On the shoulders of giants: p63, p73 and the rise of p53

Recent Research on Role of p53 Family in Small-Cell Lung Cancer

Small-cell lung cancer (SCLC) is a highly aggressive malignancy characterized by rapid proliferation, early metastasis, and frequent recurrence, which contribute to a poor prognosis. SCLC is defined by the near-universal inactivation of key tumor suppressor genes, notably TP53 and RB1, which play central roles in its pathogenesis and resistance to therapy. The p53 family of proteins, including p53, p63, and p73, is essential to maintaining cellular homeostasis and tumor suppression. TP53 mutations are almost ubiquitous in SCLC, leading to dysregulated apoptosis and cell cycle control. Moreover, p73 shows potential as a compensatory mechanism for p53 loss, while p63 has a minimal role in this cancer type. In this review, we explore the molecular and functional interplay of the p53 family in SCLC, emphasizing its members' distinct yet interconnected roles in tumor suppression, immune modulation, and therapy resistance. We highlight emerging therapeutic strategies targeting these pathways, including reactivating mutant p53, exploiting synthetic lethality, and addressing immune evasion mechanisms. Furthermore, this review underscores the urgent need for novel, isoform-specific interventions to enhance treatment efficacy and improve patient outcomes in this challenging disease.

Dichotomous transactivation domains contribute to growth inhibitory and promotion functions of TAp73

The transcription factor p73, a member of the p53 tumor-suppressor family, regulates cell death and also supports tumorigenesis, although the mechanistic basis for the dichotomous functions is poorly understood. We report here the identification of an alternate transactivation domain (TAD) located at the extreme carboxyl (C) terminus of TAp73β, a commonly expressed p73 isoform. Mutational disruption of this TAD significantly reduced TAp73β's transactivation activity, to a level observed when the amino (N)-TAD that is similar to p53's TAD, is mutated. Mutation of both TADs almost completely abolished TAp73β's transactivation activity. Expression profiling highlighted a unique set of targets involved in extracellular matrix-receptor interaction and focal adhesion regulated by the C-TAD, resulting in FAK phosphorylation, distinct from the N-TAD targets that are common to p53 and are involved in growth inhibition. Interestingly, the C-TAD targets are also regulated by the oncogenic, amino-terminal-deficient DNp73β isoform. Consistently, mutation of C-TAD reduces cellular migration and proliferation. Mechanistically, selective binding of TAp73β to DNAJA1 is required for the transactivation of C-TAD target genes, and silencing DNAJA1 expression abrogated all C-TAD-mediated effects. Taken together, our results provide a mechanistic basis for the dichotomous functions of TAp73 in the regulation of cellular growth through its distinct TADs.

A multilayered post-GWAS analysis pipeline defines functional variants and target genes for systemic lupus erythematosus (SLE)

Objectives

Systemic lupus erythematosus (SLE), an autoimmune disease with incompletely understood etiology, has a strong genetic component. Although genome-wide association studies (GWAS) have revealed multiple SLE susceptibility loci and associated single nucleotide polymorphisms (SNPs), the precise causal variants, target genes, cell types, tissues, and mechanisms of action remain largely unknown.

Methods

Here, we report a comprehensive post-GWAS analysis using extensive bioinformatics, molecular modeling, and integrative functional genomic and epigenomic analyses to optimize fine-mapping. We compile and cross-reference immune cell-specific expression quantitative trait loci ( cis - and trans -eQTLs) with promoter-capture Hi-C, allele-specific chromatin accessibility, and massively parallel reporter assay data to define predisposing variants and target genes. We experimentally validate a predicted locus using CRISPR/Cas9 genome editing, qPCR, and Western blot.

Results

Anchoring on 452 index SNPs, we selected 9,931 high-linkage disequilibrium (r 2 >0.8) SNPs and defined 182 independent non-HLA SLE loci. 3,746 SNPs from 143 loci were identified as regulating 564 unique genes. Target genes are enriched in lupus-related tissues and associated with other autoimmune diseases. Of these, 329 SNPs (106 loci) showed significant allele-specific chromatin accessibility and/or enhancer activity, indicating regulatory potential. Using CRISPR/Cas9, we validated rs57668933 as a functional variant regulating multiple targets, including SLE risk gene ELF1 , in B-cells.

Conclusion

We demonstrate and validate post-GWAS strategies for utilizing multi-dimensional data to prioritize likely causal variants with cognate gene targets underlying SLE pathogenesis. Our results provide a catalog of significantly SLE-associated SNPs and loci, target genes, and likely biochemical mechanisms, to guide experimental characterization.

Phylogenetic analysis of the MCL1 BH3 binding groove and rBH3 sequence motifs in the p53 and INK4 protein families

B-cell lymphoma 2 (Bcl-2) proteins are central, conserved regulators of apoptosis. Bcl-2 family function is regulated by binding interactions between the Bcl-2 homology 3 (BH3) motif in pro-apoptotic family members and the BH3 binding groove found in both the pro-apoptotic effector and anti-apoptotic Bcl-2 family members. A novel motif, the reverse BH3 (rBH3), has been shown to interact with the anti-apoptotic Bcl-2 homolog MCL1 (Myeloid cell leukemia 1) and have been identified in the p53 homolog p73, and the CDK4/6 (cyclin dependent kinase 4/6) inhibitor p18INK4c, (p18, cyclin-dependent kinase 4 inhibitor c). To determine the conservation of rBH3 motif, we first assessed conservation of MCL1's BH3 binding groove, where the motif binds. We then constructed neighbor-joining phylogenetic trees of the INK4 and p53 protein families and analyzed sequence conservation using sequence logos of the rBH3 locus. This showed the rBH3 motif is conserved throughout jawed vertebrates p63 and p73 sequences and in chondrichthyans, amphibians, mammals, and some reptiles in p18. Finally, a potential rBH3 motif was identified in mammalian and osteichthyan p19INK4d (p19, cyclin dependent kinase 4 inhibitor d). These findings demonstrate that the interaction between MCL1 and other cellular proteins mediated by the rBH3 motif may be conserved throughout jawed vertebrates.

Comparison of Diagnostic Reliability of p63 and Smooth Muscle Actin in Salivary Gland Neoplasms

Salivary gland neoplasms pose considerable diagnostic difficulty owing to their diverse histological features in individual lesions and the presence of a number of types and variants & similar histological features with other tumor entities. Myoepithelial and basal cells play a significant role in the pathogenesis of salivary gland neoplasm. p63 and smooth muscle actin are more reliable markers for identifying these cells and not studied much comparing their reliability in the diagnosis of salivary gland neoplasms. Hence, the aim of this study is to evaluate and compare the diagnostic reliability of immunohistochemical markers such as p63 and smooth muscle actin (SMA) in the diagnosis of various benign and malignant salivary gland neoplasms. The study comprises of 18 samples categorized into two groups: Group I comprised 9 cases, of which 4 cases were Pleomorphic adenoma, 2 cases were Myoepithelioma, 2 cases of Basal cell adenoma and 1 case was Warthin's tumor; and Group II consisted of 9cases, of which 3 was Mucoepidermoid carcinoma, 1 cases were Myoepithelial carcinoma and 5 cases were Adenoid cystic carcinoma. The selected cases were subjected to immunohistochemistry (IHC) procedure to assess the expression pattern of p63 and smooth muscle actin. The obtained data was analysed statistically by using Mann-Whitney test. In SMA, strong positivity for epithelial and connective tissue components of benign salivary neoplasm is about 22.2%respectively. In malignant salivary neoplasm, SMA was strongly positive for the epithelial and connective tissue component of about 77.7% and 88.8% cases respectively. The difference in the connective tissue components was found to be statistically significant (U = 24, P = 0.032). P63 was strongly positive for the epithelial and connective tissue component of benign salivary neoplasm of about 33.3% and 11.1% cases respectively.In malignant salivary neoplasm, p63 was strongly positive for the epithelial component of about 66.6% cases and connective tissue is completely negative. Alpha-SMA can be utilized as reliable IHC markers for salivary gland neoplasms due to its diagnostic importance in tumors with myoepithelial origin indicative of the histogenesis of salivary gland tumors and even p63 can be used as specific markers for differentiation of malignant salivary gland tumors.

Discovery of CRBN as a target of thalidomide: a breakthrough for progress in the development of protein degraders

Progress in strategies aimed at breaking down therapeutic target proteins has led to a paradigm shift in drug discovery. Thalidomide and its derivatives are the only protein degraders currently used in clinical practice. Our understanding of the molecular mechanism of action of thalidomide and its derivatives has advanced dramatically since the identification of cereblon (CRBN) as their direct target. The binding of thalidomide derivatives to CRBN, a substrate recognition receptor for Cullin 4 RING E3 ubiquitin ligase (CRL4), induces the recruitment of non-native substrates to CRL4^CRBN and their subsequent degradation. This discovery was a breakthrough in the current rapid development of protein-degrading agents because clarification of the mechanism of action of thalidomide derivatives has demonstrated the clinical value of these compounds. This review provides an overview of the mechanism of action of thalidomide and its derivatives and describes perspectives for protein degraders.

Development and validation of a gene signature predicting the risk of postmenopausal osteoporosis

AIMS

We aimed to develop a gene signature that predicts the occurrence of postmenopausal osteoporosis (PMOP) by studying its genetic mechanism.

METHODS

Five datasets were obtained from the Gene Expression Omnibus database. Unsupervised consensus cluster analysis was used to determine new PMOP subtypes. To determine the central genes and the core modules related to PMOP, the weighted gene co-expression network analysis (WCGNA) was applied. Gene Ontology enrichment analysis was used to explore the biological processes underlying key genes. Logistic regression univariate analysis was used to screen for statistically significant variables. Two algorithms were used to select important PMOP-related genes. A logistic regression model was used to construct the PMOP-related gene profile. The receiver operating characteristic area under the curve, Harrell's concordance index, a calibration chart, and decision curve analysis were used to characterize PMOP-related genes. Then, quantitative real-time polymerase chain reaction (qRT-PCR) was used to verify the expression of the PMOP-related genes in the gene signature.

RESULTS

We identified three PMOP-related subtypes and four core modules. The muscle system process, muscle contraction, and actin filament-based movement were more active in the hub genes. We obtained five feature genes related to PMOP. Our analysis verified that the gene signature had good predictive power and applicability. The outcomes of the GSE56815 cohort were found to be consistent with the results of the earlier studies. qRT-PCR results showed that RAB2A and FYCO1 were amplified in clinical samples.

CONCLUSION

The PMOP-related gene signature we developed and verified can accurately predict the risk of PMOP in patients. These results can elucidate the molecular mechanism of RAB2A and FYCO1 underlying PMOP, and yield new and improved treatment strategies, ultimately helping PMOP monitoring.Cite this article: Bone Joint Res 2022;11(8):548-560.

The steep uphill path leading to ex vivo gene therapy for genodermatoses

Cell therapy, gene therapy and tissue engineering have the potential to revolutionize the field of regenerative medicine. In particular, gene therapy is understood as the therapeutical correction of mutated genes by addition of a correct copy of the gene or site-specific gene modifications. Gene correction of somatic stem cells sustaining renewing tissues is critical to ensure long-term clinical success of ex vivo gene therapy. To date, remarkable clinical outcomes arose from combined ex vivo cell and gene therapy of different genetic diseases, such as immunodeficiencies and genodermatoses. Despite the efforts of researchers around the world, only few of these advanced approaches has yet made it to routine therapy. In fact, gene therapy poses one of the greatest technical challenges in modern medicine, spanning safety and efficacy issues, regulatory constraints, registration and market access, all of which need to be addressed to make the therapy available to rare disease patients. In this review, we survey at some of the main challenges in the development of combined cell and gene therapy of genetic skin diseases.

Requirement for TP73 and genetic alterations originating from its intragenic super-enhancer in adult T-cell leukemia

Adult T-cell leukemia/lymphoma (ATL) is a genetically complex hematological malignancy derived from mature T cells. Using an integrative approach, we previously identified genes recurrently associated with super-enhancers in ATL. One of those genes was TP73, a TP53 family gene; however, the roles and function of TP73 and its super-enhancer in ATL pathogenesis are poorly understood. Our study demonstrates that TP73 is highly activated under the control of a super-enhancer in ATL cells but not in normal T cells or other hematological malignancies examined. Full-length TP73 is required for ATL cell maintenance in vitro and in vivo via the regulation of cell proliferation and DNA damage response pathways. Notably, recurrent deletions of TP73 exons 2-3 were observed in a fraction of primary ATL cases that harbored the super-enhancer, while induction of this deletion in cell lines further increased proliferation and mutational burden. Our study suggests that formation of the TP73 intragenic super-enhancer and genetic deletion are likely sequentially acquired in relation to intracellular state of ATL cells, which leads to functional alteration of TP73 that confers additional clonal advantage.

Delineating functional mechanisms of the p53/p63/p73 family of transcription factors through identification of protein-protein interactions using interface mimicry

Members of the p53 family of transcription factors-p53, p63, and p73-share a high degree of homology; however, members can be activated in response to different stimuli, perform distinct (sometimes opposing) roles and are expressed in different tissues. The level of complexity is increased further by the transcription of multiple isoforms of each homolog, which may interact or interfere with each other and can impact cellular outcome. Proteins perform their functions through interacting with other proteins (and/or with nucleic acids). Therefore, identification of the interactors of a protein and how they interact in 3D is essential to fully comprehend their roles. By utilizing an in silico protein-protein interaction prediction method-HMI-PRED-we predicted interaction partners of p53 family members and modeled 3D structures of these protein interaction complexes. This method recovered experimentally known interactions while identifying many novel candidate partners. We analyzed the similarities and differences observed among the interaction partners to elucidate distinct functions of p53 family members and provide examples of how this information may yield mechanistic insight to explain their overlapping versus distinct/opposing outcomes in certain contexts. While some interaction partners are common to p53, p63, and p73, the majority are unique to each member. Nevertheless, most of the enriched pathways associated with these partners are common to all members, indicating that the members target the same biological pathways but through unique mediators. p63 and p73 have more common enriched pathways compared to p53, supporting their similar developmental roles in different tissues.

Rare variants in TP73 in a Frontotemporal Dementia cohort link this gene with primary progressive aphasia phenotypes

OBJECTIVE

TP73 was recently reported to cause Amyotrophic Lateral Sclerosis (ALS). ALS and Frontotemporal Dementia (FTD) are considered to be part of a continuum. We aimed to investigate whether TP73 variants may be associated with FTD.

METHODS

We studied a thoroughly investigated cohort of 65 Portuguese Frontotemporal Dementia patients by Whole-Exome Sequencing. Patients had no other known genetic cause for their disease (C9orf72 expansion was also excluded).

RESULTS

Of the 65 patients studied, two had rare variants in TP73 (p.Gly605Ser and p.Arg347Trp). Both had MAF<0.001 and are predicted to be pathogenic in silico. Both patients showed a phenotype with predominant language impairment, suggestive of non-fluent progressive aphasia.

CONCLUSION

We show that thoroughly studied patients without other known genetic changes harbour TP73 rare variants, which are pathogenic in silico. This adds evidence to the role of TP73 in the ALS-FTD spectrum and especially in primary progressive aphasia cases.

SYT7 acts as an oncogene and a potential therapeutic target and was regulated by ΔNp63α in HNSCC

Background

Head and neck squamous cell carcinoma (HNSCC) are one of the most common types of head and neck cancer, and it is urgent to find effective treatment for advanced patients. Exploring developing and progressing mechanisms of HNSCC could provide a theoretical basis to find new therapeutic targets.

Methods

In our research, we performed a whole-gene expression profile microarray analysis to identify differential expression genes between squamous cell carcinoma cells and ΔNp63 alpha (ΔNp63α) knockdown cells. As a result, an important gene Synaptotagmin VII (SYT7) was screened out.

Results

SYT7 knockdown affected the proliferation, apoptosis and cell cycle of squamous cell carcinoma cells. The rescue experiment in vitro with ΔNp63α and SYT7 double knockdown resulted in partial reversion of ΔNp63α-induced phenotypes. This was also confirmed by experiments in vivo.

Conclusions

Taken together, we found that ΔNp63α could inhibit the occurrence and progression of HNSCC throughout downregulating the expression of SYT7. Therefore, SYT7/ΔNp63α axis could be a potential therapeutic target for clinical treatment of HNSCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02394-w.

A Balancing Act: p53 Activity from Tumor Suppression to Pathology and Therapeutic Implications

TP53, encoding the p53 transcription factor, is the most frequently mutated tumor suppressor gene across all human cancer types. While p53 has long been appreciated to induce antiproliferative cell cycle arrest, apoptosis, and senescence programs in response to diverse stress signals, various studies in recent years have revealed additional important functions for p53 that likely also contribute to tumor suppression, including roles in regulating tumor metabolism, ferroptosis, signaling in the tumor microenvironment, and stem cell self-renewal/differentiation. Not only does p53 loss or mutation cause cancer, but hyperactive p53 also drives various pathologies, including developmental phenotypes, premature aging, neurodegeneration, and side effects of cancer therapies. These findings underscore the importance of balanced p53 activity and influence our thinking of how to best develop cancer therapies based on modulating the p53 pathway. Expected final online publication date for the Annual Review of Pathology: Mechanisms of Disease, Volume 17 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Mechanisms of Functional Pleiotropy of p73 in Cancer and Beyond

The transcription factor p73 is a structural and functional homolog of TP53, the most famous and frequently mutated tumor-suppressor gene. The TP73 gene can synthesize an overwhelming number of isoforms via splicing events in 5′ and 3′ ends and alternative promoter usage. Although it originally came into the spotlight due to the potential of several of these isoforms to mimic p53 functions, it is now clear that TP73 has its own unique identity as a master regulator of multifaceted processes in embryonic development, tissue homeostasis, and cancer. This remarkable functional pleiotropy is supported by a high degree of mechanistic heterogeneity, which extends far-beyond the typical mode of action by transactivation and largely relies on the ability of p73 isoforms to form protein–protein interactions (PPIs) with a variety of nuclear and cytoplasmic proteins. Importantly, each p73 isoform carries a unique combination of functional domains and residues that facilitates the establishment of PPIs in a highly selective manner. Herein, we summarize the expanding functional repertoire of TP73 in physiological and oncogenic processes. We emphasize how TP73’s ability to control neurodevelopment and neurodifferentiation is co-opted in cancer cells toward neoneurogenesis, an emerging cancer hallmark, whereby tumors promote their own innervation. By further exploring the canonical and non-canonical mechanistic patterns of p73, we apprehend its functional diversity as the result of a sophisticated and coordinated interplay of: (a) the type of p73 isoforms (b) the presence of p73 interaction partners in the cell milieu, and (c) the architecture of target gene promoters. We suppose that dysregulation of one or more of these parameters in tumors may lead to cancer initiation and progression by reactivating p73 isoforms and/or p73-regulated differentiation programs thereof in a spatiotemporally inappropriate manner. A thorough understanding of the mechanisms supporting p73 functional diversity is of paramount importance for the efficient and precise p73 targeting not only in cancer, but also in other pathological conditions where TP73 dysregulation is causally involved.

Exploiting ubiquitin ligase cereblon as a target for small-molecule compounds in medicine and chemical biology

Cereblon (CRBN), originally identified as a gene associated with intellectual disability, was identified as primary target of thalidomide. Accumulating evidence has shown that CRBN is a substrate receptor of Cullin Ring E3 ubiquitin ligase 4 (CRL4) containing DDB1, CUL4, and RBX1, which recognizes specific neosubstrates in the presence of thalidomide or its analogs and induces their ubiquitination and proteasomal degradation. A set of small-molecule, CRBN-binding drugs are known as molecular glue degraders because these compounds promote the interaction between CRBN and its neosubstrates. Moreover, CRBN-based proteolysis-targeting chimeras, heterobifunctional molecules hijacking CRBN and inducing degradation of proteins of interest, have emerged as a promising modality in drug development and are being actively investigated. Meanwhile, the original functions and regulations of CRBN are still largely elusive. In this review, we describe key findings surrounding CRBN since its discovery and then discuss a few unanswered issues.

Mechanisms of TP53 Pathway Inactivation in Embryonic and Somatic Cells-Relevance for Understanding (Germ Cell) Tumorigenesis

The P53 pathway is the most important cellular pathway to maintain genomic and cellular integrity, both in embryonic and non-embryonic cells. Stress signals induce its activation, initiating autophagy or cell cycle arrest to enable DNA repair. The persistence of these signals causes either senescence or apoptosis. Over 50% of all solid tumors harbor mutations in TP53 that inactivate the pathway. The remaining cancers are suggested to harbor mutations in genes that regulate the P53 pathway such as its inhibitors Mouse Double Minute 2 and 4 (MDM2 and MDM4, respectively). Many reviews have already been dedicated to P53, MDM2, and MDM4, while this review additionally focuses on the other factors that can deregulate P53 signaling. We discuss that P14^ARF (ARF) functions as a negative regulator of MDM2, explaining the frequent loss of ARF detected in cancers. The long non-coding RNA Antisense Non-coding RNA in the INK4 Locus (ANRIL) is encoded on the same locus as ARF, inhibiting ARF expression, thus contributing to the process of tumorigenesis. Mutations in tripartite motif (TRIM) proteins deregulate P53 signaling through their ubiquitin ligase activity. Several microRNAs (miRNAs) inactivate the P53 pathway through inhibition of translation. CCCTC-binding factor (CTCF) maintains an open chromatin structure at the TP53 locus, explaining its inactivation of CTCF during tumorigenesis. P21, a downstream effector of P53, has been found to be deregulated in different tumor types. This review provides a comprehensive overview of these factors that are known to deregulate the P53 pathway in both somatic and embryonic cells, as well as their malignant counterparts (i.e., somatic and germ cell tumors). It provides insights into which aspects still need to be unraveled to grasp their contribution to tumorigenesis, putatively leading to novel targets for effective cancer therapies.

Cereblon-Based Small-Molecule Compounds to Control Neural Stem Cell Proliferation in Regenerative Medicine

Thalidomide, a sedative drug that was once excluded from the market owing to its teratogenic properties, was later found to be effective in treating multiple myeloma. We had previously demonstrated that cereblon (CRBN) is the target of thalidomide embryopathy and acts as a substrate receptor for the E3 ubiquitin ligase complex, Cullin-Ring ligase 4 (CRL4^CRBN) in zebrafish and chicks. CRBN was originally identified as a gene responsible for mild intellectual disability in humans. Fetuses exposed to thalidomide in early pregnancy were at risk of neurodevelopmental disorders such as autism, suggesting that CRBN is involved in prenatal brain development. Recently, we found that CRBN controls the proliferation of neural stem cells in the developing zebrafish brain, leading to changes in brain size. Our findings imply that CRBN is involved in neural stem cell growth in humans. Accumulating evidence shows that CRBN is essential not only for the teratogenic effects but also for the therapeutic effects of thalidomide. This review summarizes recent progress in thalidomide and CRBN research, focusing on the teratogenic and therapeutic effects. Investigation of the molecular mechanisms underlying the therapeutic effects of thalidomide and its derivatives, CRBN E3 ligase modulators (CELMoDs), reveals that these modulators provide CRBN the ability to recognize neosubstrates depending on their structure. Understanding the therapeutic effects leads to the development of a novel technology called CRBN-based proteolysis-targeting chimeras (PROTACs) for target protein knockdown. These studies raise the possibility that CRBN-based small-molecule compounds regulating the proliferation of neural stem cells may be developed for application in regenerative medicine.

Tp63-expressing adult epithelial stem cells cross lineages boundaries revealing latent hairy skin competence

The formation of hair follicles, a landmark of mammals, requires complex mesenchymal–epithelial interactions and it is commonly believed that embryonic epidermal cells are the only cells that can respond to hair follicle morphogenetic signals in vivo. Here, we demonstrate that epithelial stem cells of non-skin origin (e.g. that of cornea, oesophagus, vagina, bladder, prostate) that express the transcription factor Tp63, a master gene for the development of epidermis and its appendages, can respond to skin morphogenetic signals. When exposed to a newborn skin microenvironment, these cells express hair-follicle lineage markers and contribute to hair follicles, sebaceous glands and/or epidermis renewal. Our results demonstrate that lineage restriction is not immutable and support the notion that all Tp63-expressing epithelial stem cells, independently of their embryonic origin, have latent skin competence explaining why aberrant hair follicles or sebaceous glands are sometimes observed in non-skin tissues (e.g. in cornea, vagina or thymus).

Adult stem cells are thought to be fate restricted to lineages distinct to their tissue of origin. Here, the authors demonstrate that Tp63 expressing epithelial stem cells from several disparate tissues can respond to skin morphogenetic signals and contribute to hair follicles, sebaceous glands and/or epidermis.

Analysis of expression of p53, p63 and proliferating cell nuclear antigen proteins in odontogenic keratocyst: An immunohistochemical study

Background:

Odontogenic keratocyst (OKC) is a benign intraosseous lesions (within the jaw bone) of odontogenic origin that account for about 10% of jaw cysts. They are characterized by an aggressive behavior with a relatively high recurrence rate. Early diagnosis and follow-up of the patient with OKC is important because the possibility of such patient there is develop to other features of Nevoid basal cell carcinoma syndrome in future. Considering the roles and effects of p53, p63 and proliferating cell nuclear antigen (PCNA) in cells proliferation, this study was designed.

Objectives:

To understand the behavior of epithelial cells in pathogenesis and biological aspects of OKC in diagnosis.

Materials and Methods:

Immunohistochemical (IHC)technique was performed in 21 cases of OKCs.

Results:

Immunological stained p53 cells were mainly located in the suprabasal layers. p63 and PCNA-positive cells were found throughout the lining epithelium including basal and suprabasal cell layers. The intensity of staining was more in p63 and PCNA than the p53 expression of the cystic epithelial lining.

Conclusions:

It is possible that the biological behavior of OKCs may be related to the suprabasal proliferative compartment in the cystic epithelium as observed. These proteins may participate in the regulation of epithelial cell differentiation. Taken together, these data may favor tumerigenesis on OKCs.

Mdm2: Open questions

The Mdm2 oncoprotein and its association with p53 were discovered 30 years ago, and a cornucopia of activities and regulatory pathways have been associated with it. In this review, we will raise questions about Mdm2 and its cousin Mdm4 that we consider worth pursuing in future research, reaching from molecular structures and intracellular activities all the way to development, evolution, and cancer therapy. We anticipate that such research will not only close a few gaps in our knowledge but could add new dimensions to our current view. This compilation of questions contributes to the preparation for the 10th Mdm2 Workshop in Tokyo.

Molecular Mechanisms of the Teratogenic Effects of Thalidomide

Thalidomide was sold worldwide as a sedative over 60 years ago, but it was quickly withdrawn from the market due to its teratogenic effects. Thalidomide was later found to have therapeutic effects in several diseases, although the molecular mechanisms remained unclear. The discovery of cereblon (CRBN), the direct target of thalidomide, a decade ago greatly improved our understanding of its mechanism of action. Accumulating evidence has shown that CRBN functions as a substrate of Cullin RING E3 ligase (CRL4^CRBN), whose specificity is controlled by ligands such as thalidomide. For example, lenalidomide and pomalidomide, well-known thalidomide derivatives, degrade the neosubstrates Ikaros and Aiolos, resulting in anti-proliferative effects in multiple myeloma. Recently, novel CRBN-binding drugs have been developed. However, for the safe handling of thalidomide and its derivatives, a greater understanding of the mechanisms of its adverse effects is required. The teratogenic effects of thalidomide occur in multiple tissues in the developing fetus and vary in phenotype, making it difficult to clarify this issue. Recently, several CRBN neosubstrates (e.g., SALL4 (Spalt Like Transcription Factor 4) and p63 (Tumor Protein P63)) have been identified as candidate mediators of thalidomide teratogenicity. In this review, we describe the current understanding of molecular mechanisms of thalidomide, particularly in the context of its teratogenicity.

Central giant cell granuloma: A clinicopathological and immunohistochemical study of macrophages, blood vessels, lymphatic vessels and regulatory proteins

OBJECTIVE

This study seeks to investigate immunohistochemical parameters that could distinguish non-aggressive Central giant cell granuloma (CGCG) from aggressive CGCG, two groups of lesions which differ in their clinical and radiographic features and prognosis.

MATERIAL AND METHODS

12 cases of non-aggressive CGCG and 11 cases of aggressive CGCG were investigated and associated the immunohistochemical expression of macrophages (CD68 and CD163), blood vessels (CD34 and CD105), lymphatic vessels (D2-40) and regulator proteins (p63 and Ki-67). Clinical and radiographic features were also studied.

RESULTS

Associations between all proteins in non-aggressive and aggressive CGCG were not significant (p > 0.05). With respect to non-aggressive CGCG, there were no significant correlations, while in aggressive CGCG there was a significant positive correlation between CD68 and CD163 (p = 0.031), between CD34 and D2-40 proteins (p = 0.04), whereas a significant negative correlation was observed between CD105 and CD68 (p = 0.040). However, regardless of aggressiveness of CGCG, there was a significant positive correlation between CD68 and CD163 (p = 0,04). Among the clinical and immunohistochemical aspects, only the symptomatology was a significant risk factor for the occurrence of aggressive CGCG (OR = 12.00/p = 0.016).

CONCLUSION

Macrophages and angiogenesis contribute to their maintenance and development of CGCG. In addition, immunohistochemistry used here was not able to differentiate their aggressiveness. However, symptomatology was proved to be a risk factor for the occurrence of aggressive CGCG. It is possible that clinical features, particularly symptomatology, represent the most appropriate parameter to attempt to distinguish GCCG.

PABPN1, a Target of p63, Modulates Keratinocyte Differentiation through Regulation of p63α mRNA Translation

p63 is expressed from two promoters and produces two N-terminal isoforms, TAp63 and ΔNp63. Alternative splicing creates three C-terminal isoforms p63α, p63β, and p63δ, whereas alternative polyadenylation (APA) in coding sequence creates two more C-terminal isoforms p63γ and p63ε. Although several transcription factors have been identified to differentially regulate the N-terminal p63 isoforms, it is unclear how the C-terminal p63 isoforms are regulated. Thus, we determined whether PABPN1, a key regulator of APA, may differentially regulate the C-terminal p63 isoforms. We found that PABPN1 deficiency increases p63γ mRNA through APA in coding sequence. We also found that PABPN1 is necessary for p63α translation by modulating the binding of translation initiation factors eIF4E and eIF4G to p63α mRNA. Moreover, we found that the p53 family, especially p63α, regulates PABPN1 transcription, suggesting that the mutual regulation between p63 and PABPN1 forms a feedback loop. Furthermore, we found that PABPN1 deficiency inhibits keratinocyte cell growth, which can be rescued by ectopic ΔNp63α. Finally, we found that PABPN1 controls the terminal differentiation of HaCaT keratinocytes by modulating ΔNp63α expression. Taken together, our findings suggest that PABPN1 is a key regulator of the C-terminal p63 isoforms through APA in coding sequence and mRNA translation and that the p63-PABPN1 loop modulates p63 activity and the APA landscape.

Molecular mechanisms of thalidomide and its derivatives

Thalidomide, originally developed as a sedative drug, causes multiple defects due to severe teratogenicity, but it has been re-purposed for treating multiple myeloma, and derivatives such as lenalidomide and pomalidomide have been developed for treating blood cancers. Although the molecular mechanisms of thalidomide and its derivatives remained poorly understood until recently, we identified cereblon (CRBN), a primary direct target of thalidomide, using ferrite glycidyl methacrylate (FG) beads. CRBN is a ligand-dependent substrate receptor of the E3 ubiquitin ligase complex cullin-RING ligase 4 (CRL4^CRBN). When a ligand such as thalidomide binds to CRBN, it recognizes various 'neosubstrates' depending on the shape of the ligand. CRL4^CRBN binds many neosubstrates in the presence of various ligands. CRBN has been utilized in a novel protein knockdown technology named proteolysis targeting chimeras (PROTACs). Heterobifunctional molecules such as dBET1 are being developed to specifically degrade proteins of interest. Herein, we review recent advances in CRBN research.

Characterization of p53 Family Homologs in Evolutionary Remote Branches of Holozoa

The p53 family of transcription factors plays key roles in development, genome stability, senescence and tumor development, and p53 is the most important tumor suppressor protein in humans. Although intensively investigated for many years, its initial evolutionary history is not yet fully elucidated. Using bioinformatic and structure prediction methods on current databases containing newly-sequenced genomes and transcriptomes, we present a detailed characterization of p53 family homologs in remote members of the Holozoa group, in the unicellular clades Filasterea, Ichthyosporea and Corallochytrea. Moreover, we show that these newly characterized homologous sequences contain domains that can form structures with high similarity to the human p53 family DNA-binding domain, and some also show similarities to the oligomerization and SAM domains. The presence of these remote homologs demonstrates an ancient origin of the p53 protein family.

The specific seroreactivity to ∆Np73 isoforms shows higher diagnostic ability in colorectal cancer patients than the canonical p73 protein

The p53-family is tightly regulated at transcriptional level. Due to alternative splicing, up to 40 different theoretical proteoforms have been described for p73 and at least 20 and 10 for p53 and p63, respectively. However, only the canonical proteins have been evaluated as autoantibody targets in cancer patients for diagnosis. In this study, we have cloned and expressed in vitro the most upregulated proteoforms of p73, ΔNp73α and ΔNp73β, for the analysis of their seroreactivity by a developed luminescence based immunoassay test using 145 individual plasma from colorectal cancer, premalignant individuals and healthy controls. ∆Np73α seroreactivity showed the highest diagnostic ability to discriminate between groups. The combination of ∆Np73α, ∆Np73β and p73 proteoforms seroreactivity were able to improve their individual diagnostic ability. Competitive inhibition experiments further demonstrated the presence of unique specific epitopes in ΔNp73 isoforms not present in p73, with several colorectal patients showing unique and specific seroreactivity to the ΔNp73 proteoforms. Overall, we have increased the complexity of the humoral immune response to the p53-family in cancer patients, showing that the proteoforms derived from the alternative splicing of p73 possess a higher diagnostic ability than the canonical protein, which might be extensive for p53 and p63 proteins.

p73 regulates epidermal wound healing and induced keratinocyte programming

p63 is a transcriptional regulator of ectodermal development that is required for basal cell proliferation and stem cell maintenance. p73 is a closely related p53 family member that is expressed in select p63-positive basal cells and can heterodimerize with p63. p73-/- mice lack multiciliated cells and have reduced numbers of basal epithelial cells in select tissues; however, the role of p73 in basal epithelial cells is unknown. Herein, we show that p73-deficient mice exhibit delayed wound healing despite morphologically normal-appearing skin. The delay in wound healing is accompanied by decreased proliferation and increased levels of biomarkers of the DNA damage response in basal keratinocytes at the epidermal wound edge. In wild-type mice, this same cell population exhibited increased p73 expression after wounding. Analyzing single-cell transcriptomic data, we found that p73 was expressed by epidermal and hair follicle stem cells, cell types required for wound healing. Moreover, we discovered that p73 isoforms expressed in the skin (ΔNp73) enhance p63-mediated expression of keratinocyte genes during cellular reprogramming from a mesenchymal to basal keratinocyte-like cell. We identified a set of 44 genes directly or indirectly regulated by ΔNp73 that are involved in skin development, cell junctions, cornification, proliferation, and wound healing. Our results establish a role for p73 in cutaneous wound healing through regulation of basal keratinocyte function.

The p53 gene family in vertebrates: Evolutionary considerations

The origin of the p53 gene family predates multicellular life since TP53 members of this gene family have been found in unicellular eukaryotes. In invertebrates one or two genes attributable to a TP53-like or TP63/73-like gene are present. The radiation into three genes, TP53, TP63, and TP73, has been reported as a vertebrate invention. TP53 is considered the "guardian of the genome" given its role in protecting cells against the DNA damage and cellular stressors. TP63 and TP73 play a role in epithelial development and neurogenesis, respectively. The evolution of the p53 gene family has been the subject of considerable analyses even if several questions remain still open. In this study we addressed the evolutionary history of the p53 gene family in vertebrates performing an extended microsyntenic investigation coupled with a phylogenetic analysis, together with protein domain organization and structure assessment. On the basis of our results we discussed a possible evolutionary scenario according to which a TP53/63/73 ancestor form gave rise to the current TP53 and a TP63/73 form, which in turn independently duplicated into two genes in agnathe and gnathostome lineages.

Contrasting Patterns of Rapid Molecular Evolution within the p53 Network across Mammal and Sauropsid Lineages

Cancer is a threat to multicellular organisms, yet the molecular evolution of pathways that prevent the accumulation of genetic damage has been largely unexplored. The p53 network regulates how cells respond to DNA-damaging stressors. We know little about p53 network molecular evolution as a whole. In this study, we performed comparative genetic analyses of the p53 network to quantify the number of genes within the network that are rapidly evolving and constrained, and the association between lifespan and the patterns of evolution. Based on our previous published data set, we used genomes and transcriptomes of 34 sauropsids and 32 mammals to analyze the molecular evolution of 45 genes within the p53 network. We found that genes in the network exhibited evidence of positive selection and divergent molecular evolution in mammals and sauropsids. Specifically, we found more evidence of positive selection in sauropsids than mammals, indicating that sauropsids have different targets of selection. In sauropsids, more genes upstream in the network exhibited positive selection, and this observation is driven by positive selection in squamates, which is consistent with previous work showing rapid divergence and adaptation of metabolic and stress pathways in this group. Finally, we identified a negative correlation between maximum lifespan and the number of genes with evidence of divergent molecular evolution, indicating that species with longer lifespans likely experienced less variation in selection across the network. In summary, our study offers evidence that comparative genomic approaches can provide insights into how molecular networks have evolved across diverse species.

The Roles of P53 and Its Family Proteins, P63 and P73, in the DNA Damage Stress Response in Organogenesis-Stage Mouse Embryos

Members of the P53 transcription factor family, P53, P63, and P73, play important roles in normal development and in regulating the expression of genes that control apoptosis and cell cycle progression in response to genotoxic stress. P53 is involved in the DNA damage response pathway that is activated by hydroxyurea in organogenesis-stage murine embryos. The extent to which P63 and P73 contribute to this stress response is not known. To address this question, we examined the roles of P53, P63, and P73 in mediating the response of Trp53-positive and Trp53-deficient murine embryos to a single dose of hydroxyurea (400 mg/kg) on gestational day 9. Hydroxyurea treatment downregulated the expression of Trp63 and upregulated Trp73 in the absence of effects on the levels of Trp53 transcripts; Trp73 upregulation was P53-dependent. At the protein level, hydroxyurea treatment increased the levels and phosphorylation of P53 in the absence of effects on P63 and P73. Upregulation of the expression of genes that regulate cell cycle arrest and apoptosis, Cdkn1a, Rb1, Fas, Trp53inp1, and Pmaip1, was P53-dependent in hydroxyurea-treated embryos. The increase in cleaved caspase-3 and cleaved mammalian sterile-20-like-1 kinase levels induced by hydroxyurea was also P53-dependent; in contrast, the increase in phosphorylated H2AX, a marker of DNA double-strand breaks, in response to hydroxyurea treatment was only partially P53-dependent. Together, our data show that P53 is the principal P53 family member that is activated in the embryonic DNA damage response.

TAp73-induced phosphofructokinase-1 transcription promotes the Warburg effect and enhances cell proliferation

The Warburg effect is a prominent metabolic feature associated with neoplastic diseases; however, the underlying mechanism remains incompletely understood. TAp73, a structural homolog of the tumor suppressor p53, is frequently overexpressed in human tumors, indicating a proliferative advantage that it can confer to tumor cells. Here we show that TAp73 stimulates the expression of phosphofructokinase-1, liver type (PFKL), which catalyzes the committed step in glycolysis. Through this regulation, TAp73 enhances glucose consumption and lactate excretion, promoting the Warburg effect. By activating PFKL, TAp73 also increases ATP production and bolsters anti-oxidant defense. TAp73 deficiency results in a pronounced reduction in tumorigenic potential, which can be rescued by forced PFKL expression. These findings establish TAp73 as a critical regulator of glycolysis and reveal a mechanism by which tumor cells achieve the Warburg effect to enable oncogenic growth.

TAp73 is a structural homolog of the tumor suppressor p53. Here they show that TAp73 is critical for promoting glycolysis as it stimulates the transcriptional expression of liver type of phosphofructokinase-1 (PFKL), which catalyzes the committed step in glycolysis.

Neuro- and nephroprotective effect of grape seed proanthocyanidin extract against carboplatin and thalidomide through modulation of inflammation, tumor suppressor protein p53, neurotransmitters, oxidative stress and histology

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Carboplatin and thalidomide induced neuro-nephrotoxicity.

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Carboplatin and thalidomide caused inflammation.

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Carboplatin and thalidomide upregulate tumor suppressor protein p53.

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Carboplatin and thalidomide disturbed cytokine production.

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Neuro-and nephroprotective effect of grape seed proanthocyanidin.

The combination of thalidomide and carboplatin is one of the most potent chemotherapeutic strategies for the treatment of cancer. However, limited studies have been conducted on the neurotoxicity and nephrotoxicity of both chemotherapeutic agents. The aim of our study was to assess the toxicity of thalidomide and carboplatin combination on brain and kidney and investigate the protective effect of grape seed proanthocyanidin extract (GSPE). Thalidomide and carboplatin induced up-regulation of the expression of p53, tumor necrosis factor-α and interleukin-6 in brain and kidney. Acetylcholinesterase, dopamine and serotonin were decreased and norepinephrine was increased. Thiobarbituric acid reactive substances, nitric oxide, lipid profile, bilirubin and creatinine were elevated, while antioxidants enzymes (GST, GPX, CAT and SOD), total antioxidant capacity and the levels of glutathione were decreased. A microscopic examination showed shrinkage of capillaries, degeneration with pyknotic nuclei, loss of normal structure and neuronal degeneration. GSPE co-treatment with thalidomide and carboplatin reduced their brain and renal damage, oxidative stress, diminished cytokines, p53, neurotransmitters and biochemical parameters, and inhibited brain and renal cell apoptosis. It can be concluded that, the protective effects of GSPE against thalidomide and carboplatin induced-brain and renal damage was associated with the minimization of oxidative stress.

p53: emerging roles in stem cells, development and beyond

Most human cancers harbor mutations in the gene encoding p53. As a result, research on p53 in the past few decades has focused primarily on its role as a tumor suppressor. One consequence of this focus is that the functions of p53 in development have largely been ignored. However, recent advances, such as the genomic profiling of embryonic stem cells, have uncovered the significance and mechanisms of p53 functions in mammalian cell differentiation and development. As we review here, these recent findings reveal roles that complement the well-established roles for p53 in tumor suppression.

Dependence of p53-deficient cells on the DHX9 DExH-box helicase

DHX9 is a DExH-box helicase family member with key regulatory roles in a broad range of cellular processes. It participates at multiple levels of gene regulation, including DNA replication, transcription, translation, RNA transport, and microRNA processing. It has been implicated in tumorigenesis and recent evidence suggests that it may be a promising chemotherapeutic target. Previous studies have determined that DHX9 suppression elicits an apoptotic or senescence response by activating p53 signaling. Here, we show that DHX9 inhibition can also have deleterious effects in cells lacking functional p53. Loss of DHX9 led to increased cell death in p53-deficient mouse lymphomas and HCT116 human colon cancer cells, and G0/G1 cell cycle arrest in p53-deficient mouse embryonic fibroblasts. Analysis of mRNA levels for p53 transcriptional targets showed that a subset of p53 targets in the p53-null lymphomas and HCT116 cells were activated despite the absence of functional p53. This implies an alternative pathway of DHX9-mediated activation of cell death and cell cycle arrest in p53-deficient cells and supports the feasibility of targeting DHX9 in p53-deficient tumors.

Suppression of PKC causes oncogenic stress for triggering apoptosis in cancer cells

Gain of functional mutations in ras occurs in more than 30% of human malignancies and in particular 90% of pancreatic cancer. Mutant ras, via activating multiple effector pathways, not only promote cell growth or survival, but also apoptosis, depending upon cell types or circumstances. In order to further study the mechanisms of apoptosis induced by oncogenic ras, we employed the ras loop mutant genes and demonstrated that Akt functioned downstream of Ras in human pancreatic cancer or HPNE cells ectopically expressing mutated K-ras for the induction of apoptosis after the concurrent suppression of PKC α and β. In this apoptotic process, the redox machinery was aberrantly switched on in the pancreatic cancer cells as well as prostate cancer DU145 cells. p73 was phosphorylated and translocated to the nucleus, accompanied with UPR activation and induction of apoptosis. The in vitro results were corroborated by the in vivo data. Thus, our study indicated that PKC α and β appeared coping with oncogenic Ras or mutated Akt to maintain the balance of the homeostasis in cancer cells. Once these PKC isoforms were suppressed, the redox state in the cancer cells was disrupted, which elicited persistent oncogenic stress and subsequent apoptotic crisis.

Epstein-Barr Virus Gene BARF1 Expression is Regulated by the Epithelial Differentiation Factor ΔNp63α in Undifferentiated Nasopharyngeal Carcinoma

Epstein-Barr Virus (EBV) BamHI-A rightward frame 1 (BARF1) protein is considered a viral oncogene in epithelial cells and has immune-modulating properties. During viral lytic replication BARF1 is expressed as an early gene, regulated by the immediate early EBV protein R. However, in viral latency BARF1 is exclusively expressed in epithelial tumors such as nasopharyngeal (NPC) and gastric carcinoma (GC) but not in lymphomas, indicating that activation of the BARF1 promoter is cell type specific. Undifferentiated NPC is characterized by high expression of ΔNp63 isoforms of the epithelial differentiation marker p63, a member of the p53 family of transcription factors. Transcription factor binding site analysis indicated potential p53 family binding sites within the BARF1 promoter region. This study investigated ability of various p53 family members to transactivate the BARF1 promoter. Using BARF1 promoter luciferase reporter constructs we demonstrate that only p63 isoform ΔNp63α is capable of transactivating the BARF1 promoter, but not the TAp63 isoforms, p53 or p73. Direct promoter binding of ΔNp63α was confirmed by Chromatin Immune Precipitation (ChIP) analysis. Deletion mutants of the BARF1 promoter revealed multiple ΔNp63 response elements to be responsible for BARF1 promoter transactivation. However, ΔNp63α alone was not sufficient to induce BARF1 in tumor cells harboring full EBV genomes, indicating that additional cofactors might be required for full BARF1 regulation. In conclusion, in EBV positive NPC and GC, BARF1 expression might be induced by the epithelial differentiation marker ΔNp63α, explaining BARF1 expression in the absence of lytic reactivation.

The Rbm38-p63 feedback loop is critical for tumor suppression and longevity

The RNA-binding protein Rbm38 is a target of p63 tumor suppressor and can in-turn repress p63 expression via mRNA stability. Thus, Rbm38 and p63 form a negative feedback loop. To investigate the biological significance of the Rbm38-p63 loop in vivo, a cohort of WT, Rbm38^-/-, TAp63^+/-, and Rbm38^-/-;TAp63^+/- mice were generated and monitored throughout their lifespan. While mice deficient in Rbm38 or TAp63 alone died mostly from spontaneous tumors, compound Rbm38^-/-;TAp63^+/- mice had an extended lifespan along with reduced tumor incidence. We also found that loss-of-Rbm38 markedly decreased the percentage of liver steatosis in TAp63^+/- mice. Moreover, we found that Rbm38 deficiency extends the lifespan of tumor-free TAp63^+/- mice along with reduced expression of senescence-associated biomarkers. Consistent with this, Rbm38^-/-;TAp63^+/- MEFs were resistant, whereas Rbm38^-/- or TAp63^+/- MEFs were prone, to cellular senescence. Importantly, we showed that the levels of inflammatory cytokines (IL17D and Tnfsf15) were significantly reduced by Rbm38 deficiency in senescence-resistant Rbm38^-/-;TAp63^+/- mouse livers and MEFs. Together, our data suggest that Rbm38 and p63 function as intergenic suppressors in aging and tumorigenesis and that the Rbm38-p63 loop may be explored for enhancing longevity and cancer management.

Role of the Inferior Alveolar Nerve in Rodent Lower Incisor Stem Cells

In developing teeth, the sequential and reciprocal interactions between epithelial and mesenchymal tissues promote stem/progenitor cell differentiation. However, the origin of the stem/progenitor cells has been the subject of considerable debate. According to recent studies, mesenchymal stem cells originate from periarterial cells and are regulated by neurons in various organs. The present study examined the role of innervation in tooth development and rodent incisor stem/progenitor cell homeostasis. Rodent incisors continuously grow throughout their lives, and the lower incisors are innervated by the inferior alveolar nerve (IAN). In this study, we resected the IAN in adult rats, and the intact contralateral side served as a nonsurgical control. Sham control rats received the same treatment as the resected rats, except for the resection process. The extent of incisor eruption was measured, and both mesenchymal and epithelial stem/progenitor cells were visualized and compared between the IAN-resected and sham-operated groups. One week after surgery, the IAN-resected incisors exhibited a chalky consistency, and the eruption rate was decreased. Micro–computed tomography and histological analyses performed 4 wk after surgery revealed osteodentin formation, disorganized ameloblast layers, and reduced enamel thickness in the IAN-resected incisors. Immunohistochemical analysis revealed a reduction in the CD90- and LRIG1-positive mesenchymal cell ratio in the IAN-resected incisors. However, the p40-positive epithelial stem/progenitor cell ratio was comparable between the 2 groups. Thus, mesenchymal stem/progenitor cell homeostasis is more related to IAN innervation than to epithelial stem/progenitor cells. Furthermore, sensory nerve innervation influences subsequent incisor growth and formation.

Identification of a novel microRNA-mRNA regulatory biomodule in human prostate cancer

Our recent study identified a list of differentially expressed microRNAs (miRNAs) in human prostate cancer (PCa) tissues compared to adjacent benign prostate tissues. In the current study, to identify the crucial miRNA-mRNA regulatory biomodule involved into prostate carcinogenesis based on the previous miRNA expression profile in PCa, we proposed an integrated systematic approach which combined miRNA-mediated gene expression regulatory network analysis, experimental validations in vitro and in vivo, as well as clinical significance evaluation. As a result, the CCND1-RNASEL-CDKN1A-TP73-MDM2-UBE2I axis was identified as a bottleneck in the miRNA-mediated gene expression regulatory network of PCa according to network topological analysis. The direct binding relationship between TP73 and PCa downregulated miR-193a-5p, and the direct binding relationship between UBE2I and PCa upregulated miR-188-5p were both experimentally validated. In addition, miR-193a-5p had a more significant regulatory effect on the tumor promoter isoform of TP73-deltaNp73 than on the tumor suppressive isoform of TP73-TAp73. Importantly, the deregulation of either the miR-193a-5p-TP73 or miR-188-5p-UBE2I axes was significantly associated with aggressive progression and poor prognosis in PCa patients. Gain- and loss-of-function experiments showed that miR-193a-5p efficiently inhibited in vitro PCa cell proliferation, migration, and invasion, and in vivo tumor growth, and markedly induced PCa cell apoptosis via regulating TP73 with a corresponding suppression of the CCND1-RNASEL-CDKN1A-MDM2 axis. In contrast, miR-188-5p exerted its tumor promoter roles through targeting UBE2I with a subsequent activation of the CCND1-RNASEL-CDKN1A-MDM2 axis. Taken together, this integrated analysis revealed the potential roles of the miR-193a-5p/TP73 and miR-188-5p/UBE2i negative regulation pairs in PCa. In addition to the significant clinical relevance, miR-193a-5p- and miR-188-5p-regulated CCND1-RNASEL-CDKN1A-TP73-MDM2-UBE2I signaling may be a novel regulatory biomodule in prostate carcinogenesis.

Pulmonary Basaloid Squamous Cell Carcinoma in a Dog

A 9-year-old neutered male crossbred dog with a 4-week history of progressive vestibulocerebellar signs was presented for necropsy examination. Gross examination revealed neoplastic growth in the lungs, thoracic lymph nodes, left kidney and cerebellum. Microscopically, the tumour consisted of an infiltrative, densely cellular, basaloid epithelial neoplastic growth with extensive areas of abrupt keratinization. Immunohistochemically, neoplastic cells expressed p63 and partially expressed cytokeratins 5/6. Based on these findings, the tumour was diagnosed as a primary pulmonary basaloid squamous cell carcinoma (BSSC) with metastasis to regional lymph nodes, kidney and brain. As far as the authors are aware, this is the first description of BSCC in an animal species.

Identification and characterization of the intercellular adhesion molecule-2 gene as a novel p53 target

The p53 tumor suppressor inhibits cell growth through the activation of both cell cycle arrest and apoptosis, which maintain genome stability and prevent cancer development. Here, we report that intercellular adhesion molecule-2 (ICAM2) is transcriptionally activated by p53. Specifically, ICAM2 is induced by the p53 family and DNA damage in a p53-dependent manner. We identified a p53 binding sequence located within the ICAM2 gene that is responsive to wild-type p53, TAp73, and TAp63. In terms of function, we found that the ectopic expression of ICAM2 inhibited cancer cell migration and invasion. In addition, we demonstrated that silencing endogenous ICAM2 in cancer cells caused a marked increase in extracellular signal-regulated kinase (ERK) phosphorylation levels, suggesting that ICAM2 inhibits migration and invasion of cancer cells by suppressing ERK signaling. Moreover, ICAM2 is underexpressed in human cancer tissues containing mutant p53 as compared to those with wild-type p53. Notably, the decreased expression of ICAM2 is associated with poor survival in patients with various cancers. Our findings demonstrate that ICAM2 induction by p53 has a key role in inhibiting migration and invasion.

How does p53 induce apoptosis and how does this relate to p53-mediated tumour suppression?

The tumour suppressor gene TP53 is mutated in ~50% of human cancers. In addition to its function in tumour suppression, p53 also plays a major role in the response of malignant as well as nontransformed cells to many anticancer therapeutics, particularly those that cause DNA damage. P53 forms a homotetrameric transcription factor that is reported to directly regulate ~500 target genes, thereby controlling a broad range of cellular processes, including cell cycle arrest, cell senescence, DNA repair, metabolic adaptation and cell death. For a long time, induction of apoptotic death in nascent neoplastic cells was regarded as the principal mechanism by which p53 prevents tumour development. This concept has, however, recently been challenged by the findings that in striking contrast to Trp53-deficient mice, gene-targeted mice that lack the critical effectors of p53-induced apoptosis do not develop tumours spontaneously. Remarkably, even mice lacking all mediators critical for p53-induced apoptosis, G1/S boundary cell cycle arrest and cell senescence do not develop any tumours spontaneously. In this review we discuss current understanding of the mechanisms by which p53 induces cell death and how this affects p53-mediated tumour suppression and the response of malignant cells to anticancer therapy.

Unifying the p73 knockout phenotypes: TAp73 orchestrates multiciliogenesis

This outlook discusses Nemajerova et al.’s finding that p73 plays a novel role in regulating motile ciliogenesis and pulmonary function.

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.

p53 and TAp63 participate in the recombination-dependent pachytene arrest in mouse spermatocytes

To protect germ cells from genomic instability, surveillance mechanisms ensure meiosis occurs properly. In mammals, spermatocytes that display recombination defects experience a so-called recombination-dependent arrest at the pachytene stage, which relies on the MRE11 complex—ATM—CHK2 pathway responding to unrepaired DNA double-strand breaks (DSBs). Here, we asked if p53 family members—targets of ATM and CHK2—participate in this arrest. We bred double-mutant mice combining a mutation of a member of the p53 family (p53, TAp63, or p73) with a Trip13 mutation. Trip13 deficiency triggers a recombination-dependent response that arrests spermatocytes in pachynema before they have incorporated the testis-specific histone variant H1t into their chromatin. We find that deficiency for either p53 or TAp63, but not p73, allowed spermatocytes to progress further into meiotic prophase despite the presence of numerous unrepaired DSBs. Even so, the double mutant spermatocytes apoptosed at late pachynema because of sex body deficiency; thus p53 and TAp63 are dispensable for arrest caused by sex body defects. These data affirm that recombination-dependent and sex body-deficient arrests occur via genetically separable mechanisms.

Meiosis is a specialized cell division that generates haploid gametes by halving chromosome content through two consecutive rounds of chromosome segregation. At the onset of the first meiotic division, SPO11 protein introduces double-strand breaks (DSBs) throughout the genome. These DSBs are repaired through homologous recombination, which promotes pairing and synapsis of the homologous chromosomes. Some DSBs will become repaired as crossovers, providing a physical connection between the homologous chromosomes which promotes correct chromosome segregation. In fact, recombination defects can lead to formation of aneuploid gametes, one of the major causes of miscarriages and chromosome abnormalities in humans. To protect germ cells from genomic instability and to produce balanced gametes, surveillance mechanisms ensure that meiosis occurs properly. It is known that in the presence of unrepaired DSBs a control mechanism promotes a spermatogenic block at the pachytene stage. Here we describe that, downstream MRE11-ATM-CHK2 pathway, p53 and TAp63 are the effectors responsible for activating recombination-dependent arrest in mouse spermatocytes.

The Regulation of Tumor Suppressor p63 by the Ubiquitin-Proteasome System

The protein p63 has been identified as a homolog of the tumor suppressor protein p53 and is capable of inducing apoptosis, cell cycle arrest, or senescence. p63 has at least six isoforms, which can be divided into two major groups: the TAp63 variants that contain the N-terminal transactivation domain and the ΔNp63 variants that lack the N-terminal transactivation domain. The TAp63 variants are generally considered to be tumor suppressors involved in activating apoptosis and suppressing metastasis. ΔNp63 variants cannot induce apoptosis but can act as dominant negative inhibitors to block the function of TAp53, TAp73, and TAp63. p63 is rarely mutated in human tumors and is predominately regulated at the post-translational level by phosphorylation and ubiquitination. This review focuses primarily on regulation of p63 by the ubiquitin E-3 ligase family of enzymes via ubiquitination and proteasome-mediated degradation, and introduces a new key regulator of the p63 protein.

The E6-TAp63β-Dicer feedback loop involves in miR-375 downregulation and epithelial-to-mesenchymal transition in HR-HPV+ cervical cancer cells

MiR-375 has been recognized as an important tumor suppressor and is usually downregulated in cervical cancer. However, how it is downregulated in cervical cancer is not clear. By using cancerous and normal cervical tissues, we observed that miR-375 and Dicer are both downregulated and were positively correlated. Overexpression of miR-375 resulted in decreased viral E6 and increased Dicer expression in both Hela and SiHa cells. Previous studies suggest that E6 can induce an accelerated degradation of TAp63β, while TAp63 can bind to and transactivate the Dicer promoter, exerting a direct regulation on transcription of Dicer. In this study, we found that miR-375 overexpression restored TAp63β expression. TAp63β overexpression significantly enhanced transcription and translation of Dicer, which further led to increased mature miR-375 levels. Therefore, we infer that there is an E6-TAp63β-Dicer feedback loop involved in miR-375 dysregulation in cervical cancer. Besides, we observed that enforced TAp63β expression significantly reduced the mesenchymal markers including N-cadherin, Vimentin, Snail, and Slug but increased the epithelial marker E-cadherin in both Hela and SiHa cells. The wound healing assay also confirmed that TAp63β overexpression significantly suppressed cervical cancer cell migration potential. These results suggest that TAp63β can inhibit epithelial-to-mesenchymal transition (EMT) of cervical cancer cells.