Human Pax-5 C-terminal isoforms possess distinct transactivation properties and are differentially modulated in normal and malignant B cells.
The transcription factor Pax-5 occupies a central role in B cell differentiation and has been implicated in the development of B cell lymphoma. The transcriptional activation function of Pax-5 requires an intact N-terminal DNA-binding domain and is strongly influenced by the C-terminal transactivation domain. We report the identification and characterization of five human Pax-5 isoforms, which occur through the alternative splicing of exons that encode for the C-terminal transactivation domain. These isoforms arise from the inclusion or exclusion of exon 7, exon 8, and/or exon 9. Three of the Pax-5 isoforms generate novel protein sequences rich in proline, serine, and threonine amino acids that are the hallmarks of transactivation domains. The Pax-5 isoforms are expressed in peripheral blood mononuclear cells, cancerous and non-cancerous B cell lines, as well as in primary B cell lymphoma tissue. Electrophoretic mobility shift assays demonstrate that the isoforms possess specific DNA binding activity and recognize the PAX-5 consensus binding sites. In reporter assays using the CD19 promoter, the transactivation properties of the various isoforms were significantly influenced by the changes in the C-terminal protein sequence. Finally, we demonstrate, for the first time, that human Pax-5 isoform expression is modulated by specific signaling pathways in B lymphocytes.
Robichaud
Gilles A
GA
Institut de Recherche Médicale Beauséjour, Université de Moncton, New Brunswick, Canada.
Nardini
Michel
M
Laflamme
Mark
M
Cuperlovic-Culf
Miroslava
M
Ouellette
Rodney J
RJ
D017398:Alternative Splicing / Q000235:genetics; D001402:B-Lymphocytes / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D015448:Leukemia, B-Cell / Q000378:metabolism*; D008969:Molecular Sequence Data; D051757:PAX5 Transcription Factor; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; D051757:PAX5 Transcription Factor; C497281:PAX5 protein, human; D020033:Protein Isoforms; D014157:Transcription Factors