Conditional Expression of E2A-HLF Induces B-Cell Precursor Death and Myeloproliferative-Like Disease in Knock-In Mice

[Clinical analysis of 7 cases of acute B cell lymphoblastic leukemia with t (17;19) (q21-22;p13)/TCF3-HLF fusion]

A retrospective analysis of the clinical data of seven acute B-lymphoblastic leukemia (B-ALL) patients with TCF3-HLF fusion gene-positive admitted to the First Affiliated Hospital of Soochow University from June 2017 to August 2022 was conducted to summarize their clinical features and prognoses. The seven B-ALL patients comprised four males and three females, with a median age of 18 (11-33) years. Five patients tested positive for CD33 expression, and four patients had a normal karyotype. Two patients had hypercalcemia at the initial diagnosis, and one patient developed hypercalcemia at relapse. Six patients presented with coagulation dysfunction at diagnosis. After induction chemotherapy, five out of seven patients achieved complete remission, of which four subsequently relapsed. Two patients did not achieve remission even after two rounds of induction chemotherapy, with one achieving complete remission after treatment with blinatumomab immunotherapy. Three patients underwent chimeric antigen receptor T cell therapy, whereas three patients subsequently underwent hematopoietic stem cell transplantation. Five patients died, while two patients survived with sustained complete remission. TCF3-HLF-positive B-ALL is rare and has a high relapse rate and poor prognosis.

Targeting the oncogenic activity of TCF3-HLF in leukemia

The oncogenic fusion transcription factor TCF3-HLF identifies an aggressive subtype of acute lymphoblastic leukemia. TCF3-HLF imposes a malignant program by activation of lineage-specific oncogenic enhancers. Among critical cofactors of the TCF3-HLF complex we identified EP300, which functional inhibition results in potent anti-leukemic activity by interference with the specific gene expression.

The Leukemogenic TCF3-HLF Complex Rewires Enhancers Driving Cellular Identity and Self-Renewal Conferring EP300 Vulnerability

The chimeric transcription factor TCF3-HLF defines an incurable acute lymphoblastic leukemia subtype. Here we decipher the regulome of endogenous TCF3-HLF and dissect its essential transcriptional components and targets by functional genomics. We demonstrate that TCF3-HLF recruits HLF binding sites at hematopoietic stem cell/myeloid lineage associated (super-) enhancers to drive lineage identity and self-renewal. Among direct targets, hijacking an HLF binding site in a MYC enhancer cluster by TCF3-HLF activates a conserved MYC-driven transformation program crucial for leukemia propagation in vivo. TCF3-HLF pioneers the cooperation with ERG and recruits histone acetyltransferase p300 (EP300), conferring susceptibility to EP300 inhibition. Our study provides a framework for targeting driving transcriptional dependencies in this fatal leukemia.

Eya2 is critical for the E2A‑HLF‑mediated immortalization of mouse hematopoietic stem/progenitor cells

The immunoglobulin enhancer‑binding factor/hepatic leukemia factor (E2A‑HLF) oncogenic fusion gene, generated by t(17;19)(q22;p13) translocation in childhood B‑cell acute lymphoblastic leukemia with a very poor prognosis, encodes a chimeric transcription factor in which the transactivation domains of E2A are fused to the DNA‑binding and dimerization domain of HLF. E2A‑HLF has been demonstrated to have an anti‑apoptotic effect. However, the molecular mechanism underlying E2A‑HLF‑mediated leukemogenesis remains unclear. The present study identified EYA transcriptional coactivator and phosphatase 2 (Eya2), the forced expression of which is known to immortalize mouse hematopoietic stem/progenitor cells (HSPCs), as a direct target molecule downstream of E2A‑HLF. E2A‑HLF‑immortalized mouse HSPCs expressed Eya2 at a high level in the aberrant self‑renewal program. Chromatin immunoprecipitation‑quantitative polymerase chain reaction and a reporter assay revealed that E2A‑HLF enhanced the Eya2 expression by binding to the promoter region containing the E2A‑HLF‑binding consensus sequence. Eya2 knockdown in E2A‑HLF‑immortalized cells resulted in reduced colony‑forming efficiency. These results suggest a critical role of Eya2 in E2A‑HLF‑mediated leukemogenesis.

Critical Modulation of Hematopoietic Lineage Fate by Hepatic Leukemia Factor

A gradual restriction in lineage potential of multipotent stem/progenitor cells is a hallmark of adult hematopoiesis, but the underlying molecular events governing these processes remain incompletely understood. Here, we identified robust expression of the leukemia-associated transcription factor hepatic leukemia factor (Hlf) in normal multipotent hematopoietic progenitors, which was rapidly downregulated upon differentiation. Interference with its normal downregulation revealed Hlf as a strong negative regulator of lymphoid development, while remaining compatible with myeloid fates. Reciprocally, we observed rapid lymphoid commitment upon reduced Hlf activity. The arising phenotypes resulted from Hlf binding to active enhancers of myeloid-competent cells, transcriptional induction of myeloid, and ablation of lymphoid gene programs, with Hlf induction of nuclear factor I C (Nfic) as a functionally relevant target gene. Thereby, our studies establish Hlf as a key regulator of the earliest lineage-commitment events at the transition from multipotency to lineage-restricted progeny, with implications for both normal and malignant hematopoiesis.