MicroRNA-143 targets ERK5 in granulopoiesis and predicts outcome of patients with acute myeloid leukemia.

Hematopoiesis, the formation of blood cells from hematopoietic stem cells (HSC), is a highly regulated process. Since the discovery of microRNAs (miRNAs), several studies have shown their significant role in the regulation of the hematopoietic system. Impaired expression of miRNAs leads to disrupted cellular pathways and in particular causes loss of hematopoietic ability. Here, we report a previously unrecognized function of miR-143 in granulopoiesis. Hematopoietic cells undergoing granulocytic differentiation exhibited increased miR-143 expression. Overexpression or ablation of miR-143 expression resulted in accelerated granulocytic differentiation or block of differentiation, respectively. The absence of miR-143 in mice resulted in a reduced number of mature granulocytes in blood and bone marrow. Additionally, we observed an association of high miR-143 expression levels with a higher probability of survival in two different cohorts of patients with acute myeloid leukemia (AML). Overexpression of miR-143 in AML cells impaired cell growth, partially induced differentiation, and caused apoptosis. Argonaute2-RNA-Immunoprecipitation assay revealed ERK5, a member of the MAPK-family, as a target of miR-143 in myeloid cells. Further, we observed an inverse correlation of miR-143 and ERK5 in primary AML patient samples, and in CD34+ HSPCs undergoing granulocytic differentiation and we confirmed functional relevance of ERK5 in myeloid cells. In conclusion, our data describe miR-143 as a relevant factor in granulocyte differentiation, whose expression may be useful as a prognostic and therapeutic factor in AML therapy.

ABR, a novel inducer of transcription factor C/EBPα, contributes to myeloid differentiation and is a favorable prognostic factor in acute myeloid leukemia.

Active BCR related (ABR) gene deactivates ras-related C3 botulinum toxin substrate 1 (RAC1), which plays an essential role in regulating normal hematopoiesis and in leukemia. BCR gene, closely related to ABR, acts as a tumor suppressor in chronic myeloid leukemia and has overlapping functions with ABR. Evidence for a putative tumor suppressor role of ABR has been shown in several solid tumors, in which deletion of ABR is present. Our results show downregulation of ABR in AML. A block of ABR prevents myeloid differentiation and leads to repression of the myeloid transcription factor C/EBPα, a major regulator of myeloid differentiation and functionally impaired in leukemia. Conversely, stable overexpression of ABR enhances myeloid differentiation. Inactivation of the known ABR target RAC1 by treatment with the RAC1 inhibitor NSC23766 resulted in an increased expression of C/EBPα in primary AML samples and in AML cell lines U937 and MV4;11. Finally, AML patients with high ABR expression at diagnosis showed a significant longer overall survival and patients who respond to azacitidine therapy showed a significant higher ABR expression. This is the first report showing that ABR expression plays a critical role in both myelopoiesis and AML. Our data indicate the tumor suppressor potential of ABR and underline its potential role in leukemia therapeutic strategies.

Estudo da expressão do Gene ABR em leucemia mieloide cronica (LMC) utilizando real-time RT-PCR (qPCR) / Expression of active BCR related (ABR) gene in chronic myeloid leukemia (CML) real-time RT-PCR (qPCR)

Leucemia mielóide crônica (LMC) é uma doença mieloproliferativa crônica resultante de alteração citogenética t(9;22) (q34; q11) que acarreta atividade constitutiva de tirosino-quinase por meio da proteína quimérica BCR-ABL. Esta alteração ocorre nas células precursoras hematopoéticas e pode ser detectada em todas as células descendentes. O mesilato de imatinibe (Glivec®) é um inibidor do receptor do fator de crescimento derivado de plaquetas (PDGF-R), proteína quinase do BCR-ABL, administrado com sucesso a pacientes portadores de LMC. Porém, algumas formas de resistência ao tratamento têm sido apontadas, e as mais conhecidas envolvem o surgimento de mutações no domínio com atividade de quinase da proteína BCR-ABL. Entretanto, parece claro que o surgimento mutações adquiridas que acarretem ganho de função não é capaz de explicar todos os casos de resistência e que outros sistemas gênicos podem estar envolvidos neste fenótipo adverso. O gene ABR possui grande homologia com o gene BCR e aparentemente apresenta funções características e outras compartilhadas com esse último. Neste trabalho, avaliamos a expressão do gene ABR em amostras de medula óssea e sangue periférico de pacientes portadores de LMC em fase crônica ao diagnóstico e em pacientes que receberam transplante alogênico de medula óssea, utilizando a técnica de RT-PCR quantitativo em tempo real (qPCR). ABR apresentou notável aumento de expressão relativa...

Chronic myeloid leukemia (CML) is a clonal proliferative disorder of the hematopoietic stem cell cytogenetically characterized by the Philadelphia (Ph) chromosome, a result of chromosomal translocation t(9;22)(q34;q11). At molecular level, the Ph chromosome results in a fusion gene, the chimerical BCR-ABL which has constitutive tyrosine kinase activity and is detected in virtually all cases at diagnosis. Indeed, the BCR-ABL gene expression has a pivotal role in the known pathogenetic mechanisms in CML cell proliferation and disease progression. Conversely, BCR-ABL inhibition with imatinib mesilate (Glivec®) efficiently produces disease remission, since it is capable of selectively block the protein through occupying its ATP binding site. However, resistance to imatinib mesilate do occur and, although acquired mutations in the tyrosine kinase domain of BCR-ABL have been described, it seems that the appearance of acquired mutations, which result in gain of function, does not suffice for the resistant phenotype. Active BCR Related (ABR) gene is similar to BCR and both have a GTPase-activating protein (GAP) domain. Increased ABR activity has been detected in different solid tumors and more recently we detected over-expression of ABR in CML cDNA (EST) library. The aim of this study was to investigate the expression levels of the ABR gene in peripheral blood and bone marrow samples of CML patients in chronic phase (CP) at diagnosis and in patients who had received bone marrow transplantation (BMT) and achieved remission by using real-time quantitative RT-PCR (qPCR). ABR gene was expressed in higher levels in...