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The B-cell receptor confers super competitor status to lymphoma cells via GSK3β inhibition I

ABSTRACT: 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE97132 | GEO | 2017/04/11

SECONDARY ACCESSION(S): PRJNA380788

REPOSITORIES: GEO

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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+), BCR-negative (BCR-) and BCR-independent lymphoma cells co-cultured for four days in presence or absence of GSK3b inhibitor, CHIR99021. This data was used to a) identify genes regulated by the BCR through GSK3b inhibition, and b) identify genes that confers BCR-independency to lymphoma variants resistant to BCR loss.

Project description:The B cell receptor (BCR) signaling, required for the survival and maturation of B cells, is a major deregulated pathway in B cell lymphomas. Several mutations are known to enhance the tonic BCR signal in Burkitt lymphomas (BL) or to mimic an activated receptor in some diffuse large B cell lymphomas (DLBCL). While the proximal events and kinases of the BCR signaling are well studied, less is known about the interactions of downstream effector pathways. In order to reach a less abstract description of this pathway we decided to employ the Modular Response Analysis-based modelling approach STASNet on more directly connected phosphorylation data. Using a Luminex proteomics platform we measured the phosphorylation of fourteen signaling and effector proteins after activating the B cell receptor (BCR) signaling and/or using inhibitors directed against seven intracellular signaling molecules in two independent Burkitt lymphoma cells (BL-2, BL-41). Application of a novel two step STASNet modelling pipeline unveiled novel feedback and crosstalk structures in the BCR-driven signaling network, including a crosstalk from p38 which negatively regulates MEK/ERK-activity in the presence of active BCR. Using Western Blot measurements, we verified and further characterized the p38-MEK/ERK crosstalk and demonstrated that it is a general mechanism in BL cells. Global Tandem Mass Tag (TMT) phosphoproteomic analysis on BL-2 cells found PI3K to be a major mediator of B-cell receptor signaling and manifested the p38-ERK crosstalk directly on ERK phosphosites and indirectly on seven bona fide ERK targets. We also noticed that the BL-2-learned pathway network structure was transferable to perturbation data from closely related BL-41 cells. Moreover, - compared to a literature-derived network - the BL-2-developed predictive pathway proved also to be a better starting point for network development in cells with aberrant BCR signaling in two representative cell lines derived from Diffuse large B cells (HBL-1, OCI-LY3). This indicates that models trained on activated B-cells are highly informative to be transferred to closely related cancer signaling network.

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The B-cell receptor confers super competitor status to lymphoma cells via GSK3β inhibition I

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