The forkhead transcription factor FOXP1 profile in B-cells and B-cell lymphoma cell lines

Expression of the forkhead transcription factor FOXP1 is essential for early B cell development, whereas downregulation of FOXP1 at the germinal center (GC) stage is required for GC B cell function. Aberrantly high FOXP1 expression is frequently observed in diffuse large B cell lymphoma (DLBCL) and mucosa-associated lymphoid tissue (MALT) lymphoma, being associated with poor prognosis. Here, by gene expression microarray [GSE51382] and quantitative RT-PCR analysis upon ectopic overexpression of FOXP1 in primary human memory B cells (MBCs) and B-cell lines, combined with chromatin immunoprecipitation-sequencing (ChIP-seq), we established that FOXP1 directly represses expression of PRDM1, IRF4, and XBP1, transcriptional master regulators of plasma cell (PC) differentiation. In accordance, FOXP1 is prominently expressed in primary human naive and MBCs but expression strongly decreases during plasma PC differentiation. Moreover, as compared to IgM+ MBCs, IgG+ MBCs combine lower expression of FOXP1 with an enhanced intrinsic PC differentiation propensity, and constitutive (over)expression of FOXP1 in B cell lines and primary human MBCs represses their ability to differentiate into PCs. Taken together, our data indicate that proper control of FOXP1 expression plays a critical role in PC differentiation, whereas aberrant overexpression of FOXP1 might contribute to lymphomagenesis by blocking terminal B cell differentiation. Overall design: OXP1 ChIP-seq profile in primary human memory B cells (MBCs) and B-cell lines