C G Begley

Amgen, Thousand Oaks, California, United States

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Publications (194)1350.21 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Iron maldistribution has been implicated in the etiology of many diseases including the anemia of inflammation (AI), atherosclerosis, diabetes and neurodegenerative disorders. Iron metabolism is controlled by hepcidin, a 25 amino acid peptide. Hepcidin is induced by inflammation and causes iron to be sequestered within cells of the reticuloendothelial system, suppressing erythropoiesis and blunting the activity of erythropoiesis stimulating agents (ESAs). For this reason neutralization of hepcidin has been proposed as a therapeutic treatment for AI. The aim of the current work was to generate fully human anti-hepcidin antibodies as a potential human therapeutic for the treatment of AI and other iron maldistribution disorders. An ELISA was established using these antibodies to identify patients likely to benefit from either ESAs or anti-hepcidin agents. Using human hepcidin knock-in mice, the mechanism-of-action of the antibodies was shown to be due to an increase in available serum iron leading to enhanced red cell hemoglobinization. One of the antibodies, 12B9m was validated in a mouse model of AI and demonstrated to modulate serum iron in cynomolgus monkeys. 12B9m was deemed to be an appropriate candidate for use as a potential therapeutic to treat AI in patients with kidney disease or cancer.
    Blood 08/2013; · 9.78 Impact Factor
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    ABSTRACT: Erythropoiesis-stimulating agents (ESAs) stimulate formation of red blood cells by binding to and activating Epo receptors (EpoR) on erythroid progenitor cells. Beyond successful treatment of anemia, ESAs have been reported to reduce damage following insult to organs, including the kidney, possibly via direct activation of EpoR. However, data on ESA effects outside hematopoietic functions are conflicting. Furthermore, limited use of appropriate EpoR-positive and EpoR-negative controls and lack of specific anti-EpoR antibodies make interpretation of data difficult. Recently positive and negative control cell types were validated and a sensitive and specific anti-EpoR antibody (A82) that detects low levels of EpoR protein was described. A82 was used to measure EpoR protein levels in tissues, human renal cells and human cell lines by western blot analysis. Surface EpoR was examined on renal cells by measuring binding of [125I]-rHuEpo or antibodies. Renal cells and cell lines were treated with rHuEpo to see if phosphorylation of signaling proteins or proliferation/survival could be induced. Small inhibitory RNA (siRNA) were used to determine if EpoR knockdown affected cell viability. Total EpoR protein was low to undetectable in tissues and renal cells with no detectable EpoR on cell surfaces. EpoR knockdown had no effect on viability of renal cell lines. RHuEpo had no detectable effect on intracellular signaling on renal cell lines with no growth-promoting or survival effect on primary human renal cells. These results suggest that functional EpoR protein is absent on renal cells and that non-EpoR mechanisms should be explored to explain non-hematopoietic effects of ESAs.
    Nephrology Dialysis Transplantation 12/2011; 27(7):2733-45. · 3.37 Impact Factor
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    ABSTRACT: Certain oncology trials showed worse clinical outcomes in the erythropoiesis-stimulating agent (ESA) arm. A potential explanation was that ESA-activated erythropoietin (Epo) receptors (EpoRs) promoted tumor cell growth. Although there were supportive data from preclinical studies, those findings often used invalidated reagents and methodologies and were in conflict with other studies. Here, we further investigate the expression and function of EpoR in tumor cell lines. EpoR mRNA levels in 209 human cell lines representing 16 tumor types were low compared with ESA-responsive positive controls. EpoR protein production was evaluated in a subset of 66 cell lines using a novel anti-EpoR antibody. EpoR(+) control cells had an estimated 10 000 to 100 000 EpoR dimers/cell. In contrast, 54 of 61 lines had EpoR protein levels lower than 100 dimers/cell. Cell lines with the highest EpoR protein levels (400-3200 dimers/cell) were studied further, and, although one line, NCI-H661, bound detectable levels of [(125)I]-recombinant human Epo (rHuEpo), none showed evidence of ESA-induced EpoR activation. There was no increased phosphorylation of STAT5, AKT, ERK, or S6RP with rHuEpo. In addition, EpoR knockdown with siRNAs did not affect viability in 2 cell lines previously reported to express functional EpoR (A2780 and SK-OV-3). These results conflict with the hypothesis that EpoR is functionally expressed in tumors.
    Blood 05/2010; 115(21):4254-63. · 9.78 Impact Factor
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    ABSTRACT: Erythropoiesis stimulating agents (ESAs) have been reported to activate erythropoietin receptors (EpoR) on cell types, including endothelial, neuronal, renal tubule, and cardiac cells. ESAs have also been reported to promote angiogenesis. However, those findings are controversial and confounded by methodologic issues. We show that EpoR mRNA was detected in essentially all cell types examined, including primary human endothelial, renal, cardiac, and neuronal cells but 10- to 100-fold lower than Epo-responsive cells using quantitative reverse-transcribed polymerase chain reaction. Total endothelial EpoR protein examined using a new monoclonal antibody was low to undetectable. Surface EpoR on endothelial cells was not detected using [(125)I]-rHuEpo surface-binding studies. There was no evidence of ESA-induced intracellular signaling in endothelial cells. There was a similar lack of EpoR expression and signaling in other cell types examined. Experiments were performed examining ESA function on these cells. An in vivo rat corneal angiogenesis assay demonstrated neo-vessel formation in response to recombinant human vascular endothelial growth factor (rHuVEGF). However, recombinant mouse Epo did not induce vessel formation. Similarly, ESAs did not reproducibly provide cytoprotection to neuronal, renal, or cardiac cells. Taken together, our data challenge the notion of presence or function of EpoR on nonhematopoietic cells, and call into question the preclinical basis for clinical studies exploring direct, "pleiotropic" actions of ESAs.
    Blood 05/2010; 115(21):4264-72. · 9.78 Impact Factor
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    ABSTRACT: Iron maldistribution has been implicated in multiple diseases, including the anemia of inflammation (AI), atherosclerosis, diabetes, and neurodegenerative disorders. Iron metabolism is controlled by hepcidin, a 25-amino acid peptide. Hepcidin is induced by inflammation, causes iron to be sequestered, and thus, potentially contributes to AI. Human hepcidin (hHepc) overexpression in mice caused an iron-deficient phenotype, including stunted growth, hair loss, and iron-deficient erythropoiesis. It also caused resistance to supraphysiologic levels of erythropoiesis-stimulating agent, supporting the hypothesis that hepcidin may influence response to treatment in AI. To explore the role of hepcidin in inflammatory anemia, a mouse AI model was developed with heat-killed Brucella abortus treatment. Suppression of hepcidin mRNA was a successful anemia treatment in this model. High-affinity antibodies specific for hHepc were generated, and hHepc knock-in mice were produced to enable antibody testing. Antibody treatment neutralized hHepc in vitro and in vivo and facilitated anemia treatment in hHepc knock-in mice with AI. These data indicate that antihepcidin antibodies may be an effective treatment for patients with inflammatory anemia. The ability to manipulate iron metabolism in vivo may also allow investigation of the role of iron in a number of other pathologic conditions.
    Blood 04/2010; 115(17):3616-24. · 9.78 Impact Factor
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    ABSTRACT: A recent article by Solar et al. (1) reported that erythropoietin (Epo) inhibits apoptosis induced by photodynamic therapy in ovarian cells. The conclusion was based on tumor immunohistochemistry data generated with anti-EpoR antibodies and in vitro studies with ovarian cell lines, SKOV3 and A2780. As acknowledged by these authors elsewhere (2), the immunohistochemistry data used a preparation of polyclonal anti-EpoR antibodies from Santa Cruz known to be nonspecific and to provide false positive results (2-4). The nonspecificity of the antibodies is further supported by the detection of multiple bands by Western blot and the misidentification of the EpoR protein; EpoR is 59 kDa not 66 kDa (3). The claim that the specificity of the antibodies was confirmed by peptide antigen inhibition is incorrect. That approach does not discriminate between EpoR and cross-reacting non-EpoR proteins with homology to the peptide (3). Furthermore, the use of BAF3 cell lysate as an EpoR-negative control is inappropriate. BAF3 cells are murine whereas the ovarian cells are human. The lack of bands in the BAF3 lane is most likely because, according to the manufacturer, the antibodies were raised against human-specific peptides. SKOV3 cells were reported to have increased resistance to hypericin/photodynamic therapy with suprapharmacologic doses of 150 units/mL of rHuEpo but no effect was observed with 5 or 30 units/mL (also suprapharmacologic doses), questioning the relevance of these findings. Because rHuEpo requires dilution in vehicle containing carrier proteins such as serum or BSA, it is important to have protein carrier controls. A figure in the article shows phosphorylation of Akt after rHuEpo treatment of A2780 cells without this critical control. We have found that rHuEpo does not induce increased phosphorylation of Erk1/2 in A2780 cells but increased phosphorylation of Erk was detected simply as a result of a cold media change (Fig. 1). Finally, the specificity of signaling through EpoR was based on results with the "Jak2" inhibitor AG490. Not only is Jak2 used by over 20 different receptor complexes, so effects observed may be due to other factors in the diluent, AG490 is neither a potent nor a specific Jak2 inhibitor. AG490 has been reported to inhibit EGFR ( approximately 100 times more potent than Jak2), plus HER2, bcr-abl, guanylyl-cyclase C, and Jak3 (5). Taken together, the multiple methodologic problems found in Solar et al. question the significance of the conclusions presented. Figure 1.Top, immunoblotting with antibodies to phosphorylated Erk1/2 and total Erk1/2 proteins on cell lysates after the addition of 1 unit/mL of rHuEpo, for the times shown, to quiescent cells (cultured overnight in 0.1% FBS). Bottom, immunoblotting with antibodies to phosphorylated Erk1/2 and total Erk1/2 proteins on cell lysates from quiescent cells (cultured overnight in 0.1% or 0.5% FBS), which were then subjected to medium change of RPMI + 0.1% FBS (769-P cells), addition of 1% BSA in medium (MCF-7 cells), and addition of fresh cold RPMI + 0.5% FBS medium (A2780 cells).
    Molecular Cancer Therapeutics 04/2010; 9(4):1070-1; author reply 1071. · 5.60 Impact Factor
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    ABSTRACT: Erythropoietin (Epo) binds and activates the Epo receptor (EpoR) on the surface of erythroid progenitor cells resulting in formation of erythrocytes. Recently, EpoR was reported to be expressed on non-erythroid cells suggesting a role for Epo outside of erythropoiesis. However those studies employed antibodies with questionable specificity and the significance of the observations are controversial. In order to accurately determine the expression of EpoR proteins in cells, we have generated a panel of novel anti-human EpoR monoclonal antibodies. One of these antibodies (A82) was particularly sensitive and it detected the EpoR protein on intact cells by flow cytometry and by western blot analysis with cell lysates. Both methods were optimized and using them, EpoR protein was detected by western immunoblotting with lysates from fewer than 200 EpoR positive control cells and the positive signals were proportional to EpoR protein expression level with a minimal signal in EpoR negative cells. The proteins detected by western blot analysis using A82 included full-length EpoR ( approximately 59kDa) as well as smaller EpoR fragments derived from the EPOR gene. These results indicate that A82 can be used to examine low level EpoR expression in cells by western and flow cytometry allowing an improved understanding of EpoR expression and metabolism.
    Journal of immunological methods 11/2009; 352(1-2):126-39. · 2.35 Impact Factor
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    ABSTRACT: The acquired activation of stem cell leukemia (SCL) during T lymphopoiesis is a common event in T-cell acute lymphoblastic leukemia (T-ALL). Here, we generated tamoxifen (TAM)-inducible transgenic mice (lck-ER(T2)-SCL) to study the consequences of acquired SCL activation during T-cell development. Aberrant activation of SCL in thymocytes resulted in the accumulation of immature CD4(+)CD8(+) (double-positive, DP) cells by preventing normal surface expression of the T-cell receptor alphabeta (TCRalphabeta) complex. SCL-induced immature DP cells were further characterized by up-regulated NOTCH1 and generated noncycling polyclonal CD8(+)TCRbeta(low) cells. The prevalence of these cells was SCL dependent because TAM withdrawal resulted in their disappearance. Furthermore, we observed that SCL activation led to a dramatic up-regulation of NOTCH1 target genes (Hes-1, Deltex1, and CD25) in thymocytes. Strikingly, NOTCH1 target gene up-regulation was already observed after short-term SCL induction, implying that enhanced NOTCH signaling is mediated by SCL and is not dependent on secondary genetic events. These data represent the basis for a novel pathway of SCL-induced leukemogenesis and provide a functional link between SCL and NOTCH1 during this process.
    Blood 12/2007; 110(10):3753-62. · 9.78 Impact Factor
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    ABSTRACT: Safety concerns surrounding the use of recombinant human erythropoietin (Epo) to treat anemia in cancer patients were raised after 2 recent clinical studies reported a worse survival outcome in patients who received epoetin alpha or epoetin beta compared with patients who received placebo. Although those findings contrasted with previous clinical studies, which demonstrated no difference in survival for cancer patients who received erythropoiesis-stimulating agents (ESAs), some investigators have suggested a potential role for ESAs in promoting tumor growth through 1) stimulation of Epo receptors (EpoR) expressed in tumors, 2) stimulation and formation of tumor vessels, and/or 3) enhanced tumor oxygenation. The first and second hypotheses appeared to be supported by some EpoR expression and ESA in vitro studies. However, these conclusions have been challenged because of poor specificity of EpoR-detection methodologies, conflicting data from different groups, and the lack of correlation between in vitro data and in vivo findings in animal tumor models. For this report, the authors reviewed the biology of EpoR in erythropoiesis and compared and contrasted the reported findings on the role of ESAs and EpoR in tumors.
    Cancer 09/2007; 110(3):477-88. · 5.20 Impact Factor
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    ABSTRACT: The Cre/LoxP system provides a powerful tool to investigate gene function in vivo. This system requires Cre-recombinase expressing mouse lines that permit control of gene recombination in a tissue-specific and time-dependent manner. To allow spatio-temporal gene deletion in specific central nervous system (CNS) neuronal populations, we generated mice with a tamoxifen-inducible Cre (Cre-ER(T)) transgene under control of the Scl/Tal1 neural promoter/enhancer -0.9E3 (-0.9E3CreER(T) transgenic mice). Using Cre-reporter mice we have shown that tamoxifen-mediated Cre-ER(T) recombination in -0.9E3CreER(T) mice recapitulated the anticipated expression pattern of Scl in the caudal thalamus, midbrain, hindbrain, and spinal cord. Cre-mediated recombination was also effectively induced during embryogenesis and marked the same population of neurons as observed in the adult. Additionally, we identified a tamoxifen-independent constitutively active -0.9E3CreER(T) mouse line that will be useful for gene deletion during early neurogenesis. These -0.9E3CreER(T) mice will provide tools to investigate the role of neuronal genes in the developing and mature CNS. CNS.
    genesis 04/2007; 45(3):145-51. · 2.58 Impact Factor
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    ABSTRACT: Abstract The basic helix-loop-helix (bHLH) transcription factor Scl displays tissue-restricted expression and is critical for the establishment of the haematopoietic system; loss of Scl results in embryonic death due to absolute anaemia. Scl is also expressed in neurons of the mouse diencephalon, mesencephalon and metencephalon; however, its requirement in those sites remains to be determined. Here we report conditional deletion of Scl in neuronal precursor cells using the Cre/LoxP system. Neuronal-Scl deleted mice died prematurely, were growth retarded and exhibited an altered motor phenotype characterized by hyperactivity and circling. Moreover, ablation of Scl in the nervous system affected brain morphology with abnormal neuronal development in brain regions known to express Scl under normal circumstances; there was an almost complete absence of Scl-null neurons in the hindbrain and partial loss of Scl-null neurons in the thalamus and midbrain from early neurogenesis onwards. Our results demonstrate a crucial role for Scl in the development of Scl-expressing neurons, including gamma-aminobutyric acid (GABA)ergic interneurons. Our study represents one of the first demonstrations of functional overlap of a single bHLH protein that regulates neural and haematopoietic cell development. This finding underlines Scl's critical function in cell fate determination of mesodermal as well as neuroectodermal tissues.
    European Journal of Neuroscience 05/2006; 23(7):1677-89. · 3.75 Impact Factor
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    ABSTRACT: Investigators using anti-EpoR antibodies for immunoblotting and immunostaining have reported erythropoietin receptor (EpoR) expression in nonhematopoietic tissues including human tumors. However, these antibodies detected proteins of 66 to 78 kDa, significantly larger than the predicted molecular weight of EpoR (56-57 kDa). We investigated the specificity of these antibodies and showed that they all detected non-EpoR proteins. C-20 detected 3 proteins in tumor cell lines (35, 66, and 100 kDa). Sequences obtained from preparative gels had similarity to the C-20-immunizing peptide. The 66-kDa protein was a heat shock protein (HSP70) to which antibody binding was abrogated in peptide competition experiments. Antibody M-20 readily identified a 59-kDa EpoR protein. However, neither M-20 nor C-20 was suitable for detection of EpoR using immunohistochemical methods. We concluded that these antibodies have limited utility for detecting EpoR. Thus, reports of EpoR expression in tumor cells using these antibodies should be viewed with caution.
    Blood 04/2006; 107(5):1892-5. · 9.78 Impact Factor
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    ABSTRACT: Previous studies have indicated that the stem cell leukemia gene (SCL) is essential for both embryonic and adult erythropoiesis. We have examined erythropoiesis in conditional SCL knockout mice for at least 6 months after loss of SCL function and report that SCL was important but not essential for the generation of mature red blood cells. Although SCL-deleted mice were mildly anemic with increased splenic erythropoiesis, they responded appropriately to endogenous erythropoietin and hemolytic stress, a measure of late erythroid progenitors. However, SCL was more important for the proliferation of early erythroid progenitors because the predominant defects in SCL-deleted erythropoiesis were loss of in vitro growth of the burst-forming erythroid unit and an in vivo growth defect revealed by transplant assays. With respect to erythroid maturation, SCL-deleted proerythroblasts could generate more mature erythroblasts and circulating red blood cells. However, SCL was required for normal expression of TER119, one of the few proposed target genes of SCL. The unexpected finding that SCL-independent erythropoiesis can proceed in the adult suggests that alternate factors can replace the essential functions of SCL and raises the possibility that similar mechanisms also explain the relatively minor defects previously observed in SCL-null hematopoietic stem cells.
    Molecular and Cellular Biology 09/2005; 25(15):6355-62. · 5.37 Impact Factor
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    ABSTRACT: Evidence for the lineage relationship between embryonic and adult hematopoietic stem cells (HSCs) in the mouse is primarily indirect. In order to study this relationship in a direct manner, we expressed the tamoxifen-inducible Cre-ER(T) recombinase under the control of the stem cell leukemia (Scl) stem-cell enhancer in transgenic mice (HSC-SCL-Cre-ER(T)). To determine functionality, HSC-SCL-Cre-ER(T) transgenics were bred with Cre reporter mice. Flow cytometric and transplantation studies revealed tamoxifen-dependent recombination occurring in more than 90% of adult long-term HSCs, whereas the targeted proportion within mature progenitor populations was significantly lower. Moreover, the transgene was able to irreversibly tag embryonic HSCs on days 10 and 11 of gestation. These cells contributed to bone marrow hematopoiesis 5 months later. In order to investigate whether the de novo HSC generation is completed during embryogenesis, HSC-SCL-Cre-ER(T)-marked fetal liver cells were transplanted into adult recipients. Strikingly, the proportion of marked cells within the transplanted and the in vivo-remaining HSC compartment was not different, implying that no further HSC generation occurred during late fetal and neonatal stages of development. These data demonstrate for the first time the direct lineage relationship between midgestation embryonic and adult HSCs in the mouse. Additionally, the HSC-SCL-Cre-ER(T) mice will provide a valuable tool to achieve temporally controlled genetic manipulation of HSCs.
    Blood 05/2005; 105(7):2724-32. · 9.78 Impact Factor
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    ABSTRACT: The unit of erythropoietic activity has long been the standard by which erythropoietic agents are judged, but the development of long-acting agents such as darbepoetin alfa has highlighted the shortcomings of this approach. To this point, we compared the in vivo activity of Epoetin alfa and darbepoetin alfa per microgram of protein core. Using the established mass-to-unit conversion for Epoetin alfa (1 microg congruent with 200 U), we then calculated darbepoetin alfa activity in units. Activity varied with treatment regimen (1 microg darbepoetin alfa congruent with 800 U for 3 times weekly dosing to 8,000 U for a single injection). This analysis reveals the inadequacy of evaluating darbepoetin alfa activity in terms of standard erythropoietic units. We therefore propose that for molecules with heightened biological activity, a more legitimate basis for comparison is the protein mass.
    Acta Haematologica 02/2005; 113(3):163-74. · 0.89 Impact Factor
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    ABSTRACT: Tumor growth is dependent in part on "neoangiogenesis." Functional involvement of bone marrow (BM)-derived cells in this process has been demonstrated. However, it remains controversial as to whether tumor endothelium itself is BM derived. Here we sought to address this issue with an endothelial-specific, inducible transgenic model. We generated Cretransgenic mice (endothelial-SCL-Cre-ER(T)) using the tamoxifen-inducible Cre-ER(T) recombinase driven by the 5' endothelial enhancer of the stem cell leukemia (SCL) locus. These mice were intercrossed with Cre reporter strains in which beta-galactosidase (LacZ) or enhanced yellow fluorescent protein (EYFP) are expressed upon Cre-mediated recombination. After tamoxifen administration, endothelial LacZ staining was observed in embryonic and adult tissues. Cre-mediated recombination was also observed in newly generated tumor endothelium. In adult BM cells we could only detect trace amounts of recombination by flow cytometry. Subsequently, BM from endothelial-SCL-Cre-ER(T);R26R mice was transplanted into irradiated recipients. When tumors were grown in recipient mice, which received tamoxifen, no tumor LacZ staining was detected. However, when tumors were grown in endothelial-SCL-Cre-ER(T);R26R mice 3 weeks after the cessation of tamoxifen treatment, there was widespread endothelial LacZ staining present. Thus, this genetic model strongly suggests that BM cells do not contribute to tumor endothelium and demonstrates the lineage relation between pre-existing endothelium and newly generated tumor endothelial cells.
    Blood 10/2004; 104(6):1769-77. · 9.78 Impact Factor
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    ABSTRACT: The stem cell leukemia (SCL) gene is essential for the development of hematopoietic stem cells in the embryo. Here, we used a conditional gene targeting approach to examine the function of SCL in adult hematopoietic stem cells (HSCs). Flow cytometry of bone marrow from SCL-deleted mice demonstrated a 4-fold increase in number of Lin(neg) c-kit(+) Sca-1(+) cells. Despite this increase in the number of phenotypic HSCs, competitive repopulation assays demonstrated a severe multilineage defect in repopulation capacity by SCL-deleted bone marrow cells. SCL-heterozygous cells also showed a mild repopulation defect, thus suggesting haploinsufficiency of SCL. The transplantation defect of SCL-deleted cells was observed within 4 weeks of transplantation, indicating a defect in a multipotent progenitor or short-term repopulating HSCs. Although the defect persisted in secondary transplants, it remained relatively stable, suggesting that SCL was not required for self-renewal of the HSCs. Generation of SCL-deleted cells within SCL-wild-type mice rescued the early repopulating defect. Together, our results suggest that SCL is required for the normal function of short-term repopulating HSCs.
    Blood 06/2004; 103(9):3342-8. · 9.78 Impact Factor
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    ABSTRACT: Analysis of cis-regulatory elements is central to understanding the genomic program for development. The scl/tal-1 transcription factor is essential for lineage commitment to blood cell formation and previous studies identified an scl enhancer (the +18/19 element) which was sufficient to target the vast majority of hematopoietic stem cells, together with hematopoietic progenitors and endothelium. Moreover, expression of scl under control of the +18/19 enhancer rescued blood progenitor formation in scl(-/-) embryos. However, here we demonstrate by using a knockout approach that, within the endogenous scl locus, the +18/19 enhancer is not necessary for the initiation of scl transcription or for the formation of hematopoietic cells. These results led to the identification of a bifunctional 5' enhancer (-3.8 element), which targets expression to hematopoietic progenitors and endothelium, contains conserved critical Ets sites, and is bound by Ets family transcription factors, including Fli-1 and Elf-1. These data demonstrate that two geographically distinct but functionally related enhancers regulate scl transcription in hematopoietic progenitors and endothelial cells and suggest that enhancers with dual hematopoietic-endothelial activity may represent a general strategy for regulating blood and endothelial development.
    Molecular and Cellular Biology 04/2004; 24(5):1870-83. · 5.37 Impact Factor
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    Rachael L Brake, Paul J Simmons, C Glenn Begley
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    ABSTRACT: Inducible transgenic mouse models that impose a constraint on both temporal and spatial expression of a given transgene are invaluable. These animals facilitate experiments that can address the role of a specific cell or group of cells within an animal or in a particular window of time. A common approach to achieve inducibility involves the site-specific recombinase 'Cre', which is linked to a modified version of one of various steroid hormone-binding domains. Thus, the expression of Cre is regulated such that a functional nuclear transgene product can only be generated with the addition of an exogenous ligand. However, critical requirements of this system are that the nuclear localization of the transgene product be tightly regulated, that the dosage of the inducing agent remains consistent among experimental animals and that the transgene cassette cannot express in the absence of the inducing agent. We used the Cre ER(T2) cassette, which is regulated by the addition of the estrogen antagonist tamoxifen to determine whether cross-contamination of tamoxifen between animals housed together can be a significant source of spurious results. We found that cross-contamination of exogenous tamoxifen does occur. It occurred in all animals tested. We suggest that the mechanism of contamination is through exposure to tamoxifen in the general environment and/or to coprophagous behavior. These results have important implications for the interpretation and design of experiments that use 'inducible' transgenic animals.
    Genetics and molecular research: GMR 02/2004; 3(4):456-62. · 0.99 Impact Factor
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    ABSTRACT: Despite its frequency and impact on clinical outcomes, anaemia in cancer patients remains poorly understood and suboptimally treated. The definition of optimum treatment schedules with erythropoietic agents requires a suitable model of chemotherapy-induced progressive anaemia. This study investigated novel strategies such as once-per-chemotherapy-cycle dosing, synchronization between erythroid supportive care and chemotherapy, and definition of the optimum timing of erythroid support. A murine model of carboplatin chemotherapy/radiotherapy (CRT)-induced anaemia was used, which caused progressive anaemia across multiple cycles. Weekly administration of recombinant human erythropoietin (rHuEPO) was effective, but the longer-acting darbepoetin alpha resulted in superior responses. In all animals, anaemia became progressive and more refractory across cycles because of accumulated bone marrow damage. Exploiting a specific enzyme-linked immunosorbent assay, which could distinguish between darbepoetin alpha and endogenous erythropoietin, the effect of CRT upon the pharmacokinetics of darbepoetin alpha showed that clearance of darbepoetin alpha, and presumably erythropoietin, was at least partially dependent on a chemotherapy-sensitive pathway. Scheduling data suggested that administration of erythropoietic agents prior to chemotherapy was more effective than administration after chemotherapy. There was no evidence that erythropoietic agents exacerbated anaemia, even when administered immediately prior to CRT in an attempt to "prime" erythroid cells for the effects of CRT.
    British Journal of Haematology 09/2003; 122(4):623-36. · 4.94 Impact Factor

Publication Stats

8k Citations
1,350.21 Total Impact Points

Institutions

  • 2006–2010
    • Amgen
      Thousand Oaks, California, United States
  • 2002–2005
    • University of Western Australia
      • Centre for Health Services Research
      Perth, Western Australia, Australia
  • 1985–2004
    • Royal Melbourne Hospital
      Melbourne, Victoria, Australia
  • 2001
    • Melbourne Health
      Melbourne, Victoria, Australia
  • 1987–2000
    • The Walter and Eliza Hall Institute of Medical Research
      • Division of Cancer and Haematology
      Melbourne, Victoria, Australia
  • 1985–2000
    • Walter And Eliza Hall Institute For Medical Research
      Melbourne, Victoria, Australia
  • 1999
    • Ludwig Institute for Cancer Research Australia
      Melbourne, Victoria, Australia
  • 1995–1999
    • University of Cambridge
      • Department of Haematology
      Cambridge, ENG, United Kingdom
  • 1996
    • The Royal Children's Hospital
      Melbourne, Victoria, Australia
  • 1989–1991
    • National Cancer Institute (USA)
      Maryland, United States
  • 1990
    • Duke University
      Durham, North Carolina, United States
    • National Institutes of Health
      • Branch of Metabolism
      Bethesda, MD, United States