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

Desmoplakin acts as a tumor suppressor by inhibition of the Wnt/β-catenin signaling pathway in human lung cancer

Desmosomes are intercellular junctions that confer strong cell-cell adhesion, thus conferring resistance against mechanical stress on epithelial tissues. A body of evidence indicates that decreased expression of desmosomal proteins is associated with poor prognosis in various cancers. As a key component of desmosomal plaque proteins, the functional role of desmoplakin (DSP) in cancer is not yet elucidated. Here, we reported the anti-tumorigenic activity of DSP in non-small cell lung cancer (NSCLC). We found by DSP DNA methylation that DSP expression was downregulated in 8 out of 11 lung cancer cell lines and in 34 out of 56 primary lung tumors . Ectopic expression of DSP in the NSCLC cell line H157 significantly inhibited cell proliferation, anchorage-independent growth, migration and invasion and also increased the sensitivity of NSCLC cells to apoptosis induced by an anticancer drug, gemcitabine. Furthermore, overexpression of DSP enhanced expression of plakoglobin (γ-catenin), resulting in decreased T-cell factor/lymphoid enhancer factor (TCF/LEF)-dependent transcriptional activity and reduced expression of the Wnt/β-catenin target genes Axin2 and matrix metalloproteinase MMP14. In accordance, DSP suppression by small interfering RNA resulted in downregulation of plakoglobin and upregulation of β-catenin and MMP14. Taken together, these data suggest that DSP is inactivated in lung cancer by an epigenetic mechanism, increases the sensitivity to anticancer drug-induced apoptosis and has tumor-suppressive function, possibly through inhibition of the Wnt/β-catenin signaling pathway in NSCLC cells. The epigenetic regulation of DSP and its ability to increase the sensitivity to anticancer drug-induced apoptosis has potential implications for clinical application.

Estimation of groin recurrence risk in patients with squamous cell vulvar carcinoma by the assessment of marker gene expression in the lymph nodes

Background

Regional lymph node (LN) status is a well-known prognostic factor for vulvar carcinoma (VC) patients. Although the reliable LN assessment in VC is crucial, it presents significant diagnostic problems. We aimed to identify specific mRNA markers of VC dissemination in the LN and to address the feasibility of predicting the risk of nodal recurrence by the patterns of gene expression.

Methods

Sentinel and inguinal LN samples from 20 patients who had undergone surgery for stage T_1-3, N_0-2, M₀ primary vulvar squamous cell carcinoma were analyzed. Gene expression profiles were assessed in four metastatic [LN(+)] and four histologically negative [LN(−)] lymph node samples obtained from four VC patients, by the Affymetrix U133 Plus 2.0 gene expression microarrays. Of the set of genes of the highest expression in the metastatic LNs compared to LN(−), seven candidate marker genes were selected: PERP, S100A8, FABP5, SFN, CA12, JUP and CSTA, and the expression levels of these genes were further analyzed by the real-time reverse transcription polymerase chain reaction (qRT-PCR) in 71 LN samples.

Results

All of the seven genes in question were significantly increased in LN(+) compared to LN(−) samples. In the initial validation of the seven putative markers of metastatic LN, the Cox proportional hazard model pointed to SFN, CA12 and JUP expression to significantly relate to the time to groin recurrence in VC patients.

Conclusions

Our findings first provided evidence that SFN, CA12 and JUP have a potential of marker genes for the prediction of the groin recurrence LN in VC patients.

Deficiency of the p53/p63 target Perp alters mammary gland homeostasis and promotes cancer

INTRODUCTION

Perp is a transcriptional target of both p53 during DNA damage-induced apoptosis and p63 during stratified epithelial development. Perp-/- mice exhibit postnatal lethality associated with dramatic blistering of the epidermis and oral mucosa, reflecting a critical role in desmosome-mediated intercellular adhesion in keratinocytes. However, the role of Perp in tissue homeostasis in other p63-dependent stratified epithelial tissues is poorly understood. Given that p63 is essential for proper mammary gland development and that cell adhesion is fundamental for ensuring the proper architecture and function of the mammary epithelium, here we investigate Perp function in the mammary gland.

METHODS

Immunofluorescence and Western blot analysis were performed to characterize Perp expression and localization in the mouse mammary epithelium throughout development. The consequences of Perp deficiency for mammary epithelial development and homeostasis were examined by using in vivo mammary transplant assays. Perp protein levels in a variety of human breast cancer cell lines were compared with those in untransformed cells with Western blot analysis. The role of Perp in mouse mammary tumorigenesis was investigated by aging cohorts of K14-Cre/+;p53fl/fl mice that were wild-type or deficient for Perp. Mammary tumor latency was analyzed, and tumor-free survival was assessed using Kaplan-Meier analysis.

RESULTS

We show that Perp protein is expressed in the mammary epithelium, where it colocalizes with desmosomes. Interestingly, although altering desmosomes through genetic inactivation of Perp does not dramatically impair mammary gland ductal development, Perp loss affects mammary epithelial homeostasis by causing the accumulation of inflammatory cells around mature mammary epithelium. Moreover, we show reduced Perp expression in many human breast cancer cell lines compared with untransformed cells. Importantly, Perp deficiency also promotes the development of mouse mammary cancer.

CONCLUSIONS

Together, these observations demonstrate an important role for Perp in normal mammary tissue function and in mammary cancer suppression. In addition, our findings highlight the importance of desmosomes in cancer suppression and suggest the merit of evaluating Perp as a potential prognostic indicator or molecular target in breast cancer therapy.

Suppression of hepatocyte proliferation by hepatocyte nuclear factor 4α in adult mice

Hepatocyte nuclear factor 4α (HNF4α) regulates genes involved in lipid and bile acid synthesis, gluconeogenesis, amino acid metabolism, and blood coagulation. In addition to its metabolic role, HNF4α is critical for hepatocyte differentiation, and loss of HNF4α is associated with hepatocellular carcinoma. The hepatocyte-specific Hnf4a knock-out mouse develops severe hepatomegaly and steatosis resulting in premature death, thereby limiting studies of the role of this transcription factor in the adult animal. In addition, gene compensation may complicate analysis of the phenotype of these mice. To overcome these issues, an acute Hnf4a knock-out mouse model was generated through use of the tamoxifen-inducible ErT2cre coupled to the serum albumin gene promoter. Microarray expression analysis revealed up-regulation of genes associated with proliferation and cell cycle control only in the acute liver-specific Hnf4α-null mouse. BrdU and ki67 staining confirmed extensive hepatocyte proliferation in this model. Proliferation was associated with induction of the hepatomitogen Bmp7 as well as reduced basal apoptotic activity. The p53/p63 apoptosis effector gene Perp was further identified as a direct HNF4α target gene. These data suggest that HNF4α maintains hepatocyte differentiation in the adult healthy liver, and its loss may directly contribute to hepatocellular carcinoma development, thus indicating this factor as a possible liver tumor suppressor gene.

PERP gene therapy attenuates lung cancer xenograft via inducing apoptosis and suppressing VEGF

Inducing apoptosis is an attractive antitumor strategy. PERP is an apoptosis-associated target of p53, and its activation alone is sufficient to induce apoptotic pathway leading to cell death. We have previously demonstrated that overexpression of PERP in tumor cell lines with low intrinsic PERP activity suppressed cancer cell growth and enhanced sensitivity to chemotherapeutical agents. We further identified that PERP was present in surgical normal lung tissue, but absent in cancerous tissue of the same patient. Here, we sought to investigate the anti-tumor effects of PERP gene therapy in vivo. Then nude mice were transplanted with p53-mutanted Anip973 human lung cancer xenografts and treated with normal saline, pcDNA3.1 (vector) and pcDNA3.1-PERP, respectively. Successful transfection and robust expression of PERP was detected. Treatment with pcDNA3.1-PERP increased apoptosis and retarded growth in the xenografts, which contributed to a 55% decrease in tumor volume compared with controls. Furthermore, PERP gene therapy activated pro-apoptotic Caspase-3 cascade and upregulated the expression of the second mitochondria-derived activator of caspase (Smac) and human TNF-related apoptosis-inducing ligand (TRAIL), while suppressed vascular endothelial growth factor (VEGF) expression, indicating apoptosis and anti-angiogenesis are involved in the inhibitory effect of the PERP gene therapy. Taken together, our results suggest PERP gene therapy may supply an alternative strategy for lung adenocarcinoma management. Furthermore, Anip973 is a p53-mutanted cell line and the findings of this study provide reference value for other p53-mutanted cancers which is common among malignant tumors.

Deconstructing p53 transcriptional networks in tumor suppression

p53 is a pivotal tumor suppressor that induces apoptosis, cell-cycle arrest and senescence in response to stress signals. Although p53 transcriptional activation is important for these responses, the mechanisms underlying tumor suppression have been elusive. To date, no single or compound mouse knockout of specific p53 target genes has recapitulated the dramatic tumor predisposition that characterizes p53-null mice. Recently, however, analysis of knock-in mice expressing p53 transactivation domain mutants has revealed a group of primarily novel direct p53 target genes that may mediate tumor suppression in vivo. We present here an overview of well-known p53 target genes and the tumor phenotypes of the cognate knockout mice, and address the recent identification of new p53 transcriptional targets and how they enhance our understanding of p53 transcriptional networks central for tumor suppression.

Cell-cell connectivity: desmosomes and disease

Cell-cell connectivity is an absolute requirement for the correct functioning of cells, tissues and entire organisms. At the level of the individual cell, direct cell-cell adherence and communication is mediated by the intercellular junction complexes: desmosomes, adherens, tight and gap junctions. A broad spectrum of inherited, infectious and auto-immune diseases can affect the proper function of intercellular junctions and result in either diseases affecting specific individual tissues or widespread syndromic conditions. A particularly diverse group of diseases result from direct or indirect disruption of desmosomes--a consequence of their importance in tissue integrity, their extensive distribution, complex structure, and the wide variety of functions their components accomplish. As a consequence, disruption of desmosomal assembly, structure or integrity disrupts not only their intercellular adhesive function but also their functions in cell communication and regulation, leading to such diverse pathologies as cardiomyopathy, epidermal and mucosal blistering, palmoplantar keratoderma, woolly hair, keratosis, epidermolysis bullosa, ectodermal dysplasia and alopecia. Here, as well as describing the importance of the other intercellular junctions, we focus primarily on the desmosome, its structure and its role in disease. We will examine the various pathologies that result from impairment of desmosome function and thereby demonstrate the importance of desmosomes to tissues and to the organism as a whole.

"Targeted disruption of the epithelial-barrier by Helicobacter pylori"

Helicobacter pylori colonizes the human gastric epithelium and induces chronic gastritis, which can lead to gastric cancer. Through cell-cell contacts the gastric epithelium forms a barrier to protect underlying tissue from pathogenic bacteria; however, H. pylori have evolved numerous strategies to perturb the integrity of the gastric barrier. In this review, we summarize recent research into the mechanisms through which H. pylori disrupts intercellular junctions and disrupts the gastric epithelial barrier.

Special AT-rich binding protein-2 (SATB2) differentially affects disease-causing p63 mutant proteins

p63, a p53 family member, is critical for proper skin and limb development and directly regulates gene expression in the ectoderm. Mice lacking p63 exhibit skin and craniofacial defects including cleft palate. In humans p63 mutations are associated with several distinct developmental syndromes. p63 sterile-α-motif domain, AEC (ankyloblepharon-ectodermal dysplasia-clefting)-associated mutations are associated with a high prevalence of orofacial clefting disorders, which are less common in EEC (ectrodactyly-ectodermal dysplasia-clefting) patients with DNA binding domain p63 mutations. However, the mechanisms by which these mutations differentially influence p63 function remain unclear, and interactions with other proteins implicated in craniofacial development have not been identified. Here, we show that AEC p63 mutations affect the ability of the p63 protein to interact with special AT-rich binding protein-2 (SATB2), which has recently also been implicated in the development of cleft palate. p63 and SATB2 are co-expressed early in development in the ectoderm of the first and second branchial arches, two essential sites where signaling is required for craniofacial patterning. SATB2 attenuates p63-mediated gene expression of perp (p53 apoptosis effector related to PMP-22), a critical downstream target gene during development, and specifically decreases p63 perp promoter binding. Interestingly, AEC but not EEC p63 mutations affect the ability of p63 to interact with SATB2 and the inhibitory effects of SATB2 on p63 transactivation of perp are most pronounced for AEC-associated p63 mutations. Our findings reveal a novel gain-of-function property of AEC-causing p63 mutations and identify SATB2 as the first p63 binding partner that differentially influences AEC and EEC p63 mutant proteins.

Desmosomes: new perpetrators in tumour suppression

Adherens junctions, which are intercellular adhesive complexes that are crucial for maintaining epithelial homeostasis, are downregulated in many cancers to promote tumour progression. However, the role of desmosomes - adhesion complexes that are related to adherens junctions - in carcinogenesis has remained elusive. Recent studies using mouse genetic approaches have uncovered a role for desmosomes in tumour suppression, demonstrating that desmosome downregulation occurs before that of adherens junctions to drive tumour development and early invasion, suggesting a two-step model of adhesion dysfunction in cancer progression.