TGF-beta-FOXO signalling maintains leukaemia-initiating cells in chronic myeloid leukaemia.

Division of Molecular Genetics, Center for Cancer and Stem Cell Research, Cancer Research Institute, Kanazawa University, Kanazawa, Ishikawa 920-0934, Japan.
Nature (Impact Factor: 42.35). 02/2010; 463(7281):676-80. DOI: 10.1038/nature08734
Source: PubMed

ABSTRACT Chronic myeloid leukaemia (CML) is caused by a defined genetic abnormality that generates BCR-ABL, a constitutively active tyrosine kinase. It is widely believed that BCR-ABL activates Akt signalling that suppresses the forkhead O transcription factors (FOXO), supporting the proliferation or inhibiting the apoptosis of CML cells. Although the use of the tyrosine kinase inhibitor imatinib is a breakthrough for CML therapy, imatinib does not deplete the leukaemia-initiating cells (LICs) that drive the recurrence of CML. Here, using a syngeneic transplantation system and a CML-like myeloproliferative disease mouse model, we show that Foxo3a has an essential role in the maintenance of CML LICs. We find that cells with nuclear localization of Foxo3a and decreased Akt phosphorylation are enriched in the LIC population. Serial transplantation of LICs generated from Foxo3a(+/+) and Foxo3a(-/-) mice shows that the ability of LICs to cause disease is significantly decreased by Foxo3a deficiency. Furthermore, we find that TGF-beta is a critical regulator of Akt activation in LICs and controls Foxo3a localization. A combination of TGF-beta inhibition, Foxo3a deficiency and imatinib treatment led to efficient depletion of CML in vivo. Furthermore, the treatment of human CML LICs with a TGF-beta inhibitor impaired their colony-forming ability in vitro. Our results demonstrate a critical role for the TGF-beta-FOXO pathway in the maintenance of LICs, and strengthen our understanding of the mechanisms that specifically maintain CML LICs in vivo.

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    ABSTRACT: Differentiation induction is currently considered as an alternative strategy for treating chronic myelogenous leukemia (CML). Our previous work has demonstrated that Sprouty-related EVH1 domainprotein2 (Spred2) was involved in imatinib mediated cytotoxicity in CML cells. However, its roles in growth and lineage differentiation of CML cells remain unknown. In this study, we found that CML CD34+ cells expressed lower level of Spred2 compared with normal hematopoietic progenitor cells, and adenovirus mediated restoration of Spred2 promoted the erythroid differentiation of CML cells. Imatinib could induce Spred2 expression and enhance erythroid differentiation in K562 cells. However, the imatinib induced erythroid differentiation could be blocked by Spred2 silence using lentiviral vector PLKO.1-shSpred2. Spred2 interference activated phosphorylated-ERK (p-ERK) and inhibited erythroid differentiation, while ERK inhibitor, PD98059, could restore the erythroid differentiation, suggesting Spred2 regulated the erythroid differentiation partly through ERK signaling. Furthermore, Spred2 interference partly restored p-ERK level leading to inhibition of erythroid differentiation in imatinib treated K562 cells. In conclusion, Spred2 was involved in erythroid differentiation of CML cells and participated in imatinib induced erythroid differentiation partly through ERK signaling.
    PLoS ONE 02/2015; 10(2):e0117573. DOI:10.1371/journal.pone.0117573 · 3.53 Impact Factor
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    ABSTRACT: Tyrosine kinase inhibitors (TKIs) have profoundly changed the natural history of chronic myeloid leukemia (CML). However, acquired resistance to imatinib, dasatinib or nilotinib (1(st) and 2(nd) generation TKIs), due in part to BCR-ABL1 kinase mutations, has been largely described. These drugs are ineffective on the T315I gatekeeper substitution, which remains sensitive to 3(rd) generation TKI ponatinib. It has recently been suggested that the hematopoietic niche could protect leukemic cells from targeted therapy. In order to investigate the role of a stromal niche in mutation-related resistance, we developed a niche-based cell mutagenesis assay. For this purpose, ENU (N-ethyl-N-nitrosourea)-exposed UT-7 cells expressing non-mutated or T315I-mutated BCR-ABL1 were cultured with or without murine MS-5 stromal cells and in the presence of imatinib, dasatinib, nilotinib, or ponatinib. In the assays relative to 1(st) and 2(nd) generation TKIs, which were performed on non-mutated BCR-ABL1 cells, our data highlighted the increasing efficacy of the latter, but did not reveal any substantial effect of the niche. In ponatinib assays performed on both non-mutated and T315I-mutated BCR-ABL1 cells, an increased number of resistant clones were observed in the presence of MS-5. Present data suggested that T315I mutants need either compound mutations (e.g. E255K/T315I) or a stromal niche to escape from ponatinib. Using array-comparative genomic hybridization experiments, we found an increased number of variations (involving some recurrent chromosome regions) in clones cultured on MS-5 feeder. Overall, our study suggests that the hematopoietic niche could play a crucial role in conferring resistance to ponatinib, by providing survival signals and favoring genetic instability.
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    ABSTRACT: Background Chronic myeloid leukemia (CML) is a clonal hematopoietic stem cell disorder in which leukemic cells display a reciprocal t(9:22) chromosomal translocation that results in the formation of the chimeric BCR-ABL oncoprotein, with a constitutive tyrosine kinase activity. Consequently, BCR-ABL causes increased proliferation, inhibition of apoptosis, and altered adhesion of leukemic blasts to the bone marrow (BM) microenvironment. It has been well documented that cancer cells can generate their own signals in order to sustain their growth and survival, and recent studies have revealed the role of cancer-derived exosomes in activating signal transduction pathways involved in cancer cell proliferation. Exosomes are small vesicles of 40¿100 nm in diameter that are initially formed within the endosomal compartment, and are secreted when a multivesicular body (MVB) fuses with the plasma membrane. These vesicles are released by many cell types including cancer cells, and are considered messengers in intercellular communication. We have previously shown that CML cells released exosomes able to affect the tumor microenvironment.ResultsCML cells, exposed up to one week, to exosomes showed a dose-dependent increased proliferation compared with controls. Moreover, exosome treatment promotes the formation of LAMA84 colonies in methylcellulose. In a CML xenograft model, treatment of mice with exosomes caused a greater increase in tumor size compared with controls (PBS-treated mice). Real time PCR and Western Blot analysis showed, in both in vitro and in vivo samples, an increase in mRNA and protein levels of anti-apoptotic molecules, such as BCL-w, BCL-xl, and survivin, and a reduction of the pro-apoptotic molecules BAD, BAX and PUMA. We also found that TGF- ß1 was enriched in CML-exosomes. Our investigations showed that exosome-stimulated proliferation of leukemia cells, as well as the exosome-mediated activation of an anti-apoptotic phenotype, can be inhibited by blocking TGF-ß1 signaling.ConclusionsCML-derived exosomes promote, through an autocrine mechanism, the proliferation and survival of tumor cells, both in vitro and in vivo, by activating anti-apoptotic pathways. We propose that this mechanism is activated by a ligand-receptor interaction between TGF-ß1, found in CML-derived exosomes, and the TGF- ß1 receptor in CML cells.
    Cell Communication and Signaling 02/2015; 13(1):8. DOI:10.1186/s12964-015-0086-x · 4.67 Impact Factor

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