GSE50514
Non-IG Aberrations of FOXP1 in B-Cell Malignancies Lead to an Aberrant Expression of N-Truncated Isoforms of FOXP1
The transcription factor FOXP1 is implicated in the pathogenesis of B-cell lymphomas through immunoglobulin heavy chain (IGH) locus-related chromosomal translocations leading to dysregulated expression of FOXP1. Translocations of FOXP1 with non-IG gene sequences have been also reported, but the molecular consequences of such aberrations remain undetermined. Here, using molecular cytogenetics and molecular biology studies, we comprehensively analyzed four lymphoma cases with non-IG rearrangements of FOXP1 and compared these with cases harboring t(3;14)(p13;q32)/IGH-FOXP1 and FOXP1-expressing lymphomas without underlying t(3p13/FOXP1). We found that non-IG rearrangements are usually acquired during evolution of lymphoma and constantly target the coding region of FOXP1, promiscuously fusing with coding and non-coding gene sequences at various reciprocal breakpoints (2q36, 10q24 and 3q11). Intriguingly, these rearrangements do not generate functional chimeric genes but commonly disrupt the full-length FOXP1 transcript leading to an aberrant expression of N-truncated FOXP1 isoforms, as shown by QRT-PCR and Western blot analysis. In contrast, cases with t(3;14)(p13;q32)/IGH-FOXP1 overexpress the full-length FOXP1. Collectively, our findings point to a dual mechanism through which FOXP1 is implicated in B-cell lymphomagenesis. The primary t(3;14)(p13;q32)/IGH-FOXP1 produces the full-length protein with potent oncogenic activity, whereas the secondary non-IG 17 rearrangements of FOXP1 generate N-truncated FOXP1 isoforms, likely driving progression of disease. Overall design: Using molecular cytogenetics and molecular biology studies (including RNA-seq), we comprehensively analyzed four lymphoma cases with non-IG rearrangements of FOXP1 and compared these with cases harboring t(3;14)(p13;q32)/IGH-FOXP1 and FOXP1-expressing lymphomas without underlying t(3p13/FOXP1).