Transcriptional repression of the RUNX3/AML2 gene by the t(8;21) and inv(16) fusion proteins in acute myeloid leukemia

Abstract

RUNX3/AML2 is a Runt domain transcription factor like RUNX1/AML1 and RUNX2/ AML3. Regulated by 2 promoters P1 and P2, RUNX3 is frequently inactivated by P2 methylation in solid tumors. Growing evidence has suggested a role of this transcription factor in hematopoiesis. However, genetic alterations have not been reported in blood cancers. In this study on 73 acute myeloid leukemia (AML) patients (44 children and 29 adults), we first showed that high RUNX3 expression among childhood AML was associated with a shortened event-free survival, and RUNX3 was significantly underexpressed in the prognostically favorable subgroup of AML with the t(8;21) and inv(16) translocations. We further demonstrated that this RUNX3 repression was mediated not by P2 methylation, but RUNX1-ETO and CBF␤-MYH11, the fusion products of t(8; 21) and inv(16), via a novel transcriptional mechanism that acts directly or indirectly in collaboration with RUNX1, on 2 conserved RUNX binding sites in the P1 promoter. In in vitro studies, ectopically expressed RUNX1-ETO and CBF␤-MYH11 also inhibited endogenous RUNX3 expression. Taken together, RUNX3 was the first transcriptional target found to be commonly repressed by the t(8;21) and inv (16) IntroductionThe Runt domain transcription factor family includes RUNX1/ AML1, RUNX2/AML3, and RUNX3/AML2. These transcription factors share a conserved Runt domain for binding to a 6-base pair (bp) DNA sequence (TGT/cGGT) and heterodimerization with core-binding factor ␤ (CBF␤). CBF␤ does not bind DNA directly but increases the ability of RUNX proteins to bind DNA and regulate transcription. 1 RUNX1 and RUNX2 are essential for hematopoiesis and osteogenesis, respectively. 2,3 Moreover, RUNX1 regulates neuron and muscle function. 4,5 On the other hand, RUNX3 is involved in neurogenesis and thymopoiesis and acts as a tumor suppressor in gastric cancer. [6][7][8] In addition, RUNX3 is inactivated frequently by promoter methylation and less frequently by gene deletion, point mutations, and protein mislocalization in various solid tumors. 9 RUNX3 and RUNX1 show prominent expression in hematopoietic cells and different subsets of neurons, 4,10 while RUNX2 is expressed mainly in bone and also other tissues including hematopoietic stem cells. 11 The expression of RUNX3 and RUNX1 can be induced by retinoic acid, suggesting that these transcription factors may jointly regulate retinoic acid-mediated hematopoietic differentiation. 10 The functional overlap was supported by the observations that hematopoietic defects due to RUNX1 deficiency could be rescued by RUNX3. 12,13 Further evidence suggesting a role of RUNX3 in hematopoiesis was reduction of mature blood cell formation in zebrafish by RUNX3 depletion. 14 The role of RUNX3 in tumorigenesis and its potential involvement in hematopoiesis suggest a role of this transcription factor in hematological malignancies. However, genetic alterations of RUNX3 have not been reported in acute myeloid leukemia (AML). 15 t(8;21)(q22;q22) and inv(16)(p13;q22) are the 2 most common t...

Expression levels of the runt-related transcription factor�1 and�3 genes in the development of acute myeloid leukemia

“…Furthermore, according to the study undertaken by Cheng et al (7), the RUNX3 gene expression level was not associated with age or sex. However, in a group of patients with a lower RUNX3 gene expression level, this was significantly associated with the presence of t(8;21) or inv(16) translocations (7). Lower RUNX3 gene expression levels were frequently identified in patients with FAB M2 and M4 AML subtypes.…”

“…However, this study was conducted on patients belonging to an FLT3 mutant group, which may have also affected EFS (35). Based on these aforementioned studies, it is possible that the RUNX3 gene expression level is associated with a shorter survival time in childhood AML (7,35). Furthermore, according to the study undertaken by Cheng et al (7), the RUNX3 gene expression level was not associated with age or sex.…”

“…The RUNX3 gene is involved in neurogenesis and thymopoiesis, and serves a role as a tumor suppressor in gastric cancer (7,(31)(32)(33). A study undertaken by Jiang et al reported that the RUNX3 expression level is associated with breast cancer development and that it is decreased in this type of cancer.…”

“…The principal cause for this inactivation mechanism may be hypermethylation in the promoter region (34). A study undertaken by Cheng et al (7) demonstrated that RUNX3 gene expression was an independent prognostic factor in childhood AML, and that a higher RUNX3 gene expression level was associated with a shorter EFS and OS time (7). The results of a study undertaken by Lacayo et al (35) also demonstrated that a higher level of RUNX3 gene expression was associated with a shortened EFS rate in childhood AML.…”

“…Among the genetic factors that are involved in the development of AML, are the runt-related transcription factor 1 (RUNX1) and runt-related transcription factor 3 (RUNX3) genes. These genes belong to the runt domain transcription factor family, which is responsible for encoding the DNA-binding α-subunits of the RUNT domain transcription factor and serve an important role in the regulation of transcription (6,7). However, they may be dysregulated in human cancer cells (as a result of mutations, translocations or inactivation), and therefore potentially serve a role in the pathogenesis of cancer (6,8).…”