The common fragile site FRA16D gene product WWOX: roles in tumor suppression and genomic stability

Unveiling the relationship between WWOX and BRCA1 in mammary tumorigenicity and in DNA repair pathway selection

Breast cancer is the leading cause of cancer-related deaths in women worldwide, with the basal-like or triple-negative breast cancer (TNBC) subtype being particularly aggressive and challenging to treat. Understanding the molecular mechanisms driving the development and progression of TNBC is essential. We previously showed that WW domain-containing oxidoreductase (WWOX) is commonly inactivated in TNBC and is implicated in the DNA damage response (DDR) through ATM and ATR activation. In this study, we investigated the interplay between WWOX and BRCA1, both frequently inactivated in TNBC, on mammary tumor development and on DNA double-strand break (DSB) repair choice. We generated and characterized a transgenic mouse model (K14-Cre;Brca1fl/fl;Wwoxfl/fl) and observed that mice lacking both WWOX and BRCA1 developed basal-like mammary tumors and exhibited a decrease in 53BP1 foci and an increase in RAD51 foci, suggesting impaired DSB repair. We examined human TNBC cell lines harboring wild-type and mutant BRCA1 and found that WWOX expression promoted NHEJ repair in cells with wild-type BRCA1. Our findings suggest that WWOX and BRCA1 play an important role in DSB repair pathway choice in mammary epithelial cells, underscoring their functional interaction and significance in breast carcinogenesis.

Identification of a novel splice-site WWOX variant with paternal uniparental isodisomy in a patient with infantile epileptic encephalopathy

WOREE syndrome is an early infantile epileptic encephalopathy characterized by drug-resistant seizures and severe psychomotor developmental delays. We report a case of a WWOX splice-site mutation with uniparental isodisomy. A 1-year and 7-month-old girl presented with nystagmus and epileptic seizures from early infancy, with no fixation or pursuit of vision. Physical examination revealed small deformities, such as swelling of both cheeks, folded fingers, rocking feet, and scoliosis. Brain imaging revealed slight hypoplasia of the cerebrum. Electroencephalogram showed focal paroxysmal discharges during the interictal phase of seizures. Vitamin B6 and zonisamide were administered for early infantile epileptic encephalopathy; however, the seizures were not relieved. Despite altering the type and dosage of antiepileptic drugs and ACTH therapy, the seizures were intractable. Whole-exome analysis revealed the homozygosity of WWOX(NM_016373.4):c.516+1G>A. The WWOX mRNA sequencing using peripheral blood RNA confirmed that exon 5 was homozygously deleted. Based on these results, the patient was diagnosed with WOREE syndrome at 5 months. The WWOX variant found in this study is novel and has never been reported before. WOREE syndrome being extremely rare, further case series and analyses of its pathophysiology are warranted.

Identification of compound heterozygous deletion of the WWOX gene in WOREE syndrome

BACKGROUND

Biallelic loss-of-function variants in WWOX cause WWOX-related epileptic encephalopathy (WOREE syndrome), which has been reported in 60 affected individuals to date. In this study, we report on an affected individual with WOREE syndrome who presented with early-onset refractory seizures and global neurodevelopmental delay and died at the age of two and a half years.

METHODS

We present clinical and molecular findings in the affected individual, including biallelic pathogenic variants in the WWOX gene. We employed different molecular approaches, such as whole exome sequencing, quantitative real-time polymerase chain reaction (qPCR), and whole-genome sequencing, to identify the genetic variants. The breakpoints were determined through gap PCR and Sanger sequencing.

RESULT

Whole exome sequencing revealed homozygous exon 6 deletion in the WWOX gene in the proband. Quantitative real-time PCR confirmed that the parents were heterozygous carriers of exon 6 deletion. However, using whole-genome sequencing, we identified three larger deletions (maternal allele with exon 6-8 deletion and paternal allele with two deletions in proximity one in intron 5 and the other in exon 6) involving the WWOX gene in the proband, with deletion sizes of 13,261 bp, 53,904 bp, and 177,200 bp. The exact breakpoints were confirmed through gap PCR and Sanger sequencing. We found that the proband inherited the discontinuous deletion of intron 5 and exon 6 from the father, and the exons 6-8 deletion from the mother using gap PCR.

CONCLUSION

Our findings extend the variant spectrum of WOREE syndrome and support the critical role of the WWOX gene in neural development.

Antineoplastic Nature of WWOX in Glioblastoma Is Mainly a Consequence of Reduced Cell Viability and Invasion

Following the discovery of WWOX, research has moved in many directions, including the role of this putative tumor suppressor in the central nervous system and related diseases. The task of determining the nature of WWOX in glioblastoma (GBM) is still considered to be at the initial stage; however, the influence of this gene on the GBM malignant phenotype has already been reported. Because most of the available in vitro research does not consider several cellular GBM models or a wide range of investigated biological assays, the present study aimed to determine the main processes by which WWOX exhibits anticancer properties in GBM, while taking into account the phenotypic heterogeneity between cell lines. Ectopic WWOX overexpression was studied in T98G, DBTRG-05MG, U251MG, and U87MG cell lines that were compared with the use of assays investigating cell viability, proliferation, apoptosis, adhesion, clonogenicity, three-dimensional and anchorage-independent growth, and invasiveness. Observations presenting the antineoplastic properties of WWOX were consistent for T98G, U251MG, and U87MG. Increased proliferation and tumor growth were noted in WWOX-overexpressing DBTRG-05MG cells. A possible explanation for this, arrived at via bioinformatics tools, was linked to the TARDBP transcription factor and expression differences of USP25 and CPNE2 that regulate EGFR surface abundance. Collectively, and despite various cell line-specific circumstances, WWOX exhibits its anticancer nature mainly via a reduction of cell viability and invasiveness of glioblastoma.

The Yin and Yang of ERBB4: Tumor Suppressor and Oncoprotein

ERBB4 (HER4) is a member of the ERBB family of receptor tyrosine kinases, a family that includes the epidermal growth factor receptor (EGFR/ERBB1/HER1), ERBB2 (Neu/HER2), and ERBB3 (HER3). EGFR and ERBB2 are oncoproteins and validated targets for therapeutic intervention in a variety of solid tumors. In contrast, the role that ERBB4 plays in human malignancies is ambiguous. Thus, here we review the literature regarding ERBB4 function in human malignancies. We review the mechanisms of ERBB4 signaling with an emphasis on mechanisms of signaling specificity. In the context of this signaling specificity, we discuss the hypothesis that ERBB4 appears to function as a tumor suppressor protein and as an oncoprotein. Next, we review the literature that describes the role of ERBB4 in tumors of the bladder, liver, prostate, brain, colon, stomach, lung, bone, ovary, thyroid, hematopoietic tissues, pancreas, breast, skin, head, and neck. Whenever possible, we discuss the possibility that ERBB4 mutants function as biomarkers in these tumors. Finally, we discuss the potential roles of ERBB4 mutants in the staging of human tumors and how ERBB4 function may dictate the treatment of human tumors. SIGNIFICANCE STATEMENT: This articles reviews ERBB4 function in the context of the mechanistic model that ERBB4 homodimers function as tumor suppressors, whereas ERBB4-EGFR or ERBB4-ERBB2 heterodimers act as oncogenes. Thus, this review serves as a mechanistic framework for clinicians and scientists to consider the role of ERBB4 and ERBB4 mutants in staging and treating human tumors.

Neonatal neuronal WWOX gene therapy rescues Wwox null phenotypes

WW domain-containing oxidoreductase (WWOX) is an emerging neural gene-regulating homeostasis of the central nervous system. Germline biallelic mutations in WWOX cause WWOX-related epileptic encephalopathy (WOREE) syndrome and spinocerebellar ataxia and autosomal recessive 12 (SCAR12), two devastating neurodevelopmental disorders with highly heterogenous clinical outcomes, the most common being severe epileptic encephalopathy and profound global developmental delay. We recently demonstrated that neuronal ablation of murine Wwox recapitulates phenotypes of Wwox-null mice leading to intractable epilepsy, hypomyelination, and postnatal lethality. Here, we designed and produced an adeno-associated viral vector (AAV9) harboring murine Wwox or human WWOX cDNA and driven by the human neuronal Synapsin I promoter (AAV-SynI-WWOX). Testing the efficacy of AAV-SynI-WWOX delivery in Wwox-null mice demonstrated that specific neuronal restoration of WWOX expression rescued brain hyperexcitability and seizures, hypoglycemia, myelination deficits, and the premature lethality and behavioral deficits of Wwox-null mice. These findings provide a proof-of-concept for WWOX gene therapy as a promising approach to curing children with WOREE and SCAR12.

Modeling genetic epileptic encephalopathies using brain organoids

Developmental and epileptic encephalopathies (DEE) are a group of disorders associated with intractable seizures, brain development, and functional abnormalities, and in some cases, premature death. Pathogenic human germline biallelic mutations in tumor suppressor WW domain-containing oxidoreductase (WWOX) are associated with a relatively mild autosomal recessive spinocerebellar ataxia-12 (SCAR12) and a more severe early infantile WWOX-related epileptic encephalopathy (WOREE). In this study, we generated an in vitro model for DEEs, using the devastating WOREE syndrome as a prototype, by establishing brain organoids from CRISPR-engineered human ES cells and from patient-derived iPSCs. Using these models, we discovered dramatic cellular and molecular CNS abnormalities, including neural population changes, cortical differentiation malfunctions, and Wnt pathway and DNA damage response impairment. Furthermore, we provide a proof of concept that ectopic WWOX expression could potentially rescue these phenotypes. Our findings underscore the utility of modeling childhood epileptic encephalopathies using brain organoids and their use as a unique platform to test possible therapeutic intervention strategies.

Neuronal deletion of Wwox, associated with WOREE syndrome, causes epilepsy and myelin defects

WOREE syndrome caused by human germline biallelic mutations in WWOX is a neurodevelopmental disorder characterized by intractable epilepsy, severe developmental delay, ataxia and premature death at the age of 2-4 years. The underlying mechanisms of WWOX actions are poorly understood. In the current study, we show that specific neuronal deletion of murine Wwox produces phenotypes typical of the Wwox-null mutation leading to brain hyperexcitability, intractable epilepsy, ataxia and postnatal lethality. A significant decrease in transcript levels of genes involved in myelination was observed in mouse cortex and hippocampus. Wwox-mutant mice exhibited reduced maturation of oligodendrocytes, reduced myelinated axons and impaired axonal conductivity. Brain hyperexcitability and hypomyelination were also revealed in human brain organoids with a WWOX deletion. These findings provide cellular and molecular evidence for myelination defects and hyperexcitability in the WOREE syndrome linked to neuronal function of WWOX.

Neurological Disorders Associated with WWOX Germline Mutations-A Comprehensive Overview

The transcriptional regulator WW domain-containing oxidoreductase (WWOX) is a key player in a number of cellular and biological processes including tumor suppression. Recent evidence has emerged associating WWOX with non-cancer disorders. Patients harboring pathogenic germline bi-allelic WWOX variants have been described with the rare devastating neurological syndromes autosomal recessive spinocerebellar ataxia 12 (SCAR12) (6 patients) and WWOX-related epileptic encephalopathy (DEE28 or WOREE syndrome) (56 patients). Individuals with these syndromes present with a highly heterogenous clinical spectrum, the most common clinical symptoms being severe epileptic encephalopathy and profound global developmental delay. Knowledge of the underlying pathophysiology of these syndromes, the range of variants of the WWOX gene and its genotype-phenotype correlations is limited, hampering therapeutic efforts. Therefore, there is a critical need to identify and consolidate all the reported variants in WWOX to distinguish between disease-causing alleles and their associated severity, and benign variants, with the aim of improving diagnosis and increasing therapeutic efforts. Here, we provide a comprehensive review of the literature on WWOX, and analyze the pathogenic variants from published and unpublished reports by collecting entries from the ClinVar, DECIPHER, VarSome, and PubMed databases to generate the largest dataset of WWOX pathogenic variants. We estimate the correlation between variant type and patient phenotype, and delineate the impact of each variant, and used GnomAD to cross reference these variants found in the general population. From these searches, we generated the largest published cohort of WWOX individuals. We conclude with a discussion on potential personalized medicine approaches to tackle the devastating disorders associated with WWOX mutations.

Characterization of WWOX expression and function in canine mast cell tumors and malignant mast cell lines

BACKGROUND

The WW domain-containing oxidoreductase (WWOX) tumor suppressor gene is frequently lost in a variety of solid and hematopoietic malignancies in humans. Dysregulation of WWOX has been implicated as playing a key role in tumor cell survival, DNA damage repair, and genomic stability. The purpose of this study was to characterize WWOX expression in spontaneous canine mast cell tumors (MCTs) and malignant cell lines and investigate the potential contribution of WWOX loss on malignant mast cell behavior.

METHODS/RESULTS

WWOX expression is decreased in primary canine MCTs and malignant mast cell lines compared to normal canine bone marrow-cultured mast cells. In transformed canine mastocytoma cell lines, overexpression of WWOX or WWOX knockdown had no effect on mast cell viability. Inhibition of WWOX enhanced clonogenic survival following treatment with ionizing radiation in the C2 mast cell line. Lastly, immunohistochemistry for WWOX was performed using a canine MCT tissue microarray, demonstrating that WWOX staining intensity and percent of cells staining for WWOX is decreased in high-grade MCTs compared to low-grade MCTs.

CONCLUSIONS

These data suggest that WWOX expression is attenuated or lost in primary canine MCTs and malignant mast cell lines. Given the observed increase in clonogenic survival in WWOX-deficient C2 mast cells treated with ionizing radiation, further investigation of WWOX and its role in mediating the DNA damage response in malignant mast cells is warranted.

Programmed DNA Damage and Physiological DSBs: Mapping, Biological Significance and Perturbations in Disease States

DNA double strand breaks (DSBs) are known to be the most toxic and threatening of the various types of breaks that may occur to the DNA. However, growing evidence continuously sheds light on the regulatory roles of programmed DSBs. Emerging studies demonstrate the roles of DSBs in processes such as T and B cell development, meiosis, transcription and replication. A significant recent progress in the last few years has contributed to our advanced knowledge regarding the functions of DSBs is the development of many next generation sequencing (NGS) methods, which have considerably advanced our capabilities. Other studies have focused on the implications of programmed DSBs on chromosomal aberrations and tumorigenesis. This review aims to summarize what is known about DNA damage in its physiological context. In addition, we will examine the advancements of the past several years, which have made an impact on the study of genome landscape and its organization.

Pleiotropic tumor suppressor functions of WWOX antagonize metastasis

Tumor progression and metastasis are the major causes of death among cancer associated mortality. Metastatic cells acquire features of migration and invasion and usually undergo epithelia-mesenchymal transition (EMT). Acquirement of these various hallmarks rely on different cellular pathways, including TGF-β and Wnt signaling. Recently, we reported that WW domain-containing oxidoreductase (WWOX) acts as a tumor suppressor and has anti-metastatic activities involving regulation of several key microRNAs (miRNAs) in triple-negative breast cancer (TNBC). Here, we report that WWOX restoration in highly metastatic MDA-MB435S cancer cells alters mRNA expression profiles; further, WWOX interacts with various proteins to exert its tumor suppressor function. Careful alignment and analysis of gene and miRNA expression in these cells revealed profound changes in cellular pathways mediating adhesion, invasion and motility. We further demonstrate that WWOX, through regulation of miR-146a levels, regulates SMAD3, which is a member of the TGF-β signaling pathway. Moreover, proteomic analysis of WWOX partners revealed regulation of the Wnt-signaling activation through physical interaction with Disheveled. Altogether, these findings underscore a significant role for WWOX in antagonizing metastasis, further highlighting its role and therapeutic potential in suppressing tumor progression.

WWOX somatic ablation in skeletal muscles alters glucose metabolism

OBJECTIVE

WWOX, a well-established tumor suppressor, is frequently lost in cancer and plays important roles in DNA damage response and cellular metabolism.

METHODS

We re-analyzed several genome-wide association studies (GWAS) using the Type 2 Diabetes Knowledge Portal website to uncover WWOX's association with metabolic syndrome (MetS). Using several engineered mouse models, we studied the effect of somatic WWOX loss on glucose homeostasis.

RESULTS

Several WWOX variants were found to be strongly associated with MetS disorders. In mouse models, somatic ablation of Wwox in skeletal muscle (WwoxΔSKM) results in weight gain, glucose intolerance, and insulin resistance. Furthermore, WwoxΔSKM mice display reduced amounts of slow-twitch fibers, decreased mitochondrial quantity and activity, and lower glucose oxidation levels. Mechanistically, we found that WWOX physically interacts with the cellular energy sensor AMP-activated protein kinase (AMPK) and that its loss is associated with impaired activation of AMPK, and with significant accumulation of the hypoxia inducible factor 1 alpha (HIF1α) in SKM.

CONCLUSIONS

Our studies uncover an unforeseen role of the tumor suppressor WWOX in whole-body glucose homeostasis and highlight the intimate relationship between cancer progression and metabolic disorders, particularly obesity and type-2 diabetes.

SUBJECT AREAS

Genetics, Metabolic Syndrome, Diabetes.

WWOX Inhibits Metastasis of Triple-Negative Breast Cancer Cells via Modulation of miRNAs

Triple-negative breast cancer (TNBC) is a heterogeneous, highly aggressive, and difficult to treat tumor type. The tumor suppressor WWOX spans FRA16D, a common fragile site that is commonly altered in breast cancer. Despite recent progress, the role of WWOX in TNBC metastasis is unknown. Here we report that WWOX inactivation correlates with advanced stages of TNBC and that its levels are frequently altered in TNBC cells. Ectopic restoration of WWOX in WWOX-negative TNBC cells inhibited metastasis while its depletion in WWOX-positive TNBC cells promoted metastasis. WWOX was a negative regulator of c-MYC, which regulated miR-146a expression and consequently fibronectin levels, contributing to an epithelial status of the cell. Treatment of TNBC cells with anti-miR-146a rescued the WWOX antimetastatic phenotype. Moreover, overexpression of MYC in WWOX-expressing TNBC cells overrode WWOX effects on miR-146a and fibronectin levels. Altogether, our data uncover an essential role for WWOX in antagonizing TNBC progression and highlight its potential use as a biomarker for metastasis. SIGNIFICANCE: These findings highlight the mechanism by which the tumor suppressor WWOX regulates metastasis of triple-negative breast cancer.See related commentary by Sharma, p. 1746.

Modeling WWOX Loss of Function in vivo: What Have We Learned?

The WW domain–containing oxidoreductase (WWOX) gene encompasses a common fragile sites (CFS) known as FRA16D, and is implicated in cancer. WWOX encodes a 46kDa adaptor protein, which contains two N-terminal WW–domains and a catalytic domain at its C–terminus homologous to short–chain dehydrogenase/reductase (SDR) family proteins. A high sequence conservation of WWOX orthologues from insects to rodents and ultimately humans suggest its significant role in physiology and homeostasis. Indeed, data obtained from several animal models including flies, fish, and rodents demonstrate WWOX in vivo requirement and that its deregulation results in severe pathological consequences including growth retardation, post–natal lethality, neuropathy, metabolic disorders, and tumorigenesis. Altogether, these findings set WWOX as an essential protein that is necessary to maintain normal cellular/physiological homeostasis. Here, we review and discuss lessons and outcomes learned from modeling loss of WWOX expression in vivo.

WWOX Tumor Suppressor Gene in Breast Cancer, a Historical Perspective and Future Directions

The WWOX tumor suppressor gene is located at 16q23. 1–23.2, which covers the region of FRA16D—a common fragile sites. Deletions within the WWOX coding sequence are observed in up to 80% of breast cancer cases, which makes it one of the most common genetic alterations in this tumor type. The WWOX gene is known to play a role in breast cancer: increased expression of WWOX inhibits cell proliferation in suspension, reduces tumor growth rates in xenographic transplants, but also enhances cell migration through the basal membrane and contributes to morphological changes in 3D matrix-based cell cultures. The WWOX protein may act in several ways, as it has three functional domains—two WW domains, responsible for protein-protein interactions and an SDR domain (short dehydrogenase/reductase domain) which catalyzes conversions of low molecular weight ligands, most likely steroids. In epithelial cells, WWOX modulates gene transcription through interaction with p73, AP-2γ, and ERBB4 proteins. In steroid hormone-regulated tissues like mammary gland epithelium, the WWOX SDR domain acts as a steroid dehydrogenase. The relationship between WWOX and hormone receptors was shown in an animal model, where WWOX(C3H)+/–mice exhibited loss of both ER and PR receptors. Moreover, in breast cancer specimens, a positive correlation was observed between WWOX expression and ER status. On the other hand, decreased WWOX expression was associated with worse prognosis, namely higher relapse and mortality rates in BC patients. Recently, it was shown that genomic instability might be driven by the loss of WWOX expression. It was reported that WWOX plays role in DNA damage response (DDR) and DNA repair by regulating ATM activation through physical interaction. A genome caretaker function has also been proposed for WWOX, as it was found that WWOX sufficiency decreases homology directed repair (HDR) and supports non-homologous end-joining (NHEJ) repair as the dominant DSB repair pathway by Brca1-Wwox interaction. In breast cancer cells, WWOX was also found to modulate the expression of glycolysis pathway genes, through hypoxia-inducible transcription factor 1α (HIF1α) regulation. The paper presents the current state of knowledge regarding the WWOX tumor suppressor gene in breast cancer, as well as future research perspectives.

Somatic loss of WWOX is associated with TP53 perturbation in basal-like breast cancer

Inactivation of WW domain-containing oxidoreductase (WWOX), the gene product of the common fragile site FRA16D, is a common event in breast cancer and is associated with worse prognosis of triple-negative breast cancer (TNBC) and basal-like breast cancer (BLBC). Despite recent progress, the role of WWOX in driving breast carcinogenesis remains unknown. Here we report that ablation of Wwox in mammary tumor-susceptible mice results in increased tumorigenesis, and that the resultant tumors resemble human BLBC. Interestingly, copy number loss of Trp53 and downregulation of its transcript levels were observed in the Wwox knockout tumors. Moreover, tumors isolated from Wwox and Trp53 mutant mice were indistinguishable histologically and transcriptionally. Finally, we find that deletion of TP53 and WWOX co-occurred and is associated with poor survival of breast cancer patients. Altogether, our data uncover an essential role for WWOX as a bona fide breast cancer tumor suppressor through the maintenance of p53 stability.

WWOX controls hepatic HIF1α to suppress hepatocyte proliferation and neoplasia

Liver cancer is one of the most lethal malignancies with very poor prognosis once diagnosed. The most common form of liver cancer is hepatocellular carcinoma (HCC). The WW domain-containing oxidoreductase (WWOX) is a large gene that is often perturbed in a wide variety of tumors, including HCC. WWOX has been shown to act as a tumor suppressor modulating cellular metabolism via regulating hypoxia-inducible factor 1α (HIF-1α) levels and function. Given that WWOX is commonly inactivated in HCC, we set to determine whether specific targeted deletion of murine Wwox affects liver biology and HCC development. WWOX liver-specific knockout mice (Wwox ΔHep ) showed more potent liver regeneration potential and enhanced proliferation as compared with their control littermates. Moreover, WWOX deficiency in hepatocytes combined with diethylnitrosamine treatment increased the tumor burden, which was associated with increased HIF1α levels and target gene transactivation. Inhibition of HIF1α by systemic treatment with digoxin significantly delayed HCC formation. Our work suggests that WWOX inactivation has a central role in promoting HCC through rewiring of cellular metabolism and modulating proliferation.

Association of WWOX rs9926344 polymorphism with poor prognosis of hepatocellular carcinoma

Introduction: The WW domain-containing oxidoreductase (WWOX), widely expressed in human tissues, is considered as a tumor suppressor gene and plays an important role in the incidence and progression of human cancer, HCC included. This study was to investigate the correlation between single nucleotide polymorphisms (SNPs) of the WWOX gene and the prognosis of hepatocellular carcinoma (HCC) patients.

Materials and Methods: After a total of 152 HCC patients were recruited, 8 cases with tumor recurrence within 2-years after operation and 8 cases without recurrence were selected randomly for SNP genotyping and screening using Affymetrix Array 6.0. And then we confirmed candidate SNPs in the remaining 136 patients by time-of-flight mass spectrometry (TOF-MS).

Results: In total, 32 SNPs were screened and identified as candidate SNPs with one SNP in particular, (rs9926344), being further verified to be valuable. We found that AA+AG genotype and A allele of WWOX rs9926344 were significantly associated with recurrent risk of HCC (p=0.002 and p=0.001, respectively). The Kaplan-Meier curve showed that patients carrying rs9926344 AA +AG genotype had poor RFS (P=0.004) and OS (P=0.005) compared to those carrying GG genotypes. The multivariate COX regression analysis showed that the AA+AG genotype were an independent prognostic factor for tumor recurrence (HR 1.787, 95% CI 1.042-3.064, P=0.035). Furthermore, IHC analysis showed that the WWOX protein down-regulation is more frequent in patients with AG genotype compared to those with GG genotype (P=0.023).

Conclusion: Our findings indicate that WWOX rs9926344 polymorphism is positively correlated with tumor recurrence and can be used as an independent prognostic marker for HCC patients after operation.

Functional genetic variant in the Kozak sequence of WW domain-containing oxidoreductase (WWOX) gene is associated with oral cancer risk

In Taiwan, oral cancer is the fourth leading cancer in males and is associated with exposure to environmental carcinogens. WW domain-containing oxidoreductase (WWOX), a tumor suppressor gene, is associated with the development of various cancers. We hypothesized that genetic variants of WWOX influence the susceptibility to oral cancer. Five polymorphisms of WWOX gene from 761 male patients with oral cancer and 1199 male cancer-free individuals were genotyped. We observed that individuals carrying the polymorphic allele of WWOX rs11545028 are more susceptible to oral cancer. Furthermore, patients with advanced-stage oral cancer were associated with a higher frequency of WWOX rs11545028 polymorphisms with the variant genotype TT than did patients with the wild-type gene. An additional integrated in silico analysis confirmed that rs11545028 affects WWOX expression, which significantly correlates with tumor expression and subsequently with tumor development and aggressiveness. In conclusion, genetic variants of WWOX contribute to the occurrence of oral cancer, and the findings regarding these biomarkers provided a prediction model for risk assessment.

DNA replication stress drives fragile site instability

DNA replication stress is one of the early drivers enabling the ongoing acquisition of genetic changes arising during tumorigenesis. As such, it is a feature of most pre-malignant and malignant cells. In this review article, we focus on the early events initiating DNA replication stress and the preferential sensitivity of common fragile sites (CFSs) to this stress. CFSs are specific genomic regions within the normal chromosomal structure, which appear as gaps and breaks in the metaphase chromosomes of cells grown under mild replication stress conditions. The main characteristics predisposing CFSs to instability include late replication timing, delayed replication completion, failure to activate additional origins, origin paucity along large genomic regions, collision between replication and transcription complexes along large genes, and the presence of AT-dinucleotide rich sequences. The contribution of these features to instability at CFSs during early cancer development is discussed.

Exploring the mechanism of WWOX growth inhibitory effects on oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is one of the most common types of head and neck neoplasms in the world. Patients diagnosed with OSCC exhibit a poor prognosis. WW domain-containing oxidoreductase (WWOX), as a candidate tumor-suppressor gene, is involved in the genesis and progression of tumors. The deletion of the WWOX gene has been identified in OSCC and oral leukoplakia, but the function and mechanism of WWOX in OSCC remain unknown. Therefore, the present study investigated the role of WWOX in oral squamous carcinoma cells. The results revealed that an elevation of WWOX expression had an inhibitory effect on the growth of three types of oral squamous carcinoma cells, with the most evident effect occurring in Tca8113 cells. Also, in the Tca8113 cells, WWOX overexpression significantly inhibited colony formation, and induced apoptosis and cell cycle arrest. Microarray analysis, reverse transcription-quantitative polymerase chain reaction and western blotting methods detected that WWOX overexpression contributed to the differential expression of the genes involved in mediating the extracellular-signal regulated protein kinase/mitogen-activated protein kinase (ERK/MAPK) signaling pathway. These results suggest that the tumor-suppressor function of the WWOX gene may be associated with the modulation of the ERK/MAPK signaling pathway, thus providing a novel target for OSCC therapy.

Tumor Suppressor Genes within Common Fragile Sites Are Active Players in the DNA Damage Response

The role of common fragile sites (CFSs) in cancer remains controversial. Two main views dominate the discussion: one suggests that CFS loci are hotspots of genomic instability leading to inactivation of genes encoded within them, while the other view proposes that CFSs are functional units and that loss of the encoded genes confers selective pressure, leading to cancer development. The latter view is supported by emerging evidence showing that expression of a given CFS is associated with genome integrity and that inactivation of CFS-resident tumor suppressor genes leads to dysregulation of the DNA damage response (DDR) and increased genomic instability. These two viewpoints of CFS function are not mutually exclusive but rather coexist; when breaks at CFSs are not repaired accurately, this can lead to deletions by which cells acquire growth advantage because of loss of tumor suppressor activities. Here, we review recent advances linking some CFS gene products with the DDR, genomic instability, and carcinogenesis and discuss how their inactivation might represent a selective advantage for cancer cells.

WWOX modulates the ATR-mediated DNA damage checkpoint response

For many decades genomic instability is considered one of the hallmarks of cancer. Role of the tumor suppressor WWOX (WW domain-containing oxidoreductase) in DNA damage response upon double strand breaks has been recently revealed. Here we demonstrate unforeseen functions for WWOX upon DNA single strand breaks (SSBs) checkpoint activation. We found that WWOX levels are induced following SSBs and accumulate in the nucleus. WWOX deficiency is associated with reduced activation of ataxia telangiectasia and Rad3-related protein (ATR) checkpoint proteins and increased chromosomal breaks. At the molecular level, we show that upon SSBs WWOX is modified at lysine 274 by ubiquitination mediated by the ubiquitin E3 ligase ITCH and interacts with ataxia telangiectasia-mutated (ATM). Interestingly, ATM inhibition was associated with reduced activation of ATR checkpoint proteins suggesting that WWOX manipulation of ATR checkpoint proteins is ATM-dependent. Taken together, the present findings indicate that WWOX plays a key role in ATR checkpoint activation, while its absence might facilitate genomic instability.

Pleiotropic Functions of Tumor Suppressor WWOX in Normal and Cancer Cells

WW domain-containing oxidoreductase (WWOX), originally marked as a likely tumor suppressor gene, has over the years become recognized for its role in a much wider range of cellular activities. Phenotypic effects displayed in animal studies, along with resolution of WWOX's architecture, fold, and binding partners, point to the protein's multifaceted biological functions. Results from a series of complementary experiments seem to indicate WWOX's involvement in metabolic regulation. More recently, clinical studies involving cases of severe encephalopathy suggest that WWOX also plays a part in controlling CNS development, further expanding our understanding of the breadth and complexity of WWOX behavior. Here we present a short overview of the various approaches taken to study this dynamic gene, emphasizing the most recent findings regarding WWOX's metabolic- and CNS-associated functions and their underlying molecular basis.

Tumor suppressor WWOX moderates the mitochondrial respiratory complex

Fragile site FRA16D exhibits DNA instability in cancer, resulting in diminished levels of protein from the WWOX gene that spans it. WWOX suppresses tumor growth by an undefined mechanism. WWOX participates in pathways involving aerobic metabolism and reactive oxygen species. WWOX comprises two WW domains as well as a short-chain dehydrogenase/reductase enzyme. Herein is described an in vivo genetic analysis in Drosophila melanogaster to identify functional interactions between WWOX and metabolic pathways. Altered WWOX levels modulate variable cellular outgrowths caused by genetic deficiencies of components of the mitochondrial respiratory complexes. This modulation requires the enzyme active site of WWOX, and the defective respiratory complex-induced cellular outgrowths are mediated by reactive oxygen species, dependent upon the Akt pathway and sensitive to levels of autophagy and hypoxia-inducible factor. WWOX is known to contribute to homeostasis by regulating the balance between oxidative phosphorylation and glycolysis. Reduction of WWOX levels results in diminished ability to respond to metabolic perturbation of normal cell growth. Thus, the ability of WWOX to facilitate escape from mitochondrial damage-induced glycolysis (Warburg effect) is, therefore, a plausible mechanism for its tumor suppressor activity.

Tumor Suppressor WWOX inhibits osteosarcoma metastasis by modulating RUNX2 function

Osteosarcoma (OS) is among the most frequently occurring primary bone tumors, primarily affecting adolescents and young adults. This malignant osteoid forming tumor is characterized by its metastatic potential, mainly to lungs. We recently demonstrated that WW domain-containing oxidoreductase (WWOX) is frequently inactivated in human OS and that WWOX restoration in WWOX-negative OS cells suppresses tumorigenicity. Of note, WWOX levels are reduced in paired OS samples of post-treatment metastastectomies as compared to pre-treatment biopsies suggesting that decreased WWOX levels are associated with a more aggressive phenotype at the metastatic site. Nevertheless, little is known about WWOX function in OS metastasis. Here, we investigated the role of tumor suppressor WWOX in suppressing pulmonary OS metastasis bothin vitroandin vivo. We demonstrated that ectopic expression of WWOX in OS cells, HOS and LM-7, inhibits OS invasion and cell migration in vitro. Furthermore, WWOX expression reduced tumor burden in vivo and inhibited metastases’ seeding and colonization. Mechanistically, WWOX function is associated with reduced levels of RUNX2 metastatic target genes implicated in adhesion and motility. Our results suggest that WWOX plays a critical role in determining the aggressive phenotype of OS, and its expression could be an attractive therapeutic target to combat this devastating adolescent disease.

WWOX guards genome stability by activating ATM

Common fragile sites (CFSs) tend to break upon replication stress and have been suggested to be “hot spots” for genomic instability. Recent evidence, however, implies that in the wake of DNA damage, WW domain-containing oxidoreductase (WWOX, the gene product of the FRA16D fragile site), associates with ataxia telangiectasia-mutated (ATM) and regulates its activation to maintain genomic integrity.