RESUMEN
RUNX1 a member of the family of runt related transcription factors (RUNX), is essential for hematopoiesis. The expression of RUNX1 gene is controlled by two promoters; the distal P1 promoter and the proximal P2 promoter. Several isoforms of RUNX1 mRNA are generated through the use of both promoters and alternative splicing. These isoforms not only differs in their temporal expression pattern but also exhibit differences in tissue specificity. The RUNX1 isoforms derived from P2 are expressed in a variety of tissues, but expression of P1-derived isoform is restricted to cells of hematopoietic lineage. However, the control of hematopoietic-cell specific expression is poorly understood. Here we report regulation of P1-derived RUNX1 mRNA by RUNX1 protein. In silico analysis of P1 promoter revealed presence of two evolutionary conserved RUNX motifs, 0.6kb upstream of the transcription start site, and three RUNX motifs within 170bp of the 5'UTR. Transcriptional contribution of these RUNX motifs was studied in myeloid and T-cells. RUNX1 genomic fragment containing all sites show very low basal activity in both cell types. Mutation or deletion of RUNX motifs in the UTR enhances basal activity of the RUNX1 promoter. Chromatin immunoprecipitation revealed that RUNX1 protein is recruited to these sites. Overexpression of RUNX1 in non-hematopoietic cells results in a dose dependent activation of the RUNX1 P1 promoter. We also demonstrate that RUNX1 protein regulates transcription of endogenous RUNX1 mRNA in T-cell. Finally we show that SCL transcription factor is recruited to regions containing RUNX motifs in the promoter and the UTR and regulates activity of the RUNX1 P1 promoter in vitro. Thus, multiple lines of evidence show that RUNX1 protein regulates its own gene transcription.
Asunto(s)
Subunidad alfa 2 del Factor de Unión al Sitio Principal/genética , Subunidad alfa 2 del Factor de Unión al Sitio Principal/metabolismo , Regulación de la Expresión Génica , Regiones Promotoras Genéticas , Transcripción Genética , Regiones no Traducidas 5' , Secuencia de Bases , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Sitios de Unión , Línea Celular Tumoral , Humanos , Datos de Secuencia Molecular , Mutación , Motivos de Nucleótidos , Unión Proteica , Proteínas Proto-Oncogénicas/metabolismo , ARN Mensajero , Alineación de Secuencia , Proteína 1 de la Leucemia Linfocítica T Aguda , Activación TranscripcionalRESUMEN
Two distantly located promoter regions regulate the dynamic expression of RUNX genes during development: distal P1 and proximal P2 promoters. We have recently described that ß-catenin increases total Runx1 mRNA levels in human CD34(+) hematopoietic progenitors and enhances spatial proximity with its translocation partner ETO. Here, we report that induction of Wnt/ß-catenin signaling in HL60 and Jurkat leukemia-derived cell lines and CD34(+) progenitors selectively activate the production of the longer distal P1-Runx1 mRNA isoform. Gain- and loss-of-function experiments revealed that the differential increase in P1-Runx1 expression is accomplished through a minimal ß-catenin responsive region that includes a highly conserved TCF/LEF-binding element, located -20/-16 bp upstream of the canonical distal P1-Runx1 transcription start site. We conclude that the distal P1-Runx1 promoter is a direct transcriptional target of Wnt/ß-catenin signaling that may be important in normal hematopoiesis or its transition into malignant stem cells during the onset or progression of leukemia.
Asunto(s)
Subunidad alfa 2 del Factor de Unión al Sitio Principal/genética , Hematopoyesis/genética , Células Madre Hematopoyéticas/metabolismo , Leucemia/genética , Subunidad alfa 2 del Factor de Unión al Sitio Principal/biosíntesis , Regulación del Desarrollo de la Expresión Génica , Humanos , Células Jurkat , Leucemia/patología , Regiones Promotoras Genéticas , Proteínas Proto-Oncogénicas/genética , ARN Mensajero/biosíntesis , ARN Mensajero/genética , Proteína 1 Compañera de Translocación de RUNX1 , Factores de Transcripción/genética , Vía de Señalización Wnt , beta Catenina/genéticaRESUMEN
Acute myeloid leukemia (AML) is a rather common disease, characterized by the presence of a clonal population of hematopoietic progenitor cells with impaired differentiation. Although traditionally AML has been considered the result of genetic alterations, more recently experimental evidence have demonstrated that epigenetic modifications are important in development and maintenance of leukemia cells. In this review we summarize current scientific knowledge of epigenetic alterations involved in leukemogenesis. We also highlight the developing of new technological strategies that are based on epigenetic processes and have been registered as Patents of Inventions in the United Nations dependent World Intellectual Property Office (WIPO) and the main Patent offices worldwide.
Asunto(s)
Leucemia Mieloide Aguda/genética , Leucemia Mieloide Aguda/patología , Diferenciación Celular/genética , Metilación de ADN , Epigenómica , HumanosRESUMEN
The RUNX1/AML1 gene is the most frequent target for chromosomal translocation, and often identified as a site for reciprocal rearrangement of chromosomes 8 and 21 in patients with acute myelogenous leukemia. Virtually all chromosome translocations in leukemia show no consistent homologous sequences at the breakpoint regions. However, specific chromatin elements (DNase I and topoisomerase II cleavage) have been found at the breakpoints of some genes suggesting that structural motifs are determinant for the double strand DNA-breaks. We analyzed the chromatin organization at intron 5 of the RUNX1 gene where all the sequenced breakpoints involved in t(8;21) have been mapped. Using chromatin immunoprecipitation assays we show that chromatin organization at intron 5 of the RUNX1 gene is different in HL-60 and HeLa cells. Two distinct features mark the intron 5 in cells expressing RUNX1: a complete lack or significantly reduced levels of Histone H1 and enrichment of hyperacetylated histone H3. Strikingly, induction of DNA damage resulted in formation of t(8;21) in HL-60 but not in HeLa cells. Taken together, our results suggest that H1 depletion and/or histone H3 hyperacetylation may have a linkage with an increase susceptibility of specific chromosomal regions to undergo translocations.