Rac2-MRC-cIII–generated ROS cause genomic instability in chronic myeloid leukemia stem cells and primitive progenitors
Chronic myeloid leukemia in chronic phase (CML-CP) is induced by BCR-ABL1 oncogenic tyrosine kinase. Tyrosine kinase inhibitors eliminate the bulk of CML-CP cells, but fail to eradicate leukemia stem cells (LSCs) and leukemia progenitor cells (LPCs) displaying innate and acquired resistance, respectively. These cells may accumulate genomic instability, leading to disease relapse and/or malignant progression to a fatal blast phase. In the present study, we show that Rac2 GTPase alters mitochondrial membrane potential and electron flow through the mitochondrial respiratory chain complex III (MRC-cIII), thereby generating high levels of reactive oxygen species (ROS) in CML-CP LSCs and primitive LPCs. MRC-cIII–generated ROS promote oxidative DNA damage to trigger genomic instability, resulting in an accumulation of chromosomal aberrations and tyrosine kinase inhibitor–resistant BCR-ABL1 mutants. JAK2(V617F) and FLT3(ITD)–positive polycythemia vera cells and acute myeloid leukemia cells also produce ROS via MRC-cIII. In the present study, inhibition of Rac2 by genetic deletion or a small-molecule inhibitor and down-regulation of mitochondrial ROS by disruption of MRC-cIII, expression of mitochondria-targeted catalase, or addition of ROS-scavenging mitochondria-targeted peptide aptamer reduced genomic instability. We postulate that the Rac2-MRC-cIII pathway triggers ROS-mediated genomic instability in LSCs and primitive LPCs, which could be targeted to prevent the relapse and malignant progression of CML.
“Cells were incubated with 1μM SS20 and SS31 for 24 hours (under pretested conditions described previously ).. ICR-SCID female mice(Taconic) were total-body irradiated with 3 Gy from biologic irradiator RS 2000 (Rad Source Technologies) and IV injected with GFP + muBMCs transfected with pMIG1-p210BCR-ABL1-IRES-GFP.. Mice received daily IP treatment with 1.5 mg/kg of SS20 or SS31 or a combination of imatinib (50 mg/kg every morning and 100 mg/kg every evening by gavage) and SS20 or SS31., CD34 + CML-CP cells were cultured for 6 weeks with 1μM imatinib and 1μM SS20 or SS31 in medium supplemented with growth factors.”