Submitted May 23, 2006
Accepted December 9, 2006
A novel PAX5-ELN fusion protein identified in B-cell acute lymphoblastic leukemia acts as a dominant negative on the wild type PAX5
Marina Bousquet, Cyril Broccardo, Cathy Quelen, Fabienne Meggetto, Emilienne Kuhlein, Georges Delsol, Nicole Dastugue, and Pierre Brousset*
Inserm U 563, Centre de physiopathologie de Toulouse Purpan, Toulouse, France
University Paul Sabatier, Toulouse, France
Laboratoire d'Anatomie Pathologique, CHU Purpan, Toulouse, France
* Corresponding author; email: brousset.p{at}chu-toulouse.fr.
We report a novel t(7;9)(q11;p13) translocation in two cases of 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's 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 co-transfected 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, 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 of PAX5 haploinsufficiency.
