Mice lacking p21CIP1/WAF1 undergo normal development, but are defective in G1 checkpoint control

p21CIP1/WAF1 is a CDK inhibitor regulated by the tumor suppressor p53 and is hypothesized to mediate G1 arrest. p53 has been suggested to derive anti-oncogenic properties from this relationship. To test these notions, we created mice lacking p21CIP1/WAF1. They develop normally and (unlike p53-/- mice) have not developed spontaneous malignancies during 7 months of observation. Nonetheless, p21-/- embryonic fibroblasts are significantly deficient in their ability to arrest in G1 in response to DNA damage and nucleotide pool perturbation. p21-/- cells also exhibit a significant growth alteration in vitro, achieving a saturation density as high as that observed in p53-/- cells. In contrast, other aspects of p53 function, such as thymocytic apoptosis and the mitotic spindle checkpoint, appear normal. These results establish the role of p21CIP1/WAF1 in the G1 checkpoint, but suggest that the anti-apoptotic and the anti-oncogenic effects of p53 are more complex.

Clinical characteristics of COVID-19-infected cancer patients: a retrospective case study in three hospitals within Wuhan, China

Background

Cancer patients are regarded as a highly vulnerable group in the current Coronavirus Disease 2019 (COVID-19) pandemic. To date, the clinical characteristics of COVID-19-infected cancer patients remain largely unknown.

Patients and methods

In this retrospective cohort study, we included cancer patients with laboratory-confirmed COVID-19 from three designated hospitals in Wuhan, China. Clinical data were collected from medical records from 13 January 2020 to 26 February 2020. Univariate and multivariate analyses were carried out to assess the risk factors associated with severe events defined as a condition requiring admission to an intensive care unit, the use of mechanical ventilation, or death.

Results

A total of 28 COVID-19-infected cancer patients were included; 17 (60.7%) patients were male. Median (interquartile range) age was 65.0 (56.0–70.0) years. Lung cancer was the most frequent cancer type (n = 7; 25.0%). Eight (28.6%) patients were suspected to have hospital-associated transmission. The following clinical features were shown in our cohort: fever (n = 23, 82.1%), dry cough (n = 22, 81%), and dyspnoea (n = 14, 50.0%), along with lymphopaenia (n = 23, 82.1%), high level of high-sensitivity C-reactive protein (n = 23, 82.1%), anaemia (n = 21, 75.0%), and hypoproteinaemia (n = 25, 89.3%). The common chest computed tomography (CT) findings were ground-glass opacity (n = 21, 75.0%) and patchy consolidation (n = 13, 46.3%). A total of 15 (53.6%) patients had severe events and the mortality rate was 28.6%. If the last antitumour treatment was within 14 days, it significantly increased the risk of developing severe events [hazard ratio (HR) = 4.079, 95% confidence interval (CI) 1.086–15.322, P = 0.037]. Furthermore, patchy consolidation on CT on admission was associated with a higher risk of developing severe events (HR = 5.438, 95% CI 1.498–19.748, P = 0.010).

Conclusions

Cancer patients show deteriorating conditions and poor outcomes from the COVID-19 infection. It is recommended that cancer patients receiving antitumour treatments should have vigorous screening for COVID-19 infection and should avoid treatments causing immunosuppression or have their dosages decreased in case of COVID-19 coinfection.

p53-independent expression of p21Cip1 in muscle and other terminally differentiating cells

Terminal differentiation is coupled to withdrawal from the cell cycle. The cyclin-dependent kinase inhibitor (CKI) p21Cip1 is transcriptionally regulated by p53 and can induce growth arrest. CKIs are therefore potential mediators of developmental control of cell proliferation. The expression pattern of mouse p21 correlated with terminal differentiation of multiple cell lineages including skeletal muscle, cartilage, skin, and nasal epithelium in a p53-independent manner. Although the muscle-specific transcription factor MyoD is sufficient to activate p21 expression in 10T1/2 cells, p21 was expressed in myogenic cells of mice lacking the genes encoding MyoD and myogenin, demonstrating that p21 expression does not require these transcription factors. The p21 protein may function during development as an inducible growth inhibitor that contributes to cell cycle exit and differentiation.

Absence of granulocyte colony-stimulating factor signaling and neutrophil development in CCAAT enhancer binding protein alpha-deficient mice

Transcription factors are master regulatory switches of differentiation, including the development of specific hematopoietic lineages from stem cells. Here we show that mice with targeted disruption of the CCAAT enhancer binding protein alpha gene (C/EBP alpha) demonstrate a selective block in differentiation of neutrophils. Mature neutrophils and eosinophils are not observed in the blood or fetal liver of mutant animals, while other hematopoietic lineages, including monocytes, are not affected. Instead, most of the white cells in the peripheral blood of mutant mice had the appearance of myeloid blasts. We also observed a selective loss of expression of a critical gene target of CCAAT enhancer binding protein alpha, the granulocyte colony-stimulating factor receptor. As a result, multipotential myeloid progenitors from the mutant fetal liver are unable to respond to granulocyte colony-stimulating factor signaling, although they are capable of forming granulocyte-macrophage and macrophage colonies in methylcellulose in response to other growth factors. Finally, we demonstrate that the lack of granulocyte development results from a defect intrinsic to the hematopoietic system; transplanted fetal liver from mutant mice can reconstitute lymphoid but not neutrophilic cells in irradiated recipients. These studies suggest a model by which transcription factors can direct the differentiation of multipotential precursors through activation of expression of a specific growth factor receptor, allowing proliferation and differentiation in response to a specific extracellular signal. In addition, the c/ebp alpha -/- mice may be useful in understanding the mechanisms involved in acute myelogenous leukemia, in which a block in differentiation of myeloid precursors is a key feature of the disease.

Inhibition of cyclin-dependent kinases by p21

p21Cip1 is a cyclin-dependent kinase (Cdk) inhibitor that is transcriptionally activated by p53 in response to DNA damage. We have explored the interaction of p21 with the currently known Cdks. p21 effectively inhibits Cdk2, Cdk3, Cdk4, and Cdk6 kinases (Ki 0.5-15 nM) but is much less effective toward Cdc2/cyclin B (Ki approximately 400 nM) and Cdk5/p35 (Ki > 2 microM), and does not associate with Cdk7/cyclin H. Overexpression of P21 arrests cells in G1. Thus, p21 is not a universal inhibitor of Cdks but displays selectivity for G1/S Cdk/cyclin complexes. Association of p21 with Cdks is greatly enhanced by cyclin binding. This property is shared by the structurally related inhibitor p27, suggesting a common biochemical mechanism for inhibition. With respect to Cdk2 and Cdk4 complexes, p27 shares the inhibitory potency of p21 but has slightly different kinase specificities. In normal diploid fibroblasts, the vast majority of active Cdk2 is associated with p21, but this active kinase can be fully inhibited by addition of exogenous p21. Reconstruction experiments using purified components indicate that multiple molecules of p21 can associate with Cdk/cyclin complexes and inactive complexes contain more than one molecule of p21. Together, these data suggest a model whereby p21 functions as an inhibitory buffer whose levels determine the threshold kinase activity required for cell cycle progression.

p57KIP2, a structurally distinct member of the p21CIP1 Cdk inhibitor family, is a candidate tumor suppressor gene

Cyclin-dependent kinases (Cdks) are positive regulators of cell proliferation, whereas Cdk inhibitors (CKIs) inhibit proliferation. We describe a new CKI, p57KIP2, which is related to p21CIP1 and p27KIP1. p57KIP2 is a potent, tight-binding inhibitor of several G1 cyclin/Cdk complexes, and its binding is cyclin dependent. Unlike CIP1, KIP2 is not regulated by p53. Overexpression of p57KIP2 arrests cells in G1. p57KIP2 proteins have a complex structure. Mouse p57KIP2 consists of four structurally distinct domains: an amino-terminal Cdk inhibitory domain, a proline-rich domain, an acidic-repeat region, and a carboxy-terminal domain conserved with p27KIP1. Human p57KIP2 appears to have conserved the amino- and carboxy-terminal domains but has replaced the internal regions with sequences containing proline-alanine repeats. In situ hybridization during mouse embryogenesis revealed that KIP2 mRNA displays a striking pattern of expression during development, showing high level expression in skeletal muscle, brain, heart, lungs, and eye. Most of the KIP2-expressing cells are terminally differentiated, suggesting that p57KIP2 is involved in decisions to exit the cell cycle during development and differentiation. Human KIP2 is located at 11p15.5, a region implicated in both sporadic cancers and Beckwith-Wiedemann syndrome, a familial cancer syndrome, marking it as a candidate tumor suppressor. The discovery of a new member of the p21CIP1 inhibitor family with novel structural features and expression patterns suggests a complex role for these proteins in cell cycle control and development.

Dominant-negative mutations of CEBPA, encoding CCAAT/enhancer binding protein-alpha (C/EBPalpha), in acute myeloid leukemia

The transcription factor C/EBPalpha (for CCAAT/enhancer binding protein-alpha; encoded by the gene CEBPA) is crucial for the differentiation of granulocytes. Conditional expression of C/EBPalpha triggers neutrophilic differentiation, and no mature granulocytes are observed in Cebpa-mutant mice. Here we identify heterozygous mutations in CEBPA in ten patients with acute myeloid leukemia (AML). We found that five mutations in the amino terminus truncate the full-length protein, but did not affect a 30-kD protein initiated further downstream. The mutant proteins block wild-type C/EBPalpha DNA binding and transactivation of granulocyte target genes in a dominant-negative manner, and fails to induce granulocytic differentiation. Ours is the first report of CEBPA mutations in human neoplasia, and such mutations are likely to induce the differentiation block found in AML.

Abnormal morphogenesis but intact IKK activation in mice lacking the IKKalpha subunit of IkappaB kinase

The oligomeric IkappaB kinase (IKK) is composed of three polypeptides: IKKalpha and IKKbeta, the catalytic subunits, and IKKgamma, a regulatory subunit. IKKalpha and IKKbeta are similar in structure and thought to have similar function-phosphorylation of the IkappaB inhibitors in response to proinflammatory stimuli. Such phosphorylation leads to degradation of IkappaB and activation of nuclear factor kappaB transcription factors. The physiological function of these protein kinases was explored by analysis of IKKalpha-deficient mice. IKKalpha was not required for activation of IKK and degradation of IkappaB by proinflammatory stimuli. Instead, loss of IKKalpha interfered with multiple morphogenetic events, including limb and skeletal patterning and proliferation and differentiation of epidermal keratinocytes.

Conjugation of biomolecules with luminophore-doped silica nanoparticles for photostable biomarkers

A new molecular conjugation method has been developed to label biomolecules with optically stable metalorganic luminophores, such as tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy), which are otherwise not possible for direct linking with the biomolecules. Unique biochemical properties of the biomolecule can, thus, be associated with photostable luminophores. This opens a general way to conjugate desired biomolecules using a sensitive signal transduction method. It also promotes the application of excellent luminescent materials, especially those based on photostable metalorganic luminophores, in biochemical analysis and biomolecular interaction studies. The conjugation method is based on uniform luminophore-doped silica (LDS) nanoparticles (63 +/- 4 nm). These nanoparticles have been prepared using a water-in-oil (W/O) microemulsion method. The controlled hydrolysis of tetraethyl orthosilicate (TEOS) in W/O microemulsion leads to the formation of monodisperse LDS nanoparticles. The luminophores are doped inside the nanoparticles, and the particle's silica surfaces can be used to covalently bind with biomolecules. The luminophores are well-protected from the environmental oxygen when they are doped inside the silica network. As an example, we used an antibody for leukemia cell recognition. The antibody was first immobilized onto the luminophore-doped nanoparticle through silica chemistry and then was used for leukemia cell identification by an optical microscopy imaging technique. The leukemia cells were identified easily, clearly, and with high efficiency using these antibody-coated nanoparticles. The advantages of using small, uniform luminophore-doped nanoparticles are discussed.

Altered cell differentiation and proliferation in mice lacking p57KIP2 indicates a role in Beckwith-Wiedemann syndrome

Mice lacking the imprinted Cdk inhibitor p57(KIP2) have altered cell proliferation and differentiation, leading to abdominal muscle defects; cleft palate; endochondral bone ossification defects with incomplete differentiation of hypertrophic chondrocytes; renal medullary dysplasia; adrenal cortical hyperplasia and cytomegaly; and lens cell hyperproliferation and apoptosis. Many of these phenotypes are also seen in patients with Beckwith-Wiedemann syndrome, a pleiotropic hereditary disorder characterized by overgrowth and predisposition to cancer, suggesting that loss of p57(KIP2) expression may play a role in the condition.

Activation of Arp2/3 complex-mediated actin polymerization by cortactin

Cortactin, a filamentous actin (F-actin)-associated protein and prominent substrate of Src, is implicated in progression of breast tumours through gene amplification at chromosome 11q13. However, the function of cortactin remains obscure. Here we show that cortactin co-localizes with the Arp2/3 complex, a de novo actin nucleator, at dynamic particulate structures enriched with actin filaments. Cortactin binds directly to the Arp2/3 complex and activates it to promote nucleation of actin filaments. The interaction of cortactin with the Arp2/3 complex occurs at an amino-terminal domain that is rich in acidic amino acids. Mutations in a conserved amino-acid sequence of DDW abolish both the interaction with the Arp2/3 complex and complex activation. The N-terminal domain is not only essential but also sufficient to target cortactin to actin-enriched patches within cells. Interestingly, the ability of cortactin to activate the Arp2/3 complex depends on an activity for F-actin binding, which is almost 20-fold higher than that of the Arp2/3 complex. Our data indicate a new mechanism for activation of actin polymerization involving an enhanced interaction between the Arp2/3 complex and actin filaments.

CCAAT/enhancer binding protein alpha is a regulatory switch sufficient for induction of granulocytic development from bipotential myeloid progenitors

The transcription factor CCAAT/enhancer binding protein alpha (C/EBPalpha) regulates a number of myeloid cell-specific genes. To delineate the role of C/EBPalpha in human granulopoiesis, we studied its expression and function in human primary cells and bipotential (granulocytic/monocytic) myeloid cell lines. We show that the expression of C/EBPalpha initiates with the commitment of multipotential precursors to the myeloid lineage, is specifically upregulated during granulocytic differentiation, and is rapidly downregulated during the alternative monocytic pathway. Conditional expression of C/EBPalpha alone in stably transfected bipotential cells triggers neutrophilic differentiation, concomitant with upregulation of the granulocyte-specific granulocyte colony-stimulating factor receptor and secondary granule protein genes. Moreover, induced expression of C/EBPalpha in bipotential precursors blocks their monocytic differentiation program. These results indicate that C/EBPalpha serves as a myeloid differentiation switch acting on bipotential precursors and directing them to mature to granulocytes.

Biochemically functionalized silica nanoparticles

In this report, we demonstrate the biochemical modification of silica based nanoparticles. Both pure and dye-doped silica nanoparticles were prepared, and their surfaces were modified with enzymes and biocompatible chemical reagents that allow them to function as biosensors and biomarkers. The nanoparticles produced in this work are uniform in size with a 1.6% relative standard deviation. They have a pure silica surface and can thus be modified easily with many biomolecules for added biochemical functionality. Specifically, we have modified the nanoparticle surfaces with enzyme molecules (glutamate dehydrogenase (GDH) and lactate dehydrogenase (LDH)) and a biocompatible reagent for cell membrane staining. Experimental results show that the silica nanoparticles are a good biocompatible solid support for enzyme immobilization. The immobilized enzyme molecules on the nanoparticle surface have shown excellent enzymatic activity in their respective enzymatic reactions. The nanoparticle surface biochemical functionalization demonstrates the feasibility of using nanoparticles for biosensing and biomarking applications.

Interleukin-17 and lung host defense against Klebsiella pneumoniae infection

Bacterial pneumonia remains an important cause of morbidity and mortality worldwide, especially in immune-compromised patients. Cytokines and chemokines are critical molecules expressed in response to invading pathogens and are necessary for normal lung bacterial host defenses. Here we show that interleukin (IL)-17, a novel cytokine produced largely by CD4+ T cells, is produced in a compartmentalized fashion in the lung after challenge with Klebsiella pneumoniae. Moreover, overexpression of IL-17 in the pulmonary compartment using a recombinant adenovirus encoding murine IL-17 (AdIL-17) resulted in the local induction of tumor necrosis factor-alpha, IL-1beta, macrophage inflammatory protein-2, and granulocyte colony-stimulating factor (G-CSF); augmented polymorphonuclear leukocyte recruitment; and enhanced bacterial clearance and survival after challenge with K. pneumoniae. However, simultaneous treatment with AdIL-17 provided no survival benefit after intranasal K. pneumoniae challenge. These data show that IL-17 may have a role in priming for enhanced chemokine and G-CSF production in the context of lung infection and that optimally timed gene therapy with IL-17 may augment host defense against bacterial pneumonia.

Negative cross-talk between hematopoietic regulators: GATA proteins repress PU.1

The process through which multipotential hematopoietic cells commit to distinct lineages involves the induction of specific transcription factors. PU.1 (also known as Spi-1) and GATA-1 are transcription factors essential for the development of myeloid and erythroid lineages, respectively. Overexpression of PU.1 and GATA-1 can block differentiation in lineages in which they normally are down-regulated, indicating that not only positive but negative regulation of these factors plays a role in normal hematopoietic lineage development. Here we demonstrate that a region of the PU.1 Ets domain (the winged helix-turn-helix wing) interacts with the conserved carboxyl-terminal zinc finger of GATA-1 and GATA-2 and that GATA proteins inhibit PU.1 transactivation of critical myeloid target genes. We demonstrate further that GATA inhibits binding of PU.1 to c-Jun, a critical coactivator of PU.1 transactivation of myeloid promoters. Finally, PU.1 protein can inhibit both GATA-1 and GATA-2 transactivation function. Our results suggest that interactions between PU.1 and GATA proteins play a critical role in the decision of stem cells to commit to erythroid vs. myeloid lineages.

Glutathione peroxidase, glial cells and Parkinson's disease

Hyperoxidation phenomena are suspected to be involved in dopaminergic cell death in Parkinson's disease, which affects preferentially the neuromelanin-containing dopaminergic neurons of the substantia nigra. Glutathione peroxidase is the major protective enzyme against hydrogen peroxide toxicity. The distribution of glutathione peroxidase-containing cells was investigated by immunohistochemistry in the midbrain of four control subjects and four patients with Parkinson's disease. (1) Glutathione peroxidase-like immunoreactivity was detected exclusively in glial cells. (2) In control brains, the density of glutathione peroxidase-positive cells was higher in the vicinity of the dopaminergic cell groups known to be resistant to the pathological process of Parkinson's disease. (3) In Parkinson's disease, an increased density of glutathione peroxidase-immunostained cells was observed, surrounding the surviving dopaminergic neurons. The increase in glutathione peroxidase-containing cells was correlated with the severity in dopaminergic cell loss in the respective cell groups. The data suggest that in control brains, a low density of glutathione peroxidase-positive cells surround the dopaminergic neurons the most vulnerable to Parkinson's disease, and that in parkinsonian brains, the increased number of glutathione peroxidase-positive cells may contribute to protect neurons against pathological death. Thus, the amount of glutathione peroxidase protein-containing cells may be critical for a protective effect against oxidative stress, although it cannot be excluded that the level of the enzyme activity remains the crucial factor.

p21(CIP1) and p57(KIP2) control muscle differentiation at the myogenin step

Cell-cycle arrest is thought to be required for differentiation of muscle cells. However, the molecules controlling cell-cycle exit and the differentiation step(s) dependent on cell-cycle arrest are poorly understood. Here we show that two Cdk inhibitors, p21(CIP1) and p57(KIP2), redundantly control differentiation of skeletal muscle and alveoli in the lungs. Mice lacking both p21 and p57 fail to form myotubes, display increased proliferation and apoptotic rates of myoblasts, and display endoreplication in residual myotubes. This point of arrest during muscle development is identical to that of mice lacking the myogenic transcription factor myogenin, indicating a role for cell-cycle exit in myogenin function. Expression of myogenin, p21, and p57 is parallel but independent, and in response to differentiation signals, these proteins are coordinately regulated to trigger both cell-cycle exit and a dependent muscle-specific program of gene expression to initiate myoblast terminal differentiation and muscle formation.

The effect of lifestyle intervention and metformin on preventing or delaying diabetes among women with and without gestational diabetes: the Diabetes Prevention Program outcomes study 10-year follow-up

CONTEXT

Gestational diabetes (GDM) confers a high risk of type 2 diabetes. In the Diabetes Prevention Program (DPP), intensive lifestyle (ILS) and metformin prevented or delayed diabetes in women with a history of GDM.

OBJECTIVE

The objective of the study was to evaluate the impact of ILS and metformin intervention over 10 years in women with and without a history of GDM in the DPP/Diabetes Prevention Program Outcomes Study.

DESIGN

This was a randomized controlled clinical trial with an observational follow-up.

SETTING

The study was conducted at 27 clinical centers.

PARTICIPANTS

Three hundred fifty women with a history of GDM and 1416 women with previous live births but no history of GDM participated in the study. The participants had an elevated body mass index and fasting glucose and impaired glucose tolerance at study entry.

INTERVENTIONS

Interventions included placebo, ILS, or metformin.

OUTCOMES MEASURE

Outcomes measure was diabetes mellitus.

RESULTS

Over 10 years, women with a history of GDM assigned to placebo had a 48% higher risk of developing diabetes compared with women without a history of GDM. In women with a history of GDM, ILS and metformin reduced progression to diabetes compared with placebo by 35% and 40%, respectively. Among women without a history of GDM, ILS reduced the progression to diabetes by 30%, and metformin did not reduce the progression to diabetes.

CONCLUSIONS

Women with a history of GDM are at an increased risk of developing diabetes. In women with a history of GDM in the DPP/Diabetes Prevention Program Outcomes Study, both lifestyle and metformin were highly effective in reducing progression to diabetes during a 10-year follow-up period. Among women without a history of GDM, lifestyle but not metformin reduced progression to diabetes.

Embryonic lethality and impairment of haematopoiesis in mice heterozygous for an AML1-ETO fusion gene

Acute myeloid leukaemia (AML) is a major haematopoietic malignancy characterized by the proliferation of a malignant clone of myeloid progenitor cells. A reciprocal translocation, t(8;21)(q22;q22), observed in the leukaemic cells of approximately 40% of patients with the M2 subtype of AML disrupts both the AML1 (CBFA2) gene on chromosome 21 and the ETO (MTG8) gene on chromosome 8 (refs 3-5). A chimaeric protein is synthesized from one of the derivative chromosomes that contains the N terminus of the AML1 transcription factor, including its DNA-binding domain, fused to most of ETO, a protein of unknown function. We generated mice that mimic human t(8;21) with a "knock-in' strategy. Mice heterozygous for an AML1-ETO allele (AML1-ETO/+) die in midgestation from haemorrhaging in the central nervous system and exhibit a severe block in fetal liver haematopoiesis. This phenotype is very similar to that resulting from homozygous disruption of the AML1 (Cbfa2) or Cbfb genes, indicating that AML1-ETO blocks normal AML1 function. However, yolk sac cells from AML1-ETO/+ mice differentiated into macrophages in haematopoietic colony forming unit (CFU) assays, unlike Cbfa2-/- or Cbfb-/-cells, which form no colonies in vitro. This indicates that AML1-ETO may have other functions besides blocking wild-type AML1, a property that may be important in leukaemogenesis.

The three-dimensional structure of a glutathione S-transferase from the mu gene class. Structural analysis of the binary complex of isoenzyme 3-3 and glutathione at 2.2-A resolution

The crystal structure of a mu class glutathione S-transferase (EC 2.5.1.18) from rat liver (isoenzyme 3-3) in complex with the physiological substrate glutathione (GSH) has been solved at 2.2-A resolution by multiple isomorphous replacement methods. The enzyme crystallized in the monoclinic space group C2 with unit cell dimensions of a = 87.98 A, b = 69.41 A, c = 81.34 A, and beta = 106.07 degrees. Oligonucleotide-directed site-specific mutagenesis played an important role in the solution of the structure in that the cysteine mutants C86S, C114S, and C173S were used to help locate the positions of mercuric ion sites in nonisomorphous derivatives with ethylmercuric phosphate and to align the sequence with the model derived from MIR phases. A complete model for the protein was not obtained until part of the solvent structure was interpreted. The dimer in the asymmetric unit refined to a crystallographic R = 0.171 for 19,298 data and I > or = 1.5 sigma (I). The final model consists of 4150 atoms, including all non-hydrogen atoms of 434 amino acid residues, two GSH molecules, and oxygen atoms of 474 water molecules. The dimeric enzyme is globular in shape with dimensions of 53 x 62 x 56 A. Crystal contacts are primarily responsible for conformational differences between the two subunits which are related by a noncrystallographic 2-fold axis. The structure of the type 3 subunit can be divided into two domains separated by a short linker, a smaller alpha/beta domain (domain I, residues 1-82), and a larger alpha domain (domain II, residues 90-217). Domain I contains four beta-strands which form a central mixed beta-sheet and three alpha-helices which are arranged in a beta alpha beta alpha beta beta alpha motif. Domain II is composed of five alpha-helices. Domain I can be considered the glutathione binding domain, while domain II seems to be primarily responsible for xenobiotic substrate binding. The active site is located in a deep (19-A) cavity which is composed of three relatively mobile structural elements: the long loop (residues 33-42) of domain I, the alpha 4/alpha 5 helix-turn-helix segment, and the C-terminal tail. GSH is bound at the active site in an extended conformation at one end of the beta-sheet of domain I with its backbone facing the cavity and the sulfur pointing toward the subunit to which it is bound.(ABSTRACT TRUNCATED AT 400 WORDS)

Reversibility of acute B-cell leukaemia induced by BCR-ABL1

Cancer is thought to arise from multiple genetic events that establish irreversible malignancy. A different mechanism might be present in certain leukaemias initiated by a chromosomal translocation. We have taken a new approach to determine if ablation of the genetic abnormality is sufficient for reversion by generating a conditional transgenic model of BCR-ABL1 (also known as BCR-ABL)-induced leukaemia. This oncogene is the result of a reciprocal translocation and is associated with different forms of leukaemia. The most common form, p210 BCR-ABL1, is found in more than 90% of patients with chronic myelogenous leukaemia (CML) and in up to 15% of adult patients with de novoacute lymphoblastic leukaemia (ALL). Efforts to establish a useful transgenic model have been hampered by embryonic lethality when the oncogene is expressed during embryogenesis, by reduced penetrance or by extremely long latency periods. One model uses the 'knock-in' approach to induce leukaemia by p190 BCR-ABL1(ref. 10). Given the limitations of models with p210, we used a different experimental approach. Lethal leukaemia developed within an acceptable time frame in all animals, and complete remission was achieved by suppression of BCR-ABL1expression, even after multiple rounds of induction and reversion. Our results demonstrate that BCR-ABL1is required for both induction and maintenance of leukaemia.