Chimeric oncoprotein E2a-Pbx1 induces apoptosis of hematopoietic cells by a p53-independent mechanism that is suppressed by Bcl-2.
The chimeric oncoprotein E2a-Pbx1 results from fusion of the E2A and PBX1 genes following t(1;19) chromosomal translocations in B cell precursor acute leukemias. Experimentally B cell progenitors do not tolerate constitutive expression of E2a-Pbx1 which contrasts with transformation of several other cell types following its stable expression both in vitro and in vivo. To further investigate the effects of E2a-Pbx1 on the B cell progenitors, we conditionally expressed E2a-Pbx1 under control of a metal response element in hematopoietic precursor cell lines in vitro. Inducible expression of E2a-Pbx1 resulted in cell death with the morphologic and molecular features of apoptosis. A structure-function analysis demonstrated that induction of apoptosis was not a dominant-negative effect of the E2a moiety but, rather, required the DNA-binding homeodomain of Pbx1. E2a-Pbx1-induced apoptosis proceeded through a BCL2-responsive checkpoint eventuating in PARP inactivation but did require p53. Constitutive expression of E2a-Pbx1 did not induce apoptosis or continued cycling of Rat-1 fibroblasts in low serum conditions. These studies demonstrate that E2a-Pbx1 initiates programmed cell death of hematopoietic precursers by a mechanism that requires its chimeric transcriptional properties, but, unlike other nuclear oncoproteins, is independent of p53.
Smith
K S
KS
Department of Pathology, Stanford University Medical Center, California 94305, USA.
Jacobs
Y
Y
Chang
C P
CP
Cleary
M L
ML
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001402:B-Lymphocytes / Q000166:cytology / Q000502:physiology; D002453:Cell Cycle / Q000502:physiology; D002460:Cell Line; D005347:Fibroblasts / Q000166:cytology; D018922:HL-60 Cells / Q000378:metabolism / Q000502:physiology; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D018398:Homeodomain Proteins / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D006801:Humans; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000502:physiology; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*
D018398:Homeodomain Proteins; D015514:Oncogene Proteins, Fusion; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; C089847:E2A-Pbx1 fusion protein