RESUMEN
PU.1 downregulation within hematopoietic stem and progenitor cells (HSPCs) is the primary mechanism for the development of acute myeloid leukemia (AML) in mice with homozygous deletion of the upstream regulatory element (URE) of PU.1 gene. p53 is a well-known tumor suppressor that is often mutated in human hematologic malignancies including AML and adds to their aggressiveness; however, its genetic deletion does not cause AML in mouse. Deletion of p53 in the PU.1(ure/ure) mice (PU.1(ure/ure)p53(-/-)) results in more aggressive AML with shortened overall survival. PU.1(ure/ure)p53(-/-) progenitors express significantly lower PU.1 levels. In addition to URE deletion we searched for other mechanisms that in the absence of p53 contribute to decreased PU.1 levels in PU.1(ure/ure)p53(-/-) mice. We found involvement of Myb and miR-155 in downregulation of PU.1 in aggressive murine AML. Upon inhibition of either Myb or miR-155 in vitro the AML progenitors restore PU.1 levels and lose leukemic cell growth similarly to PU.1 rescue. The MYB/miR-155/PU.1 axis is a target of p53 and is activated early after p53 loss as indicated by transient p53 knockdown. Furthermore, deregulation of both MYB and miR-155 coupled with PU.1 downregulation was observed in human AML, suggesting that MYB/miR-155/PU.1 mechanism may be involved in the pathogenesis of AML and its aggressiveness characterized by p53 mutation.
Asunto(s)
Leucemia Mieloide Aguda/genética , Proteínas Proto-Oncogénicas/genética , Transactivadores/genética , Proteína p53 Supresora de Tumor/genética , Animales , Modelos Animales de Enfermedad , Regulación Leucémica de la Expresión Génica , Humanos , Leucemia Mieloide Aguda/patología , Hígado/patología , Ratones , Ratones Noqueados , MicroARNs/genética , MicroARNs/metabolismo , Proteínas Oncogénicas v-myb/genética , Proteínas Oncogénicas v-myb/metabolismo , Regiones Promotoras Genéticas , Proteínas Proto-Oncogénicas c-myc/genética , Proteínas Proto-Oncogénicas c-myc/metabolismo , Bazo/patología , Activación TranscripcionalRESUMEN
Epigenetic 5-azacitidine (AZA) therapy of high-risk myelodysplastic syndromes (MDS) and acute myelogenous leukemia (AML) represents a promising, albeit not fully understood, approach. Hematopoietic transcription factor PU.1 is dynamically regulated by upstream regulatory element (URE), whose deletion causes downregulation of PU.1 leading to AML in mouse. In this study a significant group of the high-risk MDS patients, as well as MDS cell lines, displayed downregulation of PU.1 expression within CD34+ cells, which was associated with DNA methylation of the URE. AZA treatment in vitro significantly demethylated URE, leading to upregulation of PU.1 followed by derepression of its transcriptional targets and onset of myeloid differentiation. Addition of colony-stimulating factors (CSFs; granulocyte-CSF, granulocyte-macrophage-CSF and macrophage-CSF) modulated AZA-mediated effects on reprogramming of histone modifications at the URE and cell differentiation outcome. Our data collectively support the importance of modifying the URE chromatin structure as a regulatory mechanism of AZA-mediated activation of PU.1 and induction of the myeloid program in MDS.
Asunto(s)
Antimetabolitos Antineoplásicos/uso terapéutico , Azacitidina/uso terapéutico , Cromatina/genética , Síndromes Mielodisplásicos/tratamiento farmacológico , Síndromes Mielodisplásicos/genética , Proteínas Proto-Oncogénicas/genética , Transactivadores/genética , Anciano , Anciano de 80 o más Años , Antimetabolitos Antineoplásicos/farmacología , Azacitidina/farmacología , Diferenciación Celular/efectos de los fármacos , Diferenciación Celular/genética , Línea Celular Tumoral , Factores Estimulantes de Colonias/farmacología , Metilación de ADN/efectos de los fármacos , Femenino , Regulación Leucémica de la Expresión Génica/efectos de los fármacos , Humanos , Masculino , Persona de Mediana Edad , Células Madre Neoplásicas/citología , Células Madre Neoplásicas/efectos de los fármacos , Células Madre Neoplásicas/metabolismo , Proteínas Proto-Oncogénicas/metabolismo , Secuencias Reguladoras de Ácidos Nucleicos/efectos de los fármacos , Transactivadores/metabolismo , Activación Transcripcional/efectos de los fármacosRESUMEN
Four mouse bone marrow or thymus cell populations, namely granulopoietic/monocytopoietic, erythropoietic, B-lymphopoietic, and T-lymphopoietic precursor cells have been assayed by RT-PCR technique for the presence and relative amounts of adenosine A(1), A(2a), A(2b), and A(3) receptor mRNA. It has been found that (i) all four populations studied express all four adenosine receptor subtypes, (ii) the A(1), receptor is the least expressed in all populations studied, (iii) the A(3) receptor is markedly expressed in the populations of granulopoietic/monocytopoietic and erythropoietic cells, (iv) the A(2a) receptor is markedly expressed in the populations of B-lymphopoietic and T-lymphopoietic cells, and v) the A(2b) receptor does not predominate in any of the precursor cells studied. Our data offer a new possibility for the assessment of the readiness of these cells to respond, by receptor-mediated mechanisms, to adenosine or its analogs present in the tissues as a result of endogenous processes and/or following their administration.
Asunto(s)
Hematopoyesis , Células Madre Hematopoyéticas/metabolismo , ARN Mensajero/metabolismo , Receptores Purinérgicos P1/genética , Animales , Separación Celular , Femenino , Regulación de la Expresión Génica , Hematopoyesis/genética , Ratones , Ratones Endogámicos C57BL , Reacción en Cadena de la Polimerasa , Receptor de Adenosina A1/genética , Receptor de Adenosina A2A/genética , Receptor de Adenosina A2B/genética , Receptor de Adenosina A3/genéticaRESUMEN
B-lymphopoiesis in FL differs notably from that of adult B-lymphopoiesis in being resistant to suppression by oestrogens due to the lack of expression of oestrogen receptors in B-cell progenitors and precursors. We have transplanted middle-stage FL cells (E14.5) to adult male mice and demonstrated that B-lymphopoiesis derived from FL cells remained resistant to suppression by exogenous oestrogen for several months compared to adult BM cells. This significant difference strongly suggests that the latestage FL environment exerts an inductive action on the haematopoietic stem cells and is mandatory for later sensitivity of B-lymphopoiesis to suppression by oestrogens. The results also provide the first in vivo functional confirmation of a differential responsiveness of FL- and adult BM-derived B-lymphopoiesis to suppression by oestrogens.