The role of ubiquitin-mediated degradation mechanisms in the pathogenesis of diffuse large B-cell lymphoma (BCL) and follicular lymphoma is not completely understood. We show that conditional deletion of the E3 ubiquitin ligase Fbxo45 in germinal center B cells results in B-cell lymphomagenesis in homozygous (100%) and heterozygous (48%) mice. Mechanistically, FBXO45 targets the RHO guanine exchange factor ARHGEF2/GEF-H1 for ubiquitin-mediated degradation. Double genetic ablation of Fbxo45 and Arhgef2 ameliorated lymphoma formation. Transgenic knock-in mice harboring a GEF-H1 mutant unable to bind FBXO45 develop BCLs with ∼50% penetrance. Genome sequencing in human lymphomas identified mutually exclusive FBXO45 copy-number losses and ARHGEF2 gains, with combined frequencies ranging from 26.32% in follicular lymphoma to 45.12% in diffuse large BCL. Notably, FBXO45 silencing enhances sensitivity to MEK1/2 inhibition. These results identify FBXO45 and ARHGEF2 as a novel tumor suppressor and oncogene pair involved in the pathogenesis of BCLs with important implications for targeted therapies.

Significance:

We describe the identification of a previously unrecognized ubiquitin ligase–substrate (FBXO45–GEF-H1) regulatory axis that plays an important role in germinal center formation and pathogenesis of common BCLs. These studies reveal novel insights linking dysregulated ubiquitin-mediated control to exploitable vulnerabilities and novel therapeutic strategies for these cancers.

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©2025 The Authors; Published by the American Association for Cancer Research
2025
American Association for Cancer Research
This open access article is distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) license.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License .
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Supplementary data

Table S1

Supplementary Table S1 shows FBXO45 interactions by immunoprecipitation–tandem mass spectrometry. Normalized Spectral Abundance Factor (NSAF) was calculated as previously published (63). Average NSAFs (n = 3) for the indicated proteins are shown, and the data were obtained from at least three independent experiments.

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Table S2

Supplementary Table S2, Mass spectrometric (MS) identification of GEF-H1-derived peptides in FBXO45 immunoprecipitation. FLAG-tagged FBXO45 expressing B-cell lymphoma cell lines were subjected to immunoprecipitation (IP) with anti-FLAG resin. MS analysis of co-purified endogenous proteins revealed the presence of numerous GEF-H1-derived peptides.

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Table S3

Supplementary Table S3, Quantitative whole proteome analysis of pooled sorted GCB-cells from Fbxo45 homozygous knockout mice compared with identically isolated cells from wild-type littermates.

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Table S4

Supplementary Table S4, Whole genome sequencing of FL, DLBCL and transformed DLBCL reveal loss of FBXO45 as well as copy number gain encompassing ARHGEF2, the gene that encodes GEF H1 protein. Table showing frequency of genomic loss of FBXO45 and gain of ARHGEF2 in DLBCL respectively.

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Table S5

Supplementary Table S5, FISH analysis to identify copy number variations (CNV) affecting genes of interest within the corresponding genomic loci.

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Table S6

Supplementary Table S6, Details of the FISH probes used to identify copy number variations (CNV) affecting FBXO45 and ARHGEF2 in clinical samples.

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Table S7

Supplementary Table S7, Table showing source data and statistics for non-high-throughput experiments such as flow cytometry, quantitative PCR, protein experiments and other molecular and cellular assays.

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Supplementary Figures S1-S13

Supplementary Data file shows all the supplementary figures, figure legends and supplementary table legends.

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