A novel PAX5-ELN fusion protein identified in B-cell acute lymphoblastic leukemia acts as a dominant negative on wild-type PAX5.
We report a novel t(7;9)(q11;p13) translocation in 2 patients with B-cell acute lymphoblastic leukemia (B-ALL). By fluorescent in situ hybridization and 3' rapid amplification of cDNA ends, we showed that the paired box domain of PAX5 was fused with the elastin (ELN) gene. After cloning the full-length cDNA of the chimeric gene, confocal microscopy of transfected NIH3T3 cells and Burkitt lymphoma cells (DG75) demonstrated that PAX5-ELN was localized in the nucleus. Chromatin immunoprecipitation clearly indicated that PAX5-ELN retained the capability to bind CD19 and BLK promoter sequences. To analyze the functions of the chimeric protein, HeLa cells were cotransfected with a luc-CD19 construct, pcDNA3-PAX5, and with increasing amounts of pcDNA3-PAX5-ELN. Thus, in vitro, PAX5-ELN was able to block CD19 transcription. Furthermore, real-time quantitative polymerase chain reaction (RQ-PCR) experiments showed that PAX5-ELN was able to affect the transcription of endogenous PAX5 target genes. Since PAX5 is essential for B-cell differentiation, this translocation may account for the blockage of leukemic cells at the pre-B-cell stage. The mechanism involved in this process appears to be, at least in part, through a dominant-negative effect of PAX5-ELN on the wild-type PAX5 in a setting ofPAX5 haploinsufficiency.
Bousquet
Marina
M
INSERM U563, Centre de Physiopathologie de Toulouse Purpan, Place Baylac, 31059 Toulouse Cedex, France.
Broccardo
Cyril
C
Quelen
Cathy
C
Meggetto
Fabienne
F
Kuhlein
Emilienne
E
Delsol
Georges
G
Dastugue
Nicole
N
Brousset
Pierre
P
D000293:Adolescent; D000328:Adult; D000818:Animals; D018941:Antigens, CD19 / Q000096:biosynthesis / Q000235:genetics; D002051:Burkitt Lymphoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002454:Cell Differentiation / Q000235:genetics; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002897:Chromosomes, Human, Pair 7 / Q000235:genetics*; D002899:Chromosomes, Human, Pair 9 / Q000235:genetics*; D004549:Elastin / Q000096:biosynthesis / Q000235:genetics*; D005799:Genes, Dominant; D006367:HeLa Cells; D006801:Humans; D008297:Male; D051379:Mice; D041681:NIH 3T3 Cells; D015514:Oncogene Proteins, Fusion / Q000096:biosynthesis / Q000235:genetics*; D051757:PAX5 Transcription Factor / Q000096:biosynthesis / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics; D014178:Translocation, Genetic
D018941:Antigens, CD19; D015514:Oncogene Proteins, Fusion; D051757:PAX5 Transcription Factor; C497281:PAX5 protein, human; D004549:Elastin