Biology subjects

Spaargaren, M.

Publications and source records attributed to Spaargaren, M..

4 recordsLinked to original sources

bioRxiv2026

AID Shapes Proliferation and Cell-of-Origin-associated Transcriptional Programs in Diffuse Large B-cell Lymphoma

Activation-induced cytidine deaminase (AID), which is essential for antibody diversification, exhibits elevated expression in the activated B-cell-like (ABC) subtype of diffuse large B-cell lymphoma (DLBCL). Here, we demonstrate that AID modulates transcriptional programs linked to cell cycle progression, proliferation, and DLBCL subtype identity. AID loss in ABC-type DLBCL cell lines negatively impacts MYC and E2F pathway activity, while AID re-expression restores activity, establishing a causal link. Consequently, loss of AID delays G1/S cell cycle transition and reduces proliferation. In addition, AID expression skews transcriptional programs towards ABC-type DLBCL in cell lines. In agreement, AID expression correlates with ABC-type gene expression in primary DLBCL patient samples. Moreover, AID overexpression resulted in increased IRF4 protein levels, and enhanced NF-{kappa}B activity, supporting AIDs role in reinforcing the ABC-type identity. Shared enrichment of the IRF4 co-factor BATF in AID-high tumors of both ABC- and GCB-subtypes points towards a common mechanism driving subtype skewing. These findings underscore a broader role for AID in DLBCL pathogenesis, establishing AID as a key regulator of transcriptional programs linked to cell cycle progression and DLBCL subtype.

cancer biology↗

bioRxiv2024

Disruption of basal CXCR4 oligomers impairs oncogenic properties in lymphoid neoplasms

The chemokine receptor CXCR4 is overexpressed in many cancers and contributes to pathogenesis, disease progression, and resistance to therapies. CXCR4 is known to form oligomers, but the potential functional relevance in malignancies remain elusive. Using a newly established nanobody-based BRET method, we demonstrate that oligomerization of endogenous CXCR4 on lymphoid cancer cell lines correlates with enhanced expression levels. Specific disruption of CXCR4 oligomers reduced basal cell migration and pro-survival signaling via changes in the phosphoproteome, indicating the existence of basal CXCR4-oligomer-mediated signaling. Oligomer disruption also inhibited growth of primary CLL 3D spheroids and sensitized primary malignant cells to clinically used Bcl-2 inhibitor venetoclax. Given its limited efficacy in some patients and the ability to develop resistance, sensitizing malignant B-cells to venetoclax is of clinical relevance. Taken together, we established a new, non-canonical and critical role for CXCR4 oligomers in lymphoid neoplasms and demonstrated that selective targeting thereof has clinical potential. Significance statementClass A GPCRs, including the chemokine receptor CXCR4, can form oligomers, but their functional relevance remains poorly understood. This study provides evidence for the role of basal CXCR4 oligomers in lymphoid neoplasms, where they drive pro-survival signaling, migration, and tumor growth. We use a novel nanobody-based BRET method to demonstrate that endogenous CXCR4 constitutively oligomerizes in lymphoid cancer cells, correlating with receptor expression levels. Pharmacological disruption of these oligomers reduces tumor- associated signaling, impairs spheroid growth, and sensitizes patient-derived malignant cells to the apoptosis-inducing drug Venetoclax. Since CXCR4 is frequently overexpressed and potentially clustered in various malignancies, this work offers broader implications for enhancing treatment efficacy, overcoming drug resistance, and potentially reducing side effects across multiple cancer types.

biochemistry↗

bioRxiv2020

The CXCL12gamma chemokine immobilized by heparan sulfate on stromal niche cells controls adhesion and mediates drug resistance in multiple myeloma

The homing/retention, survival and proliferation of multiple myeloma (MM) cells critically depends on interaction with CXCL12 expressing stromal cells in the bone marrow (BM) niche. Here, we report a unique role in this interaction for the recently characterized CXCL12gamma isoform, which contains an extended C-terminal domain that binds heparan-sulfate proteoglycans (HSPGs) with an extraordinary high affinity. We observed that CXCL12{gamma} is expressed in situ by reticular stromal cells in both normal and MM BM, as well as by primary BM stromal-cell (BMSC) isolates and BMSC lines. Importantly, upon secretion, CXCL12{gamma}, unlike the CXCL12 isoform, was retained on the surface of these BMSCs. This membrane retention of CXCL12{gamma} is HSPG-mediated, since it was completely annulated by CRISPR-Cas9 mediated deletion of the heparan-sulfate (HS) co-polymerase EXT1. Recombinant CXCL12{gamma} was found to induce strong adhesion of MM cells to vascular cell-adhesion molecule 1 (VCAM-1) coated plates. Furthermore, CXCL12{gamma} expressed by BMSCs and membrane-retained by HSPGs, supported robust adhesion of MM cells to the BMSCs. Specific genetic deletion of either CXCL12{gamma} or of EXT1 significantly attenuated the ability of BMSCs to support MM cell adhesion and, in addition, impaired their capacity to protect MM cells from bortezomib-induced cell death. Our data indicate that CXCL12{gamma} functions as a membrane-bound niche chemokine, which plays a unique role in the interaction of MM cells with the stromal niche by controlling adhesion/retention as well as cell adhesion-mediated drug resistance (CAM-DR). These findings designate CXCL12{gamma} and associated HSPGs as potential therapeutic targets in MM.

cancer biology↗

bioRxiv2019

Targeting AKT elicits tumor suppressive functions of FOXO transcription factors and GSK3 kinase in Multiple Myeloma

The phosphatidylinositide-3 kinases (PI3K) and the downstream mediator AKT drive survival and proliferation of multiple myeloma (MM) cells and several AKT inhibitors are currently being tested in clinical trials for MM patients. AKT inhibition has pleiotropic effects, and the key aspects that determine therapeutic efficacy are not fully clear. Therefore, we investigated the antimyeloma mechanism(s) of AKT inhibition. Among the various downstream AKT targets are Forkhead box O (FOXO) transcription factors, and we demonstrate that they are crucial for changes in gene expression upon AKT inhibition. Based on gene expression profiling we defined an AKT-induced FOXO-dependent gene set that has prognostic significance in a large cohort of MM patients, where low FOXO activity correlates with inferior survival. We show that cell cycle exit and cell death of MM cells after AKT inhibition required FOXO. In addition, glycogen synthase kinase 3 (GSK3), a negatively regulated AKT substrate, proved to be pivotal to induce cell death and to inhibit cell cycle progression after AKT inhibition. Finally, we demonstrate that FOXO and GSK3 induced cell death by increasing the turnover of the myeloid cell leukemia 1 (MCL1) protein. In concordance, the AKT inhibitor MK2206 greatly sensitized MM cells for the MCL1 inhibitor S63845. Thus, our results indicate that FOXO and GSK3 are crucial mediators of the antimyeloma effects of AKT inhibition, and suggest combination therapies that may have therapeutic potential in MM.\n\nKEYPOINTSO_LIFOXO transcription factors and the GSK3 kinase are pivotal tumor suppressors downstream of AKT inhibition in MM cells.\nC_LIO_LIFOXO and GSK3 activation after AKT inhibition leads to a decrease in MCL1 levels in MM cells resulting in cell death.\nC_LI

cancer biology↗