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Kfoury, Youmna

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Kfoury

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Youmna

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Kfoury, Youmna

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2014 - 20173

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Author's Publications: search.filters.isAuthorOfPublication.73be44ff-edd3-46ce-897f-39647658b65a

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    Transmembrane Inhibitor of RICTOR/mTORC2 in Hematopoietic Progenitors
    (Elsevier, 2014) Lee, Dongjun; Sykes, Stephen M.; Kalaitzidis, Demetrios; Lane, Andrew A.; Kfoury, Youmna; Raaijmakers, Marc H.G.P.; Wang, Ying-Hua; Armstrong, Scott A.; Scadden, David T.
    Summary Central to cellular proliferative, survival, and metabolic responses is the serine/threonine kinase mTOR, which is activated in many human cancers. mTOR is present in distinct complexes that are either modulated by AKT (mTORC1) or are upstream and regulatory of it (mTORC2). Governance of mTORC2 activity is poorly understood. Here, we report a transmembrane molecule in hematopoietic progenitor cells that physically interacts with and inhibits RICTOR, an essential component of mTORC2. Upstream of mTORC2 (UT2) negatively regulates mTORC2 enzymatic activity, reducing AKTS473, PKCα, and NDRG1 phosphorylation and increasing FOXO transcriptional activity in an mTORC2-dependent manner. Modulating UT2 levels altered animal survival in a T cell acute lymphoid leukemia (T-ALL) model that is known to be mTORC2 sensitive. These studies identify an inhibitory component upstream of mTORC2 in hematopoietic cells that can reduce mortality from NOTCH-induced T-ALL. A transmembrane inhibitor of mTORC2 may provide an attractive target to affect this critical cell regulatory pathway.
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    Amino acid–insensitive mTORC1 regulation enables nutritional stress resilience in hematopoietic stem cells
    (American Society for Clinical Investigation, 2017) Kalaitzidis, Demetrios; Lee, Dongjun; Efeyan, Alejo; Kfoury, Youmna; Nayyar, Naema; Sykes, David; Mercier, Francois; Papazian, Ani; Baryawno, Ninib; Victora, Gabriel D.; Neuberg, Donna; Sabatini, David; Scadden, David
    The mTOR pathway is a critical determinant of cell persistence and growth wherein mTOR complex 1 (mTORC1) mediates a balance between growth factor stimuli and nutrient availability. Amino acids or glucose facilitates mTORC1 activation by inducing RagA GTPase recruitment of mTORC1 to the lysosomal outer surface, enabling activation of mTOR by the Ras homolog Rheb. Thereby, RagA alters mTORC1-driven growth in times of nutrient abundance or scarcity. Here, we have evaluated differential nutrient-sensing dependence through RagA and mTORC1 in hematopoietic progenitors, which dynamically drive mature cell production, and hematopoietic stem cells (HSC), which provide a quiescent cellular reserve.In nutrient-abundant conditions, RagA-deficient HSC were functionally unimpaired and upregulated mTORC1 via nutrientinsensitive mechanisms. RagA was also dispensable for HSC function under nutritional stress conditions. Similarly, hyperactivation of RagA did not affect HSC function. In contrast, RagA deficiency markedly altered progenitor population function and mature cell output. Therefore, RagA is a molecular mechanism that distinguishes the functional attributes of reactive progenitors from a reserve stem cell pool. The indifference of HSC to nutrient sensing through RagA contributes to their molecular resilience to nutritional stress, a characteristic that is relevant to organismal viability in evolution and in modern HSC transplantation approaches.
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    Non-genotoxic conditioning for hematopoietic stem cell transplantation using a hematopoietic-cell-specific internalizing immunotoxin
    (Springer Nature, 2016) Palchaudhuri, Rahul; Saez, Borja; Hoggatt, Jonathan; Schajnovitz, Amir; Sykes, David; Tate, Tiffany A; Czechowicz, Agnieszka; Kfoury, Youmna; Ruchika, FNU; Rossi, Derrick; Verdine, Gregory; Mansour, Michael; Scadden, David
    Hematopoietic stem cell transplantation (HSCT) offers curative therapy for patients with hemoglobinopathies, congenital immunodeficiencies, and other conditions, possibly including AIDS. Autologous HSCT using genetically corrected cells would avoid the risk of graft-versus-host disease (GVHD), but the genotoxicity of conditioning remains a substantial barrier to the development of this approach. Here we report an internalizing immunotoxin targeting the hematopoietic-cell-restricted CD45 receptor that effectively conditions immunocompetent mice. A single dose of the immunotoxin, CD45–saporin (SAP), enabled efficient (>90%) engraftment of donor cells and full correction of a sickle-cell anemia model. In contrast to irradiation, CD45–SAP completely avoided neutropenia and anemia, spared bone marrow and thymic niches, enabling rapid recovery of T and B cells, preserved anti-fungal immunity, and had minimal overall toxicity. This non-genotoxic conditioning method may provide an attractive alternative to current conditioning regimens for HSCT in the treatment of non-malignant blood diseases.