FOXO1 Confers Maintenance of the Dark Zone Proliferation and Survival Program and Can Be Pharmacologically Targeted in Burkitt Lymphoma.

Franziska Gehringer,Stephanie Weissinger,Thomas Wirth,Alexey Ushmorov,Peter Möller,Lotteke Swier

doi:10.3390/cancers11101427

Franziska Gehringer, Stephanie Weissinger + Show 4 more

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https://doi.org/10.3390/cancers11101427

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Journal: Cancers	Publication Date: Sep 25, 2019
Citations: 16	License type: CC BY 4.0

Affiliation: University of Ulm, University of Groningen

Abstract

The FOXO1 transcription factor plays a central role in the proliferation and survival of B cells at several stages of differentiation. B cell malignancies, with exception of classical Hodgkin lymphoma, maintain expression of FOXO1 at levels characteristic for their non-malignant counterparts. Extensive expression profiling had revealed that Burkitt lymphoma (BL) show many characteristics of the dark zone (DZ) germinal center (GC) B cell program. Here we show that FOXO1 knockdown inhibits proliferation of human BL cell lines. The anti-proliferative effect of the FOXO1 knockdown is associated with the repression of the DZ B cell program including expression of MYB, CCND3, RAG2, BACH2, and CXCR4. In addition, the induction of signaling pathways of the light zone (LZ) program like NF-κB and PI3K-AKT was observed. Using a rescue experiment we identified downregulation of the proto-oncogene MYB as a critical factor contributing to the antiproliferative effect of FOXO1 knockdown. In an attempt to estimate the feasibility of pharmacological FOXO1 repression, we found that the small molecular weight FOXO1 inhibitor AS1842856 induces cell death and growth arrest in BL cell lines at low concentrations. Interestingly, we found that overactivation of FOXO1 also induces growth inhibition in BL cell lines, indicating the importance of a tight regulation of FOXO1 activity in BL.

Highlights

Burkitt lymphoma (BL) is an aggressive B cell lymphoma [1] which originates from the germinal center (GC) [2], and is characterized by oncogenic translocations of the proto-oncogene MYC [3].The GC consists of two main histological and functional compartments known as dark zone (DZ)and light zone (LZ)
Since the activity of FOXO transcription factors is regulated by changing the nuclear localization of FOXOs, we used subcellular fractionation (Figure S1A) and immunofluorescent staining of FOXO1 in BL
Given that occasional monoallelic mutations in an N-terminal hotspot were suggested to confer FOXO1 insensitivity to AKT-dependent phosphorylation in BL, we included cell lines harboring both wild type (Ramos, BL-41, Daudi, Raji) and mutated FOXO1 alleles (Namalwa, Jiyoye) (Table S1). Both methods identified a substantial fraction of FOXO1 in the nuclei, independently of its mutational status, supporting a role of active FOXO1 in the oncogenic program of BL

Summary

Introduction

Burkitt lymphoma (BL) is an aggressive B cell lymphoma [1] which originates from the germinal center (GC) [2], and is characterized by oncogenic translocations of the proto-oncogene MYC [3].The GC consists of two main histological and functional compartments known as dark zone (DZ)and light zone (LZ). Burkitt lymphoma (BL) is an aggressive B cell lymphoma [1] which originates from the germinal center (GC) [2], and is characterized by oncogenic translocations of the proto-oncogene MYC [3]. The GC consists of two main histological and functional compartments known as dark zone (DZ). In the DZ, B cells undergo somatic hypermutation and actively proliferate and afterwards move to the LZ where they receive survival signals via the B cell receptor (BCR) and CD40 in case of successful recombination and expression of a high affinity antibody. The DZ gene expression program depends on expression of CCND3 and the transcription factors BCL6, FOXO1, and TCF3. The DZ program is repressed by BCR and CD40 signaling [4] in LZ B cells.

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