Physical interaction between Wilms tumor 1 and p73 proteins modulates their functions

The RNA-binding protein KSRP aggravates malignant progression of clear cell renal cell carcinoma through transcriptional inhibition and post-transcriptional destabilization of the NEDD4L ubiquitin ligase

BACKGROUND

KH-type splicing regulatory protein (KHSRP, also called KSRP), a versatile RNA-binding protein, plays a critical role in various physiological and pathological conditions through modulating gene expressions at multiple levels. However, the role of KSRP in clear cell renal cell carcinoma (ccRCC) remains poorly understood.

METHODS

KSRP expression was detected by a ccRCC tissue microarray and evaluated by an in silico analysis. Cell loss-of-function and gain-of-function, colony-formation, anoikis, and transwell assays, and an orthotopic bioluminescent xenograft model were conducted to determine the functional role of KRSP in ccRCC progression. Micro (mi)RNA and complementary (c)DNA microarrays were used to identify downstream targets of KSRP. Western blotting, quantitative real-time polymerase chain reaction, and promoter- and 3-untranslated region (3'UTR)-luciferase reporter assays were employed to validate the underlying mechanisms of KSRP which aggravate progression of ccRCC.

RESULTS

Our results showed that dysregulated high levels of KSRP were correlated with advanced clinical stages, larger tumor sizes, recurrence, and poor prognoses of ccRCC. Neural precursor cell-expressed developmentally downregulated 4 like (NEDD4L) was identified as a novel target of KSRP, which can reverse the protumorigenic and prometastatic characteristics as well as epithelial-mesenchymal transition (EMT) promotion by KSRP in vitro and in vivo. Molecular studies revealed that KSRP can decrease NEDD4L messenger (m)RNA stability via inducing mir-629-5p upregulation and directly targeting the AU-rich elements (AREs) of the 3'UTR. Moreover, KSRP was shown to transcriptionally suppress NEDD4L via inducing the transcriptional repressor, Wilm's tumor 1 (WT1). In the clinic, ccRCC samples revealed a positive correlation between KSRP and mesenchymal-related genes, and patients expressing high KSRP and low NEDD4L had the worst prognoses.

CONCLUSION

The current findings unveil novel mechanisms of KSRP which promote malignant progression of ccRCC through transcriptional inhibition and post-transcriptional destabilization of NEDD4L transcripts. Targeting KSRP and its pathways may be a novel pharmaceutical intervention for ccRCC.

Shikonin as a WT1 Inhibitor Promotes Promyeloid Leukemia Cell Differentiation

This study aims to observe the differentiating effect of shikonin on Wilms' tumor 1 (WT1)-positive HL-60 cells and investigate the fate of the differentiated leukemia cells. WT1 overexpression unaffected cell viability but promoted resistance to H₂O₂-induced DNA injury and cell apoptosis. The binding of shikonin to the WT1 protein was confirmed by molecular docking and drug affinity reaction target stability (DARTS). Shikonin at the non-cytotoxic concentration could decrease the WT1 protein and simultaneously reduced the CD34 protein and increased the CD11b protein in a dose-dependent manner in normal HL-60 cells but not in WT1-overexpressed HL-60 cells. Shikonin unaffected HL-60 cell viability in 48 h. However, it lasted for 10 days; could attenuate cell proliferation, mitochondrial membrane potential (MMP), and self-renewal; prevent the cell cycle; promote cell apoptosis. In a mouse leukemia model, shikonin could decrease the WT1 protein to prevent leukemia development in a dose-dependent manner. In this study, we also confirmed preliminarily the protein-protein interactions between WT1 and CD34 in molecular docking and CO-IP assay. Our results suggest that: 1. shikonin can down-regulate the WT1 protein level for leukemia differentiation therapy, and 2. the interaction between WT1 and CD34 proteins may be responsible for granulocyte/monocyte immaturity in HL-60 cells.

Consumption of oil macerated with garlic produces renovascular protective effects in adult apolipoprotein E-deficient mice

Oxidative stress and chronic inflammatory conditions contribute as key determinants in the development of vascular and renal diseases. Organosulfur compounds (OSCs) of oil macerated with garlic (OMG) are promising phytochemicals which could protect us from hyper-inflammation and oxidative stress-induced organ damage. The present work evaluated the effect of OMG intake in apolipoprotein E-knockout (ApoE-KO) mice. Adult female ApoE-KO mice were randomly divided into three groups and fed with control chow, oil-supplemented diet and OMG-supplemented diet. After 8 weeks, the animals were euthanized and blood, aorta, kidneys, liver and abdominal adipose tissues were obtained for further analysis. Biochemical parameters were measured in plasma, lipid peroxidation as malondialdehyde (MDA) levels was determined in the adipose tissue, oil red O was used to stain atherosclerotic lesions, and histological and ultrastructural analyses of the kidneys were performed. Renal expression levels of Tumor Necrosis Factor α (TNF-α), Interleukin-6 (IL-6) and Wilms' Tumor Protein (WT-1) were determined by western blotting and the co-immunoprecipitation assay (p53/WT-1). Also, transmission electron microscopy for studying the expression of mitofusin 2 (Mfn-2) was used to assess mitochondrial damage. The results showed that long-term moderate intake of OMG improved serum triglyceride levels, diminished the atheroma plaque area, and reduced lipid peroxidation. Furthermore, we found a decrease in oxidative and inflammatory markers, less apoptosis and reduced WT-1 expression in the kidneys. Also, OMG increased p53/WT-1 protein interactions and reduced mitochondrial damage. Our findings suggest that OMG intake would produce anti-atherosclerotic, antifibrotic, anti-inflammatory and antiapoptotic effects in adult ApoE-KO mice, conferring significant renovascular protective actions in a mechanism mediated, at least in part, by WT-1.

Alterations on a key nephrogenic/cardiogenic gene expression linked to hypertension development

The elevation of blood pressure produces specific organic lesions, including kidney and cardiac damage. On the other hand, cardiovascular disease usually leads to the development of hypertension. Thus, hypertension could be both a cause and a consequence of cardiovascular disease. Previous studies linked the lack of nitric oxide to cardiovascular abnormalities, including hypertension, arteriosclerosis, myocardial infarction, cardiac hypertrophy, diastolic heart failure, and reduced endothelium-derived hyperpolarizing factor responses, with shorter survival. The lack of this gas also leads to renal/cardiac abnormalities. It is widely known that nephrogenic deficiency is a risk factor for kidney disease. Besides, recent evidence suggests that alterations in WT-1, a key nephrogenic factor, could contribute to the development of hypertension. Moreover, some genes involved in the development of hypertension depend on WT-1. This knowledge makes it essential to investigate and understand the mechanisms regulating the expression of these genes during renal/cardiac development, and hypertension. As a consequence, the most in-depth knowledge of the complex aetiopathogenic mechanism responsible for the hypertensive disease will allow us to propose novel therapeutic tools.

Mediators and mechanisms of heat shock protein 70 based cytoprotection in obstructive nephropathy

Urinary heat shock protein 70 (Hsp70) is rapidly increased in patients with clinical acute kidney injury, indicating that it constitutes a component of the endogenous stress response to renal injury. Moreover, experimental models have demonstrated that Hsp70 activation is associated with the cytoprotective actions of several drugs following obstruction, including nitric oxide (NO) donors, geranylgeranylacetone, vitamin D, and rosuvastatin. Discrete and synergistic effects of the biological activities of Hsp70 may explain its cytoprotective role in obstructive nephropathy. Basic studies point to a combination of effects including inhibition of apoptosis and inflammation, repair of damaged proteins, prevention of unfolded protein aggregation, targeting of damaged protein for degradation, and cytoskeletal stabilization as primary effectors of Hsp70 action. This review summarizes our understanding of how the biological actions of Hsp70 may affect renal cytoprotection in the context of obstructive injury. The potential of Hsp70 to be of central importance to the mechanism of action of various drugs that modify the genesis of experimental obstructive nephropathy is considered.

Wilms' tumor gene 1 regulates p63 and promotes cell proliferation in squamous cell carcinoma of the head and neck

Background

Wilms’ tumor gene 1 (WT1) can act as a suppressor or activator of tumourigenesis in different types of human malignancies. The role of WT1 in squamous cell carcinoma of the head and neck (SCCHN) is not clear. Overexpression of WT1 has been reported in SCCHN, suggesting a possible oncogenic role for WT1. In the present study we aimed at investigating the function of WT1 and its previously identified protein partners p63 and p53 in the SCCHN cell line FaDu.

Methods

Silencing RNA (siRNA) technology was applied to knockdown of WT1, p63 and p53 in FaDu cells. Cell proliferation was detected using MTT assay. Chromatin immunoprecipitation (ChIP)/PCR analysis was performed to confirm the effect of WT1 on the p63 promoter. Protein co-immunoprecipitation (co-IP) was used to find protein interaction between WT1 and p53/p63. Microarray analysis was used to identify changes of gene expression in response to knockdown of either WT1 or p63. WT1 RNA level was detected using real-time quantitative PCR (RT-qPCR) in patients with SCCHN.

Results

We found that WT1 and p63 promoted cell proliferation, while mutant p53 (R248L) possessed the ability to suppress cell proliferation. We reported a novel positive correlation between WT1 and p63 expression. Subsequently, p63 was identified as a WT1 target gene. Furthermore, expression of 18 genes involved in cell proliferation, cell cycle regulation and DNA replication was significantly altered by downregulation of WT1 and p63 expression. Several known WT1 and p63 target genes were affected by WT1 knockdown. Protein interaction was demonstrated between WT1 and p53 but not between WT1 and p63. Additionally, high WT1 mRNA levels were detected in SCCHN patient samples.

Conclusions

Our findings suggest that WT1 and p63 act as oncogenes in SCCHN, affecting multiple genes involved in cancer cell growth.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1356-0) contains supplementary material, which is available to authorized users.

Mechanisms of transcriptional regulation by WT1 (Wilms' tumour 1)

The WT1 (Wilms' tumour 1) gene encodes a zinc finger transcription factor and RNA-binding protein that direct the development of several organs and tissues. WT1 manifests both tumour suppressor and oncogenic activities, but the reasons behind these opposing functions are still not clear. As a transcriptional regulator, WT1 can either activate or repress numerous target genes resulting in disparate biological effects such as growth, differentiation and apoptosis. The complex nature of WT1 is exemplified by a plethora of isoforms, post-translational modifications and multiple binding partners. How WT1 achieves specificity to regulate a large number of target genes involved in diverse physiological processes is the focus of the present review. We discuss the wealth of the growing molecular information that defines our current understanding of the versatility and utility of WT1 as a master regulator of organ development, a tumour suppressor and an oncogene.

Wt-1 Expression Linked to Nitric Oxide Availability during Neonatal Obstructive Nephropathy

The wt-1 gene encodes a zinc finger DNA-binding protein that acts as a transcriptional activator or repressor depending on the cellular or chromosomal context. The wt-1 regulates the expression of a large number of genes that have a critical role in kidney development. Congenital obstructive nephropathy disrupts normal renal development and causes chronic progressive interstitial fibrosis, which contributes to renal growth arrest, ultimately leading to chronic renal failure. Wt-1 is downregulated during congenital obstructive nephropathy, leading to apoptosis. Of great interest, nitric oxide bioavailability associated with heat shock protein 70 (Hsp70) interaction may modulate wt-1 mRNA expression, preventing obstruction-induced cell death during neonatal unilateral ureteral obstruction. Moreover, recent genetic researches have allowed characterization of many of the complex interactions among the individual components cited, but the realization of new biochemical, molecular, and functional experiments as proposed in our and other research labs allows us to establish a deeper level of commitment among proteins involved and the potential pathogenic consequences of their imbalance.

Genetic alterations of WWOX in Wilms' tumor are involved in its carcinogenesis

Loss of heterozygosity (LOH) in 16q appears in ~20-30% cases of Wilms' tumor. Within this region, known as common fragile site FRA16D, the WWOX tumor suppressor gene is located. Abnormalities of WWOX gene expression levels were observed in many tumor types and were associated with worse prognosis. The purpose of this study was to investigate the role of the WWOX tumor suppressor gene in Wilms' tumor samples. We evaluated the correlation between expression of WWOX and genes involved in proliferation (Ki67), apoptosis (BCL2, BAX), signal transduction (ERBB4, ERBB2, EGFR), cell cycle (CCNE1, CCND1), cell adhesion (CDH1) and transcription (TP73) using real-time RT-PCR in 23 tumor samples. We also analyzed the potential causes of WWOX gene expression reduction i.e., promoter methylation status (MethylScreen method) and loss of heterozygosity (LOH) status. We revealed a positive correlation between WWOX expression and BCL2, BCL2/BAX ratio, EGFR, ERBB4 isoform JM-a, TP73 and negative correlation with both cyclins. Loss of heterozygosity of the WWOX gene was observed only at intron 8, however, it had no influence on the reduction of its expression levels. Contrary to LOH, methylation of the region covering the 3' end of the promoter and part of exon 1 was associated with statistically significant reduction of WWOX gene expression levels. In the present study we reveal that in Wilms' tumors the WWOX expression levels are positively associated with the process of apoptosis, signal transduction through the ErbB4 pathway and EGFR and negatively with the regulation of the cell cycle (by cyclin E1 and D1). Moreover, our analysis indicates that in this type of tumor the expression of the WWOX gene can be regulated by an epigenetic mechanism--its promoter methylation.

p73-Binding Partners and Their Functional Significance

p73 is one of the tumor-suppressor p53 family of nuclear transcription factor. As expected from the structural similarity between p53 and p73, p73 has a tumor-suppressive function. However, p73 was rarely mutated in human primary tumors. Under normal physiological conditions, p73 is kept at an extremely low level to allow cells normal growth. In response to a certain subset of DNA damages, p73 is induced dramatically and transactivates an overlapping set of p53-target genes implicated in the promotion of cell cycle arrest and/or apoptotic cell death. Cells undergo cell cycle arrest and/or apoptotic cell death depending on the type and strength of DNA damages. p73 is regulated largely through the posttranslational modifications such as phosphorylation and acetylation. These chemical modifications are tightly linked to direct protein-protein interactions. In the present paper, the authors describe the functional significance of the protein-protein interactions in the regulation of proapoptotic p73.

Candidate genes and potential targets for therapeutics in Wilms' tumour

Wilms' tumour (WT) is the most common malignant renal tumour of childhood. During the past two decades or so, molecular studies carried out on biopsy specimens and tumour-derived cell lines have identified a multitude of chromosomal and epigenetic alterations in WT. In addition, a significant amount of evidence has been gathered to identify the genes and signalling pathways that play a defining role in its genesis, growth, survival and treatment responsiveness. As such, these molecules and mechanisms constitute potential targets for novel therapeutic strategies for refractory WT. In this report we aim to review some of the many candidate genes and intersecting pathways that underlie the complexities of WT biology.

Wilms' tumor 1 silencing decreases the viability and chemoresistance of glioblastoma cells in vitro: a potential role for IGF-1R de-repression

Wilms' tumor 1 (WT1) is a transcription factor with a multitude of downstream targets that have wide-ranging effects in non-glioma cell lines. Though its expression in glioblastomas is now well-documented, the role of WT1 in these tumors remains poorly defined. We hypothesized that WT1 functions as an oncogene to enhance glioblastoma viability and chemoresistance. WT1's role was examined by studying the effect of WT1 silencing and overexpression on DNA damage, apoptosis and cell viability. Results indicated that WT1 silencing adversely affected glioblastoma viability, at times, in synergy with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and cisplatin. To investigate other mechanisms through which WT1 could affect viability, we measured cell cycle distribution, senescence, and autophagy. WT1 silencing had no effect on these processes. Lastly, we examined WT1 regulation of IGF-1R expression. Counterintuitively, upregulation of IGF-1R was evident after WT1 silencing. In conclusion, WT1 functions as a survival factor in glioblastomas, possibly through inhibition of IGF-1R expression.

Cataloging and organizing p73 interactions in cell cycle arrest and apoptosis

We have compiled the p73-mediated cell cycle arrest and apoptosis pathways. p73 is a member of the p53 family, consisting of p53, p63 and p73. p73 exists in several isoforms, presenting different domain structures. p73 functions not only as a tumor suppressor in apoptosis but also as differentiator in embryo development. p53 mutations are responsible for half of the human cancers; p73 can partially substitute mutant p53 as tumor suppressor. The pathways we assembled create a p73-centered network consisting of 53 proteins and 176 interactions. We clustered our network into five functional categories: Upregulation, Activation, Suppression, Transcriptional Activity and Degradation. Our literature searches led to discovering proteins (c-Jun and pRb) with apparent opposing functional effects; these indicate either currently missing proteins and interactions or experimental misidentification or functional annotation. For convenience, here we present the p73 network using the molecular interaction map (MIM) notation. The p73 MIM is unique amongst MIMs, since it further implements detailed domain features. We highlight shared pathways between p53 and p73. We expect that the compiled and organized network would be useful to p53 family-based studies.

Structure of the Wilms tumor suppressor protein zinc finger domain bound to DNA

The zinc finger domain of the Wilms tumor suppressor protein (WT1) contains four canonical Cys(2)His(2) zinc fingers. WT1 binds preferentially to DNA sequences that are closely related to the EGR-1 consensus site. We report the structure determination by both X-ray crystallography and NMR spectroscopy of the WT1 zinc finger domain in complex with DNA. The X-ray structure was determined for the complex with a cognate 14 base-pair oligonucleotide, and composite X-ray/NMR structures were determined for complexes with both the 14 base-pair and an extended 17 base-pair DNA. This combined approach allowed unambiguous determination of the position of the first zinc finger, which is influenced by lattice contacts in the crystal structure. The crystal structure shows the second, third and fourth zinc finger domains inserted deep into the major groove of the DNA where they make base-specific interactions. The DNA duplex is distorted in the vicinity of the first zinc finger, with a cytidine twisted and tilted out of the base stack to pack against finger 1 and the tip of finger 2. By contrast, the composite X-ray/NMR structures show that finger 1 continues to follow the major groove in the solution complexes. However, the orientation of the helix is non-canonical, and the fingertip and the N terminus of the helix project out of the major groove; as a consequence, the zinc finger side-chains that are commonly involved in base recognition make no contact with the DNA. We conclude that finger 1 helps to anchor WT1 to the DNA by amplifying the binding affinity although it does not contribute significantly to binding specificity. The structures provide molecular level insights into the potential consequences of mutations in zinc fingers 2 and 3 that are associated with Denys-Drash syndrome and nephritic syndrome. The mutations are of two types, and either destabilize the zinc finger structure or replace key base contact residues.

p73: a chiaroscuro gene in cancer

p73 is a member of the p53 family which is gaining increasing importance in the field of cancer. Its structural homology with p53 led to the assumption that it could act as a new tumour suppressor gene. Increasing knowledge of its function, however, has cast doubts on this role. A particularly interesting characteristic of p73 is that the cell contains different isoforms with distinct and sometimes opposite functions. Evidence in the last few years clearly indicates that p73 does share some activities with p53 but also that it has some distinct functions. This review focuses on p73's role in the development and progression of cancer, analysing the gene structure and regulation and discussing similarities with p53 and differences. Recent results obtained with specific detection methods on the levels and functions of the different isoforms in tumours are also discussed.

A tumor suppressor and oncogene: the WT1 story

The Wilms' tumor 1 (WT1) gene encodes a transcription factor important for normal cellular development and cell survival. The initial discovery of WT1 as the causative gene in an autosomal-recessive condition identified it as a tumor suppressor gene whose mutations are associated with urogenital disease and the development of kidney tumors. However, this view is not in keeping with the frequent finding of wild-type, full-length WT1 in human leukemia, breast cancer and several other cancers including the majority of Wilms' tumors. Rather, these observations suggest that in those conditions, WT1 has an oncogenic role in tumor formation. In this review, we explore the literature supporting both views of WT1 in human cancer and in particular human leukemias. To understand the mechanism by which WT1 can do this, we will also examine its functional activity as a transcription factor and the influence of protein partners on its dual behavior.

Down-regulation of Wilms’ tumor 1 expression in glioblastoma cells increases radiosensitivity independently of p53

The Wilms' tumor 1 (WT1) gene is overexpressed in human glioblastoma and correlates with wild-type p53 status. In other cell types, WT1 inhibits p53-mediated apoptosis in response to DNA damaging agents. However, neither this interaction nor the relationship between WT1 and radiosensitivity has been studied in glioblastoma. To study this interaction, we generated LN-229 glioma cell lines (p53 mutant) stably expressing WT1 isoforms and induced apoptosis by transfecting with different doses of wild-type p53 plasmid expression vector. Constitutive expression of WT1 did not protect against exogenous p53-mediated apoptosis. Likewise, WT1 expression did not protect against endogenous p53-mediated cell death induced by radiotherapy in U87MG cells, which contain functional wild-type p53. We then tested the efficacy of WT1 siRNA in inhibiting WT1 expression and its effect on radiosensitivity. In T98G and LN-18 glioma cells, which possess p53 mutations, WT1 siRNA decreased WT1 protein to almost undetectable levels by 96-h post-transfection. Furthermore, WT1 siRNA transfection caused a significantly larger decrease in viability following irradiation than was seen in untransfected cells in both cell lines after treatment with ED50 of ionizing radiation. In conclusion, WT1 overexpression did not protect against p53-mediated apoptosis or ionizing radiation induced cell death. WT1 siRNA increased the radiosensitivity of two human glioma cell lines independently of p53. Anti-WT1 strategies may, therefore, prove useful in improving the response of glioblastoma to radiotherapy, thus potentially improving patient survival.

p19ras interacts with and activates p73 by involving the MDM2 protein

p73beta is a structural and functional homologue of p53, a tumor suppressor gene. In this study, we identified a novel p73beta-binding protein, p19ras, by the yeast two-hybrid screening method. Alternative splicing of the proto-oncogene H-ras pre-mRNA has led to two distinct transcripts, p19ras and p21ras. In both endogenous and overexpressed systems, we confirmed that p19ras binds to full-length p73beta in vivo and in vitro. Coexpression of p19ras with p73beta stimulated the transcriptional activity of p73beta. Ras proteins are known to be small membrane-localized guanine nucleotide-binding proteins. However, unlike other Ras proteins, p19ras is localized in the nucleus and the cytosol and its interaction with p73beta occurred exclusively in the nucleus. Oncogenic MDM2 (mouse double minutes 2) is a known repressor of p73 transcriptional activity. In this study, when p19ras was bound to MDM2, it further inhibited the association of MDM2 to the p73beta protein. In addition, p19ras abolished MDM2-mediated transcriptional repression of p73beta. Therefore, this study presents a novel pathway of Ras signaling that occurs in the nucleus, involving p19ras and p73beta. Furthermore, a p19ras-mediated novel regulatory mechanism of p73 involving the MDM2 protein is described.

Wilms' tumour: connecting tumorigenesis and organ development in the kidney

Wilms' tumour, or nephroblastoma, is a common childhood tumour that is intimately linked to early kidney development and is often associated with persistent embryonic renal tissue and other kidney abnormalities. WT1, the first gene found to be inactivated in Wilms' tumour, encodes a transcription factor that functions as both a tumour suppressor and a critical regulator of renal organogenesis. Our understanding of the roles of WT1 in tumour formation and organogenesis have advanced in parallel, providing a striking example of the intersection between tumour biology, cellular differentiation and normal organogenesis.

The Wilms Tumor Suppressor-1 Target Gene Podocalyxin Is Transcriptionally Repressed by p53

Wilms tumors are a heterogeneous class of tumors in which Wilms tumor suppressor-1 (WT1) and the p53 tumor suppressor may be variously inactivated by mutation, reduced in expression, or even overexpressed in the wild-type state. The downstream transcriptional targets of WT1 and p53 that are critical for mediating their roles in Wilms tumorigenesis are not well defined. The WiT49 cell line is characteristic of anaplastic Wilms tumors that are refractory to treatment and expresses wild-type WT1 and mutant p53. We have used the small molecule compound CP-31398 (Pfizer) to restore wild-type p53 function to the codon 248 mutant p53 present in WiT49 cells. In these cells, CP-31398 activated transcription of p53-regulated promoters and enhanced UV light-induced apoptosis without altering the overall p53 protein level. These phenotypes were accompanied by restored binding of the p53 protein to promoter sequences in vivo. Gene expression profiling of CP-31398-treated WiT49 cells revealed subsets of putative p53 target genes that were up- or down-regulated. A preferred target of p53-mediated repression in this system is the podocalyxin (PODXL) gene. PODXL is also transcriptionally regulated by WT1 and has roles in cell adhesion and anti-adhesion. Our results show that PODXL is a bona fide target of p53-mediated transcriptional repression while being positively regulated by WT1. We propose that inappropriate expression of PODXL due to changes in WT1 and/or p53 activity may contribute to Wilms tumorigenesis.

ASPP1 and ASPP2: common activators of p53 family members

We recently showed that ASPP1 and ASPP2 stimulate the apoptotic function of p53. We show here that ASPP1 and ASPP2 also induce apoptosis independently of p53. By binding to p63 and p73 in vitro and in vivo, ASPP1 and ASPP2 stimulate the transactivation function of p63 and p73 on the promoters of Bax, PIG3, and PUMA but not mdm2 or p21(WAF-1/CIP1). The expression of ASPP1 and ASPP2 also enhances the apoptotic function of p63 and p73 by selectively inducing the expression of endogenous p53 target genes, such as PIG3 and PUMA, but not mdm2 or p21(WAF-1/CIP1). Removal of endogenous p63 or p73 with RNA interference demonstrated that (16) the p53-independent apoptotic function of ASPP1 and ASPP2 is mediated mainly by p63 and p73. Hence, ASPP1 and ASPP2 are the first two identified common activators of all p53 family members. All these results suggest that ASPP1 and ASPP2 could suppress tumor growth even in tumors expressing mutant p53.

Insights into the physiological role of WT1 from studies of genetically modified mice

Discenza, Maria Teresa, and Jerry Pelletier. Insights into the physiological role of WT1 from studies of genetically modified mice. Physiol Genomics 16: 287-300, 2004; 10.1152/physiolgenomics.00164.2003.—The identification of WT1 gene mutations in children with WAGR and Denys-Drash syndromes pointed toward a role for WT1 in genitourinary system development. Biochemical analysis of the different WT1 protein isoforms showed that WT1 is a transcription factor and also has the ability to bind RNA. Analysis of WT1 complexes identified several target genes and protein partners capable of interacting with WT1. Some of these studies placed WT1, its downstream targets, and protein partners in a transcriptional regulatory network that controls urogenital system development. We review herein studies on WT1 knockout and transgenic models that have been instrumental in defining a physiological role for WT1 in normal and abnormal urogenital development.

A WT1 co-regulator controls podocyte phenotype by shuttling between adhesion structures and nucleus

Glomerular podocyte differentiation state is critical for filtration barrier function and is regulated by WT1, a zinc finger transcription factor. A yeast two-hybrid assay identified a novel, WT1-interacting protein (WTIP) that maps to human chromosome 19q13.1, a region with genes linked to familial focal segmental glomerulosclerosis. The domain structure of WTIP is similar to the zyxin subfamily of cytosolic LIM domain-containing proteins, which contain three carboxyl-terminal LIM protein-protein interaction domains and a proline-rich, pre-LIM region with a nuclear export signal. Other LIM domain-containing proteins (zyxin and mouse muscle LIM protein) did not interact with WT1 in two-hybrid assays, and WTIP did not interact with an unrelated transcription factor, LMX1B. WTIP mRNA was detected in cultured podocytes and was developmentally regulated, with expression peaking in mouse kidney at embryonic day 15-16 (E15-E16) in kidney but persisting into adulthood. In situ hybridization demonstrated WTIP expression in developing E15 glomeruli and in cultured podocytes. The partial WTIP clone, which interacted with WTIP in the two-hybrid assay, co-localized with WT1 in nuclei, co-precipitated with WT1, and inhibited WT1-dependent transcriptional activation of the amphiregulin promoter. In contrast, full-length WTIP was excluded from cell nuclei, but after the addition of leptomycin B, an inhibitor of Crm1-mediated nuclear export, it accumulated in the nucleus and co-precipitated with WT1 in whole cell lysates. Epitope-tagged WTIP co-localized with the adaptor protein CD2AP (CMS) in podocyte actin spots and with Mena at cell-cell junctions. We propose that WTIP monitors slit diaphragm protein assembly as part of a multiple protein complex, linking this specialized adhesion junction to the actin cytoskeleton, and shuttles into the nucleus after podocyte injury, providing a mechanism whereby changes in slit diaphragm structure modulate gene expression.

Assessment by molecular dynamics simulations of the structural determinants of DNA-binding specificity for transcription factor Sp1

The DNA-binding domain (DBD) of the ubiquituous transcription factor Sp1 consists of three consecutive zinc fingers that recognize a number of nucleotide sequences different from, but related to and sometimes overlapping, those recognized by the structurally better characterized early growth response protein 1 (EGR1, also known as Zif268, Krox-24, and NGFI-A). The accepted consensus binding sequence for Sp1 is usually defined by the asymmetric hexanucleotide core GGGCGG but this sequence does not include, among others, the GAG (=CTC) repeat that constitutes a high-affinity site for Sp1 binding to the wt1 promoter. Since no 3D structure of the whole DBD of Sp1 is available, either alone or in complex with DNA, a homology-based model was built and its interaction with two DNA 14-mers was studied using nanosecond molecular dynamics simulations in the presence of explicit water molecules. These oligonucleotides represent Sp1 target sites that are present in the promoters of the mdr1 and wt1 genes. For comparative purposes and validation of the protocol, the complex between the DBD of EGR1 and its DNA target site within the proximal mdr1 promoter was simulated under the same conditions. Some water molecules were seen to play an important role in recognition and stabilization of the protein-DNA complexes. Our results, which are supported by the available experimental evidence, suggest that the accuracy in the prediction of putative Sp1-binding sites can be improved by interpreting a set of rules, which are a blend of both stringency and tolerance, for the juxtaposed triplet subsites to which each zinc finger binds. Our approach can be extrapolated to WT1 and other related natural or artificial zinc-finger-containing DNA-binding proteins and may aid in the assignment of particular DNA stretches as allowed or disallowed-binding sites.

Physical interaction of p73 with c-Myc and MM1, a c-Myc-binding protein, and modulation of the p73 function

p73 shares high sequence homology with the tumor suppressor p53. Like p53, ectopic overexpression of p73 induces cell cycle arrest and/or apoptosis, and these biological activities are linked to its sequence-specific transactivation function. The COOH-terminal region of p73 is unique and has a function to modulate DNA-binding ability and transactivation activity. To identify and characterize cellular proteins that interact with the COOH-terminal region of p73 alpha and regulate its activity, we employed a yeast-based two-hybrid screen with a human fetal brain cDNA library. We found MM1, a nuclear c-Myc-binding protein, was associated with p73 alpha in both yeast two-hybrid and in vitro pull-down assays. In mammalian cells, MM1 co-immunoprecipitated with p73 alpha, whereas p73 beta and tumor suppressor p53 did not interact with MM1. Overexpression of MM1 in p53-deficient osteosarcoma SAOS-2 cells enhanced the p73 alpha-dependent transcription from the p53/p73-responsive Bax and PG13 promoters, whereas p73 beta- and p53-mediated transcriptional activation was unaffected in the presence of MM1. MM1 also stimulated the p73 alpha-mediated growth suppression in SAOS-2 cells. More importantly, we found that c-Myc was physically associated with p73 alpha and significantly impaired the transcriptional activity of p73 alpha on Bax and p21(waf1) promoters. Expression of MM1 strongly reduced the c-Myc-mediated inhibitory activity on p73 alpha. These results suggest that MM1 may act as a molecular partner for p73 to prevent the c-Myc-mediated inhibitory effect on its activity.

WT1 proteins: functions in growth and differentiation

The Wilms' tumor 1 gene (WT1) has been identified as a tumor suppressor gene involved in the etiology of Wilms' tumor. Approximately 10% of all Wilms' tumors carry mutations in the WT1 gene. Alterations in the WT1 gene have also been observed in other tumor types, such as leukemia, mesothelioma and desmoplastic small round cell tumor. Dependent on the tumor type, WT1 proteins might either function as tumor suppressor proteins or as survival factors. Mutations in the WT1 gene can also result in congenital abnormalities as observed in Denys-Drash and Frasier syndrome patients. Mouse models have proven the critical importance of WT1 expression for the development of several organs, including the kidneys, the gonads and the spleen. The WT1 proteins seem to perform two main functions. They regulate the transcription of a variety of target genes and may be involved in post-transcriptional processing of RNA. The WT1 gene encodes at least 24 protein forms. These isoforms have partially distinct biological functions and effects, which in many cases are also specific for the model system in which WT1 is studied. This review discusses the molecular mechanisms by which the various WT1 isoforms exert their functions in normal development and how alterations in WT1 may lead to developmental abnormalities and tumor growth.

p63alpha and DeltaNp63alpha can induce cell cycle arrest and apoptosis and differentially regulate p53 target genes

The p53 tumor suppressor protein plays a critical role in the regulation of the cell cycle and apoptosis. The importance of p53's functions is underscored by the high incidence of p53 mutations in human cancers. Recently, two p53-related proteins, p73 and p63, were identified as members of the p53 gene family. Multiple isoforms of p73 have been found, including DeltaN variants in which the N-termini are truncated. p63 is expressed as three major forms, p63alpha, p63beta and p63gamma, each of which differ in their C-termini. All three forms can be alternatively transcribed from a cryptic promoter located within intron 3, producing DeltaNp63alpha, DeltaNp63beta and DeltaNp63gamma. The high degree of similarity of p73 and p63 to evolutionarily conserved regions of p53 suggests that these proteins play an important and potentially redundant role in regulating cell cycle arrest and apoptosis. Here we describe the characterization of cell lines generated to inducibly express p63alpha and DeltaNp63alpha. We have found that p63alpha and DeltaNp63alpha can differentially regulate endogenous p53 target genes and induce cell cycle arrest and apoptosis. Deletion of the N-terminal 26 amino acids of DeltaNp63alpha abolished its ability to transactivate p53 target genes and induce cell cycle arrest and apoptosis. This indicates that a putative transactivation domain exists within the N-terminus of the DeltaN variants of p63. Furthermore, the differential regulation of p53 target genes by p63alpha and DeltaNp63alpha suggests that p63 and p53 utilize both similar and different signaling pathways to execute their cellular functions.

Physical interaction with Yes-associated protein enhances p73 transcriptional activity

Specific protein-protein interactions are involved in a large number of cellular processes and are mainly mediated by structurally and functionally defined domains. Here we report that the nuclear phosphoprotein p73 can engage in a physical association with the Yes-associated protein (YAP). This association occurs under physiological conditions as shown by reciprocal co-immunoprecipitation of complexes from lysates of P19 cells. The WW domain of YAP and the PPPPY motif of p73 are directly involved in the association. Furthermore, as required for ligands to group I WW domains, the terminal tyrosine (Y) of the PPPPY motif of p73 was shown to be essential for the association with YAP. Unlike p73alpha, p73beta, and p63alpha, which bind to YAP, the endogenous as well as exogenously expressed wild-type p53 (wt-p53) and the p73gamma isoform do not interact with YAP. Indeed, we documented that YAP interacts only with those members of the p53 family that have a well conserved PPXY motif, a target sequence for WW domains. Overexpression of YAP causes an increase of p73alpha transcriptional activity. Differential interaction of YAP with members of the p53 family may provide a molecular explanation for their functional divergence in signaling.

Pediatric genitourinary tumors

Each year advances are made in the evaluation and management of genitourinary tumors in children. There is increased understanding of molecular and genetic processes in tumorigenesis. In addition, knowledge concerning the current treatment modalities is increasing, thus allowing us to tailor treatments in order to decrease long-term complications. In this article, we review this past year's literature regarding pediatric genitourinary tumors with emphasis on Wilms tumor, rhabdomyosarcoma, and testicular tumors.

Wilms tumor and the WT1 gene

Wilms tumor or nephroblastoma is a pediatric kidney cancer arising from pluripotent embryonic renal precursors. Multiple genetic loci have been linked to Wilms tumorigenesis; positional cloning strategies have led to the identification of the WT1 tumor suppressor gene at chromosome 11p13. WT1 encodes a zinc finger transcription factor that is inactivated in the germline of children with genetic predisposition to Wilms tumor and in a subset of sporadic cancers. When present in the germline, specific heterozygous dominant-negative mutations are associated with severe abnormalities of renal and sexual differentiation, pointing to the essential role of WT1 for normal genitourinary development. The role of this tumor suppressor in normal organ-specific differentiation is also supported by the highly restricted temporal and spatial expression of WT1 in glomerular precursors of the developing kidney and by the failure of kidney development in wt1-null mice. Of two major alternative splicing products encoded by WT1, the (-KTS) isoform appears to mediate transcriptional activation of genes implicated in cellular differentiation, possibly also repressing proliferation-associated genes. The (+KTS) isoform, whose DNA-binding domain is disrupted by the insertion of three amino acids, may be involved in some aspect of mRNA processing. In addition to its function in genitourinary development, a role for WT1 in hematopoiesis is suggested by its aberrant expression and/or mutation in a subset of acute human leukemias. WT1 is also expressed in mesothelial cells; a specific oncogenic chromosomal translocation fusing the N-terminal domain of the Ewing sarcoma gene EWS to the three C-terminal zinc fingers of WT1 underlies desmoplastic small round cell tumor, an abdominal tumor thought to arise from the peritoneal lining. Understanding the distinct functional properties of WT1 isoforms and tumor-associated variants will provide unique insight into the link between normal organ-specific differentiation and malignancy.

Sensitization of human colon cancer cells to TRAIL-mediated apoptosis

TNF-related apoptosis-inducing ligand (TRAIL), a novel member of the tumor necrosis factor (TNF) family, is thought to induce apoptosis preferentially in cancer cells; however, increasing evidence suggests that a number of cancers are resistant to TRAIL treatment. FLICE-like inhibitory protein (FLIP), which structurally resembles caspase-8, can act as an inhibitor of apoptosis when expressed at high levels in certain cancer cells. The purpose of our present study was to determine whether human colon cancer cells are sensitive to TRAIL treatment and, if not, to identify potential mechanisms of resistance. Colon cancer cells of different metastatic potential (KM12C, KML4A, and KM20) were found to be resistant to the effects of TRAIL when used as a single agent. FLIP expression levels were increased in all three KM cell lines. Treatment with either actinomycin D (Act D;10 :g/ml) or cycloheximide (CHX; 10 :g/ml) decreased FLIP expression levels in all three cell lines. The decrease in cellular levels of FLIP was associated with sensitization to TRAIL-mediated apoptosis, as demonstrated by enhanced cell death and caspase-3 activity compared with either Act D or CHX alone. Our findings suggest that reduction of FLIP levels by Act D or CHX renders TRAIL-resistant human colon cancer cells sensitive to TRAIL-mediated apoptosis. The combination of TRAIL along with agents such as Act D or CHX, which target proteins that prevent cell death, may provide a more effective and less toxic regimen for treatment of resistant colon cancers.

P63 and P73: P53 mimics, menaces and more

Inactivation of the tumour suppressor p53 is the most common defect in cancer cells. The discovery of its two close relatives, p63 and p73, was therefore both provocative and confounding. Were these new genes tumour suppressors, p53 regulators, or evolutionary spin-offs? Both oncogenic and tumour-suppressor properties have now been attributed to the p53 homologues, perhaps reflecting the complex, often contradictory, protein products encoded by these genes. p63 and p73 are further implicated in many p53-independent pathways, including stem-cell regeneration, neurogenesis and sensory processes.

Assessment of differential gene expression patterns in human colon cancers

OBJECTIVE

To use a novel genomic approach to determine differential gene expression patterns in colon cancers of different metastatic potential.

SUMMARY BACKGROUND DATA

Colorectal cancer is the third leading cause of cancer deaths in the United States; despite aggressive treatment strategies, the 5-year survival rate for metastatic cancer has not changed in 50 years. The analysis of changes in gene expression patterns associated with metastasis may provide new treatment strategies.

METHODS

Human colon cancer cells KM12C (derived from a Dukes B colon cancer), KML4A (a metastatic variant derived from KM12C), and KM20 (derived from a Dukes D colon cancer) were extracted for RNA. In addition, RNA was extracted from normal colon, primary cancer, and liver metastasis in a patient with metastatic colon cancer. Gene expression patterns for approximately 1,200 human genes were analyzed and compared by cDNA array techniques.

RESULTS

Of the roughly 1,200 genes assessed in the KM cell lines, 9 genes were noted to have a more than threefold change in expression (either increased or decreased) in the more metastatic KML4A and KM20 cells compared with KM12C. Assessment of tissues from a patient with metastatic colon cancer demonstrated a more than threefold change in the expression of 14 genes in the primary cancer and liver metastasis compared with normal mucosa.

CONCLUSIONS

Using cDNA expression array technology, the authors identified genes with expression levels that are altered with metastasis. The ability to analyze and compare the expression patterns of multiple genes simultaneously provides a powerful technique to identify potential molecular targets for novel therapeutic strategies.

Physical and functional interaction between p53 mutants and different isoforms of p73

p53 is the most frequently inactivated tumor suppressor gene in human cancer, whereas its homologue, p73, is rarely mutated. Similarly to p53, p73 can promote growth arrest or apoptosis when overexpressed in certain p53-null tumor cells. It has previously been shown that some human tumor-derived p53 mutants can exert gain of function activity. The molecular mechanism underlying this activity remains to be elucidated. We show here that human tumor-derived p53 mutants (p53His175 and p53Gly281) associate in vitro and in vivo with p73 alpha, beta, gamma, and delta. This association occurs under physiological conditions, as verified in T47D and SKBR3 breast cancer cell lines. The core domain of mutant p53 is sufficient for the association with p73, whereas both the specific DNA binding and the oligomerization domains of p73 are required for the association with mutant p53. Furthermore, p53His175 and p53Gly281 mutants markedly reduce the transcriptional activity of the various isoforms of p73. Thus, human tumor-derived p53 mutants can associate with p73 not only physically but also functionally. These findings define a network involving mutant p53 and the various spliced isoforms of p73 that may confer upon tumor cells a selective survival advantage.