Molecular parameters of genome instability: Roles of fragile genes at common fragile sites

Base Excision Repair AP-Endonucleases-Like Genes Modulate DNA Damage Response and Virulence of the Human Pathogen Cryptococcus neoformans

Pathogenic microbes are exposed to a number of potential DNA-damaging stimuli during interaction with the host immune system. Microbial survival in this situation depends on a fine balance between the maintenance of DNA integrity and the adaptability provided by mutations. In this study, we investigated the association of the DNA repair response with the virulence of Cryptococcus neoformans, a basidiomycete that causes life-threatening meningoencephalitis in immunocompromised individuals. We focused on the characterization of C. neoformansAPN1 and APN2 putative genes, aiming to evaluate a possible role of the predicted Apurinic/apyrimidinic (AP) endonucleases 1 and 2 of the base excision repair (BER) pathway on C. neoformans response to stress conditions and virulence. Our results demonstrated the involvement of the putative AP-endonucleases Apn1 and Apn2 in the cellular response to DNA damage induced by alkylation and by UV radiation, in melanin production, in tolerance to drugs and in virulence of C. neoformans in vivo. We also pointed out the potential use of DNA repair inhibitor methoxy-amine in combination with conventional antifungal drugs, for the development of new therapeutic approaches against this human fungal pathogen. This work provides new information about the DNA damage response of the highly important pathogenic fungus C. neoformans.

Interplay between genetic and epigenetic factors governs common fragile site instability in cancer

Common fragile sites (CFSs) are regions within the normal chromosomal structure that were characterized as hotspots for genomic instability in cancer almost 30 years ago. In recent years, many efforts have been made to understand the basis of CFS fragility and their involvement in the genomic signature of instability found in malignant tumors. CFSs are among the first regions to undergo genomic instability during cancer development because of their intrinsic sensitivity to replication stress conditions, which result from oncogene expression. The preferred sensitivity of CFSs to replication stress stems from various mechanisms including: replication fork arrest at AT-rich repeats, origin paucity along large genomic regions, failure in activation of dormant origins, late replication timing, collision between replication and transcription along large genes, all leading to incomplete replication of the CFS region and resulting in chromosomal instability. Here we review shared and unique characteristics of CFSs, their underlying causes and implications, particularly for the development of cancer.

Identification of chromosome instability in Japanese quail (Coturnix japonica)

1. A study of the incidence of chromosome instability in the Japanese quail as assessed by sister chromatid exchange (SCE) and fragile site identification in chromosomes was conducted in two parent breeds and their F1 and F2 generations. 2. The mean incidence of SCEs was 6.02 ± 0.45 and the frequency of fragile sites was 1.17 ± 0.79. 3. There were moderately negative correlations of 0.51-0.64 between chromosome instability and fertility in the F1 and 0.10-0.23 in the F2. The hatch of fertilised eggs was negatively correlated with the number of SCE in male (0.31) and female (0.33) F1 and was lower in P (0.18 and 0.19, respectively), whereas the correlations were similar for the number of fragile sites in both generations (0.51-0.62).

The SNM1B/APOLLO DNA nuclease functions in resolution of replication stress and maintenance of common fragile site stability

SNM1B/Apollo is a DNA nuclease that has important functions in telomere maintenance and repair of DNA interstrand crosslinks (ICLs) within the Fanconi anemia (FA) pathway. SNM1B is required for efficient localization of key repair proteins, such as the FA protein, FANCD2, to sites of ICL damage and functions epistatically to FANCD2 in cellular survival to ICLs and homology-directed repair. The FA pathway is also activated in response to replication fork stalling. Here, we sought to determine the importance of SNM1B in cellular responses to stalled forks in the absence of a blocking lesion, such as ICLs. We found that depletion of SNM1B results in hypersensitivity to aphidicolin, a DNA polymerase inhibitor that causes replication stress. We observed that the SNM1B nuclease is required for efficient localization of the DNA repair proteins, FANCD2 and BRCA1, to subnuclear foci upon aphidicolin treatment, thereby indicating SNM1B facilitates direct repair of stalled forks. Consistent with a role for SNM1B subsequent to recognition of the lesion, we found that SNM1B is dispensable for upstream events, including activation of ATR-dependent signaling and localization of RPA, γH2AX and the MRE11/RAD50/NBS1 complex to aphidicolin-induced foci. We determined that a major consequence of SNM1B depletion is a marked increase in spontaneous and aphidicolin-induced chromosomal gaps and breaks, including breakage at common fragile sites. Thus, this study provides evidence that SNM1B functions in resolving replication stress and preventing accumulation of genomic damage.

Expression of WWOX and FHIT is downregulated by exposure to arsenite in human uroepithelial cells

Ecological studies in Taiwan, Chile, Argentina, Bangladesh, and Mexico have confirmed significant dose-dependent associations between ingestion of arsenic-contaminated drinking water and the risk of various human malignancies. The FHIT and WWOX genes are active in common fragile sites FRA3B and FRA16D, respectively. Reduced expression of FHIT or WWOX is known to be an early indicator of carcinogen-induced cancers. However, the effect of arsenite on the expressions and molecular mechanisms of these markers is still unclear. The aims of this study were (i) to observe the expression of ATR, WWOX and FHIT proteins in urothelial carcinoma (UC) between endemic and non-endemic areas of blackfoot disease (BFD) by immunohistochemical analyses; (ii) to compare expression of these genes between arsenite-treated SV-HUC-1 human epithelial cells and rat uroepithelial cells; and (iii) to determine the role of DNMT and MEK inhibitors on expressions of WWOX and FHIT in response to arsenite in SV-HUC-1. The experiments revealed that expressions of ATR, WWOX and FHIT in UC significantly differed between BFD areas and non-BFD areas (p=0.003, 0.009 and 0.021, respectively). In fact, the results for the arsenite-treated groups showed that ATR, WWOX and FHIT are downregulated by arsenite in SV-HUC-1. However, the inhibitors suppressed the effects of arsenite on WWOX and FHIT proteins and mRNA expression. In conclusion, arsenite decreased expressions of ATR, WWOX and FHIT via ERK1/2 activation in SV-HUC-1 cells. These findings confirm that dysregulations of these markers may contribute to arsenite-induced carcinogenesis.

Reduced FHIT expression is associated with mismatch repair deficient and high CpG island methylator phenotype colorectal cancer

Colorectal cancer (CRC) is a heterogeneous disease and a major contributor to world cancer mortality rates. Molecular subtypes of CRC have become standards for CRC classification and have established prognostic potential. Here, we attempt to corroborate and provide further insight pertinent to the fragile histidine triad (FHIT) gene in microsatellite instable (MSI), microsatellite stable (MSS), and CpG island methylator phenotype (CIMP) CRC subtypes. We employed array comparative genomic hybridization and multiplex ligation-dependent probe amplification (MLPA) techniques to survey genomic aberrations in FHIT gene and their effects on FHIT protein expression using immunohistochemistry (IHC) in a CRC cohort. We further studied FHIT protein expression by IHC in a larger CRC cohort defined for its mismatch repair (MMR) protein expression and genomic methylation profiles. Our results show FHIT genomic deletions centered in exons 4 and 5 in most of MSI-CRC samples. Moreover, we confirmed the significant association of FHIT protein expression diminution (p=0.035) with MSI-CRC. In the larger cohort, reduced FHIT protein expression was significantly associated with CIMP-high subtype of CRC (p=0.009) and loss of PMS2 protein expression (p=0.017). We conclude that FHIT expression may be a valuable marker for CRC subtyping, and its diagnostic, prognostic, and therapeutic potential should be perused.

Genetic instability of the tumor suppressor gene FHIT in normal human cells

Common fragile sites are hotspots for chromosome instability and co-localize to cancer genomic rearrangements. Whether these loci may be considered stable in human subjects under physiological conditions remains an open question. Here we show by molecular combing that a small but significant percentage of normal human cells carry an abnormal sequence pattern within the tumor suppressor gene FHIT (3p14.2) at FRA3B. Each sequence variation represents a unique pattern within a normal cell population, and therefore it would remain undetected or not interpreted by genome-wide analyses. Remarkably, the region is the same as in FHIT rearrangements described in tumors. By analyses on several normal cell lines (proliferating and resting primary lymphocytes, primary fibroblasts, lymphoblastoid cells including clonal cell cultures) we verified that: (a) each cell type displays altered sequence patterns at FHIT; (b) the presence of abnormal sequence patterns is specific for the FHIT locus; and (c) FHIT instability occurs de novo during cell proliferation, and heterogeneous sequence variants progressively accumulate in the cell populations. FHIT has been widely investigated in cancer cells, but to our knowledge this is the first direct evidence of spontaneous and recurrent occurrence of genomic instability at this gene in human subjects, at the same region involved in cancer rearrangements. Our results suggest that common fragile site activity is not restricted to in vitro cell culture and that genomic instability may pre-exist in normal cells in the absence of exogenous replication stress.

The complex basis underlying common fragile site instability in cancer

Common fragile sites (CFSs) were characterized almost 30 years ago as sites undergoing genomic instability in cancer. Recently, in vitro studies have found that oncogene-induced replication stress leads to CFS instability. In vivo, CFSs were found to be preferentially unstable during early stages of cancer development and to leave a unique signature of instability. It is now increasingly clear that, along the spectrum of replication features characterizing CFSs, failure of origin activation is a common feature. This and other features of CFSs, together with the replication stress characterizing early stages of cancer development, lead to incomplete replication that results in genomic instability preferentially at CFSs. Here, we review the shared and unique characteristics of CFSs, their underlying causes and their implications, particularly with respect to the development of cancer.

Assessment of chromosome instability in geese (Anser anser)

Wójcik, E. and Smalec, E. 2012. Assessment of chromosome instability in geese ( Anser anser ). Can. J. Anim. Sci. 92: 49–57. The basic test applied in the research of chromosome instability is the test of sister chromatid exchange (SCE). It makes it possible to identify single-and double-strand DNA damage caused by genotoxic factors and those that disrupt DNA damage repair mechanisms. Fragile sites in chromosomes can be found in all organisms. They are chromosome sites showing susceptibility to breakages and discontinuities in specific conditions of cell culture and also following induction with chemical substances. Chromosome instability of Anser anser geese was assessed in the research, focussing on sister chromatid exchange and the identification of fragile sites. The mean SCE/cell was 4.75±1.00. Most SCEs were identified in the proximal part of the chromosomes. Fragile sites were also identified in the chromosomes during the research. Altogether, 138 breakages were observed in the chromosomes. Apart from identifying chromosome damage, the particular instances of damage were located in the chromosomes.

Common fragile sites in colon cancer cell lines: role of mismatch repair, RAD51 and poly(ADP-ribose) polymerase-1

Common fragile sites (CFS) are specific chromosomal areas prone to form gaps and breaks when cells are exposed to stresses that affect DNA synthesis, such as exposure to aphidicolin (APC), an inhibitor of DNA polymerases. The APC-induced DNA damage is repaired primarily by homologous recombination (HR), and RAD51, one of the key players in HR, participates to CFS stability. Since another DNA repair pathway, the mismatch repair (MMR), is known to control HR, we examined the influence of both the MMR and HR DNA repair pathways on the extent of chromosomal damage and distribution of CFS provoked by APC and/or by RAD51 silencing in MMR-deficient and -proficient colon cancer cell lines (i.e., HCT-15 and HCT-15 transfected with hMSH6, or HCT-116 and HCT-116/3+6, in which a part of a chromosome 3 containing the wild-type hMLH1 allele was inserted). Here, we show that MMR-deficient cells are more sensitive to APC-induced chromosomal damage particularly at the CFS as compared to MMR-proficient cells, indicating an involvement of MMR in the control of CFS stability. The most expressed CFS is FRA16D in 16q23, an area containing the tumour suppressor gene WWOX often mutated in colon cancer. We also show that silencing of RAD51 provokes a higher number of breaks in MMR-proficient cells with respect to their MMR-deficient counterparts, likely as a consequence of the combined inhibitory effects of RAD51 silencing on HR and MMR-mediated suppression of HR. The RAD51 silencing causes a broader distribution of breaks at CFS than that observed with APC. Treatment with APC of RAD51-silenced cells further increases DNA breaks in MMR-proficient cells. The RNAi-mediated silencing of PARP-1 does not cause chromosomal breaks or affect the expression/distribution of CFS induced by APC. Our results indicate that MMR modulates colon cancer sensitivity to chromosomal breaks and CFS induced by APC and RAD51 silencing.

Hits, Fhits and Nits: beyond enzymatic function

We have briefly summarized what is known about these proteins, but in closing wish to feature the outstanding questions. Hint1 was discovered mistakenly as an inhibitor of Protein Kinase C and designated Pkci, a designation that still confuses the literature. The other Hint family members were discovered by homology to Hint1. Aprataxin was discovered as a result of the hunt for a gene responsible for AOA1. Fhit was discovered through cloning of a familial chromosome translocation breakpoint on chromosome 3 that interrupts the large FHIT gene within an intron, in the FRA3B chromosome region (Ohta et al., 1996), now known to be the region of the human genome most susceptible to DNA damage due to replication stress (Durkin et al., 2008). The NitFhit fusion genewas discovered during searches for Fhit homologs in flies and worms because the fly/worm Nit polypeptide is fused to the 5'-end of the Fhit gene; the mammalian Nit gene family was discovered because of the NitFhit fusion gene, in searches for homologs to the Nit polypeptide of the NitFhit gene. Each of the Hit family member proteins is reported to have enzymatic activities toward putative substrates involving nucleosides or dinucleosides. Most surprisingly, each of the Hit family proteins discussed has been implicated in important DNA damage response pathways and/or tumor suppression pathways. And for each of them it has been difficult to assign definite substrates, to know if the substrates and catalytic products have biological functions, to know if that function is related to the DNA damage response and suppressor functions, and to precisely define the pathways through which tumor suppression occurs. When the fly Nit sequence was found at the 5'-end of the fly Fhit gene, this gene was hailed as a Rosetta stone gene/protein that would help in discovery of the function of Fhit, because the Nit protein should be in the same signal pathway (Pace et al., 2000). However, the mammalian Nit family proteins have turned out to be at least as mysterious as the Fhit proteins, with the Nit1 substrate still unknown and the surprising finding that Nit proteins also appear to behave as tumor suppressor proteins. Whether the predicted enzymatic functions of these proteins are relevant to the observed biological functions, remain among the outstanding unanswered puzzles and raise the question: have these mammalian proteins evolved beyond the putative original enzymatic purpose, such that the catalytic function is now vestigial and subservient to signal pathways that use the protein-substrate complexes in pathways that signal apoptosis or DNA damage response? Or can these proteins be fulfilling catalytic functions independently but in parallel with signal pathway functions, as perhaps observed for Aprataxin? Or is the catalytic function indeed part of the observed biological functions, such as apoptosis and tumor suppression? Perhaps the recent, post-genomic focus on metabolomics and genome-wide investigations of signal pathway networks will lead to answers to some of these outstanding questions.

Chromosomes, conflict, and epigenetics: chromosomal speciation revisited

Since Darwin first noted that the process of speciation was indeed the "mystery of mysteries," scientists have tried to develop testable models for the development of reproductive incompatibilities-the first step in the formation of a new species. Early theorists proposed that chromosome rearrangements were implicated in the process of reproductive isolation; however, the chromosomal speciation model has recently been questioned. In addition, recent data from hybrid model systems indicates that simple epistatic interactions, the Dobzhansky-Muller incompatibilities, are more complex. In fact, incompatibilities are quite broad, including interactions among heterochromatin, small RNAs, and distinct, epigenetically defined genomic regions such as the centromere. In this review, we will examine both classical and current models of chromosomal speciation and describe the "evolving" theory of genetic conflict, epigenetics, and chromosomal speciation.

Pathology and biology associated with the fragile FHIT gene and gene product

More than 12 years and >800 scientific publications after the discovery of the first gene at a chromosome fragile site, the FHIT gene at FRA3B, there are still questions to pursue concerning the selective advantage conferred to cells by loss of expression of FHIT, the most frequent target of allele deletion in precancerous lesions and cancers. These questions are considered in light of recent investigations of genetic and epigenetic alterations to the locus and in a retrospective consideration of biological roles of the Fhit protein discovered through functional studies.

Allelic imbalance and abnormal expression of FHIT in endemic nasopharyngeal carcinoma: association with clinicopathological features

The FHIT gene is involved in the pathogenesis of many cancers. The aim of this study was to investigate allelic imbalance (AI) pattern at FHIT locus and alteration of FHIT gene in nasopharyngeal carcinoma (NPC) and analyzed potential correlation between AI, FHIT mRNA expression and clinicopathological factors. We examined AI, including loss of heterozygosity (LOH) and microsatellite instability (MSI), at FHIT locus in 41 cases of NPC by microsatellite analysis and FHIT gene status in 30 cases of NPC by nested reverse transcriptase-polymerase chain reaction and DNA sequencing. The frequencies of LOH and MSI at FHIT locus in NPC were 70.7% (29/41) and 36.6% (15/41), respectively. Thirteen of thirty (43.3%) NPCs exhibited aberrant FHIT transcripts. LOH and abnormal FHIT expression were correlated with advanced clinical stage and higher titers of immunoglobulin (Ig) A against Epstein-Barr virus capsid antigen (EBVCA-IgA) (p < 0.05). Abnormal FHIT expression was also correlated with tumor recurrence (p < 0.05). MSI was correlated with early clinical stage and higher titers of EBVCA-IgA (p < 0.05). AI at FHIT locus is a common event and contributes to genetic imbalance in NPC. The abnormalities of FHIT, presumably associated with genetic imbalance at FHIT locus, might be involved in the development and the tumor recurrence of NPC.

Persistent infections and their relationship with selected oncologic and non-tumor pathologies

Our earlier studies of hepatitis C virus (HCV) infection rates among blood donors at the Kyiv Municipal Blood Center revealed a 3.45% HCV+ prevalence in these "healthy" hosts. In the study here, we analyzed HCV (as well as cytomegalovirus [CMV]) prevalence among Chernobyl nuclear power plant (NPP) accident sufferers--cleanup workers, local residents, NPP workers, and convalescent patients--who suffered acute radiation syndrome (ARS) as a result of the 1986 accident, and individuals who had not been exposed to ionizing radiation (IR). Serological analyses of antibodies against each pathogen (via enzyme-linked immunosorbent assay [ELISA]) revealed the highest HCV (i.e., 27.2%) and CMV (85.6%) prevalence in the convalescent hosts. Though the HCV prevalence (reflecting a current/past infection) among the cleanup workers (and other groups) was lower (i.e., 11-25%), viral presence was "associated" with a higher incidence of selected somatic diseases, for example, thyroiditis, goiter, hypertension, Type 1 diabetes, chronic hepatitis/gastritis, in the cleanup workers. A similar scenario with respect to CMV was also seen, i.e., lower prevalence rates [relative to in ARS patients] and "association" between CMV status and incidence of chronic gastritis, arthritis, and bronchitis, in the cleanup workers and IR-non-exposed controls. Further, irrespective of CMV status, there was a clear delineation between incidence rate(s) of each of the pathologies and whether or not the person was/was not exposed in 1986. We also investigated, due to a high incidence of chronic lymphocytic leukemia (CLL) among Chernobyl sufferers, if there was homology between immunoglobulins (Igs) generated by these transformed cells and known antiviral and antimicrobial Igs. Polymerase chain reaction (PCR) analyses of Ig heavy-chain variable (IgHV) genes in cells from CLL patients who were/were not exposed in 1986 revealed a significant homology of some IgHV genes with Igs directed against infectious agents. However, no differences were found between the sequences from IR-exposed and IR-non-exposed CLL patients. Based on the findings here, we conclude that a past/ongoing presence of certain viral infections (i.e., CMV and/or HCV) in a host can modify (aggravate) the clinical course of certain somatic (i.e., non-tumor) diseases and promote malignancies (i.e., CLL), and that each of these outcomes could be modulated as a result of that host's past exposure to IR.

Prospects for the Use of ATR Inhibitors to Treat Cancer

ATR is an apical kinase in one of the DNA-damage induced checkpoint pathways. Despite the development of inhibitors of kinases structurally related to ATR, as well as inhibitors of the ATR substrate Chk1, no ATR inhibitors have yet been developed. Here we review the effects of ATR downregulation in cancer cells and discuss the potential for development of ATR inhibitors for clinical use.

Fhit loss in lung preneoplasia: relation to DNA damage response checkpoint activation

Loss of heterozygosity at the FHIT locus is coincident with activation of DNA damage response checkpoint proteins; thus damage at fragile loci may trigger checkpoint activation. We examined preneoplastic lesions adjacent to non-small cell lung carcinomas for alterations to expression of Fhit and activated checkpoint proteins. Expression scores were analyzed for pair-wise associations and correlations among proteins and type of lesion. Hyperplastic and dysplastic lesions were positive for nuclear gammaH2AX expression; 12/20 dysplastic lesions were negative for Fhit expression. Fhit positive lesions showed expression of most checkpoint proteins examined, while Fhit negative lesions showed absence of expression of Chk1 and phosphoChk1. The results show that loss of expression of Fhit is significantly directly correlated with absence of activated Chk1 in dysplasia, and suggest a connection between loss of Fhit and modulation of checkpoint activity.

Common chromosomal fragile sites (CFS) may be involved in normal and traumatic cognitive stress memory consolidation and altered nervous system immunity

Previous reports of specific patterns of increased fragility at common chromosomal fragile sites (CFS) found in association with certain neurobehavioural disorders did not attract attention at the time due to a shift towards molecular approaches to delineate neuropsychiatric disorder candidate genes. Links with miRNA, altered methylation and the origin of copy number variation indicate that CFS region characteristics may be part of chromatinomic mechanisms that are increasingly linked with neuroplasticity and memory. Current reports of large-scale double-stranded DNA breaks in differentiating neurons and evidence of ongoing DNA demethylation of specific gene promoters in adult hippocampus may shed new light on the dynamic epigenetic changes that are increasingly appreciated as contributing to long-term memory consolidation. The expression of immune recombination activating genes in key stress-induced memory regions suggests the adoption by the brain of this ancient pattern recognition and memory system to establish a structural basis for long-term memory through controlled chromosomal breakage at highly specific genomic regions. It is furthermore considered that these mechanisms for management of epigenetic information related to stress memory could be linked, in some instances, with the transfer of the somatically acquired information to the germline. Here, rearranged sequences can be subjected to further selection and possible eventual retrotranscription to become part of the more stable coding machinery if proven to be crucial for survival and reproduction. While linkage of cognitive memory with stress and fear circuitry and memory establishment through structural DNA modification is proposed as a normal process, inappropriate activation of immune-like genomic rearrangement processes through traumatic stress memory may have the potential to lead to undesirable activation of neuro-inflammatory processes. These theories could have a significant impact on the interpretation of risks posed by heredity and the environment and the search for neuropsychiatric candidate genes.

Enlightened protein: Fhit tumor suppressor protein structure and function and its role in the toxicity of protoporphyrin IX-mediated photodynamic reaction

The Fhit tumor suppressor protein possesses Ap(3)A (diadenosine triphosphate - ApppA) hydrolytic activity in vitro and its gene is found inactive in many pre-malignant states due to gene inactivation. For several years Fhit has been a widely investigated protein as its cellular function still remains largely unsolved. Fhit was shown to act as a molecular 'switch' of cell death via cascade operating on the influence of ATR-Chk1 pathway but also through the mitochondrial apoptotic pathway. Notably, Fhit was reported by our group to enhance the overall eradication effect of porphyrin-mediated photodynamic treatment (PDT). In this review the up-to-date findings on Fhit protein as a tumor suppressor and its role in PDT are presented.

Fragile gene product, Fhit, in oxidative and replicative stress responses

Though the fragile histidine triad gene product, Fhit, was discovered and characterized as a tumor suppressor 13 years ago, its sequence, structure, and cellular location did not provide clues to aid discovery of its mechanisms of suppression. Recently, using chemical cross-linkers and immunoprecipitation, a Fhit protein complex was identified that includes Hsp60 and Hsp10 which may mediate Fhit stability and mitochondrial localization, where Fhit binds and stabilizes ferredoxin reductase (Fdxr); when Fdxr is overexpressed, it can lead to production of reactive oxygen species (ROS) that induce apoptosis. Cancer cells expressing endogenous or exogenous Fhit, when exposed to H(2)O(2), an oxidative stress, produce higher levels of apoptosis-inducing ROS than matched, Fhit-negative cells; the Fhit-negative cancer cells survive, carrying DNA damage. In addition to this mitochondrial function, Fhit-overexpression in cancer cells exposed to replicative stress-inducing agents leads to enhanced caspase 3 activation and apoptosis, due to defective Chk1 activation. Thus, damage to the fragile FHIT locus leads to reduced expression of Fhit protein, and makes a two-pronged contribution to development of preneoplastic clonal expansion: (1) absence or reduction of Fhit leads to reduced expression of Fdxr and reduced ROS-induced apoptosis; (2) cells that escape ROS- or replicative stress-induced apoptosis can carry misrepaired DNA damage. The aberrant DNA damage response checkpoint in Fhit-deficient preneoplasias and cancers may make these lesions targets for inhibitors of proteins such as Parp1 and Chk1 with important roles in checkpoint responses, as observed for BRCA1-deficient cancer cells that also exhibit DNA damage repair deficiencies.

Fragile histidine triad protein, WW domain-containing oxidoreductase protein Wwox, and activator protein 2gamma expression levels correlate with basal phenotype in breast cancer

BACKGROUND

The expression of fragile histidine triad protein (Fhit) and WW domain-containing oxidoreductase protein (Wwox), tumor suppressors that are encoded by fragile (FRA) loci FRA3B and FRA16D, are lost concordantly in breast cancers. In the current study, the authors examined correlations among Fhit, Wwox, the activator protein 2 transcription factors AP2alpha and AP2gamma, cytokeratins 5 and 6 (CK5/6), epidermal growth factor receptor (EGFR), estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER-2) and their associations with breast cancer phenotypes.

METHODS

Tissue microarrays constructed from 837 breast cancer blocks were immunostained. Expression in >10% of tumor cells was considered positive for cytoplasmic CK5/6, membranous EGFR, and nuclear AP2alpha and AP2gamma. Cytoplasmic Fhit and Wwox staining was scored according to staining intensity. ER, PR, and HER-2 status of tumors was derived from records. Correlations among immunohistochemical markers and tumor subtypes were assessed by univariate and multivariate statistical methods.

RESULTS

Triple-negative tumors had more frequent expression of EGFR, CK5/6 (P < .001), and AP2gamma (P = .003) and more frequent loss of Fhit and Wwox (P < .001), and an inverse correlation was observed between Fhit, Wwox expression and EGFR, ER, and PR expression (P < .001). Reduced Fhit expression was more common in HER-2-positive and AP2gamma-positive cases (P < .001 and P = .002, respectively). There was a direct correlation noted between Fhit and Wwox (P < .001) and a borderline positive relation between AP2alpha and AP2gamma (P = .054).

CONCLUSIONS

The results from this investigation suggested that reduced expression levels of Fhit, Wwox, and nuclear AP2gamma have roles in the pathogenesis of basal-like differentiation in breast cancer. Alteration in the expression of fragile site genes occurs in most of these cancers and may contribute to defects in DNA repair, as observed in breast cancer 1 (BRCA1)-deficient cancers. Thus, DNA damage response checkpoint proteins may be targets for treatment.

Fhit tumor suppressor: guardian of the preneoplastic genome

Environmental agents induce intragenic alterations in the FRA3B/FHIT chromosome fragile site, resulting in fragile FHIT allele loss early in cancer development. Fhit knockout mice are predisposed to tumor development and Fhit gene therapy reduces tumor burden. Repair-deficient cancers are likely to be Fhit-deficient and Fhit-deficient cells show enhanced resistance to ultraviolet C, mitomycin C, camptothecin and oxidative stress-induced cell killing. Loss of Fhit leads to alterations in the DNA damage response checkpoint and contributes to DNA instability. Hsp60/Hsp10 are Fhit interactors, suggesting a direct role for Fhit in stress responses. Fhit also interacts with and stabilizes ferrodoxin reductase (Fdxr), a mitochondrial flavoprotein that transfers electrons from NADPH to cytochrome P450, suggesting a role for Fhit in the modulation of reactive oxygen species production and of genomic damage.

Ladder-like amplification of the type I interferon gene cluster in the human osteosarcoma cell line MG63

The organization of the type I interferon (IFN) gene cluster (9p21.3) was studied in a human osteosarcoma cell line (MG63). Array comparative genomic hybridization (aCGH) showed an amplification of approximately 6-fold which ended at both ends of the gene cluster with a deletion that extended throughout the 9p21.3 band. Spectral karyotyping (SKY) combined with fluorescence in-situ hybridization (FISH) identified an arrangement of the gene cluster in a ladder-like array of 5-7 'bands' spanning a single chromosome termed the 'IFN chromosome'. Chromosome painting revealed that the IFN chromosome is derived from components of chromosomes 4, 8 and 9. Labelling with centromeric probes demonstrated a ladder-like amplification of centromeric 4 and 9 sequences that co-localized with each other and a similar banding pattern of chromosome 4, as well as alternating with the IFN gene clusters. In contrast, centromere 8 was not detected on the IFN chromosome. One of the amplified centromeric 9 bands was identified as the functional centromere based on its location at the chromosome constriction and immunolocalization of the CENP-C protein. A model is presented for the generation of the IFN chromosome that involves breakage-fusion-bridge events.