Resistance of leukemic stem-like cells in AML cell line KG1a to natural killer cell-mediated cytotoxicity
ABSTRACT Leukemic stem cells (LSCs) play the central role in the relapse and refractory of acute myeloid leukemia (AML) and highlight the critical need for the new therapeutic strategies to directly target the LSC population. However, relatively little is known about the unique molecular mechanisms of drug and natural killer cells (NK)-killing resistance of LSCs because of very small number of LSCs in bone marrow. In this study, we investigated whether established leukemia cell line contains LSCs. We showed that KG1a leukemia cell line contained leukemic stem-like cells, which have been phenotypically restricted within the CD34(+)CD38(-) fractions. CD34(+)CD38(-) cells could generate CD34(+)CD38(+) cells in culture medium and had renewal function. Moreover, CD34(+)CD38(-) cells had self-renewal potential. We found that leukemic stem-like cells from KG1a cells were resistant to chemotherapy and NK-mediated cytotoxicity. NKG2D ligands involve in protecting LSCs from NK-mediated attack. Taken together, our studies provide a novel cell model for leukemic stem cells research. Our data also shed light on mechanism of double resistant to chemotherapy and NK cell immunotherapy, which was helpful for developing novel effective strategies for LSCs.
SourceAvailable from: Sabrina Copsel[Show abstract] [Hide abstract]
ABSTRACT: Less than a third of adults patients with acute myeloid leukemia (AML) are cured by current treatments, emphasizing the need for new approaches to therapy. We previously demonstrated that besides playing a role in drug-resistant leukemia cell lines, multidrug resistance protein 4 (MRP4/ABCC4) regulates leukemia cell proliferation and differentiation through the endogenous MRP4/ABCC4 substrate, cAMP. Here, we studied the role of MRP4/ABCC4 in tumor progression in a mouse xenograft model and in leukemic stem cells (LSCs) differentiation. We found a decrease in the mitotic index and an increase in the apoptotic index associated with the inhibition of tumor growth when mice were treated with rolipram (PDE4 inhibitor) and/or probenecid (MRPs inhibitor). Genetic silencing and pharmacologic inhibition of MRP4 reduced tumor growth. Furthermore, MRP4 knockdown induced cell cycle arrest and apoptosis in vivo. Interestingly, when LSC population was isolated, we observed that increased cAMP levels and MRP4/ABCC4 blockade resulted in LSCs differentiation. Taken together, our findings show that MRP4/ABCC4 has a relevant role in tumor growth and apoptosis and in the eradication of LSCs, providing the basis for a novel promising target in AML therapy.Oncotarget 09/2014; 5(19). · 6.63 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Breast cancer stem-like cells (BCSC) are crucial for metastasis but the underlying mechanisms remain elusive. Here we report that tumor-infiltrating natural killer (NK) cells failed to limit metastasis and were not associated with improved therapeutic outcome of BCSC-rich breast cancer. Primary BCSC were resistant to cytotoxicity medicated by autologous/allogeneic NK cells due to reduced expression of MICA and MICB, two ligands for the stimulatory NK cell receptor NKG2D. Furthermore, the downregulation of MICA/MICB in BCSCs was mediated by aberrantly expressed oncogenic miR-20a, which promoted the resistance of BCSC to NK cell cytotoxicity and resultant lung metastasis. The breast cancer cell differentiation inducing agent, all-trans-retinoic acid (ATRA), restored miR-20a-MICA/MICB axis and sensitized BCSC to NK cell-mediated killing, thereby reducing immune escape-associated BCSC metastasis. Together, our findings reveal a novel mechanism for immune escape of human BCSC, and identify the miR-20a-MICA/MICB signaling axis as a therapeutic target to limit metastatic breast cancer.Cancer Research 08/2014; 74(20). DOI:10.1158/0008-5472.CAN-13-2563 · 9.28 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Cytarabine (cytosine arabinoside) is one of the most effective drugs for the treatment of patients diagnosed with acute myeloid leukemia (AML). Despite its efficiency against AML cells, emergence of drug resistance due to prolonged chemotherapy in most patients is still a major obstacle. Several studies have shown that drug resistance mechanisms alter the sensitivity of leukemia cells to immune system effector cells. To investigate this phenomenon, parental acute myeloid cell lines HL-60 and KG-1 were continuously exposed to increasing doses of cytarabine in order to establish equivalent resistant cell lines, HL-60 (R), and KG-1(R). Our data indicate that cytarabine-resistant cells are more susceptible to NK-mediated cell lysis as compared to parental cytarabine-sensitive cells. The increased susceptibility correlates with the induction of ULBP1/2/3, NKG2D ligands, on target cells by a mechanism involving c-Myc induction. More importantly, chromatin immunoprecipitation assay revealed that ULBP1/3 are direct targets of c-Myc. Using drug resistant primary AML blasts as target cells, inhibition of c-Myc resulted in decreased expression of NKG2D ligands and the subsequent impairment of NK cell lysis. This study provides for the first time the c-Myc dependent regulation of NKG2D ligands in acute myeloid leukemia.Blood 03/2014; DOI:10.1182/blood-2013-11-536219 · 9.78 Impact Factor