title: Mitochondrial Dysfunction in Human Leukemic Stem/Progenitor Cells upon Loss of RAC2.
abstract: Leukemic stem cells (LSCs) reside within bone marrow niches that maintain their relatively quiescent state and convey resistance to conventional treatment. Many of the microenvironmental signals converge on RAC GTPases. Although it has become clear that RAC proteins fulfill important roles in the hematopoietic compartment, little has been revealed about the downstream effectors and molecular mechanisms. We observed that in BCR-ABL-transduced human hematopoietic stem/progenitor cells (HSPCs) depletion of RAC2 but not RAC1 induced a marked and immediate decrease in proliferation, progenitor frequency, cobblestone formation and replating capacity, indicative for reduced self-renewal. Cell cycle analyses showed reduced cell cycle activity in RAC2-depleted BCR-ABL leukemic cobblestones coinciding with an increased apoptosis. Moreover, a decrease in mitochondrial membrane potential was observed upon RAC2 downregulation, paralleled by severe mitochondrial ultrastructural malformations as determined by automated electron microscopy. Proteome analysis revealed that RAC2 specifically interacted with a set of mitochondrial proteins including mitochondrial transport proteins SAM50 and Metaxin 1, and interactions were confirmed in independent co-immunoprecipitation studies. Downregulation of SAM50 also impaired the proliferation and replating capacity of BCR-ABL-expressing cells, again associated with a decreased mitochondrial membrane potential. Taken together, these data suggest an important role for RAC2 in maintaining mitochondrial integrity.
authors.affiliation: Department of Experimental Hematology, Cancer Research Center Groningen, Groningen, the Netherlands.
authors.forename: Marta E
authors.initials: ME
authors.lastname: Capala
authors.affiliation: Department of Experimental Hematology, Cancer Research Center Groningen, Groningen, the Netherlands.
authors.forename: Henny
authors.initials: H
authors.lastname: Maat
authors.affiliation: Department of Experimental Hematology, Cancer Research Center Groningen, Groningen, the Netherlands.
authors.forename: Francesco
authors.initials: F
authors.lastname: Bonardi
authors.affiliation: Department of Experimental Hematology, Cancer Research Center Groningen, Groningen, the Netherlands.
authors.forename: Vincent
authors.initials: V
authors.lastname: van den Boom
authors.affiliation: Department of Cell Biology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Kuipers
authors.affiliation: Department of Experimental Hematology, Cancer Research Center Groningen, Groningen, the Netherlands.
authors.forename: Edo
authors.initials: E
authors.lastname: Vellenga
authors.affiliation: Department of Experimental Hematology, Cancer Research Center Groningen, Groningen, the Netherlands.
authors.forename: Ben N G
authors.initials: BN
authors.lastname: Giepmans
authors.affiliation: Department of Experimental Hematology, Cancer Research Center Groningen, Groningen, the Netherlands.
authors.forename: Jan Jacob
authors.initials: JJ
authors.lastname: Schuringa
mesh_terms: D017209:Apoptosis / Q000235:genetics; D001854:Bone Marrow Cells / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle / Q000235:genetics; D002460:Cell Line; D049109:Cell Proliferation / Q000235:genetics; D015536:Down-Regulation / Q000235:genetics; D016044:Fusion Proteins, bcr-abl / Q000235:genetics; D057809:HEK293 Cells; D006412:Hematopoietic Stem Cells / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics / Q000473:pathology; D053078:Membrane Potential, Mitochondrial / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics; D008928:Mitochondria / Q000235:genetics* / Q000473:pathology; D028361:Mitochondrial Diseases / Q000235:genetics* / Q000473:pathology; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000235:genetics; D011506:Proteins / Q000235:genetics; D013234:Stem Cells / Q000378:metabolism* / Q000473:pathology; D020744:rac GTP-Binding Proteins / Q000235:genetics*; D000097766:RAC2 GTP-Binding Protein
chemical_list: D016044:Fusion Proteins, bcr-abl; D008565:Membrane Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D020744:rac GTP-Binding Proteins; D000097766:RAC2 GTP-Binding Protein; C093550:MTX1 protein, human; C522815:SAMM50 protein, human