The Metabolic Enzyme Hexokinase 2 Localizes to the Nucleus in AML and Normal Hematopoietic Stem/Progenitor Cells to Maintain Stemness
Notice bibliographique
Résumé
Abstract Hematopoietic cells are arranged in a hierarchy where stem and progenitor cells differentiate into mature blood cells. Likewise, AML (Acute Myeloid Leukemia) is also hierarchical with leukemic stem and progenitor cells giving rise to more mature and differentiated blasts. Recent studies have shown that mitochondrial enzymes such as IDH2 can regulate AML stemness by altering metabolites that affect epigenetic marks. However, it is unknown whether mitochondrial metabolic enzymes can directly localize to the nucleus to regulate stemness in AML and normal hematopoietic cells. Here, we show that the mitochondrial enzyme, Hexokinase 2, localizes to the nucleus in AML and normal hematopoietic stem cells to maintain stemness. We sought to identify mitochondrial metabolic enzymes that localize to the nucleus of stem cells, by evaluating the stem and bulk fractions from 8227 leukemia cells. 8227 leukemia cells are arranged in a hierarchy with functionally defined stem cells present in the CD34+CD38- fraction. We separated 8227 cells into CD34+CD38- and CD34-CD38+ populations by FACS sorting and prepared lysates of the nuclear and cytoplasmic fractions from each population. Using immunoblotting, we measured levels of mitochondrial enzymes in the subcellular fractions of each population. We discovered that the metabolic enzyme Hexokinase 2 (HK2) was increased in the nuclear fraction of 8227 stem cells compared to bulk cells. In contrast, other mitochondrial enzymes such as Aconitase 2 and Succinate Dehydrogenase B were not detected in the nuclear fractions. HK2 is an outer mitochondrial membrane protein that phosphorylates glucose to glucose-6-phosphate, thereby initiating glycolysis and the entry of glucose metabolites into the TCA cycle in the mitochondria. The nuclear localization of HK2 in mammalian cells has not been previous reported. We confirmed that 8227 cells have nuclear HK2 by confocal fluorescent microscopy and also demonstrated nuclear HK2 in AML cell lines (OCI-AML2, NB4, K562, and MV411) and primary AML samples. We also FACS sorted normal cord blood into populations of stem/progenitor (HSC, MPP, MLP, CMP, GMP and MEP) and differentiated (B cells, T cells, NK cells, Monocytes and Granulocytes) cells. The localization of HK2 in these cell fractions was measured by immunofluorescence and quantified by Metamorph and Imaris. Nuclear HK2 was detected in the stem/progenitor cells and progressively declined to minimal levels as the cells matured (Fig 1A). The mitochondrial localization of HK2 is dependent on AKT-mediated phosphorylation of Thr-473 and inhibited by dephosphorylation by the phosphatase PHLPP1. We asked whether phosphorylation of HK2 regulates the nuclear abundance of HK2. Using AML2 cells, we showed that knockdown of PHLPP1 decreased the abundance of nuclear HK2, while inhibition of AKT increased HK2 in the nucleus. Finally, we tested whether the nuclear localization of HK2 was functionally important to maintain stemness. We over-expressed HK2 tagged with nuclear localizing signals (PKKKRKV and PAAKRVKLD) in 8227 and NB4 leukemia cells. We confirmed the selective over-expression of HK2 in the nucleus of these cells by immunoblotting and immunofluorescence. Increasing nuclear HK2 did not alter the proliferation of the cells under basal conditions. However, increasing nuclear HK2 enhanced clonogenic growth and blocked retinoic acid-mediated cell differentiation. In summary, we discovered that the unphosphorylated form of the metabolic enzyme HK2 localizes to the nucleus in malignant and normal hematopoietic stem cells and is functionally important to maintain stem/progenitor state. Thus, we define a new role for mitochondrial enzymes in the regulation of stemness and differentiation. Disclosures Schimmer: Medivir AB: Research Funding; Jazz Pharmaceuticals: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Otsuka Pharmaceuticals: Consultancy.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».