Biology subjects

Kern, K.

Publications and source records attributed to Kern, K..

4 recordsLinked to original sources

bioRxiv2025

Anti-MDA5 monoclonal antibodies from patients with dermatomyositis - B cell characteristics and differential targeting of the helicase domains

ObjectivesAutoantibodies targeting melanoma differentiation associated protein 5 (MDA5) are strongly associated with dermatomyositis (DM) and may contribute to its pathogenesis. Here we aimed to investigate MDA5+ B cells, their phenotype and generate MDA5 monoclonal antibodies to assess their epitope specificity. MethodsMDA5-reactive B cells were captured from peripheral blood of patients with anti-MDA5+ DM (n=3) using an MDA5-fluorescent probe. B cell receptor (BCR) sequences were analysed from single-sorted B cells (n=240). Selected clones were re-expressed as IgG1 monoclonal antibodies (mAbs, n=23). Reactivity was assessed using recombinant MDA5 protein constructs, peptide epitope mapping, ELISA, western blot and a commercial line blot assay. ResultsOf 240 anti-MDA5+ sorted B cells, 23 BCRs were re-expressed as mAbs, two of which showed high reactivity and specificity for MDA5. These antibody sequences originated from one CD19+IgD-CD27-CD38+ and one CD19+IgD-CD27+CD38+ IgG+ B cell with low somatic hypermutation (SHM). Both mAbs had nanomolar apparent affinity and bound to sites within the helicase domains of the MDA5 protein but with distinct epitope recognition. Serology screening confirmed targeting of a linear epitope identified in the mAb studies. ConclusionOur results show that anti-MDA5+ B cells recognize the helicase domains, which are the enzymatically active domains of the protein. These results have implications for understanding the etiopathology of anti-MDA5+ DM and development of new antigen-specific therapies.

immunology↗

bioRxiv2025

Proteomic Remodeling During Tumor Cell-Induced Platelet Aggregation Unveils Metastatic Drivers in Colorectal Cancer

BackgroundColorectal cancer (CRC) is frequently associated with metastasis, resulting in high mortality rates. Platelets are known to play a crucial role in the metastatic cascade influencing tumor microenvironment remodeling, promoting cell transformation, facilitating metastatic niche formation, and shielding circulating tumor cells from immune surveillance. However, platelet proteomic alterations during tumor cell-induced platelet aggregation (TCIPA) remain largely unexplored. This study aims to characterize the proteomic profile of TCIPA in CRC using an in vitro model that recapitulates key aspects of CRC metastasis. MethodsTCIPA was assessed via light transmission aggregometry using an in vitro model incorporating paired primary and metastatic cell cultures. Stable Isotope Labeling with Amino Acids in Cell culture (SILAC) allowed for the discrimination of healthy platelet and tumor cell proteomes prior to and following TCIPA. Data-independent acquisition mass spectrometry was employed to analyze intra- and extracellular tumor and platelet proteomes. Comparative proteomic profiling was performed using a range of bioinformatic analyses, including clustering, differential expression, and Gene Set Enrichment Analyses (GSEA). ResultsComparison of the baseline proteome profiles of the CRC cell lines SW480 and SW620 identified 263 significant differentially expressed proteins (FDR [≤] 0.05, log2FC [≥] 1). The GSEA demonstrated enrichment of the epithelial-mesenchymal transition (FDR: 5.617 x 10-5) gene set in SW480 cells. While SW480 exhibited rapid TCIPA, SW620 did not consistently interact with healthy platelets. Following TCIPA, 34 tumor proteins showed differential expression compared to their naive status (without platelet-exposure). Notably, 17 of these proteins were significantly associated with CRC progression, particularly in the promotion of EMT, metastasis, tumor cell survival, proliferation, and metabolic reprogramming. ConclusionsThis study successfully characterized the proteomic profiles of platelets, platelet secretomes, and colorectal tumor cells following TCIPA-induced activation. The findings highlight the significant role of several tumor proteins and their metabolic effects in colorectal cancer progression, particularly with regard to metastasis.

cancer biology↗

bioRxiv2020

G3BP1 tethers the TSC complex to lysosomes and suppresses mTORC1 in the absence of stress granules

G3BP1 (Ras GTPase-activating protein-binding protein 1) is widely recognized as a core component of stress granules (SG), non-membranous RNA-protein-assemblies required for cellular survival under stress. We report that in the absence of SG, G3BP1 acts as lysosomal anchor of the Tuberous Sclerosis Complex (TSC) protein complex. By tethering the TSC complex to lysosomes, G3BP1 suppresses signaling through the metabolic master regulator mTORC1 (mechanistic target of rapamycin complex 1). Like the known TSC complex subunits, G3BP1 suppresses phenotypes related to mTORC1 hyperactivity in the context of tumors and neuronal dysfunction. Thus, G3BP1 is not only a core component of SG but also a key element of lysosomal TSC-mTORC1 signaling. HighlightsThe bona fide stress granule component G3BP1 O_LIis a key element of the TSC-mTORC1 signaling axis. C_LIO_LItethers the TSC complex to lysosomes. C_LIO_LIprevents mTORC1 hyperactivation by metabolic stimuli. C_LIO_LIsuppresses mTORC1-driven cancer cell motility and epileptiform activity. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/044081v3_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@77cb4forg.highwire.dtl.DTLVardef@c4d1a0org.highwire.dtl.DTLVardef@19e83acorg.highwire.dtl.DTLVardef@1d6a378_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2019

A large-scale resource for tissue-specific CRISPR mutagenesis in Drosophila

Genetic screens are powerful tools for the functional annotation of genomes. In the context of multicellular organisms, interrogation of gene function is greatly facilitated by methods that allow spatial and temporal control of gene abrogation. Here, we describe a large-scale transgenic short guide (sg) RNA library for efficient CRISPR-based disruption of specific target genes in a constitutive or conditional manner. The library consists currently of more than 2600 plasmids and 1600 fly lines with a focus on targeting kinases, phosphatases and transcription factors, each expressing two sgRNAs under control of the Gal4/UAS system. We show that conditional CRISPR mutagenesis is robust across many target genes and can be efficiently employed in various somatic tissues, as well as the germline. In order to prevent artefacts commonly associated with excessive amounts of Cas9 protein, we have developed a series of novel UAS-Cas9 transgenes, which allow fine tuning of Cas9 expression to achieve high gene editing activity without detectable toxicity. Functional assays, as well as direct sequencing of genomic sgRNA target sites, indicates that the vast majority of transgenic sgRNA lines mediate efficient gene disruption. Furthermore, we conducted the so far largest fully transgenic CRISPR screen in any metazoan organism, which further supported the high efficiency and accuracy of our library and revealed many so far uncharacterized genes essential for development.

genetics↗