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Molecular and Cellular Biology, June 1999, p. 4443-4451, Vol. 19, No. 6
Department of Pathology, Stanford University
Medical Center, Stanford, California 94305
Received 24 November 1998/Returned for modification 4 February
1999/Accepted 10 March 1999
The hepatic leukemia factor (HLF) gene codes for a
basic region-leucine zipper (bZIP) protein that is disrupted by
chromosomal translocations in a subset of pediatric acute lymphoblastic
leukemias. HLF undergoes fusions with the E2A
gene, resulting in chimeric E2a-Hlf proteins containing the E2a
transactivation domains and the Hlf bZIP DNA binding and dimerization
motifs. To investigate the in vivo role of this chimeric bZIP protein
in oncogenic transformation, its expression was directed to the
lymphoid compartments of transgenic mice. Within the thymus, E2a-Hlf
induced profound hypoplasia, premature involution, and progressive
accumulation of a T-lineage precursor population arrested at an early
stage of maturation. In the spleen, mature T cells were present but in
reduced numbers, and they lacked expression of the transgene,
suggesting further that E2a-Hlf expression was incompatible with T-cell
differentiation. In contrast, mature splenic B cells expressed E2a-Hlf
but at lower levels and without apparent adverse or beneficial effects
on their survival. Approximately 60% of E2A-HLF mice
developed lymphoid malignancies with a mean latency of 10 months.
Tumors were monoclonal, consistent with a requirement for secondary
genetic events, and displayed phenotypes of either mid-thymocytes or,
rarely, B-cell progenitors. We conclude that E2a-Hlf disrupts the
differentiation of T-lymphoid progenitors in vivo, leading to profound
postnatal thymic depletion and rendering B- and T-cell progenitors
susceptible to malignant transformation.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Disrupted Differentiation and Oncogenic
Transformation of Lymphoid Progenitors in E2A-HLF
Transgenic Mice
*
Corresponding author. Mailing address: Department of
Pathology, Stanford University Medical Center, Stanford, CA 94305. Phone: (650) 723-5471. Fax: (650) 498-6222. E-mail:
michael.cleary{at}stanford.edu.
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