell self-renewal and differentiation throughout the regulation of SOX-2, Hey-2, TRIM32 and Notch. In addition, TAp73 is also implicated in the regulation of the differentiation and function of postmitotic neurons by regulating the expression of p75NTR and GLS2 (glutamine metabolism). Further still, the regulation of miR-34a by TAp73 indicates that microRNAs can also participate in this multifunctional role of p73 in adult brain physiology. However, contradictory results still exist in the relationship between p73 and brain disorders, and this remains an important area for further investigation.

Potential Role of Induced Pluripotent Stem Cells (IPSCs) for Cell-Based Therapy of the Ocular Surface

The integrity and normal function of the corneal epithelium are crucial for maintaining the cornea’s transparency and vision. The existence of a cell population with progenitor characteristics in the limbus maintains a dynamic of constant epithelial repair and renewal. Currently, cell-based therapies for bio replacement—cultured limbal epithelial transplantation (CLET) and cultured oral mucosal epithelial transplantation (COMET)—present very encouraging clinical results for treating limbal stem cell deficiency (LSCD) and restoring vision. Another emerging therapeutic approach consists of obtaining and implementing human progenitor cells of different origins in association with tissue engineering methods. The development of cell-based therapies using stem cells, such as human adult mesenchymal or induced pluripotent stem cells (IPSCs), represent a significant breakthrough in the treatment of certain eye diseases, offering a more rational, less invasive, and better physiological treatment option in regenerative medicine for the ocular surface. This review will focus on the main concepts of cell-based therapies for the ocular surface and the future use of IPSCs to treat LSCD.

DEK promotes HPV-positive and -negative head and neck cancer cell proliferation

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy worldwide, and patient outcomes using current treatments remain poor. Tumor development is etiologically associated with tobacco or alcohol use and/or human papillomavirus (HPV) infection. HPV-positive HNSCCs, which frequently harbor wild-type p53, carry a more favorable prognosis and are a biologically distinct subgroup when compared with their HPV-negative counterparts. HPV E7 induces expression of the human DEK gene, both in vitro and in vivo. In keratinocytes, DEK overexpression is sufficient for causing oncogenic phenotypes in the absence of E7. Conversely, DEK loss results in cell death in HPV-positive cervical cancer cells at least in part through p53 activation, and Dek knockout mice are relatively resistant to the development of chemically induced skin papillomas. Despite the established oncogenic role of DEK in HPV-associated cervical cancer cell lines and keratinocytes, a functional role of DEK has not yet been explored in HNSCC. Using an established transgenic mouse model of HPV16 E7-induced HNSCC, we demonstrate that Dek is required for optimal proliferation of E7-transgenic epidermal cells and for the growth of HNSCC tumors. Importantly, these studies also demonstrate that DEK protein is universally upregulated in both HPV-positive and -negative human HNSCC tumors relative to adjacent normal tissue. Furthermore, DEK knockdown inhibited the proliferation of HPV-positive and -negative HNSCC cells, establishing a functional role for DEK in human disease. Mechanistic studies reveal that attenuated HNSCC cell growth in response to DEK loss was associated with reduced expression of the oncogenic p53 family member, ΔNp63. Exogenous ΔNp63 expression rescued the proliferative defect in the absence of DEK, thereby establishing a functional DEK-ΔNp63 oncogenic pathway that promotes HNSCC. Taken together, our data demonstrate that DEK stimulates HNSCC cellular growth and identify ΔNp63 as a novel DEK effector.

MicroRNAs and p63 in epithelial stemness

MicroRNAs (miRs) are a class of small noncoding RNAs that suppress the expression of protein-coding genes by repressing protein translation. Although the roles that miRs and the miR processing machinery have in regulating epithelial stem cell biology are not fully understood, their fundamental contributions to these processes have been demonstrated over the last few years. The p53-family member p63 is an essential transcription factor for epidermal morphogenesis and homeostasis. p63 functions as a determinant for keratinocyte cell fate and helps to regulate the balance between stemness, differentiation and senescence. An important factor that regulates p63 function is the reciprocal interaction between p63 and miRs. Some miRs control p63 expression, and p63 regulates the miR expression profile in the epidermis. p63 controls miR expression at different levels. It directly regulates the transcription of several miRs and indirectly regulates their processing by regulating the expression of the miR processing components Dicer and DGCR8. In this review, we will discuss the recent findings on the miR–p63 interaction in epidermal biology, particularly focusing on the ΔNp63-dependent regulation of DGCR8 recently described in the ΔNp63^−/− mouse. We provide a unified view of the current knowledge and discuss the apparent discrepancies and perspective therapeutic opportunities.