A novel PAX5-ELN fusion protein identified in B-cell acute lymphoblastic leukemia acts as a dominant negative on wild-type PAX5

Abstract

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 ( IntroductionPAX5 is a member of the highly conserved paired-box (PAX) domain family of transcription factors. The PAX5 gene plays an important role in both cell differentiation as well as in embryonic development, and is located on chromosome 9p13. 1 This locus contains 2 distinct promoters, resulting in 2 alternative 5Ј exons (1a and 1b). 2 PAX5b is transcribed in the central nervous system and testis as well as in the B-lymphoid lineage, while PAX5a, also named B-cell-specific activator protein (BSAP), is specifically transcribed in the lymphoid lineage. PAX5a/BSAP is expressed from early stages of B-cell development up to mature B cells and is down-regulated during terminal differentiation into plasma cells. 3 In bone marrow of Pax5 Ϫ/Ϫ mice, B lymphopoiesis is completely arrested at the pro-B stage, revealing the essential role of this gene in early B-cell lymphopoiesis. 4 PAX5-binding sites have been identified in the regulatory sequences of a number of genes, including CD19, 5 BLK, 6 BLNK, 7 MB1 (Ig␣), N-myc, LEF1, 8 and RAG2. 9 PAX5 can act as an activator or a repressor of transcription. It has been shown to activate CD19, N-myc, MB1, and LEF1 expression and to repress PD-1 transcription. 8 PAX5 plays an essential role in B-cell lineage commitment by suppressing alternative lineage choices. [10][11][12] Indeed, it represses the transcription of Notch1, which is necessary for the commitment of lymphoid progenitors to the T-cell pathway, 13 and the transcription of M-CSFR, thus rendering B-cell precursors unresponsive to the myeloid cytokines such as macrophage colony-stimulating factor (M-CSF). 12 Chromosomal translocations involving the PAX5 gene have been described in different types of B-cell malignancies. The t(9;14)(p13;q32) translocation in B-cell non-Hodgkin lymphoma results in juxtaposition of the complete coding sequence of PAX5 to the IGH gene cluster, and leads to elevated PAX5 expression. 14,15 Moreover, PAX5 is involved in the chimeric transcript PAX5-ETV6 in patients with B-cell acute lymphoblastic leukemia (B-ALL) who have a dic(9;12)(p13;p13) translocation. 16,17 The latter fusion protein retains the paired-box domain of PAX5 fused to the helix-loop-helix and DNA-binding domain of ETV6. In this case, the chimeric protein most probably acts as an aberrant transcription factor. 17 The paired box is a DNA-binding domain that is highly conserved during evolution in all PAX genes. [18][19][20] This domain is conserved in all fusion transcripts involving a PAX gene, including PAX5-ETV6 and others described, such as PAX3-FKHR 21 and PAX8-PPARG1. 22 PAX5 also contains a conserved octapeptide motif and a partial homeodomain. The C-terminal region contains a transcriptional activation domain, and the extreme C-terminal region acts as a repr...

Cloning of genes involved in chromosomal translocations by high-resolution single nucleotide polymorphism genomic microarray

“…Their data also showed that PAX5 fusion products suppressed transcriptional activity of PAX5 in a dominant-negative fashion (23). In addition, other researcher have reported PAX5 fusion genes, including PAX5 fused to ETV6 (12p13) (23,24), FOXP1 (3p14) (23), ZNF521 (18q11) (23), ELN (7q11.23) (25), and PML (15q24) (26). We have found PAX5 fused to either ETV6, FOXP1, C20orf112 (20q11), or AUTS2 (7q11.22).…”

Genome-wide profiling of genetic alterations in acute lymphoblastic leukemia: recent insights and future directions

“…Subsequent studies have identified additional PAX5 fusions in ALL, involving multiple partner genes including ASXL1, AUTS2, BRD1, C20orf112, DACH1, ELN, HIPK1, JAK2, KIF3B, LOC392027, PML, POM121 and SLCO1B3. 47,[63][64][65][66] The overall frequency of PAX5 translocations appears low (B2.6% B-ALL cases), 66 although studies comprehensively examining PAX5 translocation in large B-ALL cohorts are awaited. Genomic resequencing of PAX5 in the St Jude study described above also identified 16 missense, insertion/deletion, splice site and frameshift mutations that clustered in the key DNA-binding and transactivating domains of PAX5.…”

PAX5 mutations occur frequently in adult B-cell progenitor acute lymphoblastic leukemia and PAX5 haploinsufficiency is associated with BCR-ABL1 and TCF3-PBX1 fusion genes: a GRAALL study

“…By contrast, a dominant-negative action was established for PAX5-ELN, 16 PAX5-ETV6 11,12 and PAX5-FOXP1 12 fusions.…”

“…9 On the other hand, PAX5 translocations have also been associated with a block of early B-cell differentiation because the PAX5-ETV6 chimeric protein, product of the dic(9;12)(p13;p13), is associated with B-cell progenitor acute lymphoblastic leukemia (BCP-ALL). 11 Additional PAX5 fusion partner genes have been identified as HIPK1 (chromosomal band 1p13), [12][13][14] LOC392027 (7p12.1), 15 AUTS2 (7q11.1), 13 POM121 (7q11), 14 ELN (7q11), 16 JAK2 (9p24), 14 SLCO1B3 (12p12), 15 DACH1 (13q21), 14 PML (15q24), 17 ZNF521 (18q11.2), 12 ASXL1 (20q11.1), 15 C20orf112 (20q11.1), [13][14][15] KIF3B (20q11.21) 15 and BRD1 (22q13). 14 PAX5-ELN, 16 PAX5-FOXP1 12 and PAX5-ETV6 12 act as constitutive repressors of the remaining PAX5 allele product, explaining the block of B-cell differentiation.…”

“…Eleven patients showed a rearrangement of the 9p13 chromosomal band (patients 49490, 49833; 41756; 62902; 66590; 114117, 144051, 144948, 196712, 301228 and 391099) and in a single case (patient 41756: 46,XY,t(7;9)(q21;p21)[17]) a translocation which fused PAX5 and ELN without loss of the remaining normal allele, was detected. 16 Thus PAX5 translocations occur in adult BCP-ALL but are a rare event (o1%). …”