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CD20 is gatekeeper of human B cell identity and activation state

ABSTRACT: B cell identity and function is dependent on the proteins residing in the B cell surfaceome and their respective nanoscale organization. Here we show that CD20 is a gatekeeper for B cell identity and function due to its control of the functional nanoscale organization of receptors within the B surfaceome and the resting state of B lymphocytes. CRISPR/Cas-based ablation of CD20 in Ramos B cells revealed that IgM class B cell antigen receptor (IgM-BCR) and the co-receptor CD19 are functionally interlinked in the absence of CD20. The resulting IgM-BCR/CD19 signalling synapse leads to transient B cell activation and the loss of B cell identity. Re-expression of CD20 involving an aptamer-controlled riboswitch restores resting-state B cell nanoscale organization and function. Treatment of naive human B cells with the anti-CD20 antibody Rituximab leads to transient B cell activation and formation of transiently activated IgM-BCR/CD19 signalling synapses providing new insights into the molecular mode of action of Rituximab. The loss of B cell identity due to CD20-deficiency is accompanied by a PAX5 to BLIMP-1 transcriptional switch and increased plasma cell development. This cellular B cell differentiation towards plasma B cells is mechanistically accompanied by a metabolic shift towards oxidative phosphorylation.

INSTRUMENT(S): Q Exactive HFX (Thermo Scientific Instrument Model)

ORGANISM(S): Homo Sapiens (ncbitaxon:9606)

SUBMITTER: Bernd Wollscheid

PROVIDER: MSV000085605 | MassIVE | Thu Jun 18 06:38:00 BST 2020

SECONDARY ACCESSION(S): PXD019874

REPOSITORIES: MassIVE

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Project description:Similar to resting mature B cells, where the B-cell antigen receptor (BCR) is essential for cellular survival, surface BCR expression is conserved in most mature B cell lymphomas. The identification of activating BCR mutations and the growth disadvantage upon BCR knockdown of cells of certain lymphoma entities has led to the view that BCR signaling is required for tumour cell survival. Consequently, the BCR signaling machinery has become a new target in the therapy of B cell malignancies. Here, we studied the effects of BCR ablation on MYC-driven mouse B cell lymphomas and compared them to observations in human Burkitt lymphoma. Whereas BCR ablation did not, per se, significantly affect lymphoma growth, BCR-negative (BCR-) tumour cells rapidly disappeared in the presence of their BCR-expressing (BCR+) counterparts in vitro and in vivo. This required neither cellular contact, nor factors released by BCR+ tumour cells. Instead, BCR loss induced the rewiring of central carbon metabolism increasing the sensitivity of receptor-less lymphoma cells to nutrient restriction. The BCR attenuated GSK3β activity to support MYC-controlled gene expression. BCR- tumour cells exhibited increased GSK3β activity and were rescued from their competitive growth disadvantage by GSK3β. BCR-negative lymphoma variants that restored competitive fitness, normalized GSK3β following constitutive activation of the MAPK pathway, commonly through Ras mutations. Similarly, in Burkitt lymphoma, activating RAS mutations may propagate Ig-crippled tumour cells, which usually represent a minority of the tumour bulk. Thus, while BCR expression enhances lymphoma cell fitness, BCR-targeted therapies may profit from combinations with drugs targeting BCR-less tumour cells. In this dataset, we included the expression data obtained from BCR-positive (BCR+) and BCR-negative (BCR-) lymphoma cells co-cultured for 4 days in presence or absence of GSK3b inhibitor, CHIR99021. These data were used to obtain genes that are regulated by the BCR through GSK3b inhibition.

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CD20 is gatekeeper of human B cell identity and activation state

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