RESUMO
The hypoxic microenvironment of the bone marrow, known as the hypoxic niche, supports hematopoietic stem cell quiescence and maintains long-term repopulation activity. Hypoxia also affects the expansion of progenitor cells and enhances erythropoiesis and megakaryopoiesis. In contrast to the known effects of hypoxia on normal hematopoiesis, the effects of the hypoxic environment of the bone marrow on the pathogenesis of myeloproliferative neoplasms (MPNs) have not been well studied. In the present study, we investigated the role of the hypoxic environment in the pathophysiology of MPNs, focusing on JAK2V617F, a major driver of mutation in Philadelphia-negative MPNs. We found that the activity of JAK2V617F was suppressed in hypoxic conditions not only in JAK2V617F-positive leukemia cells, but also in primary peripheral blood mononuclear cells from patients with polycythemia vera. Concomitant with the inhibition of JAK2V617F activity, hypoxia increased the expression of p27/KIP1, the primary negative regulator of the cell cycle, and inhibited cell cycle progression in JAK2V617F-positive leukemia cell lines. The spontaneous erythroid colony formation of primary cells from polycythemia vera patients was also suppressed under hypoxic conditions. We also revealed that the hypoxia-induced overproduction of reactive oxygen species played a crucial role in the inhibition of JAK2V617F through the oxidation and inhibition of SHP-2, a protein tyrosine phosphatase that contains SH-2, which is required for JAK2 activation. In conclusion, a hypoxic environment may modulate JAK2-positive MPN cell fate and disease progression through the suppression of SHP-2 function and the subsequent suppression of JAK2V617F activity.
Assuntos
Neoplasias Hematológicas/enzimologia , Janus Quinase 2/metabolismo , Leucócitos Mononucleares/enzimologia , Mutação de Sentido Incorreto , Proteínas de Neoplasias/metabolismo , Policitemia Vera/enzimologia , Proteína Tirosina Fosfatase não Receptora Tipo 11/metabolismo , Idoso , Idoso de 80 Anos ou mais , Substituição de Aminoácidos , Hipóxia Celular/genética , Linhagem Celular Tumoral , Inibidor de Quinase Dependente de Ciclina p27/biossíntese , Ativação Enzimática/genética , Feminino , Regulação Neoplásica da Expressão Gênica/genética , Neoplasias Hematológicas/genética , Neoplasias Hematológicas/patologia , Humanos , Janus Quinase 2/genética , Leucócitos Mononucleares/patologia , Masculino , Pessoa de Meia-Idade , Proteínas de Neoplasias/genética , Policitemia Vera/genética , Policitemia Vera/patologia , Proteína Tirosina Fosfatase não Receptora Tipo 11/genética , Espécies Reativas de Oxigênio/metabolismoRESUMO
Rearrangements of the mixed lineage leukemia MLL gene at chromosome 11q23 are common chromosomal abnormalities in human leukemia. MLL fused with numerous partner genes causes different leukemia phenotypes that depend on the function of partner genes. MLLT3-MLL is generated by translocation t(9;11), which primarily induces acute myeloid leukemia in humans, whereas MLLT3-MLL induces ALL or biphenotypic leukemia in mice. The microenvironment that surrounds leukemia cells plays a central role in this process. We report a patient with mixed phenotype acute leukemia with MLLT3-MLL. This patient, a 44-year-old woman, initially exhibited extramedullary leukemia with multiple tumors and subsequently developed bone marrow disease. The leukemia cells exhibited myeloid (CD13 and MPO) and B cell (CD19 and CD79a) phenotypes. Chromosomal analysis and RT-PCR assay revealed tumor cells with the MLLT3-MLL fusion gene. We treated this patient with a drug regimen for AML (Ara-C plus anthracycline), and complete remission was obtained. This report describes the fourth case of mixed phenotypic leukemia with extramedullary disease. The extramedullary circumstance may underlie the biphenotypic features of these patients.
Assuntos
Rearranjo Gênico/genética , Leucemia Mieloide Aguda/genética , Proteína de Leucina Linfoide-Mieloide/genética , Fatores de Transcrição/metabolismo , Translocação Genética/genética , Adulto , Feminino , Humanos , Leucemia Mieloide Aguda/diagnóstico , FenótipoRESUMO
The introduction of rituximab, an anti-CD20 monoclonal antibody, has dramatically improved the treatment outcomes of patients with B cell lymphoma. Nevertheless, the clinical response to rituximab varies, and a subpopulation of patients does not respond well to this antibody. Although several molecular events have been shown to be involved in the mechanism of action of rituximab, recent studies have demonstrated that intracellular signaling pathways and the direct effects of rituximab on cell membrane components are responsible for the antilymphoma action of this drug. In the present study, we demonstrated that rituximab activated Syk and Akt, molecules with antiapoptotic functions, in several CD20-positive lymphoma cell lines. Notably, rituximab activated Syk and Akt in all the tested primary lymphoma samples from six patients. Our results show that the cholesterol levels in lymphoma cell membranes have a crucial role in the regulation of Syk and Akt. The depletion of cholesterol from the cell membrane completely blocked rituximab-induced Syk and Akt activation. Simvastatin, an inhibitor of cholesterol synthesis, also abrogated rituximab-mediated Syk and Akt activation. Finally, we report that rituximab inhibited the apoptosis induced by chemotherapeutic drugs, which was observed solely in Akt-activated cells. This work demonstrates for the first time that rituximab paradoxically works to suppress apoptosis under certain conditions in a manner that is dependent on the cell membrane cholesterol level. Our observations provide novel insights and suggest that the cell membrane cholesterol level represents a new biomarker for predicting patient response to rituximab. Furthermore, the modulation of lipid rafts could provide a new strategy for enhancing the antilymphoma action of rituximab.