Alternative transcripts of the candidate tumor suppressor gene, WWOX, are expressed at high levels in human breast tumors

Pre-spliceosomal binding of U1 small nuclear ribonucleoprotein (RNP) and heterogenous nuclear RNP E1 is associated with suppression of a growth hormone receptor pseudoexon

Pseudoexons occur frequently in the human genome. This paper characterizes a pseudoexon in the GH receptor gene. Inappropriate activation of this pseudoexon causes Laron syndrome. Using in vitro splicing assays, pseudoexon silencing was shown to require a combination of a weak 5' pseudosplice-site and splicing silencing elements within the pseudoexon. Immunoprecipitation experiments showed that specific binding of heterogenous nuclear ribonucleoprotein E1 (hnRNP E1) and U1 small nuclear ribonucleoprotein (snRNP) in the pre-spliceosomal complex was associated with silencing of pseudoexon splicing. The possible role of hnRNP E1 was further supported by RNA interference experiments in cultured cells. Immunoprecipitation experiments with three other pseudoexons suggested that pre-spliceosomal binding of U1 snRNP is a potential general mechanism of suppression of pseudoexons.

WWOX expression in different histologic types and subtypes of non-small cell lung cancer

PURPOSE

Non-small cell lung cancer (NSCLC) has heterogeneous histopathologic classification and clinical behavior and very low survival rate. WWOX (WW domain-containing oxidoreductase) is a tumor suppressor gene, and its expression is altered in several cancers. The purpose of this study is to better define the role of WWOX in NSCLC tumorigenesis and progression by determining its pathogenetic and prognostic significance.

EXPERIMENTAL DESIGN

WWOX protein expression was evaluated by immunohistochemistry in 170 patients with NSCLC (101 squamous cell carcinomas, 66 adenocarcinomas, 3 large cell carcinomas) and was correlated with histopathologic (histotype, subtype, grade, tumor-node-metastasis, stage, index of cell proliferation Ki67/MIB1) and clinical (age, gender, local recurrences, distant metastases, overall survival, and disease-free survival) characteristics.

RESULTS

WWOX expression was absent/reduced in 84.9% of NSCLCs, whereas it was normal in 80.5% of adjacent normal lung tissues. WWOX expression was strongly associated with tumor histology (P=1.1x10(-5)) and histologic grade (P=0.0081): the percentage of cases with absent/strongly reduced WWOX expression was higher in squamous cell carcinomas and in poorly differentiated tumors. Regarding adenocarcinoma, bronchioloalveolar pattern showed normal WWOX expression in 62.5% of the cases, whereas in solid and acinar patterns, a prevalence of cases with absent/very low WWOX expression was observed (79.2% and 50%, respectively). Finally, weak WWOX staining intensity was related to the high index of cell proliferation (P=0.0012).

CONCLUSIONS

Our results suggest that the loss of WWOX expression plays different roles in tumorigenesis of distinct histotypes and subtypes of NSCLC and is related to high aggressiveness (G3; high proliferating activity) of tumors.

Targeted deletion of Wwox reveals a tumor suppressor function

The WW domain-containing oxidoreductase (WWOX) spans the second most common fragile site of the human genome, FRA16D, located at 16q23, and its expression is altered in several types of human cancer. We have previously shown that restoration of WWOX expression in cancer cells suppresses tumorigenicity. To investigate WWOX tumor suppressor function in vivo, we generated mice carrying a targeted deletion of the Wwox gene and monitored incidence of tumor formation. Osteosarcomas in juvenile Wwox(-/-) and lung papillary carcinoma in adult Wwox(+/-) mice occurred spontaneously. In addition, Wwox(+/-) mice develop significantly more ethyl nitrosourea-induced lung tumors and lymphomas in comparison to wild-type littermate mice. Intriguingly, these tumors still express Wwox protein, suggesting haploinsuffiency of WWOX itself is cancer predisposing. These results indicate that WWOX is a bona fide tumor suppressor.

WW domain-containing oxidoreductase: a candidate tumor suppressor

Common fragile site gene WWOX encodes a candidate tumor suppressor WW domain-containing oxidoreductase. Alteration of this gene, along with dramatic downregulation of WWOX protein, is shown in the majority of invasive cancer cells. Ectopic WWOX exhibits proapoptotic and tumor inhibitory functions in vitro and in vivo, probably interacting with growth regulatory proteins p53, p73 and others. Hyaluronidases regulate WWOX expression, increase cancer invasiveness and seem to be involved in the development of hormone-independent growth of invasive cancer cells. Estrogen and androgen stimulate phosphorylation and nuclear translocation of WWOX, although binding of WWOX to these sex hormones is unknown. We propose that suppression of WWOX expression by overexpressed hyaluronidases might contribute in part to the development of hormone independence in invasive cancer.

Large common fragile site genes and cancer

The common fragile sites are large regions of genomic instability that are found in all individuals and are hot spots for chromosomal rearrangements and deletions. A number of the common fragile sites have been found to span genes that are encoded by very large genomic regions. Two of these genes, FHIT and WWOX, have already been demonstrated to function as tumor suppressors. In this review we will discuss the large common fragile site genes that have been identified to date, and the role that these genes appear to play both in cellular responses to stress and in the development of cancer.

Chromosome 16 tumor-suppressor genes in breast cancer

Loss of heterozygosity on the long arm of chromosome 16 is one of the most frequent genetic events in breast cancer, suggesting the presence of one or more classic tumor-suppressor genes (TSGs). It has been shown that E-cadherin is the TSG on 16q in lobular tumors. In a search for the target genes in more frequently occurring low-grade nonlobular tumors, the smallest region of overlap (SRO) in this area of the genome has been exhaustively searched for. However, the results have demonstrated remarkable complexity, and so a clear consensus on identification of the SRO boundaries has not been reached. Several genes in the vicinity of these SROs have been scrutinized as putative TSGs in breast cancer, but so far, none has fulfilled the criteria for target genes. This review discusses the complexity of the 16q region and the different approaches that have been, are being, and will be used to detect the target genes in this area.

WWOX--the FRA16D cancer gene: expression correlation with breast cancer progression and prognosis

AIMS

WWOX is a tumour suppressor gene involved in various tumours including breast cancer. High chromosomal abnormalities in a genomic region spanned by WWOX are associated with the fact that this gene covers approximately 1 million base pairs of the second most affected among common chromosomal fragile sites FRA16D. We evaluated WWOX expression levels in breast cancer samples in association with diagnostics-prognostics markers.

METHODS

We performed quantitative real-time RT-PCR to analyse levels of expression of WWOX in 132 cases of breast cancer. We evaluated the relationship between WWOX mRNA levels, clinico-pathological factors, expression of aberrant WWOXDelta6-8 mRNA and other cancer related genes.

RESULTS

Expression of WWOX was higher in patients younger than 50 years old, in ER and PR positive tumours vs negative for those receptors and tumours without lymph node metastasis vs LN+. WWOX mRNA levels were also higher in tumours with higher apoptotic index (Bcl2/Bax ratio). Negative associations were found between WWOX expression and cytokeratins 5/6 and 17 (P<0.05). High level expression of WWOX was also associated with better disease free survival. Presence of WWOXDelta6-8 transcripts were accompanied with lower WWOX wild type mRNA level.

CONCLUSIONS

Reduced WWOX expression commonly observed in various neoplasias in cases of breast cancer is associated with markers of bad prognosis. Our findings reveal additional evidence that WWOX may be involved in steroid (estrogens) metabolism and signaling pathways. WWOX can be considered as a new target for gene therapy development due to the association of high WWOX expression with improved disease free survival.

WOX1 Is Essential for Tumor Necrosis Factor-, UV Light-, Staurosporine-, and p53-mediated Cell Death, and Its Tyrosine 33-phosphorylated Form Binds and Stabilizes Serine 46-phosphorylated p53

WW domain-containing oxidoreductase WOX1, also named WWOX or FOR, undergoes Tyr33 phosphorylation at its first N-terminal WW domain and subsequent nuclear translocation in response to sex steroid hormones and stress stimuli. The activated WOX1 binds tumor suppressor p53, and both proteins may induce apoptosis synergistically. Functional suppression of WOX1 by antisense mRNA or a dominant negative abolishes p53-mediated apoptosis. Here, we determined that UV light, anisomycin, etoposide, and hypoxic stress rapidly induced phosphorylation of p53 at Ser46 and WOX1 at Tyr33 (phospho-WOX1) and their binding interactions in several tested cancer cells. Mapping by yeast two-hybrid analysis and co-immunoprecipitation showed that phospho-WOX1 physically interacted with Ser46-phosphorylated p53. Knockdown of WOX1 protein expression by small interfering RNA resulted in L929 fibroblast resistance to apoptosis by tumor necrosis factor, staurosporine, UV light, and ectopic p53, indicating an essential role of WOX1 in stress stimuli-induced apoptosis. Notably, UV light could not induce p53 protein expression in these WOX1 knockdown cells, although p53 mRNA levels were not reduced. Suppression of WOX1 by dominant negative WOX1 (to block Tyr33 phosphorylation) also abolished UV light-induced p53 protein expression. Time course analysis showed that the stability of ectopic wild type p53, tagged with DsRed, was decreased in WOX1 knockdown cells. Inhibition of MDM2 by nutlin-3 increased the binding of p53 and WOX1 and stability of p53. Together, our data show that WOX1 plays a critical role in conferring cellular sensitivity to apoptotic stress and that Tyr33 phosphorylation in WOX1 is essential for binding and stabilizing Ser46-phosphorylated p53.

Common chromosomal fragile sites and cancer: focus on FRA16D

A growing body of experimental evidence supports the view that certain human chromosomal fragile sites have roles to play in cancer. The principle lines of evidence are at the level of mutation mechanism and gene function. Most research in this area has previously focussed on the FRA3B common fragile site and the FHIT gene that spans this site. Here we review recent progress in characterising the second most readily observed common fragile site, FRA16D, and the WWOX gene that spans it. Comparative analyses of FRA3B/FHIT and FRA16D/WWOX reveal some striking similarities suggesting that these sites and their associated genes may play a part in a normal protective response of cells to environmental stress.

WWOX gene restoration prevents lung cancer growth in vitro and in vivo

The WWOX (WW domain containing oxidoreductase) gene at the common fragile site, FRA16D, is altered in many types of cancer, including lung cancer. We have examined the tumor suppressor function of WWOX in preclinical lung cancer models. The WWOX gene was expressed in lung cancer cell lines through recombinant adenovirus (Ad) infection (Ad-WWOX), and through a drug [ponasterone A, (ponA)]-inducible system. After WWOX restoration in vitro, endogenous Wwox protein-negative cell lines (A549, H460, and H1299) underwent apoptosis through activation of the intrinsic apoptotic caspase cascade in A549 and H460 cells. Ectopic expression of Wwox caused dramatic suppression of tumorigenicity of A549, H460, and H1299 cells in nude mice after Ad-WWOX infection and after ponA induction of Wwox expression in H1299 lung cancer cells. Tumorigenicity and in vitro growth of U2020 (Wwox-positive) lung cancer cells was unaffected by Wwox overexpression. This study confirms that WWOX is a tumor suppressor gene and is highly effective in preventing growth of lung cancer xenografts, whether introduced through viral infection or by induction of a silent WWOX transgene.

Common fragile sites, extremely large genes, neural development and cancer

Common fragile sites (CFSs) are large regions of profound genomic instability found in all individuals. They are biologically significant due to their role in a number of genomic alterations that are frequently found in many different types of cancer. The first CFS to be cloned and characterized was FRA3B, the most active CFS in the human genome. Instability within this region extends for over 4.0 Mbs and contained within the center of this CFS is the FHIT gene spanning 1.5 Mbs of genomic sequence. There are frequent deletions and other alterations within this gene in multiple tumor types and the protein encoded by this gene has been demonstrated to function as a tumor suppressor in vitro and in vivo. In spite of this, FHIT is not a traditional mutational target in cancer and many tumors have large intronic deletions without any exonic alterations. There are several other very large genes found within CFS regions including Parkin (1.37 Mbs in FRA6E), GRID2 (1.47 Mbs within 4q22.3), and WWOX (1.11 Mbs within FRA16D). These genes also appear to function as tumor suppressors but are not traditional mutational targets in cancer. Each of these genes is highly conserved and the regions spanning them are CFSs in mice. We have now examined lists of the largest human genes and found forty that span over one megabase. Many of these are derived from chromosomal bands containing CFSs. BACs within these genes are being utilized as FISH probes to determine if these are also CFS genes. Thus far we have identified the following as CFS genes: CNTNAP2 (2.3 Mbs in FRA7I), DMD (2.09 Mbs in FRAXC), LRP1B (1.9 Mbs in FRA2F), CTNNA3 (1.78 Mbs in FRA10D), DAB1 (1.55 Mbs in FRA1B), and IL1RAPL1 (1.36 Mbs in FRAXC). Although, these genes are also not traditional mutational targets in cancer they do exhibit loss of expression in multiple tumor types suggesting that they may also function as tumor suppressors. Many of the large CFS genes are involved in neurological development. Parkin is mutated in autosomal recessive juvenile Parkinsonism and deletions in mice are associated with the mouse mutant Quaking (viable). Spontaneous mouse mutants in GRID2 and DAB1 are associated with Lurcher and Reelin, respectively. In humans, alterations in IL1RAPL1 cause X-linked mental retardation and loss of WWOX is associated with Tau phosphorylation. We propose that the instability-induced alterations in these genes contribute to cancer development in a two-step process. Initial alterations will primarily occur within intronic regions, as these genes are greater than 99% intronic. These are not benign. Instead, they alter the repertoire of transcripts produced from these genes. As cancer progresses deletions will begin to encompass exons resulting in gene inactivation. These two types of alterations occurring in multiple large CFS genes may contribute significantly to the heterogeneity observed in cancer. There are also important potential linkages between normal neurological development and the development of cancer mediated by alterations in these genes.

Targeted inhibition of the KLF6 splice variant, KLF6 SV1, suppresses prostate cancer cell growth and spread

Prostate cancer is a leading cause of cancer death in men. Risk prognostication, treatment stratification, and the development of rational therapeutic strategies lag because the molecular mechanisms underlying the initiation and progression from primary to metastatic disease are unknown. Multiple lines of evidence now suggest that KLF6 is a key prostate cancer tumor suppressor gene including loss and/or mutation in prostate cancer tumors and cell lines and decreased KLF6 expression levels in recurrent prostate cancer samples. Most recently, we identified a common KLF6 germ line single nucleotide polymorphism that is associated with an increased relative risk of prostate cancer and the increased production of three alternatively spliced, dominant-negative KLF6 isoforms. Here we show that although wild-type KLF6 (wtKLF6) acts as a classic tumor suppressor, the single nucleotide polymorphism-increased splice isoform, KLF6 SV1, displays a markedly opposite effect on cell proliferation, colony formation, and invasion. In addition, whereas wtKLF6 knockdown increases tumor growth in nude mice >2-fold, short interfering RNA-mediated KLF6 SV1 inhibition reduces growth by approximately 50% and decreases the expression of a number of growth- and angiogenesis-related proteins. Together, these findings begin to highlight a dynamic and functional antagonism between wtKLF6 and its splice variant KLF6 SV1 in tumor growth and dissemination.

Concordant loss of fragile gene expression early in breast cancer development

The FHIT and WWOX genes encompass the FRA3B and FRA16D fragile sites at chromosomes 3p14.2 and 16q23.3, respectively. Reduced Fhit and Wwox expression has been reported in approximately two-thirds of invasive breast tumors. Expression of these fragile gene products, as well as ErbB2 and p53, were evaluated immunohistochemically in 44 pure and 31 adjacent-to-invasive ductal carcinoma in-situ (DCIS) cases. Reduced Fhit and Wwox expression were observed in (i) 70% and 68% of pure DCIS; (ii) 52% and 55% of DCIS adjacent-to-invasive tumor cases; and (iii) 20% and 50% of adjacent normal tissue in pure DCIS cases. Reduced Wwox expression in adjacent normal tissue was observed in 30% of cases in the DCIS adjacent-to-invasive group. Reduced Fhit and Wwox expression was observed in 61% of adjoining invasive tumors. In all normal, pure DCIS, and DCIS adjacent-to-invasive lesions, Fhit and Wwox expression was positively associated (P = 0.034, P = 0.042, P = 0.004, respectively) and in the invasive component there was a positive trend toward association (P = 0.075). Fhit and Wwox were more frequently reduced in high-grade lesions in the DCIS adjacent-to-invasive (P = 0.025, P = 0.004, respectively). In the pure DCIS group, there was a statistically significant negative association between Fhit and ErbB2 expression in DCIS (P = 0.035). In summary, reduced Fhit and Wwox expression in in-situ breast cancer was associated, which may contribute to the high-grade DCIS-invasive tumor pathway.

WOX1 Is Essential for UVB Irradiation–Induced Apoptosis and Down-Regulated via Translational Blockade in UVB-Induced Cutaneous Squamous Cell Carcinoma In vivo

PURPOSE

We investigated the role of candidate tumor suppressor and proapoptotic WOX1 (also named WWOX, FOR, or WWOXv1) in UVB-induced apoptosis and formation of cutaneous squamous cell carcinomas (SCC).

EXPERIMENTAL DESIGN

Expression of WOX1 and family proteins (WWOX) in human primary cutaneous SCCs was examined by immunohistochemistry, in situ hybridization, and reverse transcription-PCR. UVB irradiation-induced WOX1 activation (Tyr33 phosphorylation and nuclear translocation), apoptosis, and cutaneous SCC formation were examined both in vitro and in vivo.

RESULTS

Up-regulation of human WOX1, isoform WOX2, and Tyr33 phosphorylation occurred during normal keratinocyte differentiation before cornification and death. Interestingly, significant reduction of these proteins and Tyr33 phosphorylation was observed in nonmetastatic and metastatic cutaneous SCCs (P < 0.001), but without down-regulation of WWOX mRNA (P > 0.05 versus normal controls), indicating a translational blockade of WWOX mRNA to protein. During acute exposure of hairless mice to UVB, WOX1 was up-regulated and activated in epidermal cells in 24 hours. In parallel with the clinical findings in humans, chronic UVB-treated mice developed cutaneous SCCs in 3 months, with significant reduction of WOX1 and Tyr33 phosphorylation and, again, without down-regulation of WWOX mRNA. Human SCC-25 and HaCaT cells were transfected with small interfering RNA-targeting WOX1 and shown to resist UVB-induced WOX1 expression, activation, and apoptosis.

CONCLUSIONS

WOX1 is essential for UVB-induced apoptosis and likely to be involved in the terminal differentiation of normal keratinocytes. During UVB-induced cutaneous SCC, epidermal cells have apparently prevented the apoptotic pressure from overexpressed WOX1 by shutting down the translation machinery for WWOX mRNA.

WWOX mRNA expression profile in epithelial ovarian cancer supports the role of WWOX variant 1 as a tumour suppressor, although the role of variant 4 remains unclear

WWOX is a candidate tumour suppressor gene that exhibits LOH or homozygous deletion in several tumour types. As well as the predominant full-length transcript (variant 1) there also exist alternatively spliced transcripts found previously only in malignant tissue. It has been suggested that proteins encoded by these variants may interfere with normal WWOX function in a dominant negative fashion. The most prevalent alternate transcript demonstrated in ovarian cancer is variant 4, which lacks exons 6-8. Here, we report the first comparison of the mRNA expression of WWOX variants 1 and 4 in human ovarian tumours and normal ovaries, and correlate expression with clinical data. We demonstrate significantly lower WWOX variant 1 expression in tumours than in normal ovaries. This reduction was not associated with any specific clinical subgroup. Variant 4 was expressed at low levels, and significantly associated with high grade and advanced stage ovarian cancer. Furthermore, tumours co-expressing variant 4 and relatively high levels of variant 1 showed significantly worse survival than tumours expressing variant 1 alone. However, variant 4 was also frequently identified in non-malignant ovarian tissue. These results support the role of WWOX variant 1 as a suppressor of ovarian tumourigenesis, but the role of variant 4 remains speculative.

FRA16D common chromosomal fragile site oxido-reductase (FOR/WWOX) protects against the effects of ionizing radiation in Drosophila

Fragile sites are chromosomal structures that have been proposed to have a determining role in cancer-associated DNA instability. The human WWOX gene spans the FRA16D chromosomal fragile site, the common minimal region of homozygous deletion found in adenocarcinomas and three out of five translocation breakpoints in multiple myeloma. Transcripts from the alternatively spliced WWOX gene encode proteins with common N-terminal WW domains and variable homology to the oxidoreductase family of proteins. In this study, the Drosophila orthologue of the WWOX gene was identified and subjected to mutagenesis via homologous recombination. The resultant DmWWOX1 mutants were viable but exhibited an increased sensitivity to ionizing radiation. This radiation sensitivity was rescued by reintroduction and expression of either the wild-type Drosophila or human WWOX genes. Thus, the protective function of DmWWOX in response to irradiation in Drosophila is conserved with human WWOX (hWWOX). This is consistent with a protective role for hWWOX where aberrant expression, as a result of breakage at the associated fragile site, could contribute directly to cancer progression.

Light-induced retinal damage involves tyrosine 33 phosphorylation, mitochondrial and nuclear translocation of WW domain-containing oxidoreductase in vivo

WW domain-containing oxidoreductase WOX1, also named WWOX or FOR, is a known proapoptotic protein and a candidate tumor suppressor. Stress stimuli activate WOX1 via tyrosine 33 (Tyr33) phosphorylation and translocation to the mitochondria and nuclei in vitro. Here, the potential role of WOX1 in light-induced retinal degeneration in vivo was investigated. WOX1 is expressed primarily in the inner retina at perinatal stages, whereas an enhanced expression of WOX1, along with its Tyr33 phosphorylation (p-WOX1), is shown specifically in the retinal ganglion cells in adults. Prolonged exposure of mature rats to constant, low-intensity light (500 lux) for 1-2 months resulted in substantial death of photoreceptors and the presence of activated microglia, astrocytes and Muller glial in the outer retina. However, the inner retina was not or barely affected. In the damaged inner and outer nuclear layers of rat retina, WOX1 and p-WOX1 were overly expressed. Also, WOX1 colocalized with fragments of opsin-positive cones. In rd mice with an inherited retinal deficiency, upregulation of WOX1 and p-WOX1 in degenerated retina was observed with age. By electron microscopy, a large number of immunogold particles of WOX1 and p-WOX1 were found in the damaged mitochondria and condensed nuclei of degenerating photoreceptors, indicating that WOX1 undergoes activation and translocation to these organelles. In contrast, little or no WOX1-positive particles were found in the Golgi apparatus. In conclusion, activated WOX1 is likely to exert apoptosis of neuronal cells in the outer retina during the light-induced injury and in mice with an inherited retinal defect.

Fragile genes as biomarkers: epigenetic control of WWOX and FHIT in lung, breast and bladder cancer

This study aimed to (a) determine if DNA methylation is a mechanism of WWOX (WW domain containing oxidoreductase) and FHIT (fragile histidine triad) inactivation in lung, breast and bladder cancers; (b) examine distinct methylation patterns in neoplastic and adjacent tissues and (c) seek correlation of methylation patterns with disease status. Protein expression was detected by immunohistochemistry, and methylation status by methylation-specific PCR (MSP) and sequencing, in lung squamous cell carcinomas and adjacent tissues, invasive breast carcinomas, adjacent tissues and normal mammary tissues and bladder transitional cell carcinomas. Wwox and Fhit expression was reduced in cancers in association with hypermethylation. Differential patterns of WWOX and FHIT methylation were observed in neoplastic vs adjacent non-neoplastic tissues, suggesting that targeted MSP amplification could be useful in following treatment or prevention protocols. WWOX promoter MSP differentiates DNA of lung cancer from DNA of adjacent lung tissue. WWOX and FHIT promoter methylation is detected in tissue adjacent to breast cancer and WWOX exon 1 MSP distinguishes breast cancer DNA from DNA of adjacent and normal tissue. Differential methylation in cancerous vs adjacent tissues suggests that WWOX and FHIT hypermethylation analyses could enrich a panel of DNA methylation markers.

Physical and functional interactions between the Wwox tumor suppressor protein and the AP-2gamma transcription factor

The WWOX gene encodes a tumor suppressor WW domain-containing protein, Wwox. Alterations of WWOX have been demonstrated in multiple types of cancer, and introduction of Wwox into Wwox-negative tumor cells has resulted in tumor suppression and apoptosis. The Wwox protein contains two WW domains that typically bind proline-rich motifs and mediate protein-protein interactions. Recently, we have described functional cross-talk between the Wwox protein and the p53 homologue, p73. To further explore the biological function of Wwox, we investigated other interacting candidates. In this report, we demonstrate a physical and functional association between AP-2gamma transcription factor and the Wwox protein. AP-2gamma at 20q13.2 encodes a transcription factor and is frequently amplified in breast carcinoma. We show that Wwox binds to the PPPY motif of AP-2gamma via its first WW domain. Alterations of tyrosine 33 in the first WW domain of Wwox or the proline-rich motif in AP-2gamma dramatically reduce this interaction. In addition, our results demonstrate that Wwox expression triggers redistribution of nuclear AP-2gamma to the cytoplasm, hence suppressing its transactivating function. Our results suggest that Wwox tumor suppressor protein inhibits AP-2gamma oncogenic activity by sequestering it in the cytoplasm.

17β-Estradiol upregulates and activates WOX1/WWOXv1 and WOX2/WWOXv2 in vitro: potential role in cancerous progression of breast and prostate to a premetastatic state in vivo

Human WWOX gene encodes a proapoptotic WW domain-containing oxidoreductase WOX1 (also named WWOX, FOR2 or WWOXv1). Apoptotic and stress stimuli activate WOX1 via Tyr33 phosphorylation and nuclear translocation. WOX1 possesses a tetrad NSYK motif in the C-terminal short-chain alcohol dehydrogenase/reductase (SDR) domain, which may bind estrogen and androgen. Here, we determined that 17beta-estradiol (E(2)) activated WOX1, p53 and ERK in COS7 fibroblasts, primary lung epithelial cells, and androgen receptor (AR)-negative prostate DU145 cells, but not in estrogen receptor (ER)-positive breast MCF7 cells. Androgen also activated WOX1 in the AR-negative DU145 cells. These observations suggest that sex hormone-mediated Tyr33 phosphorylation and nuclear translocation of WOX1 is independent of ER and AR. Stress stimuli increase physical binding of p53 with WOX1 in vivo. We determined here that E(2) increased the formation of p53/WOX1 complex and their nuclear translocation in COS7 cells; however, nuclear translocation of this complex could not occur in MCF7 cells. By immunohistochemistry, we determined that progression of prostate from normal to hyperplasia, cancerous and metastatic stages positively correlate with upregulation and activation of WOX1 and WOX2 (FOR1/WWOXv2). In contrast, breast cancer development to a premetastatic state is associated with upregulation and Tyr33 phosphorylation of cytosolic WOX1 and WOX2, followed by significant downregulation or absent expression during metastasis. These Tyr33-phosphorylated proteins are mostly located in the mitochondria without translocating to the nuclei, which is comparable to those findings in cultured breast cancer cells. Together, sex steroid hormone-induced activation of WOX1 and WOX2 is independent of ER and AR, and this activation positively correlates with cancerous progression of prostate and breast to a premetastatic state.

Loss of WWOX expression in gastric carcinoma

PURPOSE

WW domain-containing oxidoreductase (WWOX) is a tumor suppressor gene that maps to the common fragile site FRA16D on chromosome 16q23.3-24.1. To investigate the role of the WWOX gene in the development of gastric carcinoma, we examined a large series of primary adenocarcinomas and nine gastric cancer cell lines for the expression of Wwox.

EXPERIMENTAL DESIGN

Loss of heterozygosity, reverse-transcription-PCR, and immunohistochemistry were used to assess the role of WWOX in stomach cancer. A total of 81 primary gastric adenocarcinoma were analyzed.

RESULTS

Loss of heterozygosity was observed in 31% of the cases and loss of Wwox protein expression was found in 65% of gastric adenocarcinoma primary specimens and 33% of gastric cancer cell lines. In addition, we found a high correlation between Wwox and Fhit protein expression.

CONCLUSIONS

Our results indicate that alterations of the WWOX gene may be involved quite frequently in gastric tumorigenesis. Our data could be used in future studies to develop diagnostic and targeted therapy of stomach cancer.

Frequent downregulation and loss of WWOX gene expression in human hepatocellular carcinoma

The WWOX (WW-domain containing oxidoreductase) is a candidate tumour suppressor gene spanning the same chromosome region, 16q23, as the second most common fragile site (FS), FRA16D. Deletions detected by comparative genomic hybridisation (CGH) and loss of heterozygosity at microsatellite markers on chromosome 16q are common in many human cancers including hepatocellular carcinoma (HCC). The development of human HCC is closely associated with exposure to oncogenic viruses and chemical carcinogens, agents known to frequently target common FS. We examined the status of WWOX genomic DNA, RNA and protein in 18 cell lines derived from human HCC and found recurrent alterations of the gene. Loss of DNA copy-number confined to band 16q23 was detected by CGH in several cell lines. Although homozygous deletions of the WWOX gene were not detected, WWOX mRNA expression was absent or lower in 60% of cell lines. The occurrence of aberrant WWOX reverse transcription–PCR products with deletion of exons 6–8 correlated significantly with altered WWOX expression. All of the cell lines showing mRNA downregulation had a decreased or undetectable level of WWOX protein as demonstrated by Western blotting with antibody to WWOX. Furthermore, 13 out of the 18 cell lines expressed decreased levels or no WWOX protein when compared with normal liver. These results show that WWOX gene is frequently altered in HCC and raise the possibility that this gene is implicated in hepatocarcinogenesis.

Down-regulation of WW Domain-containing Oxidoreductase Induces Tau Phosphorylation in Vitro

Numerous enzymes hyperphosphorylate Tau in vivo, leading to the formation of neurofibrillary tangles (NFTs) in the neurons of Alzheimer's disease (AD). Compared with age-matched normal controls, we demonstrated here that the protein levels of WW domain-containing oxidoreductase WOX1 (also known as WWOX or FOR), its Tyr33-phosphorylated form, and WOX2 were significantly down-regulated in the neurons of AD hippocampi. Remarkably knock-down of WOX1 expression by small interfering RNA in neuroblastoma SK-N-SH cells spontaneously induced Tau phosphorylation at Thr212/Thr231 and Ser515/Ser516, enhanced phosphorylation of glycogen synthase kinase 3beta (GSK-3beta) and ERK, and enhanced NFT formation. Also an increased binding of phospho-GSK-3beta with phospho-Tau was observed in these WOX1 knock-down cells. In comparison, increased phosphorylation of Tau, GSK-3beta, and ERK, as well as NFT formation, was observed in the AD hippocampi. Activation of JNK1 by anisomycin further increased Tau phosphorylation, and SP600125 (a JNK inhibitor) and PD-98059 (an MEK1/2 inhibitor) blocked Tau phosphorylation and NFT formation in these WOX1 knock-down cells. Ectopic or endogenous WOX1 colocalized with Tau, JNK1, and GSK-3beta in neurons and cultured cells. 17Beta-estradiol, a neuronal protective hormone, increased the binding of WOX1 and GSK-3beta with Tau. Mapping analysis showed that WOX1 bound Tau via its COOH-terminal short-chain alcohol dehydrogenase/reductase domain. Together WOX1 binds Tau via its short-chain alcohol dehydrogenase/reductase domain and is likely to play a critical role in regulating Tau hyperphosphorylation and NFT formation in vivo.

Parkin gene alterations in hepatocellular carcinoma

The Parkin gene is an extremely large gene (1.5 Mb) within the highly unstable FRA6E common fragile site (CFS) region, which is frequently altered in ovarian, breast, and hepatocellular carcinomas. Because Parkin/FRA6E has genomic similarities to FHIT/FRA3B and WWOX/FRA16D, two other large tumor-suppressor genes that are within CFS regions, we were interested in characterizing Parkin gene alterations and their possible association with cancer. After analyzing 50 cancer-derived cell lines including 11 hepatocellular carcinoma (HCC) cell lines, we found that one HCC cell line, PLC/PRF/5, had a detectable homozygous deletion encompassing exon 3. Using quantitative duplex PCR and fluorescence in situ hybridization analysis to characterize the copy number changes of Parkin exons in HCC cell lines, we found that 4 of 11 HCC cell lines had heterozygous deletions of Parkin exons and one, Hep3B, had an exon duplication. Parkin protein expression was significantly decreased or absent in all 11 HCC cell lines. Furthermore, more than 50% of HCC primary tumors had decreased Parkin expression compared to that in normal liver tissue. Parkin gene-transfected PLC5 and Hep3B cells grew more slowly than vector-only transfectants and also showed increased sensitivity to apoptosis induced by cell-cycle inhibitors. Therefore, we suggest that Parkin may be involved in tumor suppression and that the loss of Parkin contributes to the development of hepatocarcinoma.

Functional association between Wwox tumor suppressor protein and p73, a p53 homolog

The WWOX gene is a recently cloned tumor suppressor gene that spans the FRA16D fragile region. Wwox protein contains two WW domains that are generally known to mediate protein-protein interaction. Here we show that Wwox physically interacts via its first WW domain with the p53 homolog, p73. The tyrosine kinase, Src, phosphorylates Wwox at tyrosine 33 in the first WW domain and enhances its binding to p73. Our results further demonstrate that Wwox expression triggers redistribution of nuclear p73 to the cytoplasm and, hence, suppresses its transcriptional activity. In addition, we show that cytoplasmic p73 contributes to the proapoptotic activity of Wwox. Our findings reveal a functional cross-talk between p73 and Wwox tumor suppressor protein.

WWOX, the common chromosomal fragile site, FRA16D, cancer gene

Gross chromosomal rearrangements and aneuploidy are among the most common somatic genomic abnormalities that occur during cancer initiation and progression, in particular in human solid tumor carcinogenesis. The loss of large chromosomal regions as consequence of gross rearrangements (e.g. deletions, monosomies, unbalanced translocations and mitotic recombination) have been traditionally associated with the existence of tumor suppressor genes within the areas affected by the loss of genetic material. The long arm of chromosome 16 was identified as being frequently associated with structural abnormalities in multiple neoplasias, that led us to focus attention on the detailed genetic dissection of this region resulting in the cloning of the putative tumor suppressor gene, WWOX (WW domain containing Oxidoreductase). Interestingly, the WWOX gene resides in the very same region as that of the common chromosomal fragile site 16D (FRA16D). The WWOX gene encodes a protein that contains two WW domains, involved in protein-protein interactions, and a short chain dehydrogenase (SDR) domain, possibly involved in sex-steroid metabolism. We have identified the WWOX WW domain ligand as the PPXY motif confirming the biochemical activity of this domain. WWOX normally resides in the Golgi and we will demonstrate that Golgi localization requires an intact SDR. Inactivation of the WWOX gene during tumorigenesis can occur by homozygous deletions and possibly mutation, however, aberrantly spliced forms of WWOX mRNA have been observed even when one allele is still intact. The aberrantly spliced mRNAs have deletions of the exons that encode the SDR and these WWOX protein isoforms display abnormal intracellular localization to the nucleus possibly functioning as dominant negative inhibitors of full length WWOX. Thus, generation of aberrant transcripts of WWOX may represent a novel mechanism to functionally inactivate WWOX without genomic alteration of the remaining allele. In this article we will review the cloning and identification of WWOX as the target of FRA16D. In addition, we will discuss the possible biochemical functions of WWOX and present evidence that ectopic WWOX expression inhibits tumor growth.

Expression of WW domain-containing oxidoreductase WOX1 in the developing murine nervous system

WW domain-containing oxidoreductase WOX1, also known as WWOX or FOR, is a proapoptotic protein and a putative tumor suppressor. Hyaluronidases such as PH-20, Hyal-1 and Hyal-2 induce the expression of WOX1, and hyaluronidases and hyaluronan are involved in the embryonic development. In the present study, we document the expression of WOX1 in the developing murine nervous system. Immunohistochemical analysis revealed that WOX1 was differentially expressed in early dividing cells from all three germ layers from embryonic to perinatal stages. In murine fetuses, WOX1 was present prevalently in the brainstem, spinal cord and peripheral nerve bundles, but its expression decreased after birth. In parallel, the expression of WOX1, as determined by Western blotting, was significantly reduced in the brain stem and spinal cord of adult mice. Notably, high levels of WOX1 immunoreactivity was observed in the neural crest-derived structures such as cranial and spinal ganglia and cranial mesenchyme during the late fetal stage. In the adult brain, WOX1 is abundant in the epithelial cells of the choroids plexus and ependymal cells, while a low to moderate level of WOX1 is observed within white matter tracts, such as axonal profiles of the corpus callosum, striatum, optic tract, and cerebral peduncle. WOX1 is shown to mediate apoptosis synergistically with p53 in vitro. Nonetheless, the expression profiles of WOX1 were found to be similar in both p53 wild type and knockout mice, suggesting that WOX1 expression is not controlled by p53-mediated gene transcription. Taken together, in this study we have shown the expression and distribution of WOX1 in developing and adult murine nervous system. The potential role of WOX1 in the neuronal differentiation is discussed.

The fragile genesFHIT andWWOX are inactivated coordinately in invasive breast carcinoma

BACKGROUND

FHIT and WWOX are a tumor suppressor and a candidate suppressor that encompass the FRA3B and FRA16D fragile sites at chromosomes 3p14.2 and 16q23.3-24.1, respectively. Reduced or absent Fhit expression has been reported in two-thirds of invasive breast tumors in association with adverse prognostic factors. Loss of 16q has been reported frequently in low-grade, invasive breast tumors.

METHODS

Expression of Fhit and Wwox was evaluated by immunohistochemical staining in 97 archived breast carcinoma specimens. Expression levels were analyzed for correlations with each other, as well as with various patient and tumor characteristics.

RESULTS

Reduced Fhit and Wwox expression in tumors was observed in 54.6% and 63.2% of specimens, respectively. Fhit and Wwox expression were correlated strongly (P = 0.001). Reduced Fhit staining was seen more frequently in premenopausal patients (P = 0.010), estrogen receptor (ER)-negative or scantly ER-positive tumors (P = 0.058 borderline), high-grade tumors (P = 0.005), and tumors with metastases (P = 0.041). Reduced Wwox staining was more common in tumors with less favorable ER status (P = 0.033). Wwox expression in normal tissue was reduced in 32.9% of specimens, especially in patients with higher stage disease (P = 0.033). Severely reduced Wwox staining (extent < 10%) in normal tissue was found only in postmenopausal women, but reduced Wwox staining (11-75%) was more common in premenopausal women (P = 0.012). Tumor status, lymph node status, and intensity of Fhit expression in tumors were related independently to survival (P = 0.003, P < 0.001, and P = 0.046, respectively).

CONCLUSIONS

The strong correlation observed between Fhit and Wwox expression was consistent with the common elevated susceptibility of fragile sites to DNA damage. Reduced Fhit expression is associated with adverse prognostic factors. The current results suggest that Wwox also has an important and complex association with steroid hormone expression and breast carcinogenesis.

Matrix attachment region (MAR) properties and abnormal expansion of AT island minisatellites in FRA16B fragile sites in leukemic CEM cells

AT-rich minisatellites (AT islands) are sites of genomic instability in cancer cells and targets for extremely lethal AT-specific drugs, such as bizelesin. Here we investigated the AT islands in the FRA16B fragile site region for their possible roles in the organization of DNA on the nuclear matrix. The FRA16B AT island nominally spans approximately 3 kb of mostly >90% A/T DNA. In silico analysis indicates that this domain exhibits characteristics of nuclear matrix attachment regions (MARs): an exceptionally intense computed 'MAR potential' and profound duplex destabilization and flexibility. FRA16B repeats specifically bind to isolated nuclear matrices, which indicates their in vitro MAR function. This binding is several-fold greater than that of a known MAR in the c-myc gene. AT islands in fragile sites FRA16B and FRA16D are significantly more abundant in CEM cells that are hypersensitive to bizelesin compared to normal WI-38 cells. FRA16B overabundance in CEM is due to an approximately 10-fold expansion of FRA16B repeats. The expanded FRA16B minisatellites in CEM cells preferentially localize to the nuclear matrix-associated DNA indicating their in vivo MAR function. The unexpanded repeats in WI-38 cells localize to the loop DNA. The c-myc MAR is also matrix-associated in CEM cells while localizing to loop DNA in WI-38 cells. These results are the first to demonstrate that AT islands in fragile sites can function as MARs both in vitro and in vivo. The ability of FRA16B-mediated MAR sites to rearrange depending on the repeat expansion status could be relevant to both genomic instability of cancer cells and their sensitivity to AT-island targeting drugs.

Molecular mechanisms underlying WOX1 activation during apoptotic and stress responses

Human WWOX gene encodes a putative tumor suppressor WW domain-containing oxidoreductase WOX1 (also known as WWOX or FOR). A high frequency of loss of heterozygosity (LOH) of this gene has been shown in prostate, lung, breast and other cancers. In addition, numerous aberrant WWOX mRNA transcripts have been found in cancer cells. WOX1 is a proapoptotic protein. In response to stress or apoptotic stimuli, WOX1 became phosphorylated at Tyr33, which enabled its complex formation with activated p53 and JNK1. The p53/WOX1 complex translocated to the mitochondria and further to the nuclei to mediate apoptosis. WOX1 mutants, which were inactivated for nuclear translocation or Tyr33 phosphorylation, failed to induce apoptosis, indicating that activation of WOX1 via Tyr33 phosphorylation, followed by nuclear translocation, is essential for inducing cell death. WOX1 induced apoptosis synergistically with p53. In contrast, transiently activated JNK1 induced anti-apoptotic response, and this protective activity inhibited WOX1-induced apoptosis. Taken together, WOX1 is involved in stress and apoptotic responses, and is likely to regulate the activation of both p53 and JNK1.

JNK1 physically interacts with WW domain-containing oxidoreductase (WOX1) and inhibits WOX1-mediated apoptosis

Transient activation of c-Jun N-terminal kinase (JNK) promotes cell survival, whereas persistent JNK activation induces apoptosis. Bovine testicular hyaluronidase PH-20 activates JNK1 and protects L929 fibroblasts from staurosporine-mediated cell death. PH-20 also induces the expression of a p53-interacting WW domain-containing oxidoreductase (WOX1, also known as WWOX or FOR) in these cells. WOX1 enhances the cytotoxic function of tumor necrosis factor and mediates apoptosis synergistically with p53. Thus, the activated JNK1 is likely to counteract WOX1 in mediating apoptosis. Here it is demonstrated that ectopic JNK1 inhibited WOX1-mediated apoptosis of L929 fibroblasts, monocytic U937 cells, and other cell types. Also, JNK1 blocked WOX1 prevention of cell cycle progression. By stimulating cells with anisomycin or UV light, JNK1 became activated, and WOX1 was phosphorylated at Tyr(33). The activated JNK1 physically interacted with the phosphorylated WOX1, as determined by co-immunoprecipitation. Alteration of Tyr(33) to Arg(33) in WOX1 abrogated its binding interaction with JNK1 and its activity in mediating cell death, indicating that Tyr(33) phosphorylation is needed to activate WOX1. A dominant negative WOX1 was developed and shown to block p53-mediated apoptosis and anisomycin-mediated WOX1 phosphorylation but could not inhibit JNK1 activation. This mutant protein bound p53 but could not interact with JNK1, as determined in yeast two-hybrid analysis. Taken together, phosphorylation of JNK1 and WOX1 is necessary for their physical interaction and functional antagonism.

Chromosomal aberrations related to metastasis of human solid tumors

The central role of sequential accumulation of genetic alterations during the development of cancer has been firmly established since the pioneering cytogenetic studies successfully defined recurrent chromosome changes in specific types of tumor. In the course of carcinogenesis, cells experience several genetic alterations that are associated with the transition from a preneoplastic lesion to an invasive tumor and finally to the metastatic state. Tumor progression is characterized by stepwise accumulation of genetic alterations. So does the dominant metastatic clone. Modern molecular genetic analyses have clarified that genomic changes accumulate during the development and progression of cancers. In comparison with the corresponding primary tumor, additional events of chromosomal aberrations (including gains or allelic losses) are frequently found in metastases, and the incidence of combined chromosomal alterations in the primary tumor, plus the occurrence of additional aberrations in the distant metastases, correlated significantly with decreased postmetastatic survival. The deletions at 3p, 4p, 6q, 8p, 10q, 11p, 11q, 12p, 13q, 16q, 17p, 18q, 21q, and 22q, as well as the over-representations at 1q, 8q, 9q, 14q and 15q, have been found to associate preferentially with the metastatic phenotype of human cancers. Among of them, the deletions on chromosomes 8p, 17p, 11p and 13p seem to be more significant, and more detail fine regions of them, including 8p11, 8p21-12, 8p22, 8p23, 17p13.3, 11p15.5, and 13q12-13 have been suggested harboring metastasis-suppressor genes. During the past decade, several human chromosomes have been functionally tested through the use of microcell-mediated chromosome transfer (MMCT), and metastasis-suppressor activities have been reported on chromosomes 1, 6, 7, 8, 10, 11, 12, 16, and 17. However, it is not actually known at what stage of the metastatic cascade these alterations have occurred. There is still controversial with the association between the chromosomal aberrations and the metastatic phenotype of cancer. As the progression of human genome project and the establishment of more and more new techniques, it is hopeful to make clear the genetic mechanisms involved in the tumor metastasis in a not very long future, and provide new clues to predicting and controlling the metastasis.