Abstract B27: B-cell lymphoma response to anti-CD20 antibodies based therapies is tightly modulated by FOXO1-mediated MS4A1 gene transcription
Authors: Zerrouqi Abdessamad , Pyrzynska Beata , Dwojak Michal , Miazek Nina , Zapala Piotr , Golab Jakub , Winiarska Magdalena 
Published: February 2019

Abstract
No remission or early relapse remains a major clinical concern in diffuse large B cell lymphoma (DLBCL) with a third of patients failing to respond to current regimens or relapsing with resistant disease. Genome and transcriptome sequencing studies have identified FOXO1 as one of the recurrent target for somatic mutations in DLBCL associated with patient short survival. These mutations enhance FOXO1 nuclear localization and activity on target genes. Herein, we determine the role FOXO1 (wild type and mutated) on the expression of the rituximabtarget, CD20. The effect of active mutated FOXO1 on CD20 expression was determined upon inhibition of AKT, exogenous expression of active myristolated AKT, and mutated FOXO1 at its N-terminal region. FOXO1 binding activity to CD20 promoter was assessed using various assays combined with an in silico analysis of a publicly available ChipSeq data. Our results show that the activation of FOXO1 using AKT inhibitors (MK2206 and GDC0068) led to a significant decrease of CD20 transcript and protein levels, which resulted in a significant resistance to rituximab mediated complement dependent cytotoxicity (CDC). Consistently, the overexpression of either wild-type or mutated FOXO1 repressed CD20 expression. Unlike the activity of exogenous wild type FOXO1 that can be inhibited by AKT1, the activity of mutated FOXO1AAA (Thr24, Ser256 and Ser319 mutated to Ala and that cannot be phosphorylated) markedly inhibits CD20 expression. Furthermore, CD20 levels remained high and unchanged by the DNA binding defective mutant of FOXO1H215R, suggesting a FOXO1 mediated regulation of CD20 transcription through FOXO1 binding to CD20 promoter, as confirmed by ChIP, EMSA and the analysis of ChIPSeq data using antiFOXO1 antibody. These results show that FOXO1 mutants that are insensitive to AKT1 kinase activity, effectively suppress CD20 expression in comparison to wild type FOXO1, through a binding to CD20 promoter.
In summary, these results establish FOXO1 as an important determinant of cell response to complement-dependent rituximab induced cytotoxicity. In addition, our findings indicate that the genetic status of FOXO1 together with its transcriptional activity need careful attention while designing rituximab-based regimens for the therapy of specific B-lymphomas.
Supported by: National Science Center, Poland (NCN#2013/11/B/NZ5/03240), STREAM project (Horizon 2020,#692180).
Citation Format: Abdessamad Zerrouqi, Beata Pyrzynska, Michal Dwojak, Nina Miazek, Piotr Zapala, Jakub Golab, Magdalena Winiarska. B-cell lymphoma response to anti-CD20 antibodies based therapies is tightly modulated by FOXO1-mediated MS4A1 gene transcription [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr B27.