Acute myeloid leukemia with t(7;21)(q11.2;q22) expresses a novel, reversed-sequence RUNX1–DTX2 chimera
Department of Hematology and Oncology, Dokkyo Medical University School of Medicine, 880 Kitakobayashi, Mibu-machi, Shimotsuga-gun, Tochigi, 321-0293, Japan. International journal of hematology
(Impact Factor: 1.92).
06/2012; 96(2):268-73. DOI: 10.1007/s12185-012-1112-z
The RUNX1 gene is frequently rearranged in acute leukemia. We cloned a novel RUNX1 chimeric gene generated by t(7;21)(q11.2;q22) in a patient with acute myeloid leukemia. 3'-rapid amplification of cDNA ends analysis showed a tail-to-tail fusion between RUNX1 on 21q22 and DTX2 on 7q11.2, with an insertion of short complementary sequence from UPK3B adjacent to DTX2. DTX2 encodes a putative E3-ubiquitin ligase with no known biological function. There are two possible functions of RUNX1-reversed UPK3B-DTX2: one from aberrant RUNX1 chimeric protein and the other from the reversed sequence of DTX2. The predicted aberrant protein expressed under the RUNX1 promoter was highly structurally similar to RUNX1a. In a reporter assay, the aberrant protein inhibited the trans-activation function of RUNX1 in a dominant-negative manner, similar to RUNX1a. In contrast, the DTX2 reversed sequence may degrade wild-type DTX2 transcript or suppress its translation. In conclusion, we identified a novel fusion RUNX1 partner, DTX2, which chimerize in a reverse direction. This is the first example of RUNX1 chimera in an opposing direction generated by chromosomal translocation in leukemia. In addition to the aberrantly truncated RUNX1 protein, the DTX2 antisense sequence may play some role in the development of leukemia carrying the t(7;21) translocation.
Available from: Amelie Giguere
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ABSTRACT: RUNX1, a key regulator of hematopoiesis, is frequently mutated or implicated in chromosomal translocations in acute leukemia. About half of RUNX1 translocations remain uncharacterized at the molecular level. We describe here one such event, a t(15;21)(q26.1;q22) translocation identified in an adult patient diagnosed with a t(9;22)(q34;q11.2)-positive acute leukemia. This previously unreported rearrangement yields a fusion of RUNX1 with the antisense strand of the SV2B gene, a new translocation partner of RUNX1, resulting in the expression of out-of-frame mRNA chimeric transcripts and the production of putative truncated RUNX1 isoforms. The t(15;21) translocation also dissociates the P1 promoter of RUNX1 from its open reading frame, reducing RUNX1 expression levels in the patient's leukemic cells. Our data suggest that RUNX1 haploinsufficiency collaborates with the BCR-ABL1 oncogene in this leukemia. The description of this atypical gene fusion is an important addition to the characterization of the pathogenomic mechanisms leading to RUNX1 structural and functional alterations. Furthermore, our data strongly suggests that inadequate dosage of this gene plays an essential role in leukemogenesis. © 2013 Wiley Periodicals, Inc.
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ABSTRACT: We have identified a new t(1;21)(p32;q22) chromosomal translocation in a MDS/AML patient that results in expression of an aberrant C-terminally truncated RUNX1 protein lacking several regulatory domains. As similar truncated RUNX1 proteins are generated by genetic aberrations including chromosomal translocations and point mutations, we used the t(1;21)(p32;q22) chromosomal translocation as a model to explore whether C-terminally truncated RUNX1 proteins trigger effects similar to those induced by well-characterized leukemogenic RUNX1 fusion genes. In vitro analysis of transduced human hematopoietic/progenitor stem cells showed that truncated RUNX1 proteins increase proliferation and self-renewal and disrupt the differentiation program by interfering with RUNX1b. These effects are similar to but milder than those induced by the RUNX1/ETO fusion protein. GSEA analysis confirmed similar altered gene expression patterns in the truncated RUNX1 and RUNX1/ETO models, with both models showing alterations in genes involved in self-renewal and leukemogenesis, including homeobox genes, primitive erythroid genes and leukemogenic transcription factors. We propose that C-terminally truncated RUNX1 proteins can contribute to leukemogenesis in a similar way to RUNX1 fusion genes but through a milder phenotype.Oncogene advance online publication, 23 March 2015; doi:10.1038/onc.2015.70.
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