ABSTRACT
The t(8;21) translocation fuses the DNA-binding domain of the hematopoietic master regulator RUNX1 to the ETO protein. The resultant RUNX1/ETO fusion protein is a leukemia-initiating transcription factor that interferes with RUNX1 function. The result of this interference is a block in differentiation and, finally, the development of acute myeloid leukemia (AML). To obtain insights into RUNX1/ETO-dependant alterations of the epigenetic landscape, we measured genome-wide RUNX1- and RUNX1/ETO-bound regions in t(8;21) cells and assessed to what extent the effects of RUNX1/ETO on the epigenome depend on its continued expression in established leukemic cells. To this end, we determined dynamic alterations of histone acetylation, RNA Polymerase II binding and RUNX1 occupancy in the presence or absence of RUNX1/ETO using a knockdown approach. Combined global assessments of chromatin accessibility and kinetic gene expression data show that RUNX1/ETO controls the expression of important regulators of hematopoietic differentiation and self-renewal. We show that selective removal of RUNX1/ETO leads to a widespread reversal of epigenetic reprogramming and a genome-wide redistribution of RUNX1 binding, resulting in the inhibition of leukemic proliferation and self-renewal, and the induction of differentiation. This demonstrates that RUNX1/ETO represents a pivotal therapeutic target in AML.
Subject(s)
Chromatin/genetics , Core Binding Factor Alpha 2 Subunit/genetics , Leukemia, Myeloid, Acute/genetics , Leukemia, Myeloid, Acute/metabolism , Proto-Oncogene Proteins/genetics , Transcription Factors/metabolism , Translocation, Genetic , Acetylation , Binding Sites , CCAAT-Binding Factor/genetics , CCAAT-Binding Factor/metabolism , Cell Differentiation/genetics , Cell Line, Tumor , Chromatin/metabolism , Chromosomes, Human, Pair 21 , Chromosomes, Human, Pair 8 , Cluster Analysis , Core Binding Factor Alpha 2 Subunit/metabolism , Gene Expression Profiling , Gene Silencing , Histones/metabolism , Humans , Mutation , Oncogene Proteins, Fusion/genetics , Oncogene Proteins, Fusion/metabolism , Protein Binding , Proto-Oncogene Proteins/metabolism , RNA Polymerase II/metabolism , RUNX1 Translocation Partner 1 Protein , Transcription Factors/genetics , Transcriptional ActivationSubject(s)
B-Lymphocytes/metabolism , Chromosomes, Human, Pair 21 , Chromosomes, Human, Pair 8 , Core Binding Factor Alpha 2 Subunit/genetics , Gene Expression , Leukemia, Myeloid, Acute/genetics , Oncogene Proteins, Fusion/genetics , Transcription Factor Brn-3A/genetics , Translocation, Genetic , Humans , RUNX1 Translocation Partner 1 ProteinSubject(s)
Alternative Splicing , Chromosomes, Human, Pair 21/genetics , Chromosomes, Human, Pair 8/genetics , Core Binding Factor Alpha 2 Subunit/genetics , Exons/genetics , Leukemia, Myeloid, Acute/genetics , Oncogene Proteins, Fusion/genetics , Translocation, Genetic/genetics , Adolescent , Adult , Aged , Blotting, Western , Clone Cells , Female , Humans , Leukemia, Myeloid, Acute/pathology , Male , Middle Aged , RNA, Messenger/genetics , RNA, Messenger/metabolism , RUNX1 Translocation Partner 1 Protein , Reverse Transcriptase Polymerase Chain Reaction , Tumor Stem Cell Assay , Young AdultABSTRACT
Cell surface expression of CD86 (mCD86) provides an important co-stimulatory signal which profoundly influences immune responses. In this report, we investigated the potential presence of a circulating soluble form of CD86 (sCD86) in normal individuals and patients with acute myeloid leukaemia (AML) or B cell chronic lymphocytic leukaemia (B-CLL). Circulating sCD86 was detected in the plasma of all normal individuals (1.04 +/- 0.33 ng/ml, n = 51) and patients analysed. Plasma collected from AML patients in remission (n = 6) contained only low levels of sCD86 but significantly elevated levels (> or =2.65 ng/ml, P < 0.0001) were detected in 10/24 AML patients analysed at the time of presentation or relapse. Significantly elevated levels of sCD86 were also detected in 2/17 B-CLL patients. There was no correlation between sCD86 levels and other clinical parameters. RT-PCR analysis demonstrated that normal monocytes and dendritic cells, as well as isolated AML (n = 2) and B-CLL (n = 4) cells, expressed an alternatively spliced transcript of CD86 which encoded a soluble form absent in normal T, B and NK cells. The finding that a proportion of leukaemia patients contain elevated levels of sCD86 and that at least some leukaemic cells express sCD86 transcript suggests a potential role for sCD86 in modulating mCD86 signalling during the malignant process.
