Mitochondrial Dysfunction in Human Leukemic Stem/Progenitor Cells upon Loss of RAC2

• DOI: 10.1371/journal.pone.0128585
• Publication Date: 2015-05-27T18:07:57Z
• Authors: Marta E. Capala; Henny Maat; Francesco Bonardi; Vincent van den Boom; Jeroen Kuipers; Edo Vellenga; Ben N. G. Giepmans; Jan Jacob Schuringa
• Keywords: NICHES; Mitochondrial Diseases; MIGRATION; Science; Fusion Proteins, bcr-abl; Down-Regulation; Apoptosis; Bone Marrow Cells; ACUTE MYELOID-LEUKEMIA; Mitochondrial Membrane Transport Proteins; Cell Line; GUANOSINE TRIPHOSPHATASES; ACTIVATION; Mitochondrial Proteins; 03 medical and health sciences; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mitochondrial Precursor Protein Import Complex Proteins; Humans; Immunoprecipitation; Cell Proliferation; Membrane Potential, Mitochondrial; LONG-TERM MAINTENANCE; 0303 health sciences; Q; Cell Cycle; R; Membrane Proteins; Proteins; Hematopoietic Stem Cells; HEMATOPOIETIC STEM-CELL; Mitochondria; SELF-RENEWAL; HEK293 Cells; PROGENITOR CELLS; GTPASES; Medicine; Research Article

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.