RESUMO
The t(12;21)(p13;q22) translocation is the most common chromosomal abnormality in pediatric leukemia. Although this rearrangement involves 2 well-characterized transcription factors, TEL and AML1, the molecular pathways affected by the result of the translocation remain largely unknown. Also in light of recent studies showing genetic and functional heterogeneities in cells responsible for cancer clone maintenance and propagation, targeting a single common deregulated pathway may be critical for the success of novel therapies. Here we describe a novel signaling pathway that is essential for oncogenic addiction in TEL-AML1 leukemia. Our data indicate a direct role for TEL-AML1, via increasing the activity of RAC1, in regulating the phosphorylation of signal transducer and activator of transcription 3 (STAT3), which results in transcriptional induction of MYC. We demonstrate that human leukemic cell lines carrying this translocation are highly sensitive to treatment with S3I-201, a specific STAT3 inhibitor, and, more interestingly, that primary human leukemic samples are also responsive to the drug in the same concentration range. Thus, STAT3 inhibition represents a promising possible therapeutic strategy for the treatment of TEL-AML1 leukemia.
Assuntos
Transformação Celular Neoplásica/genética , Subunidade alfa 2 de Fator de Ligação ao Core/fisiologia , Proteínas de Fusão Oncogênica/fisiologia , Leucemia-Linfoma Linfoblástico de Células Precursoras/genética , Fator de Transcrição STAT3/fisiologia , Animais , Apoptose/genética , Apoptose/fisiologia , Proliferação de Células , Células Cultivadas , Cromossomos Humanos Par 12/genética , Cromossomos Humanos Par 21/genética , Subunidade alfa 2 de Fator de Ligação ao Core/genética , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Proteínas de Fusão Oncogênica/genética , Oncogenes/genética , Oncogenes/fisiologia , Leucemia-Linfoma Linfoblástico de Células Precursoras/patologia , Fator de Transcrição STAT3/genética , Translocação Genética/fisiologiaRESUMO
Mixed lineage leukemia (MLL) fusion genes arise from chromosomal translocations and induce acute myeloid leukemia through a mechanism involving transcriptional deregulation of differentiation and self-renewal programs. Progression of MLL-rearranged acute myeloid leukemia is associated with increased activation of Rac GTPases. Here, we demonstrate that MLL fusion oncogenes maintain leukemia-associated Rac activity by regulating Frat gene expression, specifically Frat2. Modulation of FRAT2 leads to concomitant changes in Rac activity, and transformation of Frat knockout hematopoietic progenitor cells by MLL fusions results in leukemias displaying reduced Rac activation and increased sensitivity to chemotherapeutic drugs. FRAT2 activates Rac through a signaling mechanism that requires glycogen synthase kinase 3 and DVL. Disruption of this pathway abrogates the leukemogenic activity of MLL fusions. This suggests a rationale for the paradoxical requirement of canonical Wnt signaling and glycogen synthase kinase 3 activity for MLL fusion oncogenicity and identifies novel therapeutic targets for this disease.
Assuntos
Proteínas de Transporte/metabolismo , Proteína de Leucina Linfoide-Mieloide/metabolismo , Proteínas de Fusão Oncogênica/metabolismo , Proteínas rac de Ligação ao GTP/metabolismo , Doença Aguda , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Western Blotting , Proteínas de Transporte/genética , Transformação Celular Neoplásica/genética , Células Cultivadas , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Proteínas Desgrenhadas , Feminino , Quinase 3 da Glicogênio Sintase/genética , Quinase 3 da Glicogênio Sintase/metabolismo , Células HEK293 , Células-Tronco Hematopoéticas/metabolismo , Histona-Lisina N-Metiltransferase , Humanos , Leucemia Mieloide/genética , Leucemia Mieloide/metabolismo , Leucemia Mieloide/patologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteína de Leucina Linfoide-Mieloide/genética , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Fusão Oncogênica , Proteínas de Fusão Oncogênica/genética , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , Proteínas Proto-Oncogênicas , Interferência de RNA , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteínas rac de Ligação ao GTP/genéticaRESUMO
A significant proportion of patients suffering from acute myeloid leukemia (AML) cannot be cured by conventional chemotherapy, relapsed disease being a common problem. Molecular targeting of essential oncogenic mediators is an attractive approach to improving outcomes for this disease. The hematopoietic transcription factor c-MYB has been revealed as a central component of complexes maintaining aberrant gene expression programs in AML. We have previously screened the Connectivity Map database to identify mebendazole as an anti-AML therapeutic targeting c-MYB. In the present study we demonstrate that another hit from this screen, the steroidal lactone withaferin A (WFA), induces rapid ablation of c-MYB protein and consequent inhibition of c-MYB target gene expression, loss of leukemia cell viability, reduced colony formation and impaired disease progression. Although WFA has been reported to have pleiotropic anti-cancer effects, we demonstrate that its anti-AML activity depends on c-MYB modulation and can be partially reversed by a stabilized c-MYB mutant. c-MYB ablation results from disrupted HSP/HSC70 chaperone protein homeostasis in leukemia cells following induction of proteotoxicity and the unfolded protein response by WFA. The widespread use of WFA in traditional medicines throughout the world indicates that it represents a promising candidate for repurposing into AML therapy.
Assuntos
Leucemia Mieloide Aguda , Proteínas Proto-Oncogênicas c-myb , Humanos , Leucemia Mieloide Aguda/tratamento farmacológico , Leucemia Mieloide Aguda/genética , Leucemia Mieloide Aguda/metabolismo , Mebendazol , Oncogenes , Proteínas Proto-Oncogênicas c-myb/genética , Proteínas Proto-Oncogênicas c-myb/metabolismo , Fatores de Transcrição/genéticaRESUMO
Chromosomal translocations involving 11q23 are frequent in infant acute leukemia and give rise to the formation of MLL fusion genes. The mechanism of leukemic transformation by these fusions has been the subject of numerous investigations. However, the dependence of acute leukemia on MLL fusion activity in vivo and the efficacy of targeting this activity to eliminate disease have not been established. We have developed a model for conditional expression of MLL-ENL in hematopoietic progenitor cells, in which expression of the fusion oncogene is turned off by doxycycline. Conditionally immortalized myeloblast cells derived from these progenitors were found to induce leukemia in vivo. Leukemic cells isolated from primary recipient mice were shown to have acquired additional genetic abnormalities and, when transplanted into secondary recipients, induced leukemia with shortened latencies. However, the leukemic cells remained dependent on MLL-ENL expression in vitro and in vivo, and its ablation resulted in regression of established leukemias. This study demonstrates that even genetically complex leukemias can be reversed on inactivation of the initiating MLL fusion and has important implications for the design of novel leukemia therapies.