Disruption of KLHL6 Fuels Oncogenic Antigen Receptor Signaling in B-cell Lymphoma

Pathomechanisms that activate oncogenic B-cell receptor (BCR) signaling in diffuse large B-cell lymphoma (DLBCL), are largely unknown. Kelch-like family member 6 (KLHL6) encoding a substrate-adapter for Cullin-3-RING E3 ubiquitin-ligase (CRL) with poorly established targets is recurrently mutated in DLBCL. By applying high-throughput protein interactome screens and functional characterization, we discovered that KLHL6 regulates BCR by targeting its signaling subunits CD79A and CD79B. Loss of physiological KLHL6 expression pattern was frequent among the MCD/C5-like activated B-cell DLBCLs and was associated with higher CD79B levels and dismal outcome. Mutations in the BTB domain of KLHL6 disrupted its localization and heterodimerization, and increased surface BCR levels and signaling, whereas Kelch domain mutants had the opposite effect. Malfunctions of KLHL6 mutants extended beyond proximal BCR signaling with distinct phenotypes from KLHL6 silencing. Collectively, our findings uncover how recurrent mutations in KLHL6 alter BCR signaling and induce actionable phenotypic characteristics in DLBCL.

Diversity of intratumoral regulatory T cells in B-cell non-Hodgkin lymphoma

Tumor-infiltrating regulatory T cells (Tregs) contribute to an immunosuppressive tumor microenvironment. Despite extensive studies, the prognostic impact of tumor-infiltrating Tregs in B-cell non-Hodgkin lymphomas (B-NHLs) remains unclear. Emerging studies suggest substantial heterogeneity in the phenotypes and suppressive capacities of Tregs, emphasizing the importance of understanding Treg diversity and the need for additional markers to identify highly suppressive Tregs. Here, we applied single-cell RNA sequencing and T-cell receptor sequencing combined with high-dimensional cytometry to decipher the heterogeneity of intratumoral Tregs in diffuse large B-cell lymphoma and follicular lymphoma (FL), compared with that in nonmalignant tonsillar tissue. We identified 3 distinct transcriptional states of Tregs: resting, activated, and unconventional LAG3+FOXP3- Tregs. Activated Tregs were enriched in B-NHL tumors, coexpressed several checkpoint receptors, and had stronger immunosuppressive activity compared with resting Tregs. In FL, activated Tregs were found in closer proximity to CD4+ and CD8+ T cells than other cell types. Furthermore, we used a computational approach to develop unique gene signature matrices, which were used to enumerate each Treg subset in cohorts with bulk gene expression data. In 2 independent FL cohorts, activated Tregs was the major subset, and high abundance was associated with adverse outcome. This study demonstrates that Tregs infiltrating B-NHL tumors are transcriptionally and functionally diverse. Highly immunosuppressive activated Tregs were enriched in tumor tissue but absent in the peripheral blood. Our data suggest that a deeper understanding of Treg heterogeneity in B-NHL could open new paths for rational drug design, facilitating selective targeting to improve antitumor immunity.

What It Takes to Transform a T Cell

The role of fusion genes and cancer driver genes in malignant transformation has traditionally been explored using transgenic or chimeric mouse models. It has been challenging to develop models that fully resemble the characteristics and morphology of human cancers. This applies to anaplastic large-cell lymphoma (ALCL), a malignancy classified as a peripheral T-cell lymphoma. It is still unclear at which stage of T-cell development ALCL can occur, as well as the early molecular events required for malignant transformation. In this issue of Cancer Research, Pawlicki and colleagues introduced the NPM-ALK fusion gene and mutant variants into primary T cells from healthy donors. By monitoring transduced T-cell clones over time, they demonstrated that transformed T cells undergo a progressive loss of T-cell identity accompanied with upregulation of epithelial-to-mesenchymal transition program and reemergence of an immature, thymic profile. Introduction of NPM-ALK was, however, not sufficient to convert healthy T cells to malignant clones, as this process required activation of T-cell receptor signaling. The study sets the stage for modeling early genetic changes in human tumors.See related article by Pawlicki et al., p. 3241.

Calcium Channel Blockers Impair the Antitumor Activity of Anti-CD20 Monoclonal Antibodies by Blocking EGR-1 Induction

Direct cell death induction, in addition to immune-effector cell-mediated mechanisms, is one of the key mechanisms of action of anti-CD20 antibodies, and yet the signaling pathways implicated remain poorly investigated. Here we show that the transcription factor EGR-1 is rapidly induced by anti-CD20 antibodies and is a key mediator for CD20-induced cell death. EGR-1 induction results from an increased calcium influx induced by anti-CD20 antibodies. We show that both rituximab and obinutuzumab induce calcium influx, albeit through different mechanisms, and this influx is crucial for cell death induction. Inhibition of the calcium flux with calcium channel blockers (CCB) abolished EGR-1 induction and impaired the efficacy of anti-CD20 antibodies in preclinical in vitro and in vivo models. Finally, we investigated the impact of CCBs in patients treated with anti-CD20 antibodies included in the clinical trials GOYA and REMARC, and found that patients simultaneously receiving CCBs and anti-CD20 therapy have a shorter progression-free survival and overall survival. These results reveal EGR-1 as a key mediator of the direct cytotoxic activity of anti-CD20 antibodies and provide a rationale to evaluate EGR-1 expression as a new biomarker to predict response to anti-CD20 treatment. In addition, our findings show that calcium influx is required for anti-CD20-mediated tumor cell death and suggest that simultaneous administration of calcium channel blocking agents could be deleterious in patients receiving anti-CD20-based immunotherapy.

Abstract 4594: Induction of apoptosis by anti-CD20 antibodies requires the induction of EGR-1 and calcium influx

Background: Anti-CD20 monoclonal antibodies (mAbs) are an essential component of the treatment of patients with CD20-positive non-Hodgkin's lymphoma and chronic lymphocytic leukemia (CLL). Anti-CD20 mAbs mediate their antitumor effects by activating the immune system or by direct apoptotic signaling in target cells. In a previous preclinical study, we have shown that treatment of B-lymphoma cell lines with anti-CD20 mAbs, rituximab and obinutuzumab, resulted in upregulated expression of the transcription factor early growth factor -1 (EGR-1) (Dalle et al. 2011). However, the role of EGR-1 in response to passive immunotherapies has not been explored so far. Furthermore, EGR-1 has been described as a calcium (Ca2+) regulated transcription factor and CD20 is hypothesized to regulate transmembrane Ca2+ flux. In this study we aim to assess the role of EGR-1 and Ca2+ flux in the cytotoxic activity of anti-CD20 mAbs.

Methods: EGR-1 modulation and cell death induction by anti-CD20 mAbs rituximab and obinutuzumab were investigated in cells expressing endogenous and exogenous CD20. The cytotoxic effect of anti-CD20 mAbs was evaluated in SCID mice and in B-lymphoma cell lines overexpressing EGR-1 or knocked down for EGR-1. The impact of anti-CD20 mAbs on Ca2+ flux was investigated by flow cytometry using Indo-1 AM stained cells. Ca2+ channel blocker agent nifedipine was used to investigate the role of Ca2+ flux on obinutuzumab efficacy.

Results: EGR1 expression is rapidly upregulated in CD20+ cells following rituximab and obinutuzumab exposure. Decreasing EGR-1 expression by shRNA abolished the direct cytotoxic effect of obinutuzumab both in vitro and in vivo, indicating that EGR-1 is required for CD20-mediated apoptosis. Additionally, the overexpression of EGR-1 resulted in enhanced cytotoxic activity of obinutuzumab both in vitro and in vivo. Rescuing EGR-1 expression in EGR-1 knocked-down cells restored sensitivity to obinutuzumab. Moreover, our results indicate that both rituximab and obinutuzumab could induce calcium influx in the presence of suboptimal concentrations of ionomycin. Blocking Ca2+ flux with the calcium channel blocker nifedipine or the Ca2+ chelating agent EGTA abolished EGR-1 induction by anti-CD20 mAbs. In vivo, nifedipine treatment interfered with obinutuzumab antitumor activity against established Granta (a human mantle cell lymphoma line) xenografts in SCID mice.

Conclusion: EGR-1 plays a major role in the direct cytotoxic activity of anti-CD20 monoclonal antibodies and should be evaluated as a new biomarker to predict response to anti-CD20 treatment. Our data also show that calcium channel blockers interfere with the antitumor activity of obinutuzumab in preclinical models.

Citation Format: Ivana Spasevska, Jade Villé, Kamel Chettab, Eva-Laure Matera, Charles Dumontet. Induction of apoptosis by anti-CD20 antibodies requires the induction of EGR-1 and calcium influx [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4594. doi:10.1158/1538-7445.AM2017-4594

Mathematical and computational modeling in biology at multiple scales

A variety of topics are reviewed in the area of mathematical and computational modeling in biology, covering the range of scales from populations of organisms to electrons in atoms. The use of maximum entropy as an inference tool in the fields of biology and drug discovery is discussed. Mathematical and computational methods and models in the areas of epidemiology, cell physiology and cancer are surveyed. The technique of molecular dynamics is covered, with special attention to force fields for protein simulations and methods for the calculation of solvation free energies. The utility of quantum mechanical methods in biophysical and biochemical modeling is explored. The field of computational enzymology is examined.