ABCB1 over-expression and drug-efflux in acute lymphoblastic leukemia cell lines with t(17;19) and E2A-HLF expression.
BACKGROUND
The t(17;19)(q21;p13), which occurs in a small subset of acute lymphoblastic leukemias (ALLs) and is associated with a dismal prognosis, creates a chimeric E2A-HLF transcription factor with transforming properties.


METHODS
We used representational difference analysis to identify candidate E2A-HLF target genes. Transient transfection assays and an inducible expression model system were then used to evaluate the ability of E2A-HLF to modulate target gene expression.


RESULTS
We identified ABCB1 (MDR1, P-glycoprotein) as a gene differentially expressed in ALL cell lines with and without E2A-HLF expression and demonstrated that t(17;19)+ ALL cell lines expressed high levels of ABCB1 protein and had a drug efflux-positive phenotype. Although ABCB1 transcription is regulated by C/EBPbeta via interaction with a DNA response element that shares significant homology with the optimal E2A-HLF binding site, E2A-HLF did not directly activate transcription of reporter genes under control of ABCB1 promoter elements in transient transfection assays. However, ABCB1 expression was induced in a DNA-binding independent manner by E2A-HLF, E2A-PBX1, and truncated E2A polypeptides consisting of those portions of E2A present in leukemic fusion proteins.


CONCLUSIONS
E2A-HLF-mediated over-expression of ABCB1 may play a critical role in defining the clinical phenotype of ALLs with a t(17;19), suggesting pharmacologic modulation of ABCB1 activity as a rational therapeutic strategy for this chemotherapy resistant subtype of ALL.
Baudis
Michael
M
Department of Pediatrics, University of Florida College of Medicine and the University of Florida Shands Cancer Center, Gainesville, FL 32610-0296, USA.
Prima
Victor
V
Tung
Yoon Han
YH
Hunger
Stephen P
SP
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001665:Binding Sites; D001693:Biological Transport, Active / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D002886:Chromosomes, Human, Pair 17 / Q000235:genetics*; D002888:Chromosomes, Human, Pair 19 / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D015514:Oncogene Proteins, Fusion / Q000096:biosynthesis / Q000235:genetics*; D027361:Organic Anion Transporters / Q000187:drug effects / Q000235:genetics*; D010641:Phenotype; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism; D011379:Prognosis; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D012235:Rhodamines / Q000493:pharmacokinetics; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D014158:Transcription, Genetic; D014178:Translocation, Genetic
C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004268:DNA-Binding Proteins; C076554:E2a-Hlf fusion protein, human; D015514:Oncogene Proteins, Fusion; D027361:Organic Anion Transporters; D012333:RNA, Messenger; D012235:Rhodamines; D014157:Transcription Factors