@article{Philip J. Brown_Duncan M. Gascoyne_Linden Lyne_Hayley Spearman_Suet Ling Felce_Nora McFadden_Probir Chakravarty_Sharon Barrans_Steven Lynham_Dinis P. Calado_Malcolm Ward_Alison H. Banham_2016, place={Pavia, Italy}, title={N-terminally truncated FOXP1 protein expression and alternate internal FOXP1 promoter usage in normal and malignant B cells}, volume={101}, url={https://haematologica.org/article/view/7773}, DOI={10.3324/haematol.2016.142141}, abstractNote={Strong FOXP1 protein expression is a poor risk factor in diffuse large B-cell lymphoma and has been linked to an activated B-cell-like subtype, which preferentially expresses short FOXP1 (FOXP1<sub>S</sub>) proteins. However, both short isoform generation and function are incompletely understood. Here we prove by mass spectrometry and N-terminal antibody staining that FOXP1<sub>S</sub> proteins in activated B-cell-like diffuse large B-cell lymphoma are N-terminally truncated. Furthermore, a rare strongly FOXP1-expressing population of normal germinal center B cells lacking the N-terminus of the regular long protein (FOXP1<sub>L</sub>) was identified. Exon-targeted silencing and transcript analyses identified three alternate 5′ non-coding exons [<em>FOXP1-Ex6b(s), FOXP1-Ex7b</em> and <em>FOXP1-Ex7c</em>], downstream of at least two predicted promoters, giving rise to FOXP1<sub>S</sub> proteins. These were differentially controlled by B-cell activation and methylation, conserved in murine lymphoma cells, and significantly correlated with FOXP1<sub>S</sub> protein expression in primary diffuse large B-cell lymphoma samples. Alternatively spliced isoforms lacking exon 9 (e.g. isoform 3) did not encode FOXP1<sub>S</sub>, and an alternate long human FOXP1 protein (FOXP1<sub>AL</sub>) likely generated from a <em>FOXP1-Ex6b(L)</em> transcript was detected. The ratio of FOXP1<sub>L</sub>:FOXP1<sub>S</sub> isoforms correlated with differential expression of plasmacytic differentiation markers in U-2932 subpopulations, and altering this ratio was sufficient to modulate CD19 expression in diffuse large B-cell lymphoma cell lines. Thus, the activity of multiple alternate <em>FOXP1</em&gt; promoters to produce multiple protein isoforms is likely to regulate B-cell maturation.}, number={7}, journal={Haematologica}, author={Philip J. Brown and Duncan M. Gascoyne and Linden Lyne and Hayley Spearman and Suet Ling Felce and Nora McFadden and Probir Chakravarty and Sharon Barrans and Steven Lynham and Dinis P. Calado and Malcolm Ward and Alison H. Banham}, year={2016}, month={Jun.}, pages={861-871} }