MxA overexpression reveals a common genetic link in four Fanconi anemia complementation groups

Bank vole immunoheterogeneity may limit Nephropatia Epidemica emergence in a French non-endemic region

Ecoevolutionary processes affecting hosts, vectors and pathogens are important drivers of zoonotic disease emergence. In this study, we focused on nephropathia epidemica (NE), which is caused by Puumala hantavirus (PUUV) whose natural reservoir is the bank vole, Myodes glareolus. We questioned the possibility of NE emergence in a French region that is considered to be NE-free but that is adjacent to a NE-endemic region. We first confirmed the epidemiology of these two regions and we demonstrated the absence of spatial barriers that could have limited dispersal, and consequently, the spread of PUUV into the NE-free region. We next tested whether regional immunoheterogeneity could impact PUUV chances to circulate and persist in the NE-free region. We showed that bank voles from the NE-free region were sensitive to experimental PUUV infection. We observed high levels of immunoheterogeneity between individuals and also between regions. Antiviral gene expression (Tnf and Mx2) reached higher levels in bank voles from the NE-free region. During experimental infections, anti-PUUV antibody production was higher in bank voles from the NE-endemic region. These results indicated a lower susceptibility to PUUV for bank voles from this NE-free region, which might limit PUUV persistence and therefore, the risk of NE.

Host genetics of severe influenza: from mouse Mx1 to human IRF7

Influenza viruses cause mild to moderate respiratory illness in most people, and only rarely devastating or fatal infections. The virulence factors encoded by viral genes can explain seasonal or geographic differences at the population level but are unlikely to account for inter-individual clinical variability. Inherited or acquired immunodeficiencies may thus underlie severe cases of influenza. The crucial role of host genes was first demonstrated by forward genetics in inbred mice, with the identification of interferon (IFN)-α/β-inducible Mx1 as a canonical influenza susceptibility gene. Reverse genetics has subsequently characterized the in vivo role of other mouse genes involved in IFN-α/β and -λ immunity. A series of in vitro studies with mouse and human cells have also refined the cell-intrinsic mechanisms of protection against influenza viruses. Population-based human genetic studies have not yet uncovered variants with a significant impact. Interestingly, human primary immunodeficiencies affecting T and B cells were also not found to predispose to severe influenza. Recently however, human IRF7 was shown to be essential for IFN-α/β- and IFN-λ-dependent protective immunity against primary influenza in vivo, as inferred from a patient with life-threatening influenza revealed to be IRF7-deficient by whole exome sequencing. Next generation sequencing of human exomes and genomes will facilitate the analysis of the human genetic determinism of severe influenza.

Mx GTPases: dynamin-like antiviral machines of innate immunity

The Mx dynamin-like GTPases are key antiviral effector proteins of the type I and type III interferon (IFN) systems. They inhibit several different viruses by blocking early steps of the viral replication cycle. We focus on new structural and functional insights and discuss recent data revealing that human MxA (MX1) provides a safeguard against introduction of avian influenza A viruses (FLUAV) into the human population. The related human MxB (MX2) serves as restriction factor for HIV-1 and other primate lentiviruses.

Immunogenetic factors affecting susceptibility of humans and rodents to hantaviruses and the clinical course of hantaviral disease in humans

We reviewed the associations of immunity-related genes with susceptibility of humans and rodents to hantaviruses, and with severity of hantaviral diseases in humans. Several class I and class II HLA haplotypes were linked with severe or benign hantavirus infections, and these haplotypes varied among localities and hantaviruses. The polymorphism of other immunity-related genes including the C4A gene and a high-producing genotype of TNF gene associated with severe PUUV infection. Additional genes that may contribute to disease or to PUUV infection severity include non-carriage of the interleukin-1 receptor antagonist (IL-1RA) allele 2 and IL-1β (-511) allele 2, polymorphisms of plasminogen activator inhibitor (PAI-1) and platelet GP1a. In addition, immunogenetic studies have been conducted to identify mechanisms that could be linked with the persistence/clearance of hantaviruses in reservoirs. Persistence was associated during experimental infections with an upregulation of anti-inflammatory responses. Using natural rodent population samples, polymorphisms and/or expression levels of several genes have been analyzed. These genes were selected based on the literature of rodent or human/hantavirus interactions (some Mhc class II genes, Tnf promoter, and genes encoding the proteins TLR4, TLR7, Mx2 and β3 integrin). The comparison of genetic differentiation estimated between bank vole populations sampled over Europe, at neutral and candidate genes, has allowed to evidence signatures of selection for Tnf, Mx2 and the Drb Mhc class II genes. Altogether, these results corroborated the hypothesis of an evolution of tolerance strategies in rodents. We finally discuss the importance of these results from the medical and epidemiological perspectives.

Landscape features and helminth co-infection shape bank vole immunoheterogeneity, with consequences for Puumala virus epidemiology

Heterogeneity in environmental conditions helps to maintain genetic and phenotypic diversity in ecosystems. As such, it may explain why the capacity of animals to mount immune responses is highly variable. The quality of habitat patches, in terms of resources, parasitism, predation and habitat fragmentation may, for example, trigger trade-offs ultimately affecting the investment of individuals in various immunological pathways. We described spatial immunoheterogeneity in bank vole populations with respect to landscape features and co-infection. We focused on the consequences of this heterogeneity for the risk of Puumala hantavirus (PUUV) infection. We assessed the expression of the Tnf-α and Mx2 genes and demonstrated a negative correlation between PUUV load and the expression of these immune genes in bank voles. Habitat heterogeneity was partly associated with differences in the expression of these genes. Levels of Mx2 were lower in large forests than in fragmented forests, possibly due to differences in parasite communities. We previously highlighted the positive association between infection with Heligmosomum mixtum and infection with PUUV. We found that Tnf-α was more strongly expressed in voles infected with PUUV than in uninfected voles or in voles co-infected with the nematode H. mixtum and PUUV. H. mixtum may limit the capacity of the vole to develop proinflammatory responses. This effect may increase the risk of PUUV infection and replication in host cells. Overall, our results suggest that close interactions between landscape features, co-infection and immune gene expression may shape PUUV epidemiology.

TNF-α signaling in Fanconi anemia

Tumor necrosis factor-alpha (TNF-α) is a major pro-inflammatory cytokine involved in systemic inflammation and the acute phase reaction. Dysregulation of TNF production has been implicated in a variety of human diseases including Fanconi anemia (FA). FA is a genomic instability syndrome characterized by progressive bone marrow failure and cancer susceptibility. The patients with FA are often found overproducing TNF-α, which may directly affect hematopoietic stem cell (HSC) function by impairing HSC survival, homing and proliferation, or indirectly change the bone marrow microenvironment critical for HSC homeostasis and function, therefore contributing to disease progression in FA. In this brief review, we discuss the link between TNF-α signaling and FA pathway with emphasis on the implication of inflammation in the pathophysiology and abnormal hematopoiesis in FA.

The molecular effects of a polymorphism in the 5'UTR of solute carrier family 44, member 5 that is associated with birth weight in Holsteins

Dystocia is a major problem for the dairy cattle industry, and the observed high rates of this condition stem from genetic selection to increase subsequent milk production of the calving female. Because smaller birth size does not adversely affect subsequent milk production, selecting for cows with a smaller birth size would reduce dystocia rates and be beneficial for both the cattle and the farmers. To identify genes that regulate birth weight, we conducted a genome-wide association study using 1151 microsatellite markers and identified a single nucleotide polymorphism (SNP) associated with birth weight: A-326G in the 5' untranslated region (UTR) of solute carrier family 44, member 5 (SLC44A5). Cows with higher birth weights carried the A polymorphism in the SLC44A5 5' UTR, and the presence of the A polymorphism correlated with a high rate of dystocia. Luciferase assays and quantitative polymerase chain reaction (QPCR) assays revealed that SLC44A5 transcripts with the A polymorphism are expressed at lower levels than those carrying the G polymorphism. SLC44A5 encodes a choline transporter-like protein, and choline is a component of the major phospholipids of cell membranes. Uptake studies in HeLa cells demonstrated that SLC44A5 knockdown reduces choline efflux, whereas SLC44A5 overexpression resulted in the opposite effect. Furthermore, cell viability assays indicated that SLC44A5 knockdown increased cell proliferation, whereas SLC44A5 overexpression repressed proliferation. Taken together, our results suggest that calves with reduced SLC44A5 expression are larger due to enhanced cell proliferation. This study provides novel insights into the molecular mechanisms that control birth weight in Holsteins and suggests that SLC44A5 may serve as a potential target for preventing dystocia.

Fanconi anemia proteins and their interacting partners: a molecular puzzle

In recent years, Fanconi anemia (FA) has been the subject of intense investigations, primarily in the DNA repair research field. Many discoveries have led to the notion of a canonical pathway, termed the FA pathway, where all FA proteins function sequentially in different protein complexes to repair DNA cross-link damages. Although a detailed architecture of this DNA cross-link repair pathway is emerging, the question of how a defective DNA cross-link repair process translates into the disease phenotype is unresolved. Other areas of research including oxidative metabolism, cell cycle progression, apoptosis, and transcriptional regulation have been studied in the context of FA, and some of these areas were investigated before the fervent enthusiasm in the DNA repair field. These other molecular mechanisms may also play an important role in the pathogenesis of this disease. In addition, several FA-interacting proteins have been identified with roles in these “other” nonrepair molecular functions. Thus, the goal of this paper is to revisit old ideas and to discuss protein-protein interactions related to other FA-related molecular functions to try to give the reader a wider perspective of the FA molecular puzzle.

Fanconi anemia complementation group A (FANCA) protein has intrinsic affinity for nucleic acids with preference for single-stranded forms

The Fanconi anemia complementation group A (FANCA) gene is one of 15 disease-causing genes and has been found to be mutated in ∼60% of Fanconi anemia patients. Using purified protein, we report that human FANCA has intrinsic affinity for nucleic acids. FANCA binds to both single-stranded (ssDNA) and double-stranded (dsDNA) DNAs; however, its affinity for ssDNA is significantly higher than for dsDNA in an electrophoretic mobility shift assay. FANCA also binds to RNA with an intriguingly higher affinity than its DNA counterpart. FANCA requires a certain length of nucleic acids for optimal binding. Using DNA and RNA ladders, we determined that the minimum number of nucleotides required for FANCA recognition is ∼30 for both DNA and RNA. By testing the affinity between FANCA and a variety of DNA structures, we found that a 5'-flap or 5'-tail on DNA facilitates its interaction with FANCA. A patient-derived FANCA truncation mutant (Q772X) has diminished affinity for both DNA and RNA. In contrast, the complementing C-terminal fragment of Q772X, C772-1455, retains the differentiated nucleic acid-binding activity (RNA > ssDNA > dsDNA), indicating that the nucleic acid-binding domain of FANCA is located primarily at its C terminus, where most disease-causing mutations are found.

Human MxA protein: an interferon-induced dynamin-like GTPase with broad antiviral activity

The human myxovirus resistance protein 1 (MxA) is a key mediator of the interferon-induced antiviral response against a wide range of viruses. MxA expression is tightly regulated by type I and type III interferons, requires signal transducer and activator of transcription 1 signaling, and is not inducible directly by viruses or other stimuli. MxA shares many properties with the dynamin superfamily of large GTPases. It consists of 3 domains, namely, an N-terminal GTPase domain that binds and hydrolyses GTP, a middle domain mediating self-assembly, and a carboxy-terminal GTPase effector domain. Like dynamin, MxA has the ability to self-assemble into highly ordered oligomers and to form ring-like structures around liposomes, inducing liposome tubulation. The structural details of MxA oligomerization have recently been elucidated, providing new insights into the antiviral mechanism of this mechanochemical enzyme. The structural and functional data suggest that MxA targets the nucleoprotein of MxA-sensitive viruses. Thus, MxA may form oligomeric rings around tubular nucleocapsid structures, thereby inhibiting their transcriptional and replicative function. Here we briefly review the most salient features of MxA expression and antiviral function.

Oxidative stress in Fanconi anemia hematopoiesis and disease progression

Patients with the genomic instability syndrome Fanconi anemia (FA) commonly develop progressive bone marrow failure and have a high risk of cancer. The prominent role of the FA protein family involves DNA damage response and/or repair. Oxidative stress, defined as an imbalance between the production of reactive oxygen species and antioxidant defense, is considered to be an important pathogenic factor in leukemia-prone bone marrow diseases such as FA. Cellular responses inducing resistance to oxidative stress are important for cellular survival, organism lifespan, and cancer prevention, but until recently, mammalian factors regulating resistance to oxidative stress have not been well characterized. Significant evidence supports excessive apoptosis of hematopoietic stem/progenitor cells, induced by stresses, most significantly oxidative stress, as a critical factor in the pathogenesis of bone marrow failure and leukemia progression in FA. In this brief review, we discuss the functional link between FA proteins and oxidative DNA damage response/repair, with emphasis on the implication of oxidative stress in the pathophysiology and abnormal hematopoiesis in FA.

Induction of MxA gene expression by influenza A virus requires type I or type III interferon signaling

The human MxA gene belongs to the class of interferon (IFN)-stimulated genes (ISGs) involved in antiviral resistance against influenza viruses. Here, we studied the requirements for MxA induction by influenza A virus infection. MxA is transcriptionally upregulated by type I (alpha and beta) and type III (lambda) IFNs. Therefore, MxA is widely used in gene expression studies as a reliable marker for IFN bioactivity. It is not known, however, whether viruses can directly activate MxA expression in the absence of secreted IFN. By using an NS1-deficient influenza A virus and human cells with defects in IFN production or the STAT1 gene, we studied the induction profile of MxA by real-time reverse transcriptase PCR. The NS1-deficient virus is known to be a strong activator of the IFN system because NS1 acts as a viral IFN-antagonistic protein. Nevertheless, MxA gene expression was not inducible by this virus upon infection of IFN nonproducer cells and STAT1-null cells. Likewise, neither IFN-alpha nor IFN-lambda had a sizeable effect on the STAT1-null cells, indicating that MxA expression requires STAT1 signaling and cannot be triggered directly by virus infection. In contrast, the expression of the IFN-stimulated gene ISG56 was induced by influenza virus in these cells, confirming that ISG56 differs from MxA in being directly inducible by viral triggers in an IFN-independent way. In summary, our study reveals that MxA is a unique marker for the detection of type I and type III IFN activity during virus infections and IFN therapy.

BCR/ABL-mediated downregulation of genes implicated in cell adhesion and motility leads to impaired migration toward CCR7 ligands CCL19 and CCL21 in primary BCR/ABL-positive cells

The mechanism underlying p210(BCR/ABL) oncoprotein-mediated transformation in chronic myelogenous leukemia (CML) is not fully understood. We hypothesized that p210(BCR/ABL) suppresses expression of genes which may explain at least some of the pathogenetic features of CML. A subtractive cDNA library was created between BCR/ABL-enhanced-green-fluorescent-protein (GFP)-transduced umbilical cord blood (UCB) CD34+ cells and GFP-transduced UCB CD34+ cells to identify genes whose expression is downregulated by p210(BCR/ABL). At least 100 genes were identified. We have confirmed for eight of these genes that expression was suppressed by quantitative real-time-RT-PCR (Q-RT-PCR) of additional p210(BCR/ABL)-transduced CD34+ UCB cells as well as primary early chronic phase (CP) bone marrow (BM) CML CD34+ cells. Imatinib mesylate reversed downregulation of some genes, to approximately normal levels. Several of the genes are implicated in cell adhesion and motility, including L-selectin, intercellular adhesion molecule-1 (ICAM-1), and the chemokine receptor, CCR7, consistent with the known defect in adhesion and migration of CML cells. Compared with GFP UCB or normal (NL) BM CD34+ cells, p210 UCB and CML CD34+ cells migrated poorly towards the CCR7 ligands, CCL19 and CCL21, suggesting a possible role for CCR7 in the abnormal migratory behavior of CML CD34+ cells.

Fanconi anemia type C-deficient hematopoietic cells are resistant to TRAIL (TNF-related apoptosis-inducing ligand)-induced cleavage of pro-caspase-8

OBJECTIVE

The pathophysiology of bone marrow failure in Fanconi anemia (FA) patients is thought to involve excessive apoptosis involving signaling triggered by fas ligation and tumor necrosis factor (TNF)-alpha, or interferon (IFN)-gamma exposure. We investigated whether a new member of the TNF family, TRAIL (TNF-related apoptosis-inducing ligand), would similarly trigger preferential apoptotic cell death in FA phenotype cells.

MATERIAL AND METHODS

Hematopoietic cells from FANCC(-/-) transgenic mice and human FA-C lymphoblasts (HSC536N) as well as their phenotypically corrected counterparts (FANCC(+/+), HSC536/FA-Cneo) were compared for their response to apoptosis induction by TRAIL and fas ligation in the presence or absence of IFN-gamma. Cells were also studied for the protein and gene expression of TRAIL-receptors, caspase-8 and its inhibitory protein, FLIP.

RESULTS

TRAIL exposure by itself or in combination with IFN-gamma did not lead to preferential apoptosis induction in human and murine FA-C phenotype hematopoietic cells. This resistance was unrelated to the expression of TRAIL receptors or FLIP isoforms, but correlated with absent cleavage of pro-caspase-8. Results were validated by those from gene expression profiling of relevant genes in the two lymphoblast cell lines.

CONCLUSION

TRAIL, in contrast to fas ligation, does not induce preferential apoptosis in FA-C phenotype cells despite shared downstream signaling described in non-FA models. These data provide further insight into the complexity of FA-C-regulated apoptotic signaling.

Distinct gene expression profiles determine molecular treatment response in childhood acute lymphoblastic leukemia

Treatment resistance, as indicated by the presence of high levels of minimal residual disease (MRD) after induction therapy and induction consolidation, is associated with a poor prognosis in childhood acute lymphoblastic leukemia (ALL). We hypothesized that treatment resistance is an intrinsic feature of ALL cells reflected in the gene expression pattern and that resistance to chemotherapy can be predicted before treatment. To test these hypotheses, gene expression signatures of ALL samples with high MRD load were compared with those of samples without measurable MRD during treatment. We identified 54 genes that clearly distinguished resistant from sensitive ALL samples. Genes with low expression in resistant samples were predominantly associated with cell-cycle progression and apoptosis, suggesting that impaired cell proliferation and apoptosis are involved in treatment resistance. Prediction analysis using randomly selected samples as a training set and the remaining samples as a test set revealed an accuracy of 84%. We conclude that resistance to chemotherapy seems at least in part to be an intrinsic feature of ALL cells. Because treatment response could be predicted with high accuracy, gene expression profiling could become a clinically relevant tool for treatment stratification in the early course of childhood ALL.

Inhibition of infectious pancreatic necrosis virus replication by atlantic salmon Mx1 protein

Mx proteins form a family of interferon (IFN)-induced GTPases with potent antiviral activity against various single-stranded RNA viruses in mammals and chickens. In fish, alpha/beta IFN has been reported to inhibit the replication of infectious pancreatic necrosis virus (IPNV), but the mode of action has not been elucidated. A correlation between the inhibition of IPNV and Mx protein expression has, however, been observed. To examine whether Atlantic salmon Mx1 protein (ASMx1) possesses antiviral activity against IPNV, CHSE-214 cells constitutively expressing ASMx1 were established. ASMx1 appeared to be localized in the cytoplasm. The ASMx1-expressing clone selected showed a severely reduced IPNV-induced cytopathic effect, which was confirmed by a 500-fold reduction in virus yield. The antiviral activity against IPNV was further confirmed by the inhibition of virus protein synthesis and the reduced accumulation of virus transcripts. The present work further adds to the body of evidence which suggests that antiviral activity is a major functional role of vertebrate Mx proteins. Moreover, the list of viruses inhibited by Mx proteins is extended to include double-stranded RNA viruses.

Fanconi anemia C gene product regulates expression of genes involved in differentiation and inflammation

Loss of Fanconi anemia (FA) proteins activity by recessive inherited mutations in one of the FA genes leads to a disease characterized by bone marrow failure, myeloid leukemia and DNA damage hypersensitivity. The aim of this work was to improve our understanding of the FA syndrome defining the transcription profile of the FA complementation group C (FANCC)-deficient cells in comparison to their ectopically corrected counterpart using oligonucleotide microarrays. In this way, 49 RNAs have been isolated, which showed a consistent differential pattern of expression among FANCC mutated and corrected cells. The observed specific changes in gene expression suggest that FANCC regulates specifically myeloid differentiation and unmasks a previously unsuspected anti-inflammatory role for the FA proteins. In spite of the DNA damage hypersensitivity of the syndrome, no gene coding for a protein directly involved in DNA repair/damage response was found to be deregulated in our analysis. This observation suggests that FANCC does not directly control genes involved in DNA repair at the transcriptional level, but does not exclude a regulation at the translational or post-translational level, or by protein/protein interactions. The potential role of the differentially expressed genes in FA phenotype as well as a functional- and cellular-based clustering of the identified genes are presented and discussed.

Protein profiling of the human epidermis from the elderly reveals up-regulation of a signature of interferon-gamma-induced polypeptides that includes manganese-superoxide dismutase and the p85beta subunit of phosphatidylinositol 3-kinase

Aging of the human skin is a complex process that consists of chronological and extrinsic aging, the latter caused mainly by exposure to ultraviolet radiation (photoaging). Here we present studies in which we have used proteomic profiling technologies and two-dimensional (2D) PAGE database resources to identify proteins whose expression is deregulated in the epidermis of the elderly. Fresh punch biopsies from the forearm of 20 pairs of young and old donors (21-30 and 75-92 years old, respectively) were dissected to yield an epidermal fraction that consisted mainly of differentiated cells. One- to two-mm3 epidermal pieces were labeled with [35S]methionine for 18 h, lysed, and subjected to 2D PAGE (isoelectric focusing and non-equilibrium pH gradient electrophoresis) and phosphorimage autoradiography. Proteins were identified by matching the gels with the master 2D gel image of human keratinocytes (proteomics.cancer.dk). In selected cases 2D PAGE immunoblotting and/or mass spectrometry confirmed the identity. Quantitative analysis of 172 well focused and abundant polypeptides showed that the level of most proteins (148) remains unaffected by the aging process. Twenty-two proteins were consistently deregulated by a factor of 1.5 or more across the 20 sample pairs. Among these we identified a group of six polypeptides (Mx-A, manganese-superoxide dismutase, tryptophanyl-tRNA synthetase, the p85beta subunit of phosphatidylinositol 3-kinase, and proteasomal proteins PA28-alpha and SSP 0107) that is induced by interferon-gamma in primary human keratinocytes and that represents a specific protein signature for the effect of this cytokine. Changes in the expression of the eukaryotic initiation factor 5A, NM23 H2, cyclophilin A, HSP60, annexin I, and plasminogen activator inhibitor 2 were also observed. Two proteins exhibited irregular behavior from individual to individual. Besides arguing for a role of interferon-gamma in the aging process, the biological activities associated with the deregulated proteins support the contention that aging is linked with increased oxidative stress that could lead to apoptosis in vivo.

Genetic basis of Fanconi anemia

Fanconi anemia is a rare autosomal recessive disease characterized by bone marrow failure, developmental anomalies, a high incidence of myelodysplasia and acute nonlymphocytic leukemia, and cellular hypersensitivity to cross linking agents. Five of the seven known Fanconi anemia proteins bind together in a complex and influence the function of a sixth, FANCD2, which colocalizes with BRCA1 in nuclear foci after genotoxic stress. Carboxy-terminal truncating mutations of the seventh Fanconi anemia gene, BRCA2, are hypomorphic and lead to FA-D1 and possibly FA-B. Because the Fanconi anemia alleles of BRCA2 fail to bind to Rad51 in response to genotoxic stress and Rad51 therefore fails to localize to nuclear damage foci, many investigators in the field suspect that the Fanconi anemia pathway supports the integrity of the Rad51 and BRCA1 and BRCA2 pathways as they function in homologous recombination repair. Because these abnormalities are common to all somatic cells, it is unlikely that dysfunction of this particular pathway results in tissue-specific apoptosis of hematopoietic cells. Indeed, at least one of the Fanconi anemia proteins, FANCC, exhibits functions in hematopoietic cells in addition to its role in the complex. Because FANCC protects hematopoietic cells from apoptotic cues in ways that do not require an intact heteromeric Fanconi anemia complex, it is reasonable to expect that the other Fanconi anemia gene products will have independent cytoplasmic and nuclear functions, particularly in hematopoietic and germ cells that seem to rely so substantially on an intact portfolio of Fanconi anemia proteins.

Analysis of baseline and cisplatin-inducible gene expression in Fanconi anemia cells using oligonucleotide-based microarrays

BACKGROUND: Patients with Fanconi anemia (FA) suffer from multiple defects, most notably of the hematological compartment (bone marrow failure), and susceptibility to cancer. Cells from FA patients show increased spontaneous chromosomal damage, which is aggravated by exposure to low concentrations of DNA cross-linking agents such as mitomycin C or cisplatin. Five of the identified FA proteins form a nuclear core complex. However, the molecular function of these proteins remains obscure. METHODS: Oligonucleotide microarrays were used to compare the expression of approximately 12,000 genes from FA cells with matched controls. Expression profiles were studied in lymphoblastoid cell lines derived from three different FA patients, one from the FA-A and two from the FA-C complementation groups. The isogenic control cell lines were obtained by either transfecting the cells with vectors expressing the complementing cDNAs or by using a spontaneous revertant cell line derived from the same patient. In addition, we analyzed expression profiles from two cell line couples at several time points after a 1-hour pulse treatment with a discriminating dose of cisplatin. RESULTS: Analysis of the expression profiles showed differences in expression of a number of genes, many of which have unknown function or are difficult to relate to the FA defect. However, from a selected number of proteins involved in cell cycle regulation, DNA repair and chromatin structure, Western blot analysis showed that p21waf1/Cip1 was significantly upregulated after low dose cisplatin treatment in FA cells specifically (as well as being expressed at elevated levels in untreated FA cells). CONCLUSIONS: The observed increase in expression of p21waf1/Cip1 after treatment of FA cells with crosslinkers suggests that the sustained elevated levels of p21waf1/Cip1 in untreated FA cells detected by Western blot analysis likely reflect increased spontaneous damage in these cells.

Evaluation of bioavailability of three types of IFNbeta in multiple sclerosis patients by a new quantitative-competitive-PCR method for MxA quantification

Intracellular expression of human myxovirus protein A (MxA) is exclusively induced by type I IFNs (IFNalpha,beta,omega) or by some viruses and it is strongly increased under IFN treatment. We set up an internally controlled quantitative-competitive polymerase chain reaction (qc-PCR) that quantifies MxA mRNA expressed in human peripheral blood mononuclear cells (PBMC). Our qc-PCR is accurate because the mean ratio of copy number estimated by qc-PCR to that quantified spectrophotometrically is 1.08+/-0.03, moreover it is repeatable with high sensitivity (1 fg MxA/pg GAPDH). MxA mRNA was tested in 47 Relapsing-Remitting Multiple Sclerosis (RR-MS) untreated patients and in 48 patients treated with one of the 3 IFNbeta licensed for MS (24 with Rebif, 14 with Avonex and 10 with Betaferon). All the 48 treated patients were negative to IFNbeta neutralising antibodies (NABs) as tested in our laboratory using a cytopathic assay (CPE). MxA mRNA levels were detectable in all untreated patients (mean 24+/-18 fg MxA/pg GAPDH) and significantly higher levels were found in all the treated patients 12 h after IFNbeta administration (mean 499+/-325 fg MxA/pg GAPDH); furthermore, the three types of IFNbeta showed comparable bioavailability. Our data indicate that the bioavailability of the three available types of IFNbeta can be evaluated by MxA qc-PCR.

Fanconi anemia proteins localize to chromatin and the nuclear matrix in a DNA damage- and cell cycle-regulated manner

Fanconi anemia (FA) is a genetic disease characterized by congenital defects, bone marrow failure, and cancer susceptibility. Cells from patients with FA exhibit genomic instability and hypersensitivity to DNA cross linking agents such as mitomycin C. Despite the identification of seven complementation groups and the cloning of six genes, the function of the encoded gene products remains elusive. The FancA (Fanconi anemia complementation group A), FancC, and FancG proteins have been detected within a nuclear complex, but no change in level, binding, or localization has been reported as a result of drug treatment or cell cycle. We show that in immunofluorescence studies, FancA appears as a non-nucleolar nuclear protein that is excluded from condensed, mitotic chromosomes. Biochemical fractionation reveals that the FA proteins are found in nuclear matrix and chromatin and that treatment with mitomycin C results in increase of the FA proteins in nuclear matrix and chromatin fractions. This induction occurs in wild-type cells and mutant FA-D (Fanconi complementation group D) cells but not in mutant FA-A cells. Immunoprecipitation of FancA protein in chromatin demonstrates the coprecipitation of FancA, FancC, and FancG, showing that the FA proteins move together as a complex. Also, fractionation of mitotic cells confirms the lack of FA proteins in chromatin or the nuclear matrix. Furthermore, phosphorylation of FancG was found to be temporally correlated with exit of the FA complex from chromosomes at mitosis. Taken together, these findings suggest a role for FA proteins in chromatin and nuclear matrix.

Erythropoiesis: Current Clinical Practice: Advances in the Genetics and Biology of Fanconi Anaemia

The autosomal recessive disorder Fanconi anaemia (FA) has been the subject of intense study for over a decade. The genes mutated in FA patients are being cloned, but so far, the sequences of these genes have not given any clear indication of their function. Various models for the function of the FA proteins have been postulated to explain the spontaneous chromosomal abnormalities and clastogen sensitivity described in FA cells. This review summarises the critical experimental evidence for and against these models, and attempts to give some indication of the possible mechanisms by which mutations in FA genes cause patients to suffer pancytopaenia and acute myeloid leukaemia, as well as an increased risk of other malignancies.

Functional correction of FA-C cells with FANCC suppresses the expression of interferon gamma-inducible genes

Because hematopoietic cells derived from Fanconi anemia (FA) patients of the C-complementation group (FA-C) are hypersensitive to the inhibitory effects of interferon gamma (IFNgamma), the products of certain IFNgamma-inducible genes known to influence hematopoietic cell survival were quantified. High constitutive expression of the IFNgamma-inducible genes, IFN-stimulated gene factor 3 gamma subunit (ISGF3gamma), IFN regulatory factor-1 (IRF-1), and the cyclin-dependent kinase inhibitor p21(WAF1) was found in FANCC mutant B lymphoblasts, low-density bone marrow cells, and murine embryonic fibroblasts. Paradoxically, these cells do not activate signal transducer and activator of transcription (STAT) 1 properly. In an attempt to clarify mechanisms by which FA-C cells overexpress IFNgamma-inducible genes in the face of defective STAT1 phosphorylation, it was reasoned that decreased levels of activated STAT1 might result in reduced expression of a hematopoietic IFNgamma-responsive protein that normally modulates expression of other IFNgamma-responsive genes. Levels of the IFNgamma-inducible factor IFN consensus sequence binding protein (ICSBP), a negative trans-acting regulator of some IFNgamma-inducible genes, were quantified. ICSBP levels were reduced in FA-C B lymphoblasts and MEFs. However, enforced expression of ICSBP failed to down-regulate IRF-1, ISGF3gamma, and p21(WAF1). Thus, the FANCC protein functions to modulate expression of a family of genes that in normal cells are inducible only by specific environmental cues for apoptosis or mitogenic inhibition, but it does so independently of the classic IFN-STAT1 pathway and is not the direct result of reduced ICSBP expression.

Role of double-stranded RNA-dependent protein kinase in mediating hypersensitivity of Fanconi anemia complementation group C cells to interferon gamma, tumor necrosis factor-alpha, and double-stranded RNA

Hematopoietic cells bearing inactivating mutations of Fanconi anemia group C (FANCC) are excessively apoptotic and demonstrate hypersensitivity not only to cross-linking agents but also to interferon gamma (IFN-gamma) and tumor necrosis factor-alpha. Seeking essential signaling pathways for this phenotype, this study quantified constitutive and induced RNA-dependent protein kinase (PKR) activation in Fanconi anemia cells of the C complementation group (FA-C). PKR was constitutively phosphorylated and exhibited an increased binding affinity for double-stranded RNA (dsRNA) in FANCC(-/-) cells. FANCC(-/-) cells were hypersensitive to both dsRNA and the combination of dsRNA and IFN-gamma in that these agents induced a higher fraction of apoptosis in FANCC(-/-) cells than in normal cells. Overexpression of wild-type PKR-sensitized FANCC(-/-) cells to apoptosis induced by IFN-gamma and dsRNA. Conversely, inhibition of PKR function by enforced expression of a dominant-negative inhibitory mutant of PKR (PKRDelta6) substantially reduced the IFN and dsRNA hypersensitivity of FANCC(-/-) cells. Two PKR target molecules, IkappaB-alpha and IRF-1, were not differentially activated in FANCC(-/-) cells, but enforced expression of a nonphosphorylatable form of eukaryotic translation initiation factor-2alpha reversed the PKR-mediated block of messenger RNA translation and partially abrogated the PKR-mediated apoptosis in FANCC(-/-) cells. Because no evidence was found of a PKR/FANCC complex in normal cells, it was concluded that an essential function of FANCC is to suppress, indirectly, the activity of PKR and that FANCC inactivation results in IFN hypersensitivity, at least in part, because this function of FANCC is abrogated.

The Fanconi anemia protein FANCC binds to and facilitates the activation of STAT1 by gamma interferon and hematopoietic growth factors

Hematopoietic progenitor cells from Fanconi anemia (FA) group C (FA-C) patients display hypersensitivity to the apoptotic effects of gamma interferon (IFN-gamma) and constitutively express a variety of IFN-dependent genes. Paradoxically, however, STAT1 activation is suppressed in IFN-stimulated FA cells, an abnormality corrected by transduction of normal FANCC cDNA. We therefore sought to define the specific role of FANCC protein in signal transduction through receptors that activate STAT1. Expression and phosphorylation of IFN-gamma receptor alpha chain (IFN-gammaRalpha) and JAK1 and JAK2 tyrosine kinases were equivalent in both normal and FA-C cells. However, in coimmunoprecipitation experiments STAT1 did not dock at the IFN-gammaR of FA-C cells, an abnormality corrected by transduction of the FANCC gene. In addition, glutathione S-transferase fusion genes encoding normal FANCC but not a mutant FANCC bearing an inactivating point mutation (L554P) bound to STAT1 in lysates of IFN-gamma-stimulated B cells and IFN-, granulocyte-macrophage colony-stimulating factor- and stem cell factor-stimulated MO7e cells. Kinetic studies revealed that the initial binding of FANCC was to nonphosphorylated STAT1 but that subsequently the complex moved to the receptor docking site, at which point STAT1 became phosphorylated. The STAT1 phosphorylation defect in FA-C cells was functionally significant in that IFN induction of IFN response factor 1 was suppressed and STAT1-DNA complexes were not detected in nuclear extracts of FA-C cells. We also determined that the IFN-gamma hypersensitivity of FA-C hematopoietic progenitor cells does not derive from STAT1 activation defects because granulocyte-macrophage CFU and erythroid burst-forming units from STAT1(-/-) mice were resistant to IFN-gamma. However, BFU-E responses to SCF and erythropoietin were suppressed in STAT(-/-) mice. Consequently, because the FANCC protein is involved in the activation of STAT1 through receptors for at least three hematopoietic growth and survival factor molecules, we reason that FA-C hematopoietic cells are excessively apoptotic because of an imbalance between survival cues (owing to a failure of STAT1 activation in FA-C cells) and apoptotic and mitogenic inhibitory cues (constitutively activated in FA-C cells in a STAT1-independent fashion).

Correlation of interferon-induced expression of MxA mRNA in peripheral blood mononuclear cells with the response of patients with chronic active hepatitis C to IFN-alpha therapy

MxA, a protein with selective activity against certain viruses, is an accepted specific indicator of type I interferon (IFN) activity. We have developed an internally controlled quantitative-competitive PCR to measure the amounts of MxA mRNA expressed in peripheral blood mononuclear cells (PBMC). This assay is more sensitive, quantitative, and easily applied to serial clinical samples than previously described methods. We have applied this assay retrospectively to 27 patients with chronic active hepatitis C given IFN-alpha2. Most such patients gain no sustained benefit but nevertheless suffer from the side effects, expense, and inconvenience of the treatment. Fourteen of the 27 had been classified on clinical grounds as responders and 13 as nonresponders at the end of a 6 month treatment period. We measured MxA mRNA in PBMC obtained before and after 8 weeks of IFN-alpha2 treatment. All the patients expressed some level of mRNA before treatment began, and after 8 weeks of treatment, the level rose in 19. This increase was significant (p < 0.001) only in patients classified as responders. This strongly suggests that hepatitis C virus (HCV) patients who express increased amounts of MxA mRNA in their PBMC during IFN-alpha treatment are most likely to obtain long-term benefit. If this finding is confirmed in future prospective studies, it will provide an extremely important predictive marker for managing IFN-alpha therapy in patients with HCV.

Fanconi anemia C protein acts at a switch between apoptosis and necrosis in mitomycin C-induced cell death

Deregulation of apoptosis seems to be a hallmark of the Fanconi anemia (FA) syndrome. In order to further define the role of the FA protein from complementation group C (FAC) in apoptosis, we characterized parameters modified during the mitomycin-C (MMC)-induced apoptotic program. It is shown that despite a higher level of cell death for FA compared to normal lymphoblasts after MMC treatment, FA cells do not display a marked DNA fragmentation. Furthermore, while playing a central role in MMC apoptosis of normal lymphoblasts, the activity of caspase-3-like proteases is altered in FA cells. Interestingly, the disruption of the mitochondrial transmembrane potential (Deltapsi), an early event that can lead to apoptotic or to necrotic death, is accomplished similarly in FA and in normal cells. Finally, it is shown that the overexpressed FAC protein inhibited the apoptotic steps, with the exception of the decrease of the Deltapsi. Altogether, our results indicate that the FAC protein acts at a step preceding the activation of the caspases and after the modification of the Deltapsi, a decision point at which cells can be pushed toward either apoptosis or necrosis and which, consequently, regulates the balance between the two modes of cell death.

Abnormal Microsomal Detoxification Implicated in Fanconi Anemia Group C by Interaction of the FAC Protein With NADPH Cytochrome P450 Reductase

The FAC protein encoded by the Fanconi anemia (FA) complementation group C gene is thought to function in the cytoplasm at a step before DNA repair. Because FA cells are susceptible to mitomycin C, we considered the possibility that FAC might interact with enzymes involved in the bioreductive activation of this drug. Here we report that FAC binds to NADPH cytochrome-P450 reductase (RED), a microsomal membrane protein involved in electron transfer, in both transfected COS-1 and normal murine liver cells. FAC-RED interaction requires the amino-terminal region of FAC and the cytosolic, membrane-proximal domain of the reductase. The latter contains a known binding site for flavin mononucleotide (FMN). Addition of FMN to cytosolic lysates disrupts FAC-reductase complexes, while flavin dinucleotide, which binds to a distinct carboxy-terminal domain, fails to alter FAC-RED complexes at concentrations similar to FMN. FAC is also functionally coupled to this enzyme as its expression in COS-1 cells suppresses the ability of RED to reduce cytochrome c in the presence of NADPH. We propose that FAC plays a fundamental role in vivo by attenuating the activity of RED, thereby regulating a major detoxification pathway in mammalian cells.

© 1998 by The American Society of Hematology.

Abnormal Microsomal Detoxification Implicated in Fanconi Anemia Group C by Interaction of the FAC Protein With NADPH Cytochrome P450 Reductase

The FAC protein encoded by the Fanconi anemia (FA) complementation group C gene is thought to function in the cytoplasm at a step before DNA repair. Because FA cells are susceptible to mitomycin C, we considered the possibility that FAC might interact with enzymes involved in the bioreductive activation of this drug. Here we report that FAC binds to NADPH cytochrome-P450 reductase (RED), a microsomal membrane protein involved in electron transfer, in both transfected COS-1 and normal murine liver cells. FAC-RED interaction requires the amino-terminal region of FAC and the cytosolic, membrane-proximal domain of the reductase. The latter contains a known binding site for flavin mononucleotide (FMN). Addition of FMN to cytosolic lysates disrupts FAC-reductase complexes, while flavin dinucleotide, which binds to a distinct carboxy-terminal domain, fails to alter FAC-RED complexes at concentrations similar to FMN. FAC is also functionally coupled to this enzyme as its expression in COS-1 cells suppresses the ability of RED to reduce cytochrome c in the presence of NADPH. We propose that FAC plays a fundamental role in vivo by attenuating the activity of RED, thereby regulating a major detoxification pathway in mammalian cells.

© 1998 by The American Society of Hematology.

Domains mediating intramolecular folding and oligomerization of MxA GTPase

MxA is an interferon-induced GTPase of human cells that inhibits the multiplication of several RNA viruses by a still poorly understood mechanism. Previous biochemical studies indicated that the C terminus of MxA folds back to form a functional GTP-binding pocket, and that an internal fragment contains a domain required for oligomerization. Using the yeast two-hybrid system, we have now mapped these domains. MxA sequences located downstream of amino acid 564 were found to strongly interact with an internal domain that includes amino acids 372 to 540. This interaction was abolished by mutating phenylalanine 382 or leucine 612, which is part of a leucine zipper motif. Neither the C-terminal nor the internal MxA fragments formed homo-oligomers. Using a mammalian nuclear transport assay that can detect protein-protein interactions, we further found that full-length MxA forms complexes with MxA fragments that include amino acids 372 to 540. This interaction was not observed when phenylalanine 382 was exchanged for alanine or arginine. Furthermore, interaction of two full-length MxA molecules occurred only if at least one of them carried a functional C-terminal leucine zipper motif. These results suggest that C-terminal back-folding and oligomerization are two alternative outcomes of the same type of interaction between the C-terminal and the internal domains of MxA. Intramolecular interaction is believed to result in the formation of MxA monomers, whereas intermolecular interaction may induce the formation of large MxA oligomers.

Cloning and characterization of cDNAs for a bovine (Bos taurus) Mx protein

Mx proteins are GTPases that are stringently induced in cells from many vertebrates on exposure to type I interferons (IFNs), and expression of some Mx proteins potently inhibits replication of specific viruses. Two cDNAs encoding bovine Mx proteins were isolated from an endometrial phage library. The open reading frames (ORFs) of these two clones predict proteins of 654 (Mxl) and 648 (Mxl-a) residues. Both possess the tripartite GTPase domains, dynamin signature, and leucine zipper motifs conserved in all other Mx proteins identified. The bovine protein sequences show highest identity to ovine Mx (93%) and are substantially similar to human MxA (73%) and mouse Mx1 (63%). Based on differences between the two bovine clones in the coding and 3'-untranslated regions, it was concluded that they represent two alleles of one gene, and heterozygous and homozygous cattle were identified. Expression of Mx mRNA was rapidly induced in cultured bovine cells by treatment with IFN.

Is Fanconi anemia caused by a defect in the processing of DNA damage?

Fanconi anemia (FA) is an autosomal genetic disease characterized by a complex array of developmental disorders, a high predisposition to bone marrow failure and to acute myelogenous leukemia. The chromosomal instability and the hypersensitivity to DNA cross-linking agents led to its classification with the DNA repair disorders. This review aimed at establishing whether it is still appropriate to consider 1/approximately FA within a DNA repair framework taking into account the recently discovered genetic heterogeneity characteristics of the defect (eight complementation groups). We discuss the possibility that the FA proteins interact to form a complex which may control different functions, including the processing of specific DNA lesions. Such a complex may act as a sensor to initiate protective systems as well as transcription of specific genes specifying, among others proteins, growth factors. Such steps may be organized as a linear cascade or more likely under the form of a web network.

MxA GTPase: oligomerization and GTP-dependent interaction with viral RNP target structures

MxA protein is an interferon-induced GTPase of human cells that inhibits the multiplication of several RNA viruses, including influenza viruses and bunyaviruses. Studies on MxA transgenic mice have shown that MxA is a powerful antiviral agent in vivo. It has been suggested that this cellular protein also protects humans from viral disease, but the mechanism(s) by which MxA exerts its antiviral action is still poorly understood. Using an in vitro cosedimentation assay, we now demonstrate that MxA tightly interacts with components of the ribonucleoprotein complex of Thogoto virus, an influenza-like virus transmitted by ticks. This assay demonstrates for the first time a physical interaction between MxA GTPase and a viral target structure. It is based on three elements, namely, highly active MxA GTPases as effector molecules, viral ribonucleoprotein particles as viral targets, and GTPgammaS as a stabilizing factor. Furthermore, using a simple nuclear translocation assay, we show that human MxA protein forms oligomers in vivo. This assay provides a stringent test for tight association of partner molecules in intact mammalian cells. It not only will be useful for studying physical interactions of MxA with partner molecules, but may also be applicable to other studies on protein-protein interactions in living cells.

Fanconi anemia group A and D cell lines respond normally to inhibitors of cell cycle regulation

Cells from patients with Fanconi anemia (FA) show decreased viability and decreased chromosome stability after treatment with DNA cross-linking agents, compared to normal cells. FA cells also show a relative accumulation at the G2/M transition after such treatment. This has suggested a possible checkpoint abnormality. In the studies presented here, treatment with hydroxyurea, caffeine or inhibitors of cell cycle kinases did not reveal abnormalities in survival or chromosome stability in FA-A or FA-D cells. Chromosomal breaks introduced by hydrogen peroxide or methyl methanesulfonate accumulated to the same extent in FA-A or FA-D cells as in normal cells. We conclude that FA-A and FA-D cells respond normally to agents known to alter the cell cycle or introduce DNA strand breaks. FA cells process strand breaks and a variety of DNA monoadducts normally. Our results are compatible with repair of DNA crosslinks being slower in FA than in normal cells and FA cells having normal cell cycle checkpoints.