Deregulated beta-catenin induces a p53- and ARF-dependent growth arrest and cooperates with Ras in transformation

Depletion of enhancer zeste homolog 2 (EZH2) directs transcription factors associated with T cell differentiation through epigenetic regulation of Yin Yang 1(YY1) in combating non-small cell lung cancer (NSCLC)

Non-Small Cell Lung Cancer (NSCLC) is the leading cause of death in all countries alike. In the current study, we have found out that Histone H3Lys4trimethylation is abnormal on YY1 in CD4⁺T Helper (T_H) cells of NSCLC patients which is evident by Histone H3Lys27 trimethylation mediated via EZH2. We investigated the status of Yin Yang 1 (YY1) and the involvement of certain transcription factors that lead to tumorigenesis after depleting endogenous EZH2 in vitro by CRISPR/Cas9 in the CD4⁺T_H1-or-T_H2-polarized cells isolated initially as CD4⁺T_H0 cells from the PBMC of the control subjects and patients suffering from NSCLC. After depletion of endogenous EZH2, RT-qPCR based mRNA expression analysis showed that there was an increase in the expression of T_H1 specific genes and a decrease in the expression of T_H2 specific genes in NSCLC patients CD4⁺T_H cells. We can conclude that this group of NSCLC patients may have the tendency at least in vitro to elucidate adaptive/protective immunity through the depletion of endogenous EZH2 along with the reduction in the expression of YY1. Moreover, depletion of EZH2 not only suppressed the CD4⁺CD25⁺FOXP3⁺Regulatory T cells (Treg) but also it aided the generation of CD8⁺Cytotoxic T Lymphocytes (CTL) which were involved in killing of the NSCLC cells. Thus the transcription factors involved in EZH2 mediated T cell differentiation linked to malignancies offers us an appealing avenue of targeted therapeutic intervention for NSCLC.

Multiple Actions of Telomerase Reverse Transcriptase in Cell Death Regulation

Telomerase reverse transcriptase (TERT), a core part of telomerase, has been known for a long time only for its telomere lengthening function by reverse transcription of RNA template. Currently, TERT is considered as an intriguing link between multiple signaling pathways. The diverse intracellular localization of TERT corresponds to a wide range of functional activities. In addition to the canonical function of protecting chromosome ends, TERT by itself or as a part of the telomerase complex participates in cell stress responses, gene regulation and mitochondria functioning. Upregulation of TERT expression and increased telomerase activity in cancer and somatic cells relate to improved survival and persistence of such cells. In this review, we summarize the data for a comprehensive understanding of the role of TERT in cell death regulation, with a focus on the interaction of TERT with signaling pathways involved in cell survival and stress response.

Molecular mechanisms of alveolar epithelial cell senescence and idiopathic pulmonary fibrosis: a narrative review

Background and Objective

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial pneumonia of unknown etiology. An increasing number of studies have reported that the incidence of IPF increases with age. Simultaneously, the number of senescent cells increased in IPF. Epithelial cell senescence, an important component of epithelial cell dysfunction, plays a key role in IPF pathogenesis. This article summarizes the molecular mechanisms associated with alveolar epithelial cell senescence and recent advances in the applications of drugs targeting pulmonary epithelial cell senescence to explore novel therapeutic approaches for the treatment of pulmonary fibrosis.

Methods

All literature published in English on PubMed, Web of Science, and Google Scholar were electronically searched online using the following keyword combinations: aging, alveolar epithelial cell, cell senescence, idiopathic pulmonary fibrosis, WNT/β-catenin, phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt), mammalian target of rapamycin (mTOR), and nuclear factor kappa B (NF-κB).

Key Content and Findings

We focused on signaling pathways associated with alveolar epithelial cell senescence in IPF, including WNT/β-catenin, PI3K/Akt, NF-κB, and mTOR signaling pathways. Some of these signaling pathways are involved in alveolar epithelial cell senescence by affecting cell cycle arrest and secretion of senescence-associated secretory phenotype-associated markers. We also found that changes in lipid metabolism in alveolar epithelial cells can be induced by mitochondrial dysfunction, both of which contribute to cellular senescence and development of IPF.

Conclusions

Decreasing senescent alveolar epithelial cells may be a promising strategy for the treatment of IPF. Therefore, further investigations into new treatments of IPF by applying inhibitors of relevant signaling pathways, as well as senolytic drugs, are warranted.

Black Ginseng Ameliorates Cellular Senescence via p53-p21/p16 Pathway in Aged Mice

Simple Summary

The goal of this study was to examine if BG impacts the aging process, specifically cellular senescence, using in vitro and aged mouse models. Primary mouse embryonic fibroblasts (MEFs) and aged mice (18 months old) showed that BG supplementation retarded cellular senescence. Of note, BG-supplemented aged mice had remarkedly altered hepatic genes involved in the aging process as it caused less activation of the canonical senescence pathway. These observations demonstrated that BG positively impacts the age-related phenotype by controlling the expression of cellular senescence in the liver and other metabolic organs such as skeletal muscle and white adipose tissue.

Abstract

Cellular senescence, one of the hallmarks of aging, refers to permanent cell cycle arrest and is accelerated during the aging process. Black ginseng (BG), prepared by a repeated steaming and drying process nine times from fresh ginseng (Panax ginseng C.A. Meyer), is garnering attention for herbal medicine due to its physiological benefits against reactive oxygen species (ROS), inflammation, and oncogenesis, which are common cues to induce aging. However, which key nodules in the cellular senescence process are regulated by BG supplementation has not been elucidated yet. In this study, we investigated the effects of BG on cellular senescence using in vitro and aged mouse models. BG-treated primary mouse embryonic fibroblasts (MEFs) in which senescence was triggered by ionizing radiation (IR) expressed less senescence-associated β-galactosidase (SA-β-gal)-positive stained cells. In our aged mice (18 months old) study, BG supplementation (300 mg/kg) for 4 weeks altered hepatic genes involved in the aging process. Furthermore, we found BG supplementation downregulated age-related inflammatory genes, especially in the complement system. Based on this observation, we demonstrated that BG supplementation led to less activation of the canonical senescence pathway, p53-dependent p21 and p16, in multiple metabolic organs such as liver, skeletal muscle and white adipose tissue. Thus, we suggest that BG is a potential senolytic candidate that retards cellular senescence.

Cross-Talk between p53 and Wnt Signaling in Cancer

Targeting cancer hallmarks is a cardinal strategy to improve antineoplastic treatment. However, cross-talk between signaling pathways and key oncogenic processes frequently convey resistance to targeted therapies. The p53 and Wnt pathway play vital roles for the biology of many tumors, as they are critically involved in cancer onset and progression. Over recent decades, a high level of interaction between the two pathways has been revealed. Here, we provide a comprehensive overview of molecular interactions between the p53 and Wnt pathway discovered in cancer, including complex feedback loops and reciprocal transactivation. The mutational landscape of genes associated with p53 and Wnt signaling is described, including mutual exclusive and co-occurring genetic alterations. Finally, we summarize the functional consequences of this cross-talk for cancer phenotypes, such as invasiveness, metastasis or drug resistance, and discuss potential strategies to pharmacologically target the p53-Wnt interaction.

β-Catenin Expression and Its Association with Prognostic Factors in Hepatocellular Carcinoma: A Study on Alpha-fetoprotein, Histologic Grade, and Microvascular Invasion

Background. Hepatocellular carcinoma (HCC), the most common primary liver cancer. In addition to its high incidence, the disease burden is high due to its poor prognosis and high recurrence rate. Some of the currently known clinicopathologic prognostic factors include alpha-fetoprotein (AFP) level, histologic grade, and microvascular invasion. At the molecular level, β-catenin is one of the most common driver mutation found in HCC. The Wnt/β-catenin pathway regulates cellular processes related to initiation, growth, survival, migration, differentiation, and apoptosis. Although the underlying pathogenesis of hepatocarcinogenesis is known, clinical application warrants a greater understanding of the molecular characteristics and tumor phenotype, especially for determining the prognosis. This study aims to analyze the expression of β-catenin and its association with AFP, histologic grade, and microvascular invasion. Materials and methods. Thirty-five samples of surgically resected HCCs at Cipto Mangunkusumo National Referral Hospital were examined. Diagnoses were made based on histopathological and immunohistochemical findings followed by β-catenin staining. β-catenin expression was analyzed to determine difference between variables. Results and conclusions. Here we show that β-catenin expression is significantly associated with low serum alpha-fetoprotein and well to moderate differentiation Implications. Strong nuclear β-catenin expression implies better prognosis in HCC.

Crosstalk of the Wnt/β-Catenin Signaling Pathway in the Induction of Apoptosis on Cancer Cells

The Wnt/β-catenin signaling pathway plays a major role in cell survival and proliferation, as well as in angiogenesis, migration, invasion, metastasis, and stem cell renewal in various cancer types. However, the modulation (either up- or downregulation) of this pathway can inhibit cell proliferation and apoptosis both through β-catenin-dependent and independent mechanisms, and by crosstalk with other signaling pathways in a wide range of malignant tumors. Existing studies have reported conflicting results, indicating that the Wnt signaling can have both oncogenic and tumor-suppressing roles, depending on the cellular context. This review summarizes the available information on the role of the Wnt/β-catenin pathway and its crosstalk with other signaling pathways in apoptosis induction in cancer cells and presents a modified dual-signal model for the function of β-catenin. Understanding the proapoptotic mechanisms induced by the Wnt/β-catenin pathway could open new therapeutic opportunities.

Epidermal ROCK2 induces AKT1/GSK3β/β-catenin, NFκB and dermal tenascin C; but enhanced differentiation and p53/p21 inhibit papilloma

ROCK2 roles in epidermal differentiation and carcinogenesis have been investigated in mice expressing an RU486-inducible, 4HT-activated ROCK2 transgene (K14.creP/lslROCKer). RU486/4HT-mediated ROCKer activation induced epidermal hyperplasia similar to cutaneous oncogenic rasHa (HK1.ras); however ROCKer did not elicit papillomas. Instead, anomalous basal-layer ROCKer expression corrupted normal ROCK2 roles underlying epidermal rigidity/stiffness and barrier maintanance, resulting in premature keratin K1, loricrin and filaggrin expression. Also, hyperproliferative/stress-associated keratin K6 was reduced; possibly reflecting altered ROCK2 roles in epidermal rigidity and keratinocyte flexibility/migration during wound healing. Consistent with increased proliferation, K14.creP/lslROCKer hyperplasia displayed supra-basal-to-basal increases in activated p-AKT1, inactivated p-GSK3β ser9 and membranous/nuclear β-catenin expression together with weak NFκB, which were absent in equivalent HK1.ras hyperplasia. Furthermore, ROCKer-mediated increases in epidermal rigidity via p-MypT1 inactivation/elevated MLC, coupled to anomalous β-catenin expression, induced tenascin C-positive dermal fibroblasts. Alongside an altered ECM, these latent tenascin C-positive dermal fibroblasts may become putative pre-cancer-associated fibroblasts (pre-CAFs) and establish a susceptibility that subsequently contributes to tumour progression. However, anomalous differentiation was also accompanied by an immediate increase in basal-layer p53/p21 expression; suggesting that while ROCK2/AKT1/β-catenin activation increased keratinocyte proliferation resulting in hyperplasia, compensatory p53/p21 and accelerated differentiation helped inhibit papillomatogenesis.

Citrus Alkaline Extracts Inhibit Senescence of A549 Cells to Alleviate Pulmonary Fibrosis via the β-Catenin/P53 Pathway

BACKGROUND Idiopathic pulmonary fibrosis (IPF) is a disease related to aging, which has become increasingly prevalent as the population has aged. However, there remains no effective treatment for the disease. Alveolar epithelial type II cell (AEC II) senescence plays an important role in the occurrence and development of IPF. Therefore, enhancing our understanding of aging AEC IIs might facilitate the development of a new therapeutic strategy for the prevention and treatment of IPF. The aim of this study was to investigate the effect of citrus alkaline extracts (CAE) on senescence in A549 cells and elucidate the mechanism by which CAE function. MATERIAL AND METHODS Adriamycin RD (ARD) induces the senescence of A549 cells. Relevant indicators were identified following administration of 3 concentrations of CAE (50 μg/mL, 100 μg/mL, and 200 μg/mL) to A549 cells. RESULTS CAE inhibited senescence in ARD-induced A549 cells. It inhibited p16, p21, p53, and a senescence-associated secretory phenotype, and reduced expression of the senescence-related positive cells of ß-galactosidase. Further study revealed that activation of the ß-catenin signaling pathway is closely associated with p53. CAE inhibited senescence in A549 cells via the ß-catenin/p53 pathway. Further, inhibition of b-catenin was associated with reduced expression levels of p53 and p21, and the anti-aging effects of CAE were enhanced. When expression of p53 was inhibited, expression levels of ß-catenin also tended to decrease. CONCLUSIONS In summary, our study showed that CAE can inhibit aging in A549 cells to alleviate pulmonary fibrosis, and thus limit the secretion of the extracellular matrix and collagen in lung fibroblasts.

Non-Canonical Functions of the ARF Tumor Suppressor in Development and Tumorigenesis

P14ARF (ARF; Alternative Reading Frame) is an extensively characterized tumor suppressor which, in response to oncogenic stimuli, mediates cell cycle arrest and apoptosis via p53-dependent and independent routes. ARF has been shown to be frequently lost through CpG island promoter methylation in a wide spectrum of human malignancies, such as colorectal, prostate, breast, and gastric cancers, while point mutations and deletions in the p14ARF locus have been linked with various forms of melanomas and glioblastomas. Although ARF has been mostly studied in the context of tumorigenesis, it has been also implicated in purely developmental processes, such as spermatogenesis, and mammary gland and ocular development, while it has been additionally involved in the regulation of angiogenesis. Moreover, ARF has been found to hold important roles in stem cell self-renewal and differentiation. As is often the case with tumor suppressors, ARF functions as a pleiotropic protein regulating a number of different mechanisms at the crossroad of development and tumorigenesis. Here, we provide an overview of the non-canonical functions of ARF in cancer and developmental biology, by dissecting the crosstalk of ARF signaling with key oncogenic and developmental pathways.

LEF1 Induces DHRS2 Gene Expression in Human Acute Leukemia Jurkat T-Cells

Objective

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive disease resulting from the accumulation of genetic changes that affect the development of T-cells. The precise role of lymphoid enhancer-binding factor 1 (LEF1) in T-ALL has been controversial since both overexpression and inactivating LEF1 mutations have been reported to date. Here, we investigate the potential gene targets of LEF1 in the Jurkat human T-cell leukemia cell line.

Materials and Methods

We used small interfering RNA (siRNA) technology to knock down LEF1 in Jurkat cells and then compared the gene expression levels in the LEF1 knockdown cells with non-targeting siRNA-transfected and non-transfected cells by employing microarray analysis.

Results

We identified DHRS2, a tumor suppressor gene, as the most significantly downregulated gene in LEF1 knockdown cells, and we further confirmed its downregulation by real-time quantitative polymerase chain reaction (qRT-PCR) in mRNA and at protein level by western blotting.

Conclusion

Our results revealed that DHRS2 is positively regulated by LEF1 in Jurkat cells, which indicates the capability of LEF1 as a tumor suppressor and, together with previous reports, suggests that LEF1 exhibits a regulatory role in T-ALL via not only its oncogenic targets but also tumor suppressor genes.

Melanocyte Precursors in the Hair Follicle Bulge of Repigmented Vitiligo Skin Are Controlled by RHO-GTPase, KCTD10, and CTNNB1 Signaling

In repigmentation of human vitiligo, the melanocyte (MC) precursors in the hair follicle bulge proliferate, migrate, and differentiate to repopulate the depigmented epidermis. Here, we present a comprehensive characterization of pathways and signals in the bulge that control the repigmentation process. Using biopsies from patients with vitiligo, we have selectively harvested, by laser capture microdissection, MC and keratinocyte precursors from the hair follicle bulge of untreated vitiligo skin and vitiligo skin treated with narrow-band UVB. The captured material was subjected to whole transcriptome RNA-sequencing. With this strategy, we found that repigmentation in the bulge MC precursors is driven by KCTD10, a signal with unknown roles in the skin, and CTNNB1 (encoding β-catenin) and RHO guanosine triphosphatase [RHO GTPase, RHO], two signaling pathways previously shown to be involved in pigmentation biology. Knockdown studies in cultured human MCs of RHOJ, the upmost differentially expressed RHO family component, corroborated with our findings in patients with vitiligo, identified RHOJ involvement in UV response and melanization, and confirmed previously identified roles in melanocytic cell migration and apoptosis. A better understanding of mechanisms that govern repigmentation in MC precursors will enable the discovery of molecules that induce robust repigmentation phenotypes in vitiligo.

Mechanism of tumor-suppressive cell competition in flies

Oncogenic mutations often trigger antitumor cellular response such as induction of apoptosis or cellular senescence. Studies in the last decade have identified the presence of the third guardian against mutation‐induced tumorigenesis, namely “cell competition.” Cell competition is a context‐dependent cell elimination whereby cells with higher fitness eliminate neighboring cells with lower fitness by inducing cell death. While oncogene‐induced apoptosis or oncogene‐induced senescence acts as a cell‐autonomous tumor suppressor, cell competition protects the tissue from tumorigenesis via cell‐cell communication. For instance, in Drosophila epithelium, oncogenic cells with cell polarity mutations overproliferate and develop into tumors on their own but are eliminated from the tissue when surrounded by wild‐type cells. Genetic studies in flies have unraveled that such tumor‐suppressive cell competition is regulated by at least three mechanisms: direct cell‐cell interaction between polarity‐deficient cells and wild‐type cells, secreted factors from epithelial cells, and systemic factors from distant organs. Molecular manipulation of tumor‐suppressive cell competition could provide a novel therapeutic strategy against human cancers.

Regulation of expression of drug-metabolizing enzymes by oncogenic signaling pathways in liver tumors: a review

Mutations in genes encoding key players in oncogenic signaling pathways trigger specific downstream gene expression profiles in the respective tumor cell populations. While regulation of genes related to cell growth, survival, and death has been extensively studied, much less is known on the regulation of drug-metabolizing enzymes (DMEs) by oncogenic signaling. Here, a comprehensive review of the available literature is presented summarizing the impact of the most relevant genetic alterations in human and rodent liver tumors on the expression of DMEs with a focus on phases I and II of xenobiotic metabolism. Comparably few data are available with respect to DME regulation by p53-dependent signaling, telomerase expression or altered chromatin remodeling. By contrast, DME regulation by constitutive activation of oncogenic signaling via the RAS/RAF/mitogen-activated protein kinase (MAPK) cascade or via the canonical WNT/β-catenin signaling pathway has been analyzed in greater depth, demonstrating mostly positive-regulatory effects of WNT/β-catenin signaling and negative-regulatory effects of MAPK signaling. Mechanistic studies have revealed molecular interactions between oncogenic signaling and nuclear xeno-sensing receptors which underlie the observed alterations in DME expression in liver tumors. Observations of altered DME expression and inducibility in liver tumors with a specific gene expression profile may impact pharmacological treatment options.

MiR-532-3p suppresses colorectal cancer progression by disrupting the ETS1/TGM2 axis-mediated Wnt/β-catenin signaling

The expression panel of plasma microRNA defined miR-532-3p as a valuable biomarker for colorectal adenoma (CRA). However, its expression pattern and function in colorectal cancer (CRC) have remained unclear. The present study investigated the expression levels of miR-532-3p and found that it was in situ downregulated both in CRA and CRC. Moreover, it functioned as a sensitizer for chemotherapy in CRC by inducing cell cycle arrest and early apoptosis via its activating effects on p53 and apoptotic signaling pathways. In addition, miR-532-3p was found to restrain cell growth, metastasis, and epithelial–mesenchymal transition (EMT) phenotype of CRC. A study on the mechanism behind these effects revealed that miR-532-3p directly binds to 3′UTR regions of ETS1 and TGM2, ultimately repressing the canonical Wnt/β-catenin signaling. Further investigation showed that TGM2 was transcriptionally regulated by ETS1 and ETS1/TGM2 axis served as a vital functional target of miR-532-3p in suppressing CRC progression. To conclude, miR-532-3p mimics could act as potential candidate for molecular therapy in CRC through inactivation of the canonical Wnt/β-catenin signaling and enhancement of chemosensitivity.

Vitamin D and Wnt3A have additive and partially overlapping modulatory effects on gene expression and phenotype in human colon fibroblasts

The Wnt/β-catenin signalling pathway is essential for intestinal epithelium homeostasis, but its aberrant activation is a hallmark of colorectal cancer (CRC). Several studies indicate that the bioactive vitamin D metabolite 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) inhibits proliferation and promotes epithelial differentiation of colon carcinoma cells in part through antagonism of the Wnt/β-catenin pathway. It is now accepted that stromal fibroblasts are crucial in healthy and pathologic intestine: pericryptal myofibroblasts are constituents of the stem cell niche and cancer-associated fibroblasts (CAFs) contribute to CRC progression. However, studies on the combined action of 1,25(OH)₂D₃ and Wnt factors in colon fibroblasts are lacking. Here we show by global transcriptomic studies that 1,25(OH)₂D₃ and Wnt3A have profound, additive, partially overlapping effects on the gene expression profile of CCD-18Co human colon myofibroblasts. Moreover, 1,25(OH)₂D₃ and Wnt3A inhibit CCD-18Co cell proliferation and migration, while 1,25(OH)₂D₃ reduces, but Wnt3A increases, their capacity to contract collagen gels (a marker of fibroblast activation). These data were largely confirmed in patient-derived primary colon normal fibroblasts and CAFs, and in fibroblasts from other origins. Our results indicate that 1,25(OH)₂D₃ and Wnt3A are strong regulators of colon fibroblast biology and contribute to a better knowledge of intestinal homeostasis and stromal fibroblast action in CRC.

Anti-senescence effect and molecular mechanism of the major royal jelly proteins on human embryonic lung fibroblast (HFL-I) cell line

Royal jelly (RJ) from honeybee has been widely used as a health promotion supplement. The major royal jelly proteins (MRJPs) have been identified as the functional component of RJ. However, the question of whether MRJPs have anti-senescence activity for human cells remains. Human embryonic lung fibroblast (HFL-I) cells were cultured in media containing no MRJPs (A), MRJPs at 0.1 mg/ml (B), 0.2 mg/ml (C), or 0.3 mg/ml (D), or bovine serum albumin (BSA) at 0.2 mg/ml (E). The mean population doubling levels of cells in media B, C, D, and E were increased by 12.4%, 31.2%, 24.0%, and 10.4%, respectively, compared with that in medium A. The cells in medium C also exhibited the highest relative proliferation activity, the lowest senescence, and the longest telomeres. Moreover, MRJPs up-regulated the expression of superoxide dismutase-1 (SOD1) and down-regulated the expression of mammalian target of rapamycin (MTOR), catenin beta like-1 (CTNNB1), and tumor protein p53 (TP53). Raman spectra analysis showed that there were two unique bands related to DNA synthesis materials, amide carbonyl group vibrations and aromatic hydrogens. These results suggest that MRJPs possess anti-senescence activity for the HFL-I cell line, and provide new knowledge illustrating the molecular mechanism of MRJPs as anti-senescence factors.

In Vitro Expansion of Primary Human Hepatocytes with Efficient Liver Repopulation Capacity

Transplantation of human hepatocytes (HHs) holds significant potential for treating liver diseases. However, the supply of transplantable HHs is severely constrained by limited donor availability and compromised capacity for in vitro expansion. In response to chronic injury, some HHs are reprogrammed into proliferative cells that express both hepatocyte and progenitor markers, suggesting exploitable strategies for expanding HHs in vitro. Here, we report defined medium conditions that allow 10,000-fold expansion of HHs. These proliferating HHs are bi-phenotypic, partially retaining hepatic features while gaining expression of progenitor-associated genes. Importantly, these cells engraft into injured mouse liver at a level comparable to primary HHs, and they undergo maturation following transplantation in vivo or differentiation in vitro. Thus, this study provides a protocol that enables large-scale expansion of transplantable HHs, which could be further developed for modeling and treating human liver disease.

High-frequency deregulated expression of Wnt signaling pathway members in breast carcinomas

Purpose

Breast carcinoma is the most common malignancy and leading cause of cancer-related deaths in women worldwide including Saudi Arabia. Breast cancer in Saudi women develops at a much early age with median age of onset of 49 years compared to 62 years observed in patients from USA. Aberrations in wingless and integration site growth factor (Wnt) signaling pathway have been pathologically implicated in development of breast cancers and hence its role was examined in Saudi patients.

Materials and methods

We immunohistochemically examined various components of Wnt signaling pathway including β-catenin, tumor suppressor proteins, adenomatous polyposis coli (APC), and Axin, expression of naturally occurring pathway antagonists such as Dickkopf Wnt signaling pathway inhibitor 3 (DKK3), FRP2, and WIF1, as well as Wnt target cyclin D1 and c-Myc to establish if the pathway is constitutively activated in breast cancers arising in Saudi women.

Results

Cytoplasmic β-catenin, indicative of activation of the pathway, was observed in 24% of cases. Expression of APC and Axin, which are components of β-catenin destruction complex, was lost in 5% and 10% of tumors, respectively. Additionally, Wnt signaling inhibitors DKK3, FRP2, and Wnt inhibitory factor 1 (WIF1) were not expressed in 8%, 14%, and 5% breast tumors, respectively. Overall, accumulation of cytoplasmic β-catenin and downregulation of other Wnt pathway proteins (APC/Axin/DKK3/FRP2/WIF1) were found in approximately half of the breast cancers (47%) in our cohort. Consistent with this, analysis of Wnt target genes demonstrated moderate-to-strong expression of c-Myc in 58% and cyclin D1 in 50% of breast cancers. Deregulation of Wnt pathway was not associated with age of onset of the disease, tumor grade, and triple-negative status of breast cancers.

Conclusions

High level of deregulated expression of Wnt pathway proteins suggests its important role in pathogenesis of breast cancers arising in Saudi women who may benefit from development of therapeutic drugs targeting this pathway.

A Small Molecule Inhibitor of the β-Catenin-TCF4 Interaction Suppresses Colorectal Cancer Growth In Vitro and In Vivo

Colorectal cancer is associated with aberrant activation of the Wnt pathway. β-Catenin plays essential roles in the Wnt pathway by interacting with T-cell factor 4 (TCF4) to transcribe oncogenes. We synthesized a small molecule, referred to as HI-B1, and evaluated signaling changes and biological consequences induced by the compound. HI-B1 inhibited β-catenin/TCF4 luciferase activity and preferentially caused apoptosis of cancer cells in which the survival is dependent on β-catenin. The formation of the β-catenin/TCF4 complex was disrupted by HI-B1 due to the direct interaction of HI-B1 with β-catenin. Colon cancer patient-derived xenograft (PDX) studies showed that a tumor with higher levels of β-catenin expression was more sensitive to HI-B1 treatment, compared to a tumor with lower expression levels of β-catenin. The different sensitivities of PDX tumors to HI-B1 were dependent on the β-catenin expression level and potentially could be further exploited for biomarker development and therapeutic applications against colon cancer.

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HI-B1 is a synthesized compound identified as a β-catenin inhibitor suppressing the β-catenin-TCF4 protein interaction.

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HI-B1 preferentially causes apoptosis in β-catenin-dependent cancer cells.

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A colon cancer PDX mouse model with a high level of β-catenin is sensitive to HI-B1.

β-catenin is an important protein that facilitates colon cancer. Shin et al. synthesized and identified HI-B1 as a direct β-catenin inhibitor. HI-B1 disrupted formation of the β-catenin-TCF4 protein complex. HI-B1 preferentially caused apoptosis of cancer cells in which the survival is dependent on β-catenin. In a comparison of two colon cancer PDX models with different β-catenin levels, they showed that β-catenin-high PDX is more sensitive to HI-B1 treatment than β-catenin-low PDX. HI-B1 could thus be further developed as a colon cancer drug, and β-catenin expression levels might be a predictive biomarker for colon cancer therapy using β-catenin inhibitors.

Role of Nuclear Constitutive Androstane Receptor in Regulation of Hepatocyte Proliferation and Hepatocarcinogenesis

Activation of the constitutive androstane receptor (CAR) in hepatocytes occurs as a body adaptation in response to a number of external influences, and its functional activity is primarily related to induction of enzymes detoxifying xenobiotics. However, special attention was recently given to CAR due to the fact that its key role becomes unveiled in various physiological and pathophysiological processes occurring in the liver: gluconeogenesis, metabolism of fatty acids and bilirubin, hormonal regulation, proliferation of hepatocytes, and hepatocarcinogenesis. Here we review the main pathways and mechanisms that elevate hepatocyte proliferative activity related to CAR and whose disturbance may be a pivotal factor in hepatocarcinogenesis.

Regulation of the Mdm2-p53 signaling axis in the DNA damage response and tumorigenesis

The p53 tumor suppressor acts as a guardian of the genome in mammalian cells undergoing DNA double strand breaks induced by a various forms of cell stress, including inappropriate growth signals or ionizing radiation. Following damage, p53 protein levels become greatly elevated in cells and p53 functions primarily as a transcription factor to regulate the expression a wide variety of genes that coordinate this DNA damage response. In cells undergoing high amounts of DNA damage, p53 can promote apoptosis, whereas in cells undergoing less damage, p53 promotes senescence or transient cell growth arrest and the expression of genes involved in DNA repair, depending upon the cell type and level of damage. Failure of the damaged cell to undergo growth arrest or apoptosis, or to respond to the DNA damage by other p53-coordinated mechanisms, can lead to inappropriate cell growth and tumorigenesis. In cells that have successfully responded to genetic damage, the amount of p53 present in the cell must return to basal levels in order for the cell to resume normal growth and function. Although regulation of p53 levels and function is coordinated by many proteins, it is now widely accepted that the master regulator of p53 is Mdm2. In this review, we discuss the role(s) of p53 in the DNA damage response and in tumor suppression, and how post-translational modification of Mdm2 regulates the Mdm2-p53 signaling axis to govern p53 activities in the cell.

β-Catenin C-terminal signals suppress p53 and are essential for artery formation

Increased activity of the tumour suppressor p53 is incompatible with embryogenesis, but how p53 is controlled is not fully understood. Differential requirements for p53 inhibitors Mdm2 and Mdm4 during development suggest that these control mechanisms are context-dependent. Artery formation requires investment of nascent endothelial tubes by smooth muscle cells (SMCs). Here, we find that embryos lacking SMC β-catenin suffer impaired arterial maturation and die by E12.5, with increased vascular wall p53 activity. β-Catenin-deficient SMCs show no change in p53 levels, but greater p53 acetylation and activity, plus impaired growth and survival. In vivo, SMC p53 inactivation suppresses phenotypes caused by loss of β-catenin. Mechanistically, β-catenin C-terminal interactions inhibit Creb-binding protein-dependent p53 acetylation and p53 transcriptional activity, and are required for artery formation. Thus in SMCs, the β-catenin C-terminus indirectly represses p53, and this function is essential for embryogenesis. These findings have implications for angiogenesis, tissue engineering and vascular disease.

How p53 is restrained in arterial maturation during embryonic development is unclear. Here, the authors show that β-catenin C-terminal interactions inhibit CREB binding protein-mediated acetylation and activation of p53 in smooth muscle cells, and that this function is essential for artery formation.

Prognostic significance of survivin, β-catenin and p53 expression in urothelial carcinoma

Survivin, β-catenin, and p53 are well-known cell-cycle and apoptosis regulators of tumorigenesis. Urothelial carcinomas (UCs) are the most common of the human cancers. Compared to superficial tumors (Ta, CIS, or T1), invasive UCs are important with regard to recurrence, progression, and mortality. Therefore, we examined whether survivin, β-catenin, and p53 could be used as the biomarkers for the early prediction of the invasiveness of UCs and the overall survival of the patients. We investigated the prognostic expressions of those biomarkers in UC (n=147) and in non-muscle invasive UC (NMI-UC) (n=113), using tissue microarray and immunohistochemistry. Spearman's correlation analysis and multivariate Cox regression analyses were used for statistical interpretation. High expressions of β-catenin, survivin, and p53 were associated with a high T stage, recurrence, progression, mortality, low recurrence-free survival, low progression-free survival and low overall survival (p <0.01). Similar findings were achieved for recurrence and progression in the NMI-UC group, except for mortality. Moreover, a positive correlation was shown between p53 and β-catenin and between p53 and survivin (r=0.221, p <0.01; r=0.236, p <0.01, respectively). Survivin, p53, and β-catenin overexpression, as prognostic markers, might suggest that the UCs are biologically aggressive with the poor prognosis. Thus, dysregulation of those these cell-cycle and apoptosis regulators in bladder carcinoma could be used as a molecular marker to determine the best treatment strategy and could contribute to the development of targeted therapies.

MicroRNA-29 induces cellular senescence in aging muscle through multiple signaling pathways

The mechanisms underlying the development of aging-induced muscle atrophy are unclear. By microRNA array and individual qPCR analyses, we found significant up-regulation of miR-29 in muscles of aged rodents vs. results in young. With aging, p85α, IGF-1 and B-myb muscle levels were lower while the expression of certain cell arrest proteins (p53, p16 and pRB) increased. When miR-29 was expressed in muscle progenitor cells (MPC), their proliferation was impaired while SA-βgal expression increased signifying the development of senescence. Impaired MPC proliferation resulted from interactions between miR-29 and the 3'-UTR of p85a, IGF-1 and B-myb, suppressing the translation of these mediators of myoblast proliferation. In vivo, electroporation of miR-29 into muscles of young mice suppressed the proliferation and increased levels of cellular arrest proteins, recapitulating aging-induced responses in muscle. A potential stimulus of miR-29 expression is Wnt-3a since we found that exogenous Wnt-3a stimulated miR-29 expression 2.7-fold in primary cultures of MPCs. Thus, aging-induced muscle senescence results from activation of miR-29 by Wnt-3a leading to suppressed expression of several signaling proteins (p85α, IGF-1 and B-myb) that act coordinately to impair the proliferation of MPCs contributing to muscle atrophy. The increase in miR-29 provides a potential mechanism for aging-induced sarcopenia.

Activating CAR and β-catenin induces uncontrolled liver growth and tumorigenesis

Aberrant β-catenin activation contributes to a third or more of human hepatocellular carcinoma (HCC), but β-catenin activation alone is not sufficient to induce liver cancer in mice. Differentiated hepatocytes proliferate upon acute activation of either β-catenin or the nuclear xenobiotic receptor CAR. These responses are strictly limited and are tightly linked, since β-catenin is activated in nearly all of the CAR-dependent tumors generated by the tumor promoter phenobarbital. Here we show that full activation of β-catenin in the liver induces senescence and growth arrest, which is overcome by combined CAR activation, resulting in uncontrolled hepatocyte proliferation, hepatomegaly, and rapid lethality despite maintenance of normal liver function. Combining CAR activation with limited β-catenin activation induces tumorigenesis, and the tumors share a conserved gene expression signature with β-catenin positive human HCC. These results reveal an unexpected route for hepatocyte proliferation and define a murine model of hepatocarcinogenesis with direct relevance to human HCC.

Down-regulation of survivin alleviates experimental arthritis

Survivin is a proto-oncogene that regulates cell division and apoptosis. It is a molecular marker of cancer. Recently, survivin has emerged as a feature of RA, associated with severe joint damage and poor treatment response. The present study examined if inhibition of survivin affects experimental arthritis, which was induced in mBSA-immunized mice by an injection of mBSA in the knee joint or developed spontaneously in collagen type II-immunized mice. The inhibition of survivin transcription by a lentivirus shRNA construct alleviated joint inflammation and reduced bone damage. The inhibition of survivin reduced the levels of metalloproteinases, β-catenin, and vimentin, limiting the invasive capacity of synovia, while no inhibition of osteoclastogenesis could be found. The inhibition of survivin led to a p53-independent reduction of T cell proliferation and favored the transcription and activity of Blimp-1, which limited IL-2 production and facilitated formation of regulatory Foxp3(+)CD4(+) and effector CD8(+) T cells. The study shows that the inhibition of survivin is sufficient to reduce joint inflammation and bone damage in preclinical models of arthritis. Antiarthritic effects of survivin inhibition are related to p53-independent control of lymphocyte proliferation.

Secretory Leukocyte Protease Inhibitor (SLPI) expression downregulates E-cadherin, induces β-catenin re-localisation and triggers apoptosis-related events in breast cancer cells

BACKGROUND INFORMATION

Epithelial cadherin (E-cadherin) is involved in cell-cell adhesion through its extracellular domain, whereas the intracellular domain interacts with adaptor proteins, i.e. β-catenin, links E-cadherin to the actin cytoskeleton and participates in signal transduction events. E-cadherin protects mammary epithelial cells from apoptosis and its loss during tumour progression has been documented. Secretory Leukocyte Protease Inhibitor (SLPI) has anti- and pro-tumourigenic activities but its role in breast cancer has not been fully elucidated. Notwithstanding its relevance, how SLPI affects E-cadherin in breast cancer is still unknown. This study evaluated the effect of SLPI upon E-cadherin/β-catenin expression and apoptosis-related markers in murine (F3II) and human (MCF-7) breast tumour cells either treated with exogenous recombinant human SLPI (rhSLPI) or stably transfected with a plasmid encoding its sequence.

RESULTS

Addition of rhSLPI to F3II cells caused a decrease (P < 0.05) in E-cadherin transcript and protein levels. Similar results were observed in SLPI-stable F3II transfectants (2C1), and treatment of 2C1 cells with a siRNA toward SLPI restored E-cadherin to control levels. SLPI-expressing cells showed disruption of E-cadherin/β-catenin complex and increased (P < 0.05) percentage of cells depicting nuclear β-catenin localisation. Associated to these changes, 2C1 cells showed increased Bax/Bcl-2 ratio and p21 protein levels, decreased c-Myc protein levels and decreased Cyclin D1 and Claudin-1 transcript levels. No differences in N- and P-cadherin were observed between SLPI-transfected cells and controls. Addition of rhSLPI to MCF-7 cells or stable transfection with SLPI caused a decrease (P < 0.05) in E-cadherin expression (transcript/protein) and its redistribution to the cytoplasm, as well as β-catenin re-localisation to the cell nucleus.

CONCLUSIONS

Expression of SLPI was associated to a decrease in E-cadherin expression and re-localisation of E-cadherin to the cell cytoplasm and β-catenin to the cell cytoplasm and nucleus, and had pro-apoptotic and cell cycle-arrest effects.

Increased expression of prothymosin-α, independently or combined with TP53, correlates with poor prognosis in colorectal cancer

Human prothymosin-α (PTMA) plays an important role in tumorigenesis, and its overexpression triggers a TP53 response. In this study, we identified that PTMA expression was up-regulated at both the transcriptional and translational level in tumor tissue compared to that in adjacent normal tissue. PTMA overexpression was significantly associated with the depth of tumor invasion, lymph node metastasis (LNM), distant metastasis, advanced AJCC stage, and tumor differentiation. There was also a significant association between PTMA over-expression and mutant TP53 expression (r=0.515, P < 0.001). Survival analysis revealed that the disease-free survival (DFS) and overall survival (OS) rates were significantly lower among patients with PTMA- and TP53-positive tumors. Hence, PTMA might play an important role in the progression of CRC, and the assessment of both PTMA and mutant TP53 expression can help predict colon cancer prognosis.

Pygo2 regulates β-catenin-induced activation of hair follicle stem/progenitor cells and skin hyperplasia

Understanding the epigenetic mechanisms that control the activation of adult stem cells holds the promise of tissue and organ regeneration. Hair follicle stem cells have emerged as a prime model to study stem cell activation. Wnt/β-catenin signaling controls multiple aspects of skin epithelial regeneration, with its excessive activity promoting the hyperactivation of hair follicle stem/progenitor cells and tumorigenesis. The contribution of chromatin factors in regulating Wnt/β-catenin pathway function in these processes is unknown. Here, we show that chromatin effector Pygopus homolog 2 (Pygo2) produced by the epithelial cells facilitates depilation-induced hair regeneration, as well as β-catenin-induced activation of hair follicle stem/early progenitor cells and trichofolliculoma-like skin hyperplasia. Pygo2 maximizes the expression of Wnt/β-catenin targets, but is dispensable for β-catenin-mediated expansion of LIM/homeobox protein Lhx2(+) cells, in the stem/early progenitor cell compartment of the hair follicle. Moreover, β-catenin and Pygo2 converge to induce the accumulation and acetylation of tumor suppressor protein p53 upon the cell cycle entry of hair follicle early progenitor cells and in cultured keratinocytes. These findings identify Pygo2 as an important regulator of Wnt/β-catenin function in skin epithelia and p53 activation as a prominent downstream event of β-catenin/Pygo2 action in stem cell activation.

Csnk1a1 inhibition has p53-dependent therapeutic efficacy in acute myeloid leukemia

Despite extensive insights into the underlying genetics and biology of acute myeloid leukemia (AML), overall survival remains poor and new therapies are needed. We found that casein kinase 1 α (Csnk1a1), a serine-threonine kinase, is essential for AML cell survival in vivo. Normal hematopoietic stem and progenitor cells (HSPCs) were relatively less affected by shRNA-mediated knockdown of Csnk1a1. To identify downstream mediators of Csnk1a1 critical for leukemia cells, we performed an in vivo pooled shRNA screen and gene expression profiling. We found that Csnk1a1 knockdown results in decreased Rps6 phosphorylation, increased p53 activity, and myeloid differentiation. Consistent with these observations, p53-null leukemias were insensitive to Csnk1a1 knockdown. We further evaluated whether D4476, a casein kinase 1 inhibitor, would exhibit selective antileukemic effects. Treatment of leukemia stem cells (LSCs) with D4476 showed highly selective killing of LSCs over normal HSPCs. In summary, these findings demonstrate that Csnk1a1 inhibition causes reduced Rps6 phosphorylation and activation of p53, resulting in selective elimination of leukemia cells, revealing Csnk1a1 as a potential therapeutic target for the treatment of AML.

The p53-Mdm2 loop: a critical juncture of stress response

The presence of a functional p53 protein is a key factor for the proper suppression of cancer development. A loss of p53 activity, by mutations or inhibition, is often associated with human malignancies. The p53 protein integrates various stress signals into a growth restrictive cellular response. In this way, p53 eliminates cells with a potential to become cancerous. Being a powerful decision maker, it is imperative that p53 will be activated properly, efficiently and temporarily in response to stress. Equally important is that p53 activation will be extinguished upon recovery from stress, and that improper activation of p53 will be avoided. Failure to achieve these aims is likely to have catastrophic consequences for the organism. The machinery that governs this tight regulation is largely based on the major inhibitor of p53, Mdm2, which both blocks p53 activities and promotes its destabilization. The interplay between p53 and Mdm2 involves a complex network of positive and negative feedback loops. Relief from Mdm2 suppression is required for p53 to be stabilized and activated in response to stress. Protection from Mdm2 entails a concerted action of modifying enzymes and partner proteins. The association of p53 with the PML-nuclear bodies may provide an infrastructure in which this complex regulatory network can be orchestrated. In this chapter we use examples to illustrate the regulatory machinery that drives this network.

Activation of the tumor suppressor p53 upon impairment of ribosome biogenesis

Errors in ribosome biogenesis can result in quantitative or qualitative defects in protein synthesis and consequently lead to improper execution of the genetic program and the development of specific diseases. Evidence has accumulated over the last decade suggesting that perturbation of ribosome biogenesis triggers a p53-activating checkpoint signaling pathway, often referred to as the ribosome biogenesis stress checkpoint pathway. Although it was originally suggested that p53 has a prominent role in preventing diseases by monitoring the fidelity of ribosome biogenesis, recent work has demonstrated that p53 activation upon impairment of ribosome biogenesis also mediates pathological manifestations in humans. Perturbations of ribosome biogenesis can trigger a p53-dependent checkpoint signaling pathway independent of DNA damage and the tumor suppressor ARF through inhibitory interactions of specific ribosomal components with the p53 negative regulator, Mdm2. Here we review the recent advances made toward understanding of this newly-recognized checkpoint signaling pathway, its role in health and disease, and discuss possible future directions in this exciting research field. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.

Wnt/β-catenin signaling mediates the senescence of bone marrow-mesenchymal stem cells from systemic lupus erythematosus patients through the p53/p21 pathway

Recent studies have shown that allogeneic bone marrow (BM)-mesenchymal stem cell transplantation (MSCT) appears to be effective in systemic lupus erythematosus (SLE) patients and lupus-prone mice, contrary to studies in syngeneic BM-MSCT. These studies indicated that the abnormalities of BM-MSCs may be involved in the pathogenesis of SLE. Our studies and other previous studies have revealed that BM-MSCs from SLE patients exhibited early signs of senescence, such as flattened morphology, slow proliferation, increased senescence-associated β-galactosidase (SA-β-gal) activity, and so on. However, the mechanisms by which these cells senescences were still unclear. Previous studies have demonstrated that Wnt/β-catenin signaling plays an important role in stem cell senescence. In the current study, we investigated whether Wnt/β-catenin signaling mediates the senescence of BM-MSCs from SLE patients. We have found that Wnt/β-catenin signaling and the p53/p21 pathway were significantly hyperactivated in senescent SLE BM-MSCs. Treatment with 100 ng/mL Dickkopf-1 (DKK1), a Wnt/β-catenin signaling inhibitor or β-catenin siRNA for 48 h could reverse the senescent features of SLE BM-MSCs. Additionally, the expression levels of p53 and p21 were reduced in treated-SLE BM-MSCs compared with the untreated group. In summary, our study indicated that Wnt/β-catenin signaling may play a critical role in the senescence of SLE BM-MSCs through the p53/p21 pathway.

The THO ribonucleoprotein complex is required for stem cell homeostasis in the adult mouse small intestine

RNA processing and transport are mediated by cotranscriptionally assembled ribonucleoprotein (RNP) complexes. RNPs have been postulated to help specify coordinated gene expression, but the requirements for specific RNP complexes in mammalian development and tissue homeostasis have not been extensively evaluated. THO is an evolutionarily conserved RNP complex that links transcription with nuclear export. THO is not essential for Saccharomyces cerevisiae viability, but it is essential for early mouse embryonic development. Embryonic lethality has limited the characterization of THO requirements in adult tissues. To overcome this limitation, a mouse model has been generated that allows widespread inducible deletion of Thoc1, which encodes an essential protein subunit of THO. Widespread Thoc1 deletion disrupts homeostasis within the small intestine but does not have detectable effects in other epithelial tissues such as the related mucosa of the large intestine. Thoc1 loss compromises the proliferation and lineage-generating capacity of small intestinal stem cells, disrupting the supply of differentiated cells in this rapidly renewing tissue. These findings demonstrate that the effects of THO deficiency in the adult mouse are tissue and cell type dependent.

Plakoglobin interacts with the transcription factor p53 and regulates the expression of 14-3-3σ

Plakoglobin (γ-catenin), a constituent of the adherens junction and desmosomes, has signaling capabilities typically associated with tumor/metastasis suppression through mechanisms that remain undefined. To determine the role of plakoglobin during tumorigenesis and metastasis, we expressed plakoglobin in human tongue squamous cell carcinoma (SCC9) cells and compared the mRNA profiles of parental SCC9 cells and their plakoglobin-expressing transfectants (SCC9-PG). We detected several p53-target genes whose levels were altered upon plakoglobin expression. In this study, we identified the p53 regulated tumor suppressor 14-3-3σ as a direct plakoglobin-p53 target gene. Coimmunoprecipitation experiments revealed that plakoglobin and p53 interact, and chromatin immunoprecipitation and electrophoretic mobility shift assays revealed that plakoglobin and p53 associate with the 14-3-3σ promoter. Furthermore, luciferase reporter assays showed that p53 transcriptional activity is increased in the presence of plakoglobin. Finally, knockdown of plakoglobin in MCF-7 cells followed by luciferase assays confirmed that p53 transcriptional activity is enhanced in the presence of plakoglobin. Our data suggest that plakoglobin regulates gene expression in conjunction with p53 and that plakoglobin may regulate p53 transcriptional activity, which may account, in part, for the tumor/metastasis suppressor activity of plakoglobin.

Molecular basis for the tissue specificity of β-catenin oncogenesis

Wnt-β-catenin-T-cell factor signaling is causally linked to c-myc-dependent tumorigenesis in mouse and human colon epithelial cells. By contrast, β-catenin is not similarly associated with oncogenic transformation of other tissues, including T cells. The molecular basis for tissue specificity of β-catenin-dependent oncogenesis is unknown. Here, we demonstrate that adenomatous polyposis coli mutant APC(Min/+) mice, which have increased expression of β-catenin in all tissues, develop severe intestinal neoplasia, but fail to develop thymic lymphoma. Whereas β-catenin-dependent signals elicit a proliferative response from intestinal cells, thymocytes experience oncogene-induced senescence (OIS), growth arrest and apoptosis. We demonstrate that the differential cellular response of thymocytes and intestinal epithelial cells is a direct consequence of the gene expression elicited by β-catenin expression in each tissue. We find that whereas intestinal cells induce genes that promote proliferation thymocytes induce expression of genes associated with OIS, growth arrest and p53-dependent apoptosis. We correlate gene expression pattern with the role β-catenin plays in the development of each tissue and suggest that susceptibility of transformation by β-catenin is intimately related to its function during development. We propose that when oncogenes are used as signaling molecules, safety nets in the form of OIS, growth arrest and apoptosis prevent accidental transformation.

WNT signalling pathways as therapeutic targets in cancer

Since the initial discovery of the oncogenic activity of WNT1 in mouse mammary glands, our appreciation for the complex roles for WNT signalling pathways in cancer has increased dramatically. WNTs and their downstream effectors regulate various processes that are important for cancer progression, including tumour initiation, tumour growth, cell senescence, cell death, differentiation and metastasis. Although WNT signalling pathways have been difficult to target, improved drug-discovery platforms and new technologies have facilitated the discovery of agents that can alter WNT signalling in preclinical models, thus setting the stage for clinical trials in humans.

The Regulation of Multiple p53 Stress Responses is Mediated through MDM2

The MDM2 oncogene is a key negative regulator of the p53 tumor suppressor protein. MDM2 and p53 form an autoregulatory feedback loop to tightly control the proper cellular responses to various stress signals in order to prevent mutations and tumor formation. The levels and function of the MDM2 protein, an E3 ubiquitin ligase, are regulated by a wide variety of extracellular and intracellular stress signals through distinct signaling pathways and mechanisms. These signals regulate the E3 ubiquitin ligase activity of MDM2, the ability of MDM2 to interact with p53 and a number of other proteins, and the cellular localization of MDM2, which in turn impact significantly upon p53 function. This review provides an overview of the regulation of MDM2 activities by the signals and factors that regulate the MDM2 protein, including genotoxic stress signals, oncogenic activation, cell cycle transition, ribosomal stress, chronic stress, neurohormones, and microRNAs. Disruption of the proper regulation of the MDM2-p53 negative feedback loop impacts significantly upon the frequency of tumorigenesis in a host. A better understanding of the complex regulation of MDM2 and its impact upon p53 function in cells under different conditions will help to develop novel and more effective strategies for cancer therapy and prevention.

Wnt/β-catenin signaling induces the aging of mesenchymal stem cells through promoting the ROS production

Recent studies have demonstrated that the Wnt/β-catenin signaling plays an important role in stem cell aging. However, the mechanisms of cell senescence induced by Wnt/β-catenin signaling are still poorly understood. Our preliminary study has indicated that activated Wnt/β-catenin signaling can induce MSC aging. In this study, we reported that the Wnt/β-catenin signaling was a potent activator of reactive oxygen species (ROS) generation in MSCs. After scavenging ROS with N-acetylcysteine, Wnt/β-catenin signaling-induced MSC aging was significantly attenuated and the DNA damage and the expression of p16(INK4A), p53, and p21 were reduced in MSCs. These results indicated that the Wnt/β-catenin signaling could induce MSC aging through promoting the intracellular production of ROS, and ROS may be the main mediators of MSC aging induced by excessive activation of Wnt/β-catenin signaling.

High levels of β-catenin promote IFNγ-induced apoptosis in hepatocellular carcinoma cells

β-catenin is a multifunctional protein that is involved in cellular structure and the Wnt/β-catenin signaling pathway. Wnt/β-catenin signaling is believed to be an inducer of cell proliferation in different tumors. However, in certain physiological contexts β-catenin also promotes apoptosis. High levels of β-catenin are found in a number of cancer cell types. Recent studies have shown that β-catenin may be correlated with carcinogenesis. Its effects and interaction with interferon (IFN)γ signaling in hepatocellular carcinoma (HCC) cells remains unknown. In the present study, high levels of β-catenin did not induce antiproliferative effects or apoptosis and did not lead to changes in the levels of caspases or activated STATs. However, high levels of β-catenin did cause positive p53 accumulation and Bcl-XL downregulation in HepG2 cells, a HCC cell line. When treated with IFNγ, apoptosis was induced more rapidly compared with cells with low β-catenin levels (P<0.05), whereas caspases 3, 8 and 9 were markedly activated. The caspase inhibitor Z-VAD-FMK and the STAT3 inhibitor blocked this IFNγ-induced apoptosis. Therefore, we report that high levels of β-catenin promote IFNγ-induced apoptosis in HCC in a caspase- and STAT3-dependent manner, and facilitate the activation of executor caspases, possibly via regulation of p53 and Bcl-XL levels. These findings may provide foundations for the development of new IFN-based therapies against liver cancer.

Kindlin 2 forms a transcriptional complex with β-catenin and TCF4 to enhance Wnt signalling

Kindlin 2, as a focal adhesion protein, controls integrin activation. However, the association of Kindlin 2 with cancer-related signalling pathways is unknown. Here we identified a new direct interaction between Kindlin 2 and the active β-catenin. Importantly, Kindlin 2 forms a tripartite complex with β-catenin and TCF4. Mechanistically, Kindlin 2 selectively strengthens the occupancy of β-catenin on the Wnt target gene Axin2 and enhances Axin2 gene expression. Functionally, the β-catenin-Axin2-Snail cascade is required for Kindlin 2-induced tumour cell invasion. Our data indicate that Kindlin 2 is a new regulator of Wnt signalling, providing a mechanistic insight into the role of Kindlin 2 in cancer progression.

Immunohistochemical investigation of cell cycle and apoptosis regulators (survivin, β-catenin, p53, caspase 3) in canine appendicular osteosarcoma

Background

Osteosarcoma (OSA) represents the most common canine primary bone tumour. Despite several pathways have been investigated so far, few molecules have been identified as prognostic tools or potential therapeutic targets, and there is still the need to find out molecular pathways with specific influence over OSA progression to facilitate earlier prognosis and treatment.

Aims of the present study were to evaluate the immunohistochemical pattern and levels of expression of a panel of molecules (survivin, β-catenin, caspase 3 -inactive and active forms- and p53) involved in cell cycle and apoptosis regulation in canine OSA samples, known to be of interest in the study also of human OSA, and to detect specific relations among them and with histological tumour grade, disease free interval (DFI) and overall survival (OS).

Results

Nuclear β-catenin immunostaining was detected in normal osteoblasts adjacent to the tumour, and in 47% of the cases. Cytoplasmic and/or membranous immunostaining were also observed. Nuclear survivin and p53 positive cells were found in all cases. Moderate/high cytoplasmic β-catenin expression (≥10% positive cells) was significantly associated with the development of metastasis (P = 0.014); moderate/high nuclear p53 expression (≥10% positive cells) was significantly associated with moderate/high histological grade (P = 0.017) and shorter OS (P = 0.049). Moderate/high nuclear survivin expression (≥15% positive cells) showed a tendency toward a longer OS (P = 0,088).

Conclusions

The present results confirmed p53 as negative prognostic marker, while suggested survivin as a potential positive prognostic indicator, rather than indicative of a poor prognosis. The detection of nuclear β-catenin immunostaining in normal osteoblasts and the absent/low expression in most of the OSAs, suggested that this pathway could not play a major role in oncogenic transformation of canine osteoblasts. Further studies are needed to confirm these hypotheses.

Physical and functional interaction between ribosomal protein L11 and the tumor suppressor ARF

The ARF tumor suppressor protein activates p53 in response to oncogenic stress, whereas ribosomal protein L11 induces p53 following ribosomal stress. Both proteins bind to central, albeit non-overlapping, regions of MDM2 and suppress MDM2 activity toward p53. However, it is not known whether the two pathways are functionally connected. Here we show that ARF directly binds to L11 in vitro and in cells, which then forms a complex with MDM2 and p53. L11 collaboratively enhances ARF-induced p53 transcriptional activity and cell cycle arrest. Supporting these results, knocking down L11 reduces ARF-mediated p53 accumulation and alleviates ARF-induced cell cycle arrest. Interestingly, overexpression of ARF increases the levels of ribosome-free L11 and enhances the interaction of L11 with MDM2 and p53. These results demonstrate that ARF activates p53, at least partly by induction of ribosomal stress, which results in L11 suppression of MDM2, and suggest that the ARF-MDM2-p53 and the L11-MDM2-p53 pathways are functionally connected.

MOLECULAR NETWORKS IN MICROARRAY ANALYSIS

Microarray-based characterization of tissues, cellular and disease states, and environmental condition and treatment responses provides genome-wide snapshots containing large amounts of invaluable information. However, the lack of inherent structure within the data and strong noise make extracting and interpreting this information and formulating and prioritizing domain relevant hypotheses difficult tasks. Integration with different types of biological data is required to place the expression measurements into a biologically meaningful context. A few approaches in microarray data interpretation are discussed with the emphasis on the use of molecular network information. Statistical procedures are demonstrated that superimpose expression data onto the transcription regulation network mined from scientific literature and aim at selecting transcription regulators with significant patterns of expression changes downstream. Tests are suggested that take into account network topology and signs of transcription regulation effects. The approaches are illustrated using two different expression datasets, the performance is compared, and biological relevance of the predictions is discussed.

Wnt/β-catenin signaling induces the aging of mesenchymal stem cells through the DNA damage response and the p53/p21 pathway

Recent studies have demonstrated the importance of cellular extrinsic factors in the aging of adult stem cells. However, the effects of an aged cell–extrinsic environment on mesenchymal stem cell (MSC) aging and the factors involved remain unclear. In the current study, we examine the effects of old rat serum (ORS) on the aging of MSCs, and explore the effects and mechanisms of Wnt/β-catenin signaling on MSC aging induced by ORS treatment. Senescence-associated changes in the cells are examined with SA-β-galactosidase staining and ROS staining. The proliferation ability is detected by MTT assay. The surviving and apoptotic cells are determined using AO/EB staining. The results suggest that ORS promotes MSC senescence and reduces the proliferation and survival of cells. The immunofluorescence staining shows that the expression of β-catenin increases in MSCs of old rats. To identify the effects of Wnt/β-catenin signaling on MSC aging induced with ORS, the expression of β-catenin, GSK-3β, and c-myc are detected. The results show that the Wnt/β-catenin signaling in the cells is activated after ORS treatment. Then we examine the aging, proliferation, and survival of MSCs after modulating Wnt/β-catenin signaling. The results indicate that the senescence and dysfunction of MSCs in the medium containing ORS is reversed by the Wnt/β-catenin signaling inhibitor DKK1 or by β-catenin siRNA. Moreover, the expression of γ-H2A.X, a molecular marker of DNA damage response, p16^INK4a, p53, and p21 is increased in senescent MSCs induced with ORS, and is also reversed by DKK1 or by β-catenin siRNA. In summary, our study indicates the Wnt/β-catenin signaling may play a critical role in MSC aging induced by the serum of aged animals and suggests that the DNA damage response and p53/p21 pathway may be the main mediators of MSC aging induced by excessive activation of Wnt/β-catenin signaling.