Mice lacking the p53/p63 target gene Perp are resistant to papilloma development

AKT and PERP Show Higher Expression in Precancerous than in Malignant Skin Neoplasms: Profiling in an Animal Model of Sequential Skin Carcinogenesis

The primary aim of this study was to evaluate the activation of the PERP and Akt oncogenes in the induction of skin cancer in FVB/N mice by a stepwise chemical process. Forty four-week-old female FVB/N mice were randomly divided into a control group (n = 8) and two experimental groups (group A: n = 16, group B: n = 16). In the study, the groups were subjected to a two-stage carcinogenesis procedure. This consisted of an initial application of 97.4 nmol DMBA to shaved skin on the back, followed by applications of 32.4 nmol TPA after thirteen weeks for group A and after twenty weeks for group B. The control group received no treatment. Skin conditions were monitored weekly for tumor development. At the end of the experiment, the animals were euthanized for further tissue sampling. Examination of the skin lesions in the experimental groups showed a correlation with tumor progression, ranging from dysplasia to carcinoma. Tumor samples were examined both histologically and immunohistochemically. Notably, and PERP expression was higher in precancerous than in malignant tumors. The differences in expression between precancerous and benign tumors provide further evidence of a role for PERP and Akt in the transition from benign to malignant states. Our findings underscore the critical roles of PERP and Akt in the pathogenesis of skin cancer and suggest their potential as biomarkers for early detection and targets for therapeutic intervention.

Regulation of neural stem cell proliferation and survival by protein arginine methyltransferase 1

Protein arginine methyltransferase 1 (PRMT1), a major type I arginine methyltransferase in mammals, methylates histone and non-histone proteins to regulate various cellular functions, such as transcription, DNA damage response, and signal transduction. PRMT1 is highly expressed in neural stem cells (NSCs) and embryonic brains, suggesting that PRMT1 is essential for early brain development. Although our previous reports have shown that PRMT1 positively regulates oligodendrocyte development, it has not been studied whether PRMT1 regulates NSC proliferation and its survival during development. To examine the role of PRMT1 in NSC activity, we cultured NSCs prepared from embryonic mouse forebrains deficient in PRMT1 specific for NSCs and performed neurosphere assays. We found that the primary neurospheres of PRMT1-deficient NSCs were small and the number of spheres was decreased, compared to those of control NSCs. Primary neurospheres deficient in PRMT1 expressed an increased level of cleaved caspase-3, suggesting that PRMT1 deficiency-induced apoptosis. Furthermore, p53 protein was significantly accumulated in PRMT1-deficient NSCs. In parallel, p53-responsive pro-apoptotic genes including Pmaip1 and Perp were upregulated in PRMT1-deficient NSCs. p53-target p21 mRNA and its protein levels were shown to be upregulated in PRMT1-deficient NSCs. Moreover, the 5-bromo-2'-deoxyuridine (BrdU) incorporation assay showed that the loss of PRMT1 led to cell cycle defects in the embryonic NSCs. In contrast to the above in vitro observations, NSCs normally proliferated and survived in the fetal brains of NSC-specific PRMT1-deficient mice. We also found that Lama1, which encodes the laminin subunit α1, was significantly upregulated in the embryonic brains of PRMT1-deficient mice. These data implicate that extracellular factors provided by neighboring cells in the microenvironment gave a trophic support to NSCs in the PRMT1-deficient brain and recovered NSC activity to maintain brain homeostasis. Our study implies that PRMT1 plays a cell-autonomous role in the survival and proliferation of embryonic NSCs.

Anticachectic regulator analysis reveals Perp-dependent antitumorigenic properties of 3-methyladenine in pancreatic cancer

Approximately 80% of pancreatic cancer patients suffer from cachexia, and one-third die due to cachexia-related complications such as respiratory failure and cardiac arrest. Although there has been considerable research into cachexia mechanisms and interventions, there are, to date, no FDA-approved therapies. A major contributing factor for the lack of therapy options could be the failure of animal models to accurately recapitulate the human condition. In this study, we generated an aged model of pancreatic cancer cachexia to compare cachexia progression in young versus aged tumor-bearing mice. Comparative skeletal muscle transcriptome analyses identified 3-methyladenine (3-MA) as a candidate antiwasting compound. In vitro analyses confirmed antiwasting capacity, while in vivo analysis revealed potent antitumor effects. Transcriptome analyses of 3-MA-treated tumor cells implicated Perp as a 3-MA target gene. We subsequently (a) observed significantly higher expression of Perp in cancer cell lines compared with control cells, (b) noted a survival disadvantage associated with elevated Perp, and (c) found that 3-MA-associated Perp reduction inhibited tumor cell growth. Finally, we have provided in vivo evidence that survival benefits conferred by 3-MA administration are independent of its effect on tumor progression. Taken together, we report a mechanism linking 3-MA to Perp inhibition, and we further implicate Perp as a tumor-promoting factor in pancreatic cancer.

Novel function of PERP-428 variants impacts lung cancer risk through the differential regulation of PTEN/MDM2/p53-mediated antioxidant activity

Lung cancer is the leading cause of cancer-related deaths worldwide. Identifying genetic risk factors and understanding their mechanisms will help reduce lung cancer incidence. The p53 apoptosis effect is related to PMP-22 (PERP), a tetraspan membrane protein, and an apoptotic effector protein downstream of p53. Although historically considered a tumor suppressor, PERP is highly expressed in lung cancers. Stable knockdown of PERP expression induces CL1-5 and A549 lung cancer cell death, but transient knockdown has no effect. Interestingly, relative to the PERP-428GG genotype, PERP-428CC was associated with the highest lung cancer risk (OR = 5.38; 95% CI = 2.12-13.65, p < 0.001), followed by the PERP-428CG genotype (OR = 2.34; 95% CI = 1.55-3.55, p < 0.001). Ectopic expression of PERP-428G, but not PERP-428C, protects lung cancer cells against ROS-induced DNA damage. Mechanistically, PERP-428 SNPs differentially regulate p53 protein stability. p53 negatively regulates the expression of the antioxidant enzymes catalase (CAT) and glutathione reductase (GR), thereby modulating redox status. p53 protein stability is higher in PERP-428C-expressing cells than in PERP-428G-expressing cells because MDM2 expression is decreased and p53 Ser20 phosphorylation is enhanced in PERP-428C-expressing cells. The MDM2 mRNA level is decreased in PERP-428C-expressing cells via PTEN-mediated downregulation of the MDM2 constitutive p1 promoter. This study reveals that in individuals with PERP-428CC, CAT/GR expression is decreased via the PTEN/MDM2/p53 pathway. These individuals have an increased lung cancer risk. Preventive antioxidants and avoidance of ROS stressors are recommended to prevent lung cancer or other ROS-related chronic diseases.

PERP-ing into diverse mechanisms of cancer pathogenesis: Regulation and role of the p53/p63 effector PERP

The tetraspan plasma membrane protein PERP (p53 apoptosis effector related to PMP22) is a lesser-known transcriptional target of p53 and p63. A member of the PMP22/GAS3/EMP membrane protein family, PERP was originally identified as a p53 target specifically trans-activated during apoptosis, but not during cell-cycle arrest. Several studies have since shown downregulation of PERP expression in numerous cancers, suggesting that PERP is a tumour suppressor protein. This review focusses on the important advances made in elucidating the mechanisms regulating PERP expression and its function as a tumour suppressor in diverse human cancers, including breast cancer and squamous cell carcinoma. Investigating PERP's role in clinically-aggressive uveal melanoma has revealed that PERP engages a positive-feedback loop with p53 to regulate its own expression, and that p63 is required beside p53 to achieve pro-apoptotic levels of PERP in this cancer. Furthermore, the recent discovery of the apoptosis-mediating interaction of PERP with SERCA2b at the plasma membrane-endoplasmic reticulum interface demonstrates a novel mechanism of PERP stabilisation, and how PERP can mediate Ca²⁺ signalling to facilitate apoptosis. The multi-faceted role of PERP in cancer, involving well-documented functions in mediating apoptosis and cell-cell adhesion is discussed, alongside PERP's emerging roles in epithelial-mesenchymal transition, and PERP crosstalk with inflammation signalling pathways, and other signalling pathways. The potential for restoring PERP expression as a means of cancer therapy is also considered.

Pilot study of loss of the p53/p63 target gene PERP at the surgical margin as a potential predictor of local relapse in head and neck squamous cell carcinoma

BACKGROUND

PERP (p53 apoptosis effector related to PMP22) localizes to desmosomes and suppresses squamous cell carcinoma development. Loss of PERP leads to worse local control in head and neck squamous cell carcinoma (HNSCC), likely by destabilizing desmosomes. We evaluated PERP loss at HNSCC surgical margins as a predictor of local relapse.

METHODS

Combining discovery (n = 17) and validation (n = 31) cohorts, we examined membranous PERP protein expression by immunohistochemistry in surgical mucosal margins with competing risk analysis of the relationship between local relapse and PERP expression.

RESULTS

Of the 44 analyzable patients, the 2-year cumulative incidence of local relapse was 44.4% for the PERP-negative group and 16.4% for the PERP-positive group (P = .01). A trend toward worse progression-free survival (P = .09) and overall survival (P = .06) was observed with loss of PERP.

CONCLUSIONS

PERP loss at surgical margins is associated with higher risk of local recurrence in HNSCC, warranting further evaluation in a larger prospective study.

The Spatiotemporal Pattern and Intensity of p53 Activation Dictates Phenotypic Diversity in p53-Driven Developmental Syndromes

Inappropriate activation of the p53 transcription factor contributes to numerous developmental syndromes characterized by distinct constellations of phenotypes. How p53 drives exquisitely specific sets of symptoms in diverse syndromes, however, remains enigmatic. Here, we deconvolute the basis of p53-driven developmental syndromes by leveraging an array of mouse strains to modulate the spatial expression pattern, temporal profile, and magnitude of p53 activation during embryogenesis. We demonstrate that inappropriate p53 activation in the neural crest, facial ectoderm, anterior heart field, and endothelium induces distinct spectra of phenotypes. Moreover, altering the timing and degree of p53 hyperactivation substantially affects the phenotypic outcomes. Phenotypes are associated with p53-driven cell-cycle arrest or apoptosis, depending on the cell type, with gene expression programs, rather than extent of mitochondrial priming, largely governing the specific response. Together, our findings provide a critical framework for decoding the role of p53 as a mediator of diverse developmental syndromes.

The potential role of circRNA_004229 in hair/epidermal regulation after MED1 ablation in keratinocytes

Background/Aims: Mediator complex subunit 1 (MED1) is an important transcriptional co-activator involved in multiple signaling pathways. Previous studies indicated an essential role of MED1 in hair cycling and wound repair through regulating the transcription of mRNAs. Circular RNAs (circRNAs), as a novel class of non-coding RNAs, are involved in various skin biological functions. Our study aimed to investigate the circRNAs expression profile in MED1 epidermal conditional knockout mice (KO), and provide potential candidates as well as the mechanism underlying the circRNAs regulation in both hair follicles and epidermis. Method: Microarray based circRNA expression was determined in MED1 KO mice and wild type mice (WT). The expression level was further confirmed by qRT-PCR. We predicted a possible interaction network of circRNA/microRNA/mRNA by bioinformatics and constructed them with Cytoscape software. Expression of several candidate target mRNAs was verified using qRT-PCR. A TUNEL assay was performed to assess the apoptosis level of MED1 KO and WT skin. Results: Here we identified 109 (34-up, 75-down) distinct circRNAs through microarrays that are differently expressed in MED1 KO mice compared with WT mice (FC > 2 and p-value < 0.05), suggesting a potential role of circRNAs in epidermal regulation. Among these circRNAs, circRNA_004229 was found to decrease significantly after MED1 deletion. The most likely potential targets miRNA for circRNA_004229 include miR-149-5p and miR-207, which possibly further impede the expression of their target mRNA, Tnfrsf19 and Perp, respectively. Apoptosis was suppressed in MED1 KO mice, which implies a potential role of circRNAs in regulating epidermal biological processes including apoptosis. Conclusion: Our study determined the expression profile of circRNAs in MED1 KO skin, and provided hints that circRNA_004229 might be involved in the regulation of keratinocytes in both hair follicles and interfollicular epidermis through a ceRNA mechanism.

We demonstrated that circRNA_004229 might inhibit apoptosis through binding miR-207 and miR-149-5p after MED1 deletion in keratinocytes.

Cancer Stem Cells: Emergent Nature of Tumor Emergency

A functional analysis of 167 genes overexpressed in Krebs-2 tumor initiating cells was performed. In the first part of the study, the genes were analyzed for their belonging to one or more of the three groups, which represent the three major phenotypic manifestation of malignancy of cancer cells, namely (1) proliferative self-sufficiency, (2) invasive growth and metastasis, and (3) multiple drug resistance. 96 genes out of 167 were identified as possible contributors to at least one of these fundamental properties. It was also found that substantial part of these genes are also known as genes responsible for formation and/or maintenance of the stemness of normal pluri-/multipotent stem cells. These results suggest that the malignancy is simply the ability to maintain the stem cell specific genes expression profile, and, as a consequence, the stemness itself regardless of the controlling effect of stem niches. In the second part of the study, three stress factors combined into the single concept of "generalized cellular stress," which are assumed to activate the expression of these genes, were defined. In addition, possible mechanisms for such activation were identified. The data obtained suggest the existence of a mechanism for the de novo formation of a pluripotent/stem phenotype in the subpopulation of "committed" tumor cells.

Mutations in PERP Cause Dominant and Recessive Keratoderma

Investigation of genetic determinants of Mendelian skin disorders has substantially advanced understanding of epidermal biology. Here we show that mutations in PERP, encoding a crucial component of desmosomes, cause both dominant and recessive human keratoderma. Heterozygosity for a C-terminal truncation, which produces a protein that appears to be unstably incorporated into desmosomes, causes Olmsted syndrome with severe periorificial and palmoplantar keratoderma in multiple unrelated kindreds. Homozygosity for an N-terminal truncation ablates expression and causes widespread erythrokeratoderma, with expansion of epidermal differentiation markers. Both exhibit epidermal hyperproliferation, immature desmosomes lacking a dense midline observed via electron microscopy, and impaired intercellular adhesion upon mechanical stress. Localization of other desmosomal components appears normal, which is in contrast to other conditions caused by mutations in genes encoding desmosomal proteins. These discoveries highlight the essential role of PERP in human desmosomes and epidermal homeostasis and further expand the heterogeneous spectrum of inherited keratinization disorders.

Neat-en-ing up our understanding of p53 pathways in tumor suppression

Although the p53 transcription factor has a well-established role in tumor suppression, little is known about how the non-coding targets of p53 mediate its tumor suppression function. Analysis of ncRNAs regulated by p53 revealed Neat1 as a direct p53 target gene. Neat1 has physiological roles in the development and differentiation of the mammary gland and corpus luteum, but its roles in cancer have been conflicting. To unequivocally understand Neat1 function in cancer, we used Neat1 null mice. Interestingly, we found that Neat1 deficiency promotes transformation both in oncogene-expressing fibroblasts and in a mouse model for pancreatic cancer. Specifically, Neat1 loss in the pancreas results in the enhanced development of preneoplastic lesions associated with dampened expression of differentiation genes. While the exact mechanisms underlying tumor suppression are unknown, there are several described mechanisms that may be responsible for Neat1-mediated tumor suppression. Collectively, these findings suggest that Neat1 enforces differentiation to suppress pancreatic cancer.

New insights into the pathogenesis of bladder exstrophy-epispadias complex

Bladder exstrophy-epispadias complex (BEEC) is a complex and debilitating congenital disease. Familial and twin studies suggest a possible genetic component in BEEC pathogenesis. Bladder mesenchyme (detrusor) development requires induction by a signal from bladder urothelium, and we and others have shown the Shh-Gli-Bmp4 signalling pathway is likely to be involved. P63 is a master regulator in epithelial stratification and is expressed in urothelium. We have shown that p63 knock-out mice undergo excessive urothelial apoptosis. Failure of mesenchymal induction by epithelium leads to BEEC. We further demonstrated that insertion/deletion (in/del) polymorphisms (1 base pair (bp) ins and 4 bp ins., and 12 bp del) in the ΔNP63 promoter reduce transcriptional efficiency, and are associated with a statistically significant increase in the risk of BEEC in humans. Furthermore, a Genome-Wide Expression Profiling (GWEP) study suggests possible involvement of PERP in human BEEC. Intriguingly, PERP is a direct target of p63 during development, and is also involved in epithelial stratification. PERP co-localizes with desmosome, and both PERP and desmosome are essential for maintaining tissue integrity by cellular adhesion and epithelial stratification. A recent study showed that PERP and desmosome expression levels are abnormal in human BEEC patients. This review describes the role of the P63 > PERP > desmosome pathway in the development of human bladder during embryogenesis. We hypothesize that disruption of this pathway may increase the risk of BEEC.

Loss of the p53/p63 target PERP is an early event in oral carcinogenesis and correlates with higher rate of local relapse

BACKGROUND

PERP is a p53/p63-regulated gene encoding a desmosomal protein that plays a critical role in cell-cell adhesion and tumor suppression.

STUDY DESIGN

We evaluated PERP expression in different grades of oral dysplasia (34 cases) and at different stages of invasive squamous cell carcinoma (SCC), and correlated the latter with clinical outcome. A tissue microarray consisting of nondysplastic mucosa, carcinoma in situ, SCC, and nodal metastases from 33 patients with human papilloma virus-negative SCC was stained for PERP and E-cadherin.

RESULTS

Complete loss of PERP expression was associated with worse local control in patients with SCC. The 5-year local control rate was 91% for patients with partial PERP loss versus 31% for those with complete loss (P = .01).

CONCLUSIONS

This is the first study to show that loss of PERP expression correlates with the transition to SCC and with increased local relapse in patients with oral cavity SCC.

Transmembrane protein PERP is a component of tessellate junctions and of other junctional and non-junctional plasma membrane regions in diverse epithelial and epithelium-derived cells

Protein PERP (p53 apoptosis effector related to PMP-22) is a small (21.4 kDa) transmembrane polypeptide with an amino acid sequence indicative of a tetraspanin character. It is enriched in the plasma membrane and apparently contributes to cell-cell contacts. Hitherto, it has been reported to be exclusively a component of desmosomes of some stratified epithelia. However, by using a series of newly generated mono- and polyclonal antibodies, we show that protein PERP is not only present in all kinds of stratified epithelia but also occurs in simple, columnar, complex and transitional epithelia, in various types of squamous metaplasia and epithelium-derived tumors, in diverse epithelium-derived cell cultures and in myocardial tissue. Immunofluorescence and immunoelectron microscopy allow us to localize PERP predominantly in small intradesmosomal locations and in variously sized, junction-like peri- and interdesmosomal regions ("tessellate junctions"), mostly in mosaic or amalgamated combinations with other molecules believed, to date, to be exclusive components of tight and adherens junctions. In the heart, PERP is a major component of the composite junctions of the intercalated disks connecting cardiomyocytes. Finally, protein PERP is a cobblestone-like general component of special plasma membrane regions such as the bile canaliculi of liver and subapical-to-lateral zones of diverse columnar epithelia and upper urothelial cell layers. We discuss possible organizational and architectonic functions of protein PERP and its potential value as an immunohistochemical diagnostic marker.

Alterations in keratins and associated proteins during 4- Nitroquinoline-1-oxide induced rat oral carcinogenesis

Background:

Oral squamous cell carcinoma (OSCC) is the sixth largest group of malignancies globally and the single largest group of malignancies in the Indian subcontinent. Despite the advances in treatment and therapeutic modalities the five year survival rate of OSCC has not changed in the last few decades, and remains less than 40%. Several studies have focused on defining molecular markers that can either detect cancer at an early stage or can predict patient's outcome. However, such markers are still undefined. Keratins (K) are epithelia predominant intermediate filament proteins which are expressed in a differentiation dependent and site specific manner. Keratins are being used as biomarkers in different epithelial disorders including cancer. They are associated with desmoplakin and α6β4 integrin which are components of desmosomes and hemidesmosomes respectively.

Materials and Methods:

4-Nitroquinoline 1-Oxide (4NQO) was used as a carcinogen for the development of various stages of oral carcinogenesis in rat lingual mucosa. Two-Dimentional gel electrophoresis was performed for the separation of Keratins followed by western blotting for their specific identification. Western blotting and RT PCR was carried out for desmoplakin and α6β4 integrin respectively to understand their levels. Immunohistochemical analysis was carried out to further study the localization of desmoplakin and α6 integrin.

Results:

In this study we have analysed the alterations in Keratins and associated proteins during sequential stages of 4NQO induced rat oral carcinogenesis. Our results showed that the alterations primarily begin after the dysplastic changes in the lingual epithelium like the elevation of Keratins 5/6a, ectopic expression of Keratin 8, increase in suprabasal expression of α6 integrin and increase in desmoplakin levels. Most of these alterations persisted till the development of SCC except desmoplakin, the levels of which were downregulated in papillomatous lesions and SCC. Many of these alterations have also been documented in human oral carcinogensis.

Conclusion:

Thus, 4NQO model of rat lingual carcinogenesis reproduces majority of the changes that are seen in human oral carcinogenesis and it can be exploited for the development of biomarkers.

Unimpaired skin carcinogenesis in Desmoglein 3 knockout mice

The contribution of adherens junction inactivation, typically by downregulation or mutation of the transmembrane core component E-cadherin, to cancer progression is well recognized. In contrast, the role of the desmosomal cadherin components of the related cell-cell adhesion junction, the desmosome, in cancer development has not been well explored. Here, we use mouse models to probe the functional role of desmosomal cadherins in carcinogenesis. Because mice lacking the desmosomal cadherin Desmoglein 3 (Dsg3) have revealed a crucial role for Dsg3 in cell-cell adhesion in stratified epithelia, we investigate the consequence of Dsg3 loss in two models of skin carcinogenesis. First, using Dsg3−/− keratinocytes, we show that these cells display adhesion defects in vitro and compromised tumor growth in allograft assays, suggesting that Dsg3 enables tumor formation in certain settings. In contrast, using an autochthonous model for SCC development in response to chronic UVB treatment, we discover a surprising lack of enhanced tumorigenesis in Dsg3−/− mice relative to controls, unlike mice lacking the desmosomal component Perp. Accordingly, there is no defect in the apoptotic response to UVB or enhanced immune cell infiltration upon Dsg3 loss that could promote tumorigenesis. Thus, Dsg3 does not display a clear function as a tumor suppressor in these mouse skin cancer models. Continued unraveling of the roles of Dsg3 and other desmosomal constituents in carcinogenesis in different contexts will be important for ultimately improving cancer diagnosis, prognostication, and treatment.

Digital transcriptome profiling of normal and glioblastoma-derived neural stem cells identifies genes associated with patient survival

Background

Glioblastoma multiforme, the most common type of primary brain tumor in adults, is driven by cells with neural stem (NS) cell characteristics. Using derivation methods developed for NS cells, it is possible to expand tumorigenic stem cells continuously in vitro. Although these glioblastoma-derived neural stem (GNS) cells are highly similar to normal NS cells, they harbor mutations typical of gliomas and initiate authentic tumors following orthotopic xenotransplantation. Here, we analyzed GNS and NS cell transcriptomes to identify gene expression alterations underlying the disease phenotype.

Methods

Sensitive measurements of gene expression were obtained by high-throughput sequencing of transcript tags (Tag-seq) on adherent GNS cell lines from three glioblastoma cases and two normal NS cell lines. Validation by quantitative real-time PCR was performed on 82 differentially expressed genes across a panel of 16 GNS and 6 NS cell lines. The molecular basis and prognostic relevance of expression differences were investigated by genetic characterization of GNS cells and comparison with public data for 867 glioma biopsies.

Results

Transcriptome analysis revealed major differences correlated with glioma histological grade, and identified misregulated genes of known significance in glioblastoma as well as novel candidates, including genes associated with other malignancies or glioma-related pathways. This analysis further detected several long non-coding RNAs with expression profiles similar to neighboring genes implicated in cancer. Quantitative PCR validation showed excellent agreement with Tag-seq data (median Pearson r = 0.91) and discerned a gene set robustly distinguishing GNS from NS cells across the 22 lines. These expression alterations include oncogene and tumor suppressor changes not detected by microarray profiling of tumor tissue samples, and facilitated the identification of a GNS expression signature strongly associated with patient survival (P = 1e-6, Cox model).

Conclusions

These results support the utility of GNS cell cultures as a model system for studying the molecular processes driving glioblastoma and the use of NS cells as reference controls. The association between a GNS expression signature and survival is consistent with the hypothesis that a cancer stem cell component drives tumor growth. We anticipate that analysis of normal and malignant stem cells will be an important complement to large-scale profiling of primary tumors.

Loss of the p53/p63 regulated desmosomal protein Perp promotes tumorigenesis

Dysregulated cell–cell adhesion plays a critical role in epithelial cancer development. Studies of human and mouse cancers have indicated that loss of adhesion complexes known as adherens junctions contributes to tumor progression and metastasis. In contrast, little is known regarding the role of the related cell–cell adhesion junction, the desmosome, during cancer development. Studies analyzing expression of desmosome components during human cancer progression have yielded conflicting results, and therefore genetic studies using knockout mice to examine the functional consequence of desmosome inactivation for tumorigenesis are essential for elucidating the role of desmosomes in cancer development. Here, we investigate the consequences of desmosome loss for carcinogenesis by analyzing conditional knockout mice lacking Perp, a p53/p63 regulated gene that encodes an important component of desmosomes. Analysis of Perp-deficient mice in a UVB-induced squamous cell skin carcinoma model reveals that Perp ablation promotes both tumor initiation and progression. Tumor development is associated with inactivation of both of Perp's known functions, in apoptosis and cell–cell adhesion. Interestingly, Perp-deficient tumors exhibit widespread downregulation of desmosomal constituents while adherens junctions remain intact, suggesting that desmosome loss is a specific event important for tumorigenesis rather than a reflection of a general change in differentiation status. Similarly, human squamous cell carcinomas display loss of PERP expression with retention of adherens junctions components, indicating that this is a relevant stage of human cancer development. Using gene expression profiling, we show further that Perp loss induces a set of inflammation-related genes that could stimulate tumorigenesis. Together, these studies suggest that Perp-deficiency promotes cancer by enhancing cell survival, desmosome loss, and inflammation, and they highlight a fundamental role for Perp and desmosomes in tumor suppression. An understanding of the factors affecting cancer progression is important for ultimately improving the diagnosis, prognostication, and treatment of cancer.

Changes in tissue architecture, such as loss of adhesion between cells, have been shown to facilitate cancer development, especially metastasis where cells can detach from a tumor and spread throughout the body. While various studies have demonstrated that inactivation of an adhesion complex known as the adherens junction promotes cancer development and metastasis, little is known about the role of the desmosome—a related cell–cell adhesion complex—in tumorigenesis. Here we examine the consequence of desmosome-deficiency for tumor development by studying mice lacking a key component of desmosomes in the skin, a protein known as Perp. Using a mouse model for human skin cancer, in which ultraviolet light promotes skin cancer development, we demonstrate that Perp-deficiency indeed leads to accelerated skin tumorigenesis. We similarly observe that PERP is lost during human skin cancer development, suggesting that PERP is also important as a tumor suppressor in humans. These findings demonstrate that desmosome-deficiency achieved by Perp inactivation can promote cancer and suggest the potential utility of monitoring PERP status for staging, prognostication, or treatment of human cancers.

p53 regulates metanephric development

p53 is best known as a tumor suppressor that regulates cell-cycle, differentiation, and apoptosis pathways, but its potential role in embryonic development and organogenesis remains controversial. Here, p53(-/-) embryos bred on C57Bl6 background exhibited a spectrum of congenital abnormalities of the kidney and urinary tract, including ureteric bud (UB) ectopia, double ureters/collecting systems, delayed primary branching of the UB, and hypoplastic metanephroi. We observed ectopic UB outgrowth from the Wolffian duct (WD) in one third of p53(-/-) embryos. The prevalence of duplex was higher in embryos than in neonates, and ex vivo organ culture suggested that ectopic ureters can regress over time, leaving behind a dysplastic pole ("segmental dysgenesis"). Transgenic expression of dominant negative p53 or conditional inactivation of p53 in the UB but not in the metanephric mesenchyme lineage recapitulated the duplex phenotype. Mechanistically, p53 inactivation in the WD associated with enhanced sensitivity to glial cell line-derived neurotrophic factor (GDNF)-induced ectopic budding and potentiated phosphatidylinositol-3 kinase activation by GDNF in UB cells. Unlike several other models of UB ectopia, hypersensitivity of p53(-/-) WD to GDNF is not accompanied by reduced Sprouty-1 or anterior expansion of the GDNF domain. In summary, our data lend support for a restrictive role for p53 activity in UB outgrowth from the WD.

PERP, a p53 proapoptotic target, mediates apoptotic cell death in renal ischemia

The p53 tumor suppressor gene plays a crucial role in mediating apoptotic cell death in renal ischemia-reperfusion injury (IRI). To further elucidate the p53-dependent pathway, we investigated the role of the p53 apoptosis effector related to PMP-22 (PERP), an apoptosis-associated p53 transcriptional target. PERP mRNA and protein are highly induced in the outer medullary proximal tubular cells (PTC) of ischemic kidneys postreperfusion at 3, 12, and 24 h in a p53-dependent manner. In PTC, overexpression of PERP augmented the rate of apoptosis following hypoxia by inducing mitochondrial permeability and subsequent release of cytochrome c, apoptosis-inducing factor (AIF), and caspase 9 activation. In addition, silencing of the PERP gene with short hairpin RNA prevented apoptosis in hypoxia-mediated injury by precluding mitochondrial dysfunction and consequent cytochrome c and AIF translocation. These data suggest that PERP is a key effector of p53-mediated apoptotic pathways and is a potential therapeutic target for renal IRI.

Plakophilin3 downregulation leads to a decrease in cell adhesion and promotes metastasis

Plakophilin3 is a desmosomal plaque protein whose levels are reduced in poorly differentiated tumors of the oropharyngeal cavity and in invasive colon carcinomas. To test the hypothesis that plakophilin3 loss stimulates neoplastic progression, plakophilin3 expression was inhibited by DNA vector driven RNA interference in 3 epithelial cell lines, HCT116, HaCaT and fetal buccal mucosa. The plakophilin3-knockdown clones showed a decrease in cell-cell adhesion as assessed in a hanging drop assay, which was accompanied by an increase in cell migration. The HCT116 plakophilin3-knockdown clones showed a decrease in desmosome size as revealed by electron microscopy. These altered desmosomal properties were accompanied by colony formation in soft agar and growth to high density in culture. The HCT116-derived clones showed accelerated tumor formation in nude mice and increased metastasis to the lung, a phenotype consistent with the increased migration observed in vitro and is consistent with data from human tumors that suggests that plakophililn3 is lost in invasive and metastatic tumors. These data indicate that plakophilin3 loss leads to a decrease in cell-cell adhesion leading to the stimulation of neoplastic progression and metastasis.

Mouse skin chemical carcinogenesis is inhibited by antizyme in promotion-sensitive and promotion-resistant genetic backgrounds

Elevated polyamine content and increased ornithine decarboxylase (ODC) activity have been associated with neoplastic growth in numerous animal models and human tissues. Antizyme (AZ) is a negative regulator of polyamine metabolism that inhibits ODC activity, stimulates ODC degradation, and suppresses polyamine uptake. Preliminary evidence, obtained from transgenic mice with tissue specific overexpression of AZ indicates that tumor development can be suppressed by AZ. To extend these studies, we have examined the effect of keratin 5 (K5)- or K6-driven AZ transgenes on 7,12-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) chemical carcinogenesis of the skin, in promotion-resistant C57BL/6 and promotion-sensitive DBA/2 mice. On both genetic backgrounds, K6-AZ mice showed a reduction in tumor multiplicity, with 85% fewer tumors than wild-type controls on the C57BL/6 background and 50% fewer tumors on the DBA/2 background. K5-AZ mice developed 50% fewer tumors than controls on both backgrounds. The percent of mice with tumors and tumor size were also reduced in the K5-AZ and K6-AZ groups. Tumor and TPA-treated skin sections from K6-AZ mice exhibited the strongest AZ expression, with localization mainly in suprabasal keratinocytes. K6-AZ mice also had slightly reduced cell proliferation rates in tumors and TPA-treated skin. The lack of a more pronounced effect on cell proliferation is probably explained by the observation that AZ staining did not colocalize with proliferating cell nuclear antigen (PCNA), a marker for the proliferative compartment. These studies demonstrate a tumor-suppressive effect of AZ in C57BL/6 and DBA/2 mice, and confirm the importance of ODC and polyamines in tumor development.

Expression of p53-induced apoptosis effector PERP in primary uveal melanomas: downregulation is associated with aggressive type

Expression of PERP (p53 apoptosis effector related to PMP-22) was investigated in primary uveal melanomas and its variation was analyzed in relation to clinico-pathological and cytogenetical characteristics of these tumors. The transcriptional level of PERP gene was measured by quantitative real-time RT-PCR in 26 uveal melanomas with known chromosomes 3 and 8 status. PERP protein levels were assessed by Western blot analysis of 22 fresh-frozen tumors and by immunohistochemical analysis of 16 paraffin-embedded tumor specimens. Differential expression of PERP was identified in primary choroidal melanoma specimens, both at transcriptional and protein level. Reduced PERP mRNA level was significantly associated with monosomy 3 (two-way ANOVA and t-test, p=0.004) but not with gains in chromosome 8. Transcriptional downregulation of PERP did not present a statistically significant association with ciliary body involvement, size, PAS-positive loops or cell type. Immunoblotting and immunohistochemistry further demonstrated significantly reduced PERP protein level in monosomy 3 melanomas, as compared with disomy 3 tumors. The altered expression of PERP highlighted this apoptosis-specific target of p53 as a possible contributor to apoptosis in uveal melanoma with PERP downregulation being particularly relevant to the aggressive (monosomy 3) type of uveal melanoma. As PERP is a novel type of p53 effector that is likely to stimulate apoptosis through a mechanism distinct from that of Bcl-2-related mitochondrial effectors, further elucidation of its role in uveal melanoma pathogenesis will assist in the design of novel therapeutic approaches aimed at increasing the rate of apoptosis in this tumor.

The requirement for perp in postnatal viability and epithelial integrity reflects an intrinsic role in stratified epithelia

Mice lacking the desmosome protein Perp exhibit blistering in their stratified epithelia and display postnatal lethality. However, it is unclear if these phenotypes are strictly related to Perp function in stratified epithelia, as Perp expression is not restricted to these tissues during embryogenesis, and certain desmosomal blistering diseases such as pemphigus vulgaris and pemphigus foliaceus have non-cell-intrinsic bases. Furthermore, we show here that Perp is expressed in the heart, raising the possibility that defects in heart function could account for lethality in the Perp-deficient mice. To determine conclusively if Perp function in stratified epithelia is crucial for postnatal survival and epithelial adhesion, we specifically ablated Perp in stratified epithelia by breeding conditional Perp knockout mice to keratin 5 (K5)-Cre transgenic mice. We found that the majority of mice lacking Perp in stratified epithelia die within 10 days after birth, accompanied by blistering and hyperproliferation in the epithelia, similar to the constitutive Perp null mice. Together, these findings indicate that Perp's requirement for both viability and epithelial integrity reflects a role in the stratified epithelial compartment.