Biology subjects

Geiger, B.

Publications and source records attributed to Geiger, B..

At least 19 recordsLinked to original sources

bioRxiv2026

Correlation-aware discovery of co-occurring mutational signatures in cancer

Somatic mutations in cancer genomes record the activities of diverse mutational processes. Mutational signature analysis has advanced mechanistic understanding of mutagenesis and informed clinical decision-making, yet existing methods assume independence among signatures--an unrealistic assumption that can produce composite or contaminated signatures, reduce detection power, and yield inconsistent results. Here we present Cornet (CORrelated NMF ExTraction), a framework for mutational signature discovery that explicitly models co-occurring processes and jointly infers signatures and their correlation structure. Benchmarking on simulated data shows Cornet more accurately recovers distinct signatures under strong correlations. Applied to cancer genomes, Cornet enables unsupervised discovery of the colibactin-associated signature SBS88 in oral cancers and identifies the tobacco smoking signature SBS4 in bladder cancer, where it was previously thought absent. Cornet also uncovers a novel mutational process implicated in early-onset colorectal cancer and a signature arising from the interplay between tobacco smoking and ERCC2-mutation-driven nucleotide-excision repair deficiency. Together, these results demonstrate that modeling correlations among mutational processes is essential for high-resolution signature discovery and dissecting the mutational etiology of human cancer.

bioinformatics↗

bioRxiv2026

A Lymphomimetic Synthetic Immune Niche, Consisting of CCL21 and ICAM1, Accelerates the Expansion of Potent CAR T-cells

Background: Chimeric Antigen Receptor (CAR) T-cell therapy has transformed the treatment of hematologic malignancies, yet, its broader clinical application often faces major challenges, including slow expansion rates, variable transduction efficiency, exhaustion, and functional heterogeneity. Recent studies have demonstrated that a Synthetic Immune Niche (SIN) composed of immobilized CCL21 and ICAM1 promotes the proliferation of murine and human T-cells while preserving their cytotoxic potency. In this study, we explored the capacity of immobilized CCL21 and ICAM1 to enhance the production of highly potent CAR T-cells by facilitating both their expansion and cytotoxic capacity. Methods: CD19-directed CAR T-cells were generated from PBMCs of healthy donors using a clinical-grade protocol. Following retroviral transduction, the cells were expanded on CCL21 and ICAM1 coated plates, or on uncoated control plates. The effects of the SIN treatment on CAR T-cell expansion, morphology, physical properties, phenotypic markers, and potency were systematically evaluated. Results: SIN exposure significantly enhanced CAR T-cell expansion, achieving a 9.3-fold higher total cell yield by day 13, compared with control cultures. This proliferative advantage persisted even after withdrawal of the cells from the synthetic niche on day 10. SIN stimulation preferentially expanded the CAR-transduced population, increasing CAR T-cell frequencies from 45.4% to 77.6%, resulting in a 14.6-fold increase in the absolute number of CAR T-cells compared with untreated cultures. Morphological and phenotypic analyses revealed distinct activated cell morphology, manifested by increased cell size, polarity and granularity, and elevated expression of the activation markers CD137 and CD69. Importantly, CAR T-cells transiently exposed to the SIN retained cytokine secretion and cytotoxic activity comparable to that of continuously SIN-treated cells, indicating that the SIN effect is persistent. Overall, SIN-conditioned CAR T-cells displayed robust antigen-dependent IFN-{gamma} secretion and cytotoxicity against CD19-expressing target cells. Conclusion: Stimulation of CAR T-cells with a synthetic immune niche consisting of immobilized CCL21 and ICAM1 enhances overall expansion while selectively enriching the CAR-transduced population, thereby substantially increasing both the number and prominence of therapeutically relevant CAR T-cells. This effect is accompanied by a persistent activation phenotype and high functional potency. We propose that incorporating SIN stimulation into CAR T-cell manufacturing represents a simple and scalable strategy for improving CAR T-cell yield while maintaining high cytotoxic efficacy.

immunology↗

bioRxiv2026

Decoupling T Cell Cytotoxicity: A CCL21+ICAM1-Based Synthetic Immune Niche Enhances Tumor Elimination by Accelerating Lytic Hit Delivery

Preserving T cell cytotoxic function during ex vivo expansion remains a major challenge for adoptive cancer immunotherapy. A synthetic immune niche (SIN) composed of immobilized CCL21 and ICAM1 was shown to improve T cell expansion while preserving cytotoxicity; however, it remains unclear which specific step of the T cell killing process is enhanced by the SIN stimulation. Here, we combined advanced imaging based on time-lapse microscopy with a mean-field model to analyze the distinct stages in killing of B16 melanoma cells by CD8+ T cells. This framework enabled us to resolve the tumor cell killing process into discrete steps throughout target cell engagement with SIN-treated T cells and lytic hit delivery. We found that tumor cell death is best explained by a multi-hit process, requiring approximately four discrete hits to trigger cell death. Model-based analysis identified an increase in the lytic hit delivery as the parameter that best accounts for the enhanced cytotoxicity of SIN-treated T cells, a difference not explained by changes in target encounter frequency or conjugate stability. Global sensitivity analysis further showed that tumor control is more strongly improved by enhancing lytic hit delivery than by increasing target encounter rates. These findings fundamentally reorient our understanding of optimized T cell manufacturing, suggesting that the lytic execution step may be the primary rate-limiting bottleneck in this in-vitro system, and that engineering strategies targeting granule polarization or discharge warrant prioritization alongside affinity-enhancement approaches.

immunology↗

bioRxiv2026

Topographical archetypes of somatic mutagenesis in cancer

The genome of every cancer cell carries a record of the mutational processes that have acted throughout its history. Mutational signature analysis, which infers the activity of mutagenic processes from their characteristic base-change patterns, has become an indispensable tool for interpreting somatic mutations. However, this framework captures only which types of mutations a process generates and not where in the genome they occur -- a distribution influenced by replication timing, chromatin organization, transcription, DNA secondary structure, and other genomic features. Here, we present a generative probabilistic framework (MuTopia) that jointly infers mutational spectra and their genome-wide topography as nonlinear functions of genomic and epigenomic state. Applied to whole-genome sequencing data from 15 tumor types, MuTopia reveals that mutational processes fall into eight conserved topographic archetypes, or topotypes, shaped primarily by replication timing and chromatin state. Diverse mutational processes converge upon this limited repertoire, indicating that the genomic distribution of mutagenesis is constrained less by the source of damage than by how that damage is processed. Individual mutational processes exhibit state-dependent variation in their genomic distributions: the same signature can adopt distinct topotypes depending on repair proficiency and replication stress. For instance, SBS8 shifts from a canonical late-replicating profile in homologous recombination-proficient tumors to an early-replicating, stress-associated topotype in HR-deficient tumors, and replication stress similarly reshapes the genomic distribution of APOBEC editing. Topotypes, therefore, provide a classification of mutagenesis distinct from spectral signatures, capturing aspects of tumor biology that spectra alone cannot resolve.

bioinformatics↗

bioRxiv2025

VASP regulates the polar organization of adhesion-associated actin filaments

Focal adhesions (FAs) are dynamic macromolecular assemblies that anchor the actin cytoskeleton to the extracellular matrix via integrin receptors, thereby regulating cell morphology and migration. Although FA maturation and organization have been extensively studied, it remains unclear how regulatory proteins influence the 3D architecture of FAs. Here, we show that loss of the vasodilator-stimulated phosphoprotein (VASP) impairs adhesion dynamics. We employed CRISPR/Cas9-mediated knockout of VASP and/or the mechanosensitive adaptor protein zyxin to investigate their respective roles in actin-adhesion coupling. Loss of VASP and zyxin correlates with altered FA morphology and impaired dynamics. Using cryo-electron tomography (cryo-ET), we resolved the polarity of individual actin filaments associated with FAs and identified a contractility-related actin layer enriched with tropomyosin. VASP and zyxin are required for the assembly of dense and aligned actin bundles with uniform polarity, oriented with their barbed ends towards the cell edge. In contrast, the tropomyosin-decorated dorsal actin layer remains unaffected by these perturbations. Our findings reveal distinct, layered architectures within FAs and underscore the cooperative role of VASP and zyxin in stabilizing the organization of actin filaments at functional adhesion sites.

cell biology↗

bioRxiv2025

Elevated surface La promotes hyperfusion and contributes to impaired resorption in osteopetrosis.

The skeleton is a living, biological tissue responding to the biomechanical demands placed upon it throughout life. The individual bones creating this physiological system are each shaped by a multinucleated cell type - the osteoclast - that sculpts each bone in collaboration with local cellular partners, which offer chemical and even tactile feedback of many sorts. Unfortunately, the perturbation of osteoclast formation and function underpins a broad range of human skeletal pathologies, including osteopetrosis - a systemic pathology characterized by impaired osteoclast resorption leading to skeletal thickening, brittle bones, frailty, and lethality. Here, we describe a molecular dysfunction observed in murine and human models of two forms of osteoclast-rich, autosomal recessive osteopetrosis, and our approach for exploiting this molecular dysfunction to correct pathologic osteoclast hyperfusion and resorptive impairment. We find that La - a manager of osteoclast fusion and subsequent resorptive activity - is greatly elevated at the surface of osteoclasts upon loss of SNX10 or OSTM1. Using inhibitory antibodies, we suppress excessive La surface function in these mutant osteoclasts, impede osteopetrotic hyperfusion and restore osteoclast resorptive function. We share these observations as proofs-of-principle that osteoclast fusion represents a viable therapeutic target for addressing osteoclast dysfunction in diseases underpinned by excessive osteoclast multinucleation and perturbed resorptive function.

cell biology↗

bioRxiv2025

Actin Networking Collapse Under STAT5A Deficiency Drives Mitochondrial Dysfunction and Autocrine IFN-beta Production

Coordination between actin cytoskeleton networking and mitochondrial organization and health underpins cellular homeostasis. Here, we found STAT5A to be a pivotal transcription factor that sustains the expression of key actin regulators, including ACTN1. STAT5A, but not STAT5B deficiency dismantles F-actin architecture leading to amorphous cell shape, reduced cellular motility, and corrals mitochondria around the nucleus. This actin networking disruption impairs mitochondrial DRP1 recruitment and dynamic equilibrium, leading to ROS-associated DNA damage and cGAS-STING mediated type I IFN production. Consequently, this establishes a chronically IFN-stimulated state in neighboring cells. Conversely, overexpression of STAT5A increases actin cytoskeleton networking and promotes faster cell motility. Moreover, ectopic expression of ACTN1 in the background of STAT5A-knockout cells is sufficient to restore the actin cytoskeleton organization and mitochondrial network morphology, eliminating DNA damage and IFN-signaling. Giving the importance of actin in cellular homeostasis, our findings place actin abundance, as regulated by the STAT5A-ACTN1 axis as essential for linking cytoskeletal integrity with mitochondrial health, restraining aberrant innate immune activation. Graphic Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=172 SRC="FIGDIR/small/656095v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@1cee57aorg.highwire.dtl.DTLVardef@3be0cdorg.highwire.dtl.DTLVardef@123ed52org.highwire.dtl.DTLVardef@1b1bfcc_HPS_FORMAT_FIGEXP M_FIG C_FIG Key pointsSTAT5A deficiency disrupts cytoskeletal integrity via ACTN1 loss. The disrupted actin-cytoskeleton impairs mitochondria organization, causing ROS production and DNA damage. STAT5A knockout activates cGAS-STING signaling and IFN-{beta} production. Restoring ACTN1 rescues cytoskeleton, mitochondrial function, and immune balance.

cell biology↗

bioRxiv2025

The molecular and cellular interplay between the osteopetrosis-associated proteins SNX10, OSTM1, and CLC-7 during osteoclastogenesis

Bone-resorbing osteoclasts (OCLs) are large, multi-nucleated cells that are formed through well-regulated differentiation and cell fusion of monocyte-macrophage precursors. Disruption of OCL-mediated bone resorption perturbs bone formation, remodeling, and homeostasis that, in turn, can lead to severe illnesses, such as autosomal recessive osteopetrosis (ARO). Mutations in the intracellular trafficking-associated protein sorting nexin 10 (SNX10) lead to "OCL-rich" ARO, in which OCLs are produced but are inactive. Furthermore, OCL fusion is deregulated in SNX10-knockout (SKO) mice: mature mutant OCLs fuse continuously to generate gigantic cells, in vitro and in vivo, unlike wild-type OCLs that stop fusing with each other upon maturation. Mutations in CLC-7, the lysosomal voltage-gated Cl-/H+ exchanger, and OSTM1, the beta-chain of the exchanger, also induce ARO in humans and in mouse models, and are associated with the presence of large OCLs. This study explored the molecular interplay between SNX10, CLC-7 and OSTM1 by directly comparing the phenotypes of cultured OCLs lacking one of these proteins. We show that loss of SNX10, OSTM1, or CLC-7 leads to the formation of similarly-gigantic OCLs in culture, due to deregulated fusion between mature OCLs that proceeds with similar kinetics. All three proteins are associated with LAMP1-positive lysosomes, localized in both perinuclear and peripheral regions of mature wild-type OCLs. Co-immunoprecipitation studies indicated that SNX10 physically interacts with CLC-7. Notably, SNX10-KO OCLs exhibited a significant reduction in peripheral lysosomes containing CLC-7 and OSTM1, suggesting that SNX10 is required for their transport to the cell periphery. Taken together, these findings indicate that SNX10 regulates the subcellular distribution of lysosomes containing CLC-7 and OSTM1, thereby controlling both the fusion and functionality of mature OCLs.

cell biology↗

bioRxiv2025

Differential effects of immobilized CCL21 and ICAM1 on TILs with distinct expansion properties

Adoptive T cell therapy (ACT), particularly tumor-infiltrating lymphocyte (TIL), holds great promise for cancer treatment, yet it still faces major challenges such as variability in expansion rates, cytotoxic potency and immune suppression. Recent studies suggest that a "synthetic immune niche" (SIN), composed of immobilized CCL21 and ICAM-1, enhances both the expansion and cytotoxicity of murine and patient-derived T cells. Here, we investigate the mechanism underlying the expansion variability by identifying morphological and molecular markers that distinguish low- and high-expanding TILs and predict their ex vivo expansion potential. We further developed novel SIN-based strategies that differentially reinforce the efficacy of both low- and high-expanding TILs. We demonstrate that a 14-day REP with feeder cells and SIN facilitates the proliferation of the low-expanding cells, while the high-expanding counterparts benefit from a sequential expansion protocol of 7 days with feeder cells only, followed by 7 days with SIN treatment. At the end of the REP both TIL populations display high levels of granzyme B and perforin and reduced levels of exhaustion markers. In conclusion, our findings demonstrate that the refined CCL21+ICAM1 SIN treatment improves expansion rates and activation profiles of both TIL populations, thereby enabling personalized SIN-enhanced protocols for TIL-based immunotherapy.

bioengineering↗

bioRxiv2024

Molecular mechanisms underlying the modulation of T-cell proliferation and cytotoxicity by immobilized CCL21 and ICAM1

BackgroundAdoptive cancer immunotherapy, using engineered T-cells, expressing chimeric antigen receptor (CARs) or autologous tumor infiltrating lymphocytes (TILs) became, in recent years, a major therapeutic approach for diverse types of cancer. However, despite the transformative potential of adoptive cancer immunotherapy, this field still faces a major challenge manifested by the complex interplay between the proliferation rate and cytotoxic capacity of effector CD8+ T cells. MethodsWe performed integrated analysis of specific differentiation markers via flow cytometry, together with gene expression profiling to explore the molecular mechanisms through which a "synthetic immune niche" (SIN), composed of immobilized CCL21 and ICAM1, modulates the interplay between the proliferation and cytotoxic potency of effector CD8+ T cells. ResultsOn day 3, the transcriptomic effect induced by the SIN was largely similar for both DC/OVA and anti CD3/CD28-activated cells. Cell proliferation increased and the cells exhibited high killing capacity. On day 4 and on, the proliferation/cytotoxicity phenotypes were radically "activation-specific"; The DC/OVA-activated cells lost their cytotoxic activity, which, in turn, was rescued by the SIN treatment. Upon longer incubation, the cytotoxic activity further declined, and on day7, could not be rescued by the SIN. SIN stimulation following activation with antiCD3/CD28 beads resulted in a highly proliferative phenotype with low cytotoxicity, yet the cells regained killing activity on day 7. Potential molecular regulations of the SIN effects were identified, based on transcriptomic and multispectral imaging profiling. ConclusionsThese data indicate that cell proliferation and cytotoxicity are negatively correlated, and the interplay between them is differentially regulated by the mode of initial activation. The SIN stimulation greatly enhanced the cell expansion, following both activation modes, while maintaining high cytotoxic potency, suggesting that it could reinforce adoptive cancer immunotherapy.

immunology↗

bioRxiv2022

Multi-site assessment of reproducibility in high-content live cell imaging data

High-content image-based cell phenotyping provides fundamental insights in a broad variety of life science areas. Striving for accurate conclusions and meaningful impact demands high reproducibility standards, even more importantly with the advent of data sharing initiatives. However, the sources and degree of biological and technical variability, and thus the reproducibility and usefulness of meta-analysis of results from live-cell microscopy have not been systematically investigated. Here, using high content data describing features of cell migration and morphology, we determine the sources of variability across different scales, including between laboratories, persons, experiments, technical repeats, cells and time points. Significant technical variability occurred between laboratories, providing low value to direct meta-analysis on the data from different laboratories. However, batch effect removal markedly improved the possibility to combine image-based datasets of perturbation experiments. Thus, reproducible quantitative high-content cell image data and meta-analysis depend on standardized procedures and batch correction applied to studies of perturbation effects.

cell biology↗

bioRxiv2022

A network of mixed actin polarity in the leading edge of spreading cells

Physical interactions of cells with the underlying extracellular matrix (ECM) play key roles in multiple cellular processes, such as tissue morphogenesis, cell motility, wound healing, cancer invasion and metastasis. The actin cytoskeletal network is a central driver and regulator of cellular dynamics, that produces membrane protrusions such as lamellipodia and filopodia. In this study, we examined actin organization in the expanding lamellipodia during the early stages of cell spreading. To gain insight into the 3D actin organization, at a molecular resolution, we plated cultured fibroblasts on galectin-8 coated EM grids, an ECM protein presents in disease states. We then combined cryo-electron tomography (cryo-ET) with advanced image processing tools for reconstructing the structure of F-actin in the lamellipodia. This approach enabled us to resolve the polarity and orientation of the filaments, and the structure of the Arp2/3 complexes associated with F-actin branches. We show here that F-actin in lamellipodial protrusions forms a dense network with three distinct sub-domains. One consists primarily of radial filaments, with their barbed ends pointing towards the membrane, the other is enriched with parallel filaments that run between the radial fibers, in addition to an intermediate sub-domain. Surprisingly, a minor, yet significant ([~]10%) population of actin filaments, are oriented with their barbed ends towards the cell center. Our results provide novel structural insights into F-actin assembly and dynamic reorganization in the leading edge of spreading cells.

cell biology↗

bioRxiv2022

How talin allosterically activates vinculin

The talin-vinculin axis is a key mechanosensing component of cellular focal adhesions. How talin and vinculin respond to forces and regulate one another remains unclear. By combining single molecule magnetic tweezer experiments, Molecular Dynamics simulations, actin bundling assays, and adhesion assembly experiments in live cells, we here discover a two-ways allosteric network within vinculin as a regulator of the talin-vinculin interaction. We directly observe a maturation process of vinculin upon talin binding which reinforces the binding to talin at a rate of 0.03 s-1. This allosteric transition can compete with force-induced dissociation of vinculin from talin only at 7-10 pN. Mimicking the allosteric activation by mutation yields a vinculin molecule that bundles actin and localizes to focal adhesions in a force-independent manner. Hence, the allosteric switch confines talin-vinculin interactions and focal adhesion build-up to intermediate force levels. The allosteric vinculin mutant is a valuable molecular tool to further dissect the mechanical and biochemical signalling circuits at focal adhesions and elsewhere.

biophysics↗

bioRxiv2022

Modulating the proliferative and cytotoxic properties of human TIL by a synthetic immune niche of immobilized CCL21 and ICAM1

The major challenge in developing an effective adoptive cancer immunotherapy, is the ex-vivo generation of tumor-reactive cells, in sufficient numbers and with enhanced cytotoxic potential. It was recently demonstrated, that culturing of activated murine CD8+ T-cells on a "Synthetic Immune Niche" (SIN), consisting of immobilized CCL21 and ICAM-1, enhances T-cell expansion, increases cytotoxicity against cultured cancer cells and suppresses tumor growth in vivo [1, 2]. In the study reported here, we have tested the effect of the CCL21+ICAM1 SIN, on the expansion and cytotoxic phenotype of Tumor Infiltrating Lymphocytes (TIL), following activation with immobilized anti-CD3/CD28 stimulation, or commercial activation beads. The majority of TIL tested, displayed higher expansion when cultured on the coated SIN compared to cells incubated on uncoated substrate. Comparable enhancement of TIL proliferation was obtained by the CCL21+ICAM1 SIN, in a clinical setting that includes a 14-day rapid expansion procedure (REP), initiated with feeder cells, anti CD3 and IL-2. Co-incubation of post-REP TIL with matching target cancerous cells, demonstrated increased IFN{gamma} secretion beyond baseline in most of the TILs and a significant increase in granzyme B levels following activation on SIN. The SIN did not significantly alter the relative frequency of CD8/CD4 populations, as well as the expression of CD28, CD25 and several exhaustion markers. These results demonstrate the potential capacity of the CCL21+ICAM1 SIN to reinforce TIL-based immunotherapy.

immunology↗

bioRxiv2022

Deciphering the involvement of the Hippo pathway co-regulators, YAP/TAZ in invadopodia formation and matrix degradation

Invadopodia are adhesive, actin-rich protrusions, formed by metastatic cancer cells that degrade the extracellular matrix and facilitate invasion. They support the metastatic cascade by a spatially and temporally coordinated process whereby invading cells bind to the matrix, degrade it by specific metalloproteinases, and mechanically penetrate diverse tissue barriers by forming actin-rich extensions. However, despite the apparent involvement of invadopodia in the metastatic process, the molecular mechanisms that regulate invadopodia formation and function are still largely unclear. In this study, we have explored the involvement of the key Hippo pathway co-regulators, namely YAP, and TAZ, in invadopodia formation and matrix degradation. Towards that goal, we tested the effect of depletion of YAP, TAZ, or both on invadopodia formation and activity in multiple human cancer cell lines. We report that knockdown of YAP and TAZ or their inhibition by verteporfin induce a significant elevation in matrix degradation and invadopodia formation in several cancer cell lines. Conversely, overexpression of these proteins strongly suppresses invadopodia formation and matrix degradation. Proteomic and transcriptomic profiling of MDA-MB-231 cells, following co-knockdown of YAP and TAZ, revealed a significant change in the levels of key invadopodia-associated proteins, including the crucial proteins Tks5 and MT1-MMP (MMP14). Collectively, our findings show that YAP and TAZ act as negative regulators of invadopodia formation in diverse cancer lines, most likely by reducing the levels of essential invadopodia components. Dissecting the molecular mechanisms of invadopodia formation in cancer invasion may eventually reveal novel targets for therapeutic applications against invasive cancer.

cancer biology↗

bioRxiv2022

Chiral growth of adherent filopodia

Adherent filopodia are elongated finger-like membrane protrusions, extending from the edges of diverse cell types and participating in cell adhesion, spreading, migration and environmental sensing. The formation and elongation of filopodia are driven by the polymerization of parallel actin filaments, comprising the filopodia cytoskeletal core. Here, we report that adherent filopodia, formed during the spreading of cultured cells on galectin-8-coated substrates, tend to change the direction of their extension in a chiral fashion, acquiring a left-bent shape. Cryo-electron tomography examination indicated that turning of the filopodia tip to the left is accompanied by the displacement of the actin core bundle to the right of the filopodia midline. Reduction of the adhesion to galectin-8 by treatment with thiodigalactoside abolished the filopodia chirality. By modulating the expression of a variety of actin-associated filopodia proteins, we identified myosin-X and formin DAAM1 as major filopodia chirality promoting factors. Formin mDia1, actin filament elongation factor VASP, and actin filament crosslinker fascin were also shown to be involved. Thus, the simple actin cytoskeleton of filopodia, together with a small number of associated proteins are sufficient to drive a complex navigation process, manifested by the development of left-right asymmetry in these cellular protrusions.

cell biology↗

bioRxiv2022

Rock inhibitors target SRSF2 leukemia by disrupting cell mitosis and nuclear morphology

Spliceosome machinery mutations are common early mutations in myeloid malignancies, however effective targeted therapies against them are still lacking. In the current study, we used an in vitro high-throughput drug screen among four different isogenic cell lines and identified ROCK inhibitors (ROCKi) as selective inhibitors of SRSF2 mutants. ROCKi targeted SRSF2 Mut primary human samples in a xenografts model and were not toxic to mice nor human cells. ROCKi induced mitotic catastrophe through their apparent effects on microtubules and nuclear organization. Transmission electron microscopy revealed that SRSF2 mutations induce deep nuclear indentation and segmentation, driven by microtubule-rich cytoplasmic intrusions, which were exacerbated by ROCKi. The severe nuclear deformation driven by the combination of SRSF2 Mut and ROCKi prevent cells from completing mitosis. These findings shed light on new ways to target SRSF2 and on the role of the microtubule system in SRSF2 Mut cells.

cancer biology↗

bioRxiv2021

The Serine Protease HtrA2 mediates radiation-induced senescence in cancer cells

Radiation therapy can induce cellular senescence in cancer cells leading to short-term tumor growth arrest, yet increased long-term recurrence. To better understand the molecular mechanisms involved, we developed a model of radiation-induced senescence in cultured cancer cells, which exhibited a typical senescent phenotype, including upregulation of p53 and its target p21, followed by sustained reduction in cellular proliferation, changes in cell size and cytoskeleton organization, and senescence-associated beta-galactosidase activity. A functional siRNA screen using a cell death-related library identified the mitochondrial Ser protease HtrA2 as necessary for senescence development. Mass spectrometry-based proteomic profiling of the senescent cells indicated downregulation of proteins involved in cell cycle progression and DNA repair, and upregulation of proteins associated with malignancy, while irradiation with HtrA2 inhibition upregulated cell proliferation components. In search of direct HtrA2 substrates following radiation, we determined that HtrA2 cleaves the intermediate filament protein vimentin, affecting its cytoplasmic organization. Ectopic expression of active cytosolic HtrA2 resulted in similar changes to vimentin filament assembly. Thus HtrA2, contributes to several hallmarks of senescence and is involved in the cytoskeletal reorganization that accompanies radiation-induced senescence. SummaryHere the authors identify the Ser protease HtrA2 as a novel mediator of radiation-induced senescence, necessary for sustained proliferation arrest and reorganization of the vimentin filament network.

cancer biology↗