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- Morcos, M. N. F., et al.
(författare)
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Continuous mitotic activity of primitive hematopoietic stem cells in adult mice
- 2020
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Ingår i: Journal of Experimental Medicine. - : Rockefeller University Press. - 0022-1007 .- 1540-9538. ; 217:6
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Tidskriftsartikel (refereegranskat)abstract
- The proliferative activity of aging hematopoietic stem cells (HSCs) is controversially discussed. Inducible fluorescent histone 2B fusion protein (H2B-FP) transgenic mice are important tools for tracking the mitotic history of murine HSCs in label dilution experiments. A recent study proposed that primitive HSCs symmetrically divide only four times to then enter permanent quiescence. We observed that background fluorescence due to leaky H2B-FP expression, occurring in all H2B-FP transgenes independent of label induction, accumulated with age in HSCs with high repopulation potential. We argue that this background had been misinterpreted as stable retention of induced label. We found cell division-independent half-lives of H2B-FPs to be short, which had led to overestimation of HSC divisional activity. Our data do not support abrupt entry of HSCs into permanent quiescence or sudden loss of regeneration potential after four divisions, but show that primitive HSCs of adult mice continue to cycle rarely.
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| 3. |
- Nilsen-Moe, Astrid, et al.
(författare)
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Proton-Coupled Electron Transfer from Tyrosine in the Interior of a de novo Protein : Mechanisms and Primary Proton Acceptor
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 142:26, s. 11550-11559
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Tidskriftsartikel (refereegranskat)abstract
- Proton-coupled electron transfer (PCET) from tyrosine produces a neutral tyrosyl radical (Y-center dot) that is vital to many catalytic redox reactions. To better understand how the protein environment influences the PCET properties of tyrosine, we have studied the radical formation behavior of Y-32 in the alpha Y-3 model protein. The previously solved alpha Y-3 solution NMR structure shows that Y-32 is sequestered similar to 7.7 +/- 0.3 angstrom below the protein surface without any primary proton acceptors nearby. Here we present transient absorption kinetic data and molecular dynamics (MD) simulations to resolve the PCET mechanism associated with Y-32 oxidation. Y-32(center dot). was generated in a bimolecular reaction with [Ru(bpy)(3)](3+) formed by flash photolysis. At pH > 8, the rate constant of Y-32(center dot). formation (k(P)(CET)) increases by one order of magnitude per pH unit, corresponding to a proton-first mechanism via tyrosinate (PTET). At lower pH < 7.5, the pH dependence is weak and shows a previously measured KIE approximate to 2.5, which best fits a concerted mechanism. k(PC)(ET) is independent of phosphate buffer concentration at pH 6.5. This provides clear evidence that phosphate buffer is not the primary proton acceptor. MD simulations show that one to two water molecules can enter the hydrophobic cavity of alpha Y-3 and hydrogen bond to Y-32, as well as the possibility of hydrogen-bonding interactions between Y-32 and E-13, through structural fluctuations that reorient surrounding side chains. Our results illustrate how protein conformational motions can influence the redox reactivity of a tyrosine residue and how PCET mechanisms can be tuned by changing the pH even when the PCET occurs within the interior of a protein.
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- Pearson, A. D. J., et al.
(författare)
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Paediatric Strategy Forum for medicinal product development for acute myeloid leukaemia in children and adolescents ACCELERATE in collaboration with the European Medicines Agency with participation of the Food and Drug Administration
- 2020
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Ingår i: European Journal of Cancer. - : Elsevier BV. - 0959-8049. ; 136, s. 116-129
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The current standard-of-care for front-line therapy for acute myeloid leukaemia (AML) results in short-term and long-term toxicity, but still approximately 40% of children relapse. Therefore, there is a major need to accelerate the evaluation of innovative medicines, yet drug development continues to be adult-focused. Furthermore, the large number of competing agents in rare patient populations requires coordinated prioritisation, within the global regulatory framework and cooperative group initiatives. Methods: The fourth multi-stakeholder Paediatric Strategy Forum focused on AML in children and adolescents. Results: CD123 is a high priority target and the paediatric development should be accelerated as a proof-of-concept. Efforts must be coordinated, however, as there are a limited number of studies that can be delivered. Studies of FLT3 inhibitors in agreed paediatric investigation plans present challenges to be completed because they require enrolment of a larger number of patients than actually exist. A consensus was developed by industry and academia of optimised clinical trials. For AML with rare mutations that are more frequent in adolescents than in children, adult trials should enrol adolescents and when scientifically justified, efficacy data could be extrapolated. Methodologies and definitions of minimal residual disease need to be standardised internationally and validated as a new response criterion. Industry supported, academic sponsored platform trials could identify products to be further developed. The Leukaemia and Lymphoma Society PedAL/EUpAL initiative has the potential to be a major advance in the field. Conclusion: These initiatives continue to accelerate drug development for children with AML and ultimately improve clinical outcomes. (C) 2020 Elsevier Ltd. All rights reserved.
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