Showing papers by "St. Jude Children's Research Hospital published in 2006"

Treatment of acute lymphoblastic leukemia.

Abstract: Although the overall cure rate of acute lymphoblastic leukemia (ALL) in children is about 80 percent, affected adults fare less well. This review considers recent advances in the treatment of ALL, emphasizing issues that need to be addressed if treatment outcome is to improve further.

Regulation and Function of IKK and IKK-Related Kinases

Abstract: Members of the nuclear factor kappa B (NF-kappaB) family of dimeric transcription factors (TFs) regulate expression of a large number of genes involved in immune responses, inflammation, cell survival, and cancer. NF-kappaB TFs are rapidly activated in response to various stimuli, including cytokines, infectious agents, and radiation-induced DNA double-strand breaks. In nonstimulated cells, some NF-kappaB TFs are bound to inhibitory IkappaB proteins and are thereby sequestered in the cytoplasm. Activation leads to phosphorylation of IkappaB proteins and their subsequent recognition by ubiquitinating enzymes. The resulting proteasomal degradation of IkappaB proteins liberates IkappaB-bound NF-kappaB TFs, which translocate to the nucleus to drive expression of target genes. Two protein kinases with a high degree of sequence similarity, IKKalpha and IKKbeta, mediate phosphorylation of IkappaB proteins and represent a convergence point for most signal transduction pathways leading to NF-kappaB activation. Most of the IKKalpha and IKKbeta molecules in the cell are part of IKK complexes that also contain a regulatory subunit called IKKgamma or NEMO. Despite extensive sequence similarity, IKKalpha and IKKbeta have largely distinct functions, due to their different substrate specificities and modes of regulation. IKKbeta (and IKKgamma) are essential for rapid NF-kappaB activation by proinflammatory signaling cascades, such as those triggered by tumor necrosis factor alpha (TNFalpha) or lipopolysaccharide (LPS). In contrast, IKKalpha functions in the activation of a specific form of NF-kappaB in response to a subset of TNF family members and may also serve to attenuate IKKbeta-driven NF-kappaB activation. Moreover, IKKalpha is involved in keratinocyte differentiation, but this function is independent of its kinase activity. Several years ago, two protein kinases, one called IKKepsilon or IKK-i and one variously named TBK1 (TANK-binding kinase), NAK (NF-kappaB-activated kinase), or T2K (TRAF2-associated kinase), were identified that exhibit structural similarity to IKKalpha and IKKbeta. These protein kinases are important for the activation of interferon response factor 3 (IRF3) and IRF7, TFs that play key roles in the induction of type I interferon (IFN-I). Together, the IKKs and IKK-related kinases are instrumental for activation of the host defense system. This Review focuses on the functions of IKK and IKK-related kinases and the molecular mechanisms that regulate their activities.

Specificity in Toll-like receptor signalling through distinct effector functions of TRAF3 and TRAF6

Abstract: Toll-like receptors (TLRs) are activated by pathogen-associated molecular patterns to induce innate immune responses and production of pro-inflammatory cytokines, interferons and anti-inflammatory cytokines. TLRs activate downstream effectors through adaptors that contain Toll/interleukin-1 receptor (TIR) domains, but the mechanisms accounting for diversification of TLR effector functions are unclear. To dissect biochemically TLR signalling, we established a system for isolating signalling complexes assembled by dimerized adaptors. Using MyD88 as a prototypical adaptor, we identified TNF receptor-associated factor 3 (TRAF3) as a new component of TIR signalling complexes that is recruited along with TRAF6. Using myeloid cells from TRAF3- and TRAF6-deficient mice, we show that TRAF3 is essential for the induction of type I interferons (IFN) and the anti-inflammatory cytokine interleukin-10 (IL-10), but is dispensable for expression of pro-inflammatory cytokines. In fact, TRAF3-deficient cells overproduce pro-inflammatory cytokines owing to defective IL-10 production. Despite their structural similarity, the functions of TRAF3 and TRAF6 are largely distinct. TRAF3 is also recruited to the adaptor TRIF (Toll/IL-1 receptor domain-containing adaptor-inducing IFN-beta) and is required for marshalling the protein kinase TBK1 (also called NAK) into TIR signalling complexes, thereby explaining its unique role in activation of the IFN response.

Hierarchical regulation of mitochondrion-dependent apoptosis by BCL-2 subfamilies.

Abstract: Although the BCL-2 family constitutes a crucial checkpoint in apoptosis, the intricate interplay between these family members remains elusive. Here, we demonstrate that BIM and PUMA, similar to truncated BID (tBID), directly activate BAX-BAK to release cytochrome c. Conversely, anti-apoptotic BCL-2-BCL-X(L)-MCL-1 sequesters these 'activator' BH3-only molecules into stable complexes, thus preventing the activation of BAX-BAK. Extensive mutagenesis of BAX-BAK indicates that their activity is not kept in check by BCL-2-BCL-X(L)-MCL-1. Anti-apoptotic BCL-2 members are differentially inactivated by the remaining 'inactivator' BH3-only molecules including BAD, NOXA, BMF, BIK/BLK and HRK/DP5. BAD displaces tBID, BIM or PUMA from BCL-2-BCL-X(L) to activate BAX-BAK, whereas NOXA specifically antagonizes MCL-1. Coexpression of BAD and NOXA killed wild-type but not Bax, Bak doubly deficient cells or Puma deficient cells with Bim knockdown, indicating that activator BH3-only molecules function downstream of inactivator BH3-only molecules to activate BAX-BAK. Our data establish a hierarchical regulation of mitochondrion-dependent apoptosis by various BCL-2 subfamilies.

Signalling pathways and molecular interactions of NOD1 and NOD2

Abstract: NOD1 and NOD2 are intracellular sensors of microbial components derived from bacterial peptidoglycan. This Review describes the signalling pathways of these NOD proteins and details their role in the maintenance of mucosal homeostasis and the induction of mucosal immunity. The NOD (nucleotide-binding oligomerization domain) proteins NOD1 and NOD2 have important roles in innate immunity as sensors of microbial components derived from bacterial peptidoglycan. The importance of these molecules is underscored by the fact that mutations in the gene that encodes NOD2 occur in a subpopulation of patients with Crohn's disease, and NOD1 has also been shown to participate in host defence against infection with Helicobacter pylori. Here, we focus on the molecular interactions between these NOD proteins and other intracellular molecules to elucidate the mechanisms by which NOD1 and NOD2 contribute to the maintenance of mucosal homeostasis and the induction of mucosal inflammation.

Insights into the Interaction between Influenza Virus and Pneumococcus

Abstract: Bacterial infections following influenza are an important cause of morbidity and mortality worldwide. Based on the historical importance of pneumonia as a cause of death during pandemic influenza, the increasingly likely possibility that highly pathogenic avian influenza viruses will trigger the next worldwide pandemic underscores the need to understand the multiple mechanisms underlying the interaction between influenza virus and bacterial pathogens such as Streptococcus pneumoniae. There is ample evidence to support the historical view that influenza virus alters the lungs in a way that predisposes to adherence, invasion, and induction of disease by pneumococcus. Access to receptors is a key factor and may be facilitated by the virus through epithelial damage, by exposure or up-regulation of receptors, or by provoking the epithelial regeneration response to cytotoxic damage. More recent data indicate that alteration of the immune response by diminishing the ability of the host to clear pneumococcus or by amplification of the inflammatory cascade is another key factor. Identification and exploration of the underlying mechanisms responsible for this synergism will provide targets for prevention and treatment using drugs and vaccines.

Risk-adapted craniospinal radiotherapy followed by high-dose chemotherapy and stem-cell rescue in children with newly diagnosed medulloblastoma (St Jude Medulloblastoma-96): long-term results from a prospective, multicentre trial

Abstract: Summary Background Current treatment for medulloblastoma, which includes postoperative radiotherapy and 1 year of chemotherapy, does not cure many children with high-risk disease. We aimed to investigate the effectiveness of risk-adapted radiotherapy followed by a shortened period of dose-intense chemotherapy in children with medulloblastoma. Methods After resection, patients were classified as having average-risk medulloblastoma (≤1·5 cm 2 residual tumour and no metastatic disease) or high-risk medulloblastoma (>1·5 cm 2 residual disease or metastatic disease localised to neuraxis) medulloblastoma. All patients received risk-adapted craniospinal radiotherapy (23·4 Gy for average-risk disease and 36·0–39·6 Gy for high-risk disease) followed by four cycles of cyclophosphamide-based, dose-intensive chemotherapy. Patients were assessed regularly for disease status and treatment side-effects. The primary endpoint was 5-year event-free survival; we also measured overall survival. This study is registered with ClinicalTrials.gov, number NCT00003211. Findings Of 134 children with medulloblastoma who underwent treatment (86 average-risk, 48 high-risk), 119 (89%) completed the planned protocol. No treatment-related deaths occurred. 5-year overall survival was 85% (95% CI 75–94) in patients in the average-risk group and 70% (54–84) in those in the high-risk group (p=0·04); 5-year event-free survival was 83% (73–93) and 70% (55–85), respectively (p=0·046). For the 116 patients whose histology was reviewed centrally, histological subtype correlated with 5-year event-free survival (p=0·04): 84% (74–95) for classic histology, 77% (49–100) for desmoplastic tumours, and 57% (33–80) for large-cell anaplastic tumours. Interpretation Risk-adapted radiotherapy followed by a shortened schedule of dose-intensive chemotherapy can be used to improve the outcome of patients with high-risk medulloblastoma.

Genomics Identifies Medulloblastoma Subgroups That Are Enriched for Specific Genetic Alterations

Abstract: Purpose Traditional genetic approaches to identify gene mutations in cancer are expensive and laborious. Nonetheless, if we are to avoid rejecting effective molecular targeted therapies, we must test these drugs in patients whose tumors harbor mutations in the drug target. We hypothesized that gene expression profiling might be a more rapid and cost-effective method of identifying tumors that contain specific genetic abnormalities. Materials and Methods Gene expression profiles of 46 samples of medulloblastoma were generated using the U133av2 Affymetrix oligonucleotide array and validated using real-time reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry. Genetic abnormalities were confirmed using fluorescence in situ hybridization (FISH) and direct sequencing. Results Unsupervised analysis of gene expression profiles partitioned medulloblastomas into five distinct subgroups (subgroups A to E). Gene expression signatures that distinguished these subgroups predicted the prese...

Spatial organization of the mammalian genome surveillance machinery in response to DNA strand breaks

Abstract: We show that DNA double-strand breaks (DSBs) induce complex subcompartmentalization of genome surveillance regulators. Chromatin marked by γ-H2AX is occupied by ataxia telangiectasia–mutated (ATM) kinase, Mdc1, and 53BP1. In contrast, repair factors (Rad51, Rad52, BRCA2, and FANCD2), ATM and Rad-3–related (ATR) cascade (ATR, ATR interacting protein, and replication protein A), and the DNA clamp (Rad17 and -9) accumulate in subchromatin microcompartments delineated by single-stranded DNA (ssDNA). BRCA1 and the Mre11–Rad50–Nbs1 complex interact with both of these compartments. Importantly, some core DSB regulators do not form cytologically discernible foci. These are further subclassified to proteins that connect DSBs with the rest of the nucleus (Chk1 and -2), that assemble at unprocessed DSBs (DNA-PK/Ku70), and that exist on chromatin as preassembled complexes but become locally modified after DNA damage (Smc1/Smc3). Finally, checkpoint effectors such as p53 and Cdc25A do not accumulate at DSBs at all. We propose that subclassification of DSB regulators according to their residence sites provides a useful framework for understanding their involvement in diverse processes of genome surveillance.

Pharmacogenomics and Individualized Drug Therapy

Abstract: Pharmacogenetics deals with inherited differences in the response to drugs. The best-recognized examples are genetic polymorphisms of drug-metabolizing enzymes, which affect about 30% of all drugs. Loss of function of thiopurine S-methyltransferase (TPMT) results in severe and life-threatening hematopoietic toxicity if patients receive standard doses of mercaptopurine and azathioprine. Gene duplication of cytochrome P4502D6 (CYP2D6), which metabolizes many antidepressants, has been identified as a mechanism of poor response in the treatment of depression. There is also a growing list of genetic polymorphisms in drug targets that have been shown to influence drug response. A major limitation that has heretofore moderated the use of pharmacogenetic testing in the clinical setting is the lack of prospective clinical trials demonstrating that such testing can improve the benefit/risk ratio of drug therapy.

Divorcing ARF and p53: an unsettled case

Abstract: Mammalian cells that sustain oncogenic insults can invoke defensive programmes that either halt their division or trigger their apoptosis, but these countermeasures must be finely tuned to discriminate between physiological and potentially harmful growth-promoting states. By functioning specifically to oppose abnormally prolonged and sustained proliferative signals produced by activated oncogenes, the ARF tumour suppressor antagonizes functions of MDM2 to induce protective responses that depend on the p53 transcription factor and its many target genes. However, ARF has been reported to physically associate with proteins other than MDM2 and to have p53-independent activities, most of which remain controversial and poorly understood.

Large-Scale Sequence Analysis of Avian Influenza Isolates

Abstract: The spread of H5N1 avian influenza viruses (AIVs) from China to Europe has raised global concern about their potential to infect humans and cause a pandemic. In spite of their substantial threat to human health, remarkably little AIV whole-genome information is available. We report here a preliminary analysis of the first large-scale sequencing of AIVs, including 2196 AIV genes and 169 complete genomes. We combine this new information with public AIV data to identify new gene alleles, persistent genotypes, compensatory mutations, and a potential virulence determinant.

Inactivation of the p53 pathway in retinoblastoma

Abstract: Most human tumours have genetic mutations in their Rb and p53 pathways, but retinoblastoma is thought to be an exception. Studies suggest that retinoblastomas, which initiate with mutations in the gene retinoblastoma 1 (RB1), bypass the p53 pathway because they arise from intrinsically death-resistant cells during retinal development. In contrast to this prevailing theory, here we show that the tumour surveillance pathway mediated by Arf, MDM2, MDMX and p53 is activated after loss of RB1 during retinogenesis. RB1-deficient retinoblasts undergo p53-mediated apoptosis and exit the cell cycle. Subsequently, amplification of the MDMX gene and increased expression of MDMX protein are strongly selected for during tumour progression as a mechanism to suppress the p53 response in RB1-deficient retinal cells. Our data provide evidence that the p53 pathway is inactivated in retinoblastoma and that this cancer does not originate from intrinsically death-resistant cells as previously thought. In addition, they support the idea that MDMX is a specific chemotherapeutic target for treating retinoblastoma.

Mitochondrial outer membrane permeabilization during apoptosis: the innocent bystander scenario.

Abstract: Mitochondrial outer membrane permeabilization (MOMP) is considered the 'point of no return' as this event is responsible for engaging the apoptotic cascade in numerous cell death pathways. MOMP is directly governed by a subset of the BCL-2 family of proapoptotic proteins, which induce disruptions in the outer mitochondrial membrane (OMM) and subsequent release of death-promoting proteins like cytochrome c. The proposal here is centered on our hypothesis that MOMP is dictated by an interaction between the cytosol and the OMM, and although proteins of the OMM may be important in the process, the 'decision' to undergo apoptosis originates within the cytosol with no participation (in terms of yes, no and when) by mitochondria.

An increased specificity score matrix for the prediction of SF2/ASF-specific exonic splicing enhancers

Abstract: Numerous disease-associated point mutations exert their effects by disrupting the activity of exonic splicing enhancers (ESEs). We previously derived position weight matrices to predict putative ESEs specific for four human SR proteins. The score matrices are part of ESEfinder, an online resource to identify ESEs in query sequences. We have now carried out a refined functional SELEX screen for motifs that can act as ESEs in response to the human SR protein SF2/ASF. The test BRCA1 exon under selection was internal, rather than the 3'-terminal IGHM exon used in our earlier studies. A naturally occurring heptameric ESE in BRCA1 exon 18 was replaced with two libraries of random sequences, one seven nucleotides in length, the other 14. Following three rounds of selection for in vitro splicing via internal exon inclusion, new consensus motifs and score matrices were derived. Many winner sequences were demonstrated to be functional ESEs in S100-extract-complementation assays with recombinant SF2/ASF. Motif-score threshold values were derived from both experimental and statistical analyses. Motif scores were shown to correlate with levels of exon inclusion, both in vitro and in vivo. Our results confirm and extend our earlier data, as many of the same motifs are recognized as ESEs by both the original and our new score matrix, despite the different context used for selection. Finally, we have derived an increased specificity score matrix that incorporates information from both of our SF2/ASF-specific matrices and that accurately predicts the exon-skipping phenotypes of deleterious point mutations.

Cell-mediated Protection in Influenza Infection

Abstract: Current vaccine strategies against influenza focus on generating robust antibody responses. Because of the high degree of antigenic drift among circulating influenza strains over the course of a year, vaccine strains must be reformulated specifically for each influenza season. The time delay from isolating the pandemic strain to large-scale vaccine production would be detrimental in a pandemic situation. A vaccine approach based on cell-mediated immunity that avoids some of these drawbacks is discussed here. Specifically, cell-mediated responses typically focus on peptides from internal influenza proteins, which are far less susceptible to antigenic variation. We review the literature on the role of CD4+ and CD8+ T cell–mediated immunity in influenza infection and the available data on the role of these responses in protection from highly pathogenic influenza infection. We discuss the advantages of developing a vaccine based on cell-mediated immune responses toward highly pathogenic influenza virus and potential problems arising from immune pressure.

mTOR and cancer therapy.

Abstract: Proteins regulating the mammalian target of rapamycin (mTOR), as well as some of the targets of the mTOR kinase, are overexpressed or mutated in cancer. Rapamycin, the naturally occurring inhibitor of mTOR, along with a number of recently developed rapamycin analogs (rapalogs) consisting of synthetically derived compounds containing minor chemical modifications to the parent structure, inhibit the growth of cell lines derived from multiple tumor types in vitro, and tumor models in vivo. Results from clinical trials indicate that the rapalogs may be useful for the treatment of subsets of certain types of cancer. The sporadic responses from the initial clinical trials, based on the hypothesis of general translation inhibition of cancer cells are now beginning to be understood owing to a more complete understanding of the dynamics of mTOR regulation and the function of mTOR in the tumor microenvironment. This review will summarize the preclinical and clinical data and recent discoveries of the function of mTOR in cancer and growth regulation.

Dissecting p53-dependent apoptosis

Abstract: The complexity of the p53 protein, coupled with the vast cellular responses to p53, is simply astonishing. As new isoforms, functional domains and protein-protein interactions are described; each morsel of information forces us to think (and re-think) about how it 'fits' into the current p53 paradigm. One aspect of p53 signaling that is under refinement is the mechanism(s) leading to apoptosis. Here we discuss what is known about p53-induced apoptosis, what proteins and protein-protein interactions are responsible for regulating apoptosis, how can this cascade be genetically dissected, and what pharmacological tools are available to modulate p53-dependent apoptosis. While everything may not comfortably fit into our understanding of p53, all of these data will certainly broaden our viewpoint on the complexity and significance of the p53-induced apoptotic pathway. Here, our discussion is primarily focused on the works presented at the 12th International p53 Workshop, except where appropriate background is required.

Six2 is required for suppression of nephrogenesis and progenitor renewal in the developing kidney.

Abstract: During kidney development and in response to inductive signals, the metanephric mesenchyme aggregates, becomes polarized, and generates much of the epithelia of the nephron. As such, the metanephric mesenchyme is a renal progenitor cell population that must be replenished as epithelial derivatives are continuously generated. The molecular mechanisms that maintain the undifferentiated state of the metanephric mesenchymal precursor cells have not yet been identified. In this paper, we report that functional inactivation of the homeobox gene Six2 results in premature and ectopic differentiation of mesenchymal cells into epithelia and depletion of the progenitor cell population within the metanephric mesenchyme. Failure to renew the mesenchymal cells results in severe renal hypoplasia. Gain of Six2 function in cortical metanephric mesenchymal cells was sufficient to prevent their epithelial differentiation in an organ culture assay. We propose that in the developing kidney, Six2 activity is required for maintaining the mesenchymal progenitor population in an undifferentiated state by opposing the inductive signals emanating from the ureteric bud.

H5N1 Outbreaks and Enzootic Influenza

Abstract: Ongoing outbreaks of H5N1 avian influenza in migratory waterfowl, domestic poultry, and humans in Asia during the summer of 2005 present a continuing, protean pandemic threat. We review the zoonotic source of highly pathogenic H5N1 viruses and their genesis from their natural reservoirs. The acquisition of novel traits, including lethality to waterfowl, ferrets, felids, and humans, indicates an expanding host range. The natural selection of nonpathogenic viruses from heterogeneous subpopulations cocirculating in ducks contributes to the spread of H5N1 in Asia. Transmission of highly pathogenic H5N1 from domestic poultry back to migratory waterfowl in western China has increased the geographic spread. The spread of H5N1 and its likely reintroduction to domestic poultry increase the need for good agricultural vaccines. In fact, the root cause of the continuing H5N1 pandemic threat may be the way the pathogenicity of H5N1 viruses is masked by cocirculating influenza viruses or bad agricultural vaccines.

VE-Cadherin-Cre-recombinase transgenic mouse: a tool for lineage analysis and gene deletion in endothelial cells.

Abstract: The ability to target gene deletion to a specific cellular compartment via the Cre/loxP system has been a powerful tool in the analysis of broadly expressed genes. Here, we report the generation of a transgenic mouse line in which expression of Cre-recombinase is under the regulatory control of the VE-Cadherin promoter. Temporal distribution and activity of the enzyme was evaluated with two independent Cre reporter lines. Histological analysis was performed throughout development and in the adult. Recombination of lox P sites with subsequent expression of beta-galactosidase or GFP was detected as early as E7.5 in endothelial cells of the yolk sac. Progressive staining of the embryonic vasculature was noted from E8.5-13.5; however, more contiguous reporter expression was only seen by E14.5 onward in all endothelial compartments including arteries, veins, and capillaries. In addition, we found Cre activity in lymphatic endothelial cells. Unlike other endothelial-specific Cre mice, this model showed expression in the adult quiescent vasculature. Furthermore, the constitutive nature of the VE-Cadherin promoter in the adult can be advantageous for analysis of gene deletion in pathological settings.

Factors influencing agreement between child self-report and parent proxy-reports on the Pediatric Quality of Life Inventory 4.0 (PedsQL) generic core scales.

Abstract: In situations where children are unable or unwilling to respond for themselves, measurement of quality of life (QOL) is often obtained by parent proxy-report. However the relationship between child self and parent proxy-reports has been shown to be poor in some circumstances. Additionally the most appropriate statistical method for comparing ratings between child and parent proxy-reports has not been clearly established. The objectives of this study were to assess the: 1) agreement between child and parent proxy-reports on an established child QOL measure (the PedsQL™) using two different statistical methods; 2) effect of chronological age and domain type on agreement between children's and parents' reports on the PedsQL™; 3) relationship between parents' own well-being and their ratings of their child's QOL. One hundred and forty-nine healthy children (5.5 – 6.5, 6.5 – 7.5, and 7.5 – 8.5 years) completed the PedsQL™. One hundred and three of their parents completed these measures in relation to their child, and a measure of their own QOL (SF-36). Consistency between child and parent proxy-reports on the PedsQL™ was low, with Intra-Class correlation coefficients ranging from 0.02 to 0.23. Correlations were higher for the oldest age group for Total Score and Psychosocial Health domains, and for the Physical Health domain in the youngest age group. Statistically significant median differences were found between child and parent-reports on all subscales of the PedsQL™. The largest median differences were found for the two older age groups. Statistically significant correlations were found between parents' own QOL and their proxy-reports of child QOL across the total sample and within the middle age group. Intra-Class correlation coefficients and median difference testing can provide different information on the relationship between parent proxy-reports and child self-reports. Our findings suggest that differences in the levels of parent-child agreement previously reported may be an artefact of the statistical method used. In addition, levels of agreement can be affected by child age, domains investigated, and parents' own QOL. Further studies are needed to establish the optimal predictors of levels of parent-child agreement.

The neurodegenerative disease protein aprataxin resolves abortive DNA ligation intermediates

Abstract: Ataxia oculomotor apraxia-1 (AOA1) is a neurological disorder caused by mutations in the gene (APTX) encoding aprataxin1, 2. Aprataxin is a member of the histidine triad (HIT) family of nucleotide hydrolases and transferases3, and inactivating mutations are largely confined to this HIT domain. Aprataxin associates with the DNA repair proteins XRCC1 and XRCC4, which are partners of DNA ligase III and ligase IV, respectively4, 5, 6, 7, suggestive of a role in DNA repair. Consistent with this, APTX-defective cell lines are sensitive to agents that cause single-strand breaks and exhibit an increased incidence of induced chromosomal aberrations4, 5, 8. It is not, however, known whether aprataxin has a direct or indirect role in DNA repair, or what the physiological substrate of aprataxin might be. Here we show, using purified aprataxin protein and extracts derived from either APTX-defective chicken DT40 cells or Aptx-/- mouse primary neural cells, that aprataxin resolves abortive DNA ligation intermediates. Specifically, aprataxin catalyses the nucleophilic release of adenylate groups covalently linked to 5'-phosphate termini at single-strand nicks and gaps, resulting in the production of 5'-phosphate termini that can be efficiently rejoined. These data indicate that neurological disorders associated with APTX mutations may be caused by the gradual accumulation of unrepaired DNA strand breaks resulting from abortive DNA ligation events.

Role of abcg2/bcrp in biology and medicine

Abstract: The protein variously named ABCG2/BCRP/MXR/ABCP is a recently described ATP-binding cassette (ABC) transporter originally identified by its ability to confer drug resistance that is independent of Mrp1 (multidrug-resistance protein 1) and Pgp (P-glycoprotein). Unlike Mrp1 and Pgp, ABCG2 is a half-transporter that must homodimerize to acquire transport activity. ABCG2 is found in a variety of stem cells and may protect them from exogenous and endogenous toxins. ABCG2 expression is upregulated under low-oxygen conditions, consistent with its high expression in tissues exposed to low-oxygen environments. ABCG2 interacts with heme and other porphyrins and protects cells and/or tissues from protoporphyrin accumulation under hypoxic conditions. Individuals who carry ABCG2 alleles that have impaired function may be more susceptible to porphyrin-induced toxicity. Abcg2 knock-out models have allowed in vivo studies of Abcg2 function in host and cellular defense. In combination with immunohistochemical analyses, these studies have revealed how ABCG2 influences the absorption, distribution, and excretion of drugs and cytotoxins.