Comparative genomics reveals multistep pathogenesis of E2A-PBX1 acute lymphoblastic leukemia
Jesús Duque-Afonso, Jue Feng, Florian Scherer, Chiou-Hong Lin, Stephen H.K. Wong, Zhong Wang, Masayuki Iwasaki, Michael L. Cleary
Jesús Duque-Afonso, Jue Feng, Florian Scherer, Chiou-Hong Lin, Stephen H.K. Wong, Zhong Wang, Masayuki Iwasaki, Michael L. Cleary
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Research Article Oncology

Comparative genomics reveals multistep pathogenesis of E2A-PBX1 acute lymphoblastic leukemia

Abstract

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer; however, its genetic diversity limits investigation into the molecular pathogenesis of disease and development of therapeutic strategies. Here, we engineered mice that conditionally express the E2A-PBX1 fusion oncogene, which results from chromosomal translocation t(1;19) and is present in 5% to 7% of pediatric ALL cases. The incidence of leukemia in these mice varied from 5% to 50%, dependent on the Cre-driving promoter (Cd19, Mb1, or Mx1) used to induce E2A-PBX1 expression. Two distinct but highly similar subtypes of B cell precursor ALLs that differed by their pre–B cell receptor (pre-BCR) status were induced and displayed maturation arrest at the pro-B/large pre–B II stages of differentiation, similar to human E2A-PBX1 ALL. Somatic activation of E2A-PBX1 in B cell progenitors enhanced self-renewal and led to acquisition of multiple secondary genomic aberrations, including prominent spontaneous loss of Pax5. In preleukemic mice, conditional Pax5 deletion cooperated with E2A-PBX1 to expand progenitor B cell subpopulations, increasing penetrance and shortening leukemia latency. Recurrent secondary activating mutations were detected in key signaling pathways, most notably JAK/STAT, that leukemia cells require for proliferation. These data support conditional E2A-PBX1 mice as a model of human ALL and suggest targeting pre-BCR signaling and JAK kinases as potential therapeutic strategies.

Authors

Jesús Duque-Afonso, Jue Feng, Florian Scherer, Chiou-Hong Lin, Stephen H.K. Wong, Zhong Wang, Masayuki Iwasaki, Michael L. Cleary

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Figure 1

Conditional E2A-PBX1 Tg mice consistently develop leukemia.

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Conditional E2A-PBX1 Tg mice consistently develop leukemia. (A) Schemati...
(A) Schematic representation of WT, targeted, and recombined E2A alleles. Cre-mediated recombination results in deletion of 3′ E2A exons (13, E12, E47, and 16) and the PGK neocassette (neo), fusing in-frame the human PBX1a cDNA linked with EGFP by an IRES element. Cre-recombinase was expressed from the B cell–specific promoter Cd19 or Mb1 (CD79a, Igα), or in HSCs from the Mx1 promoter. (B) Representative Western blots show E2A and E2A-PBX1 protein levels in sorted progenitor B cells from WT (Lin–CD19+CD43+) and healthy preleukemic (Lin–CD19+CD43+GFP+) Tg(E2A-PBX1) Cd19-Cre mice. The ratio of E2A/GAPDH and E2A-PBX1/GAPDH levels (shown below) was determined by densitometry. (C) Kaplan-Meier plots show disease-free survival of conditional E2A-PBX1 mice crossed with the Cre-recombinase lines Cd19 (n = 153), Mb1 (n = 74), and Mx1 (n = 44). The incidence of leukemia at 12 months is shown on the right. (D) Flow cytometric plots show GFP expression in BM cells from a leukemic mouse. (E) May-Grünwald Giemsa staining of peripheral blood smear (PB) and BM cytospin (BM) show leukemic blast morphology. (F) Spleens are shown for representative WT, preleukemic, and leukemic mice (left panel). Graph shows spleen weights from WT (n = 11), healthy E2A-PBX1 preleukemic (n = 42), and leukemic (n = 35) mice (horizontal bars denote the mean) (right panel). (G) Hematologic findings at leukemia presentation (n = 8). Gray shadows represent normal reference values; horizontal bars denote the mean for the analyzed mice. Hgb, hemoglobin; Plt, platelets, wbc, white blood cells.