Project description:UNLABELLED:Genetic lesions such as BCR-ABL1, E2A-PBX1, and MLL rearrangements (MLLr) are associated with unfavorable outcomes in adult B-cell precursor acute lymphoblastic leukemia (B-ALL). Leukemia oncoproteins may directly or indirectly disrupt cytosine methylation patterning to mediate the malignant phenotype. We postulated that DNA methylation signatures in these aggressive B-ALLs would point toward disease mechanisms and useful biomarkers and therapeutic targets. We therefore conducted DNA methylation and gene expression profiling on a cohort of 215 adult patients with B-ALL enrolled in a single phase III clinical trial (ECOG E2993) and normal control B cells. In BCR-ABL1-positive B-ALLs, aberrant cytosine methylation patterning centered around a cytokine network defined by hypomethylation and overexpression of IL2RA(CD25). The E2993 trial clinical data showed that CD25 expression was strongly associated with a poor outcome in patients with ALL regardless of BCR-ABL1 status, suggesting CD25 as a novel prognostic biomarker for risk stratification in B-ALLs. In E2A-PBX1-positive B-ALLs, aberrant DNA methylation patterning was strongly associated with direct fusion protein binding as shown by the E2A-PBX1 chromatin immunoprecipitation (ChIP) sequencing (ChIP-seq), suggesting that E2A-PBX1 fusion protein directly remodels the epigenome to impose an aggressive B-ALL phenotype. MLLr B-ALL featured prominent cytosine hypomethylation, which was linked with MLL fusion protein binding, H3K79 dimethylation, and transcriptional upregulation, affecting a set of known and newly identified MLL fusion direct targets with oncogenic activity such as FLT3 and BCL6. Notably, BCL6 blockade or loss of function suppressed proliferation and survival of MLLr leukemia cells, suggesting BCL6-targeted therapy as a new therapeutic strategy for MLLr B-ALLs. SIGNIFICANCE:We conducted the first integrative epigenomic study in adult B-ALLs, as a correlative study to the ECOG E2993 phase III clinical trial. This study links for the first time the direct actions of oncogenic fusion proteins with disruption of epigenetic regulation mediated by cytosine methylation. We identify a novel clinically actionable biomarker in B-ALLs: IL2RA (CD25), which is linked with BCR-ABL1 and an inflammatory signaling network associated with chemotherapy resistance. We show that BCL6 is a novel MLL fusion protein target that is required to maintain the proliferation and survival of primary human adult MLLr cells and provide the basis for a clinical trial with BCL6 inhibitors for patients with MLLr.

Project description:Glucocorticoids (GCs) are a mainstay of contemporary, multi-drug chemotherapy in the treatment of acute lymphoblastic leukemia (ALL). Although overall survival rates of childhood ALL have improved, resistance to antileukemic agents remains a major clinical concern. In particular, resistance to GCs is predictive of ALL relapse and poor clinical outcome, and it therefore represents a major hurdle limiting further improvements in survival rates. While advances have been made in identifying genes and transcriptional signatures implicated in ALL GC resistance, there remains an insufficient understanding of the impact of glucocorticoid response element (GRE) alterations in GC resistance. To therefore better understand the role of gene regulatory alterations in GC resistance, we comprehensively mapped the GC gene regulatory network in two ALL cell lines using orthogonal functional genomic assays and identified tens of thousands of GREs in the ALL genome. A closer examination revealed binding profiles that were consistent with the long-range flexible billboard model of gene regulation. GCs also induced the formation of over 250 super-enhancers, and these GC-responsive super-enhancers control the expression of genes mediating GC resistance. By further integrating our results with genetic and epigenetic data in primary ALL cells from patient cohorts at St. Jude, we identified 45 DNA sequence variants associated with ex vivo GC resistance that map to GREs and validated an associated variant within the TLE1 gene locus. We also uncovered that 1929 accessible chromatin sites associated with ex vivo GC resistance were significantly enriched at GREs. A CRISPR interference screen of these elements validated their effects on GC resistance. Overall, these data suggest that GCs initiate pervasive, genome-wide effects on the leukemia epigenome and transcriptome, while genetic and epigenetic alterations to GREs are mechanisms contributing to GC resistance in childhood ALL.

Dataset Information

Epigenomic profiling of glucocorticoid responses identifies cis-regulatory disruptions impacting steroid resistance in childhood acute lymphoblastic leukemia.

Publications

Epigenomic profiling of glucocorticoid responses identifies cis-regulatory disruptions impacting steroid resistance in childhood acute lymphoblastic leukemia.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets