Biology subjects

Janssen, G.

Publications and source records attributed to Janssen, G..

4 recordsLinked to original sources

bioRxiv2025

CRISPR activation screen uncovers MARCKSL1 as a gauge for extracellular vesicle secretion.

Extracellular vesicles (EVs) are crucial mediators of intercellular communication that originate through one of two pathways: outward budding of the plasma membrane (PM) or fusion of mature (late) endosomes with the PM. How cells balance these EV biogenesis routes remains unclear. To address this, we performed a genome-wide CRISPR activation screen for genes that increase cell surface levels of the tetraspanin CD63--an EV marker that shuttles between late endosomes and the PM. This unbiased approach identified a membrane adaptor protein, MARCKSL1, commonly upregulated in diverse tumor types. Follow-up studies, integrating genomic activation/ablation with microscopic and proteomic approaches, revealed that MARCKSL1 potentiates EV secretion from the PM, (in part) at the expense of late endosome--PM fusion. Probing the molecular context of MARCKSL1 function, we implicate PM-bridging cytoskeletal components (e.g., Radixin) and SNARE-associated proteins (e.g., STXBP3) as collaborators of MARCKSL1. Collectively, our findings reveal new mechanistic underpinnings of PM remodeling and position MARCKSL1 as a gauge between different platforms of EV biogenesis.

cell biology↗

bioRxiv2023

Proinsulin degradation and presentation of a proinsulin B-chain autoantigen involves ER-associated protein degradation (ERAD)-enzyme UBE2G2

Type 1 diabetes (T1D) is characterized by HLA class I-mediated presentation of autoantigens on the surface of pancreatic {beta}-cells. Recognition of these autoantigens by CD8+ T cells results in the destruction of pancreatic {beta}-cells and, consequently, insulin deficiency. Most epitopes presented at the surface of {beta}-cells derive from the insulin precursor molecule proinsulin. The intracellular processing pathway(s) involved in the generation of these peptides are poorly defined. In this study, we show that a proinsulin B-chain antigen (PPIB5-14) originates from proinsulin molecules that are processed by ER-associated protein degradation (ERAD) and thus originate from ER-resident proteins. Furthermore, screening genes encoding for E2 ubiquitin conjugating enzymes, we identified UBE2G2 to be involved in proinsulin degradation. These results indicate that insulin-derived peptides, presented by HLA-class I molecules at the cell surface, originate from ER-resident proinsulin that has been dislocated to the cytosol for subsequent degradation. These insights into the pathway involved in the generation of insulin-derived peptides emphasize the importance of proinsulin processing in the ER to T1D pathogenesis and identify novel targets for future therapies that may cure or even prevent T1D. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=172 HEIGHT=200 SRC="FIGDIR/small/545333v1_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@131d5org.highwire.dtl.DTLVardef@6eb4b3org.highwire.dtl.DTLVardef@196674org.highwire.dtl.DTLVardef@1957af6_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2020

ERAP2 facilitates a subpeptidome of Birdshot Uveitis-associated HLA-A29

Birdshot Uveitis (BU) is a blinding inflammatory eye condition that only affects HLA-A29-positive individuals. Genetic association studies linked ERAP2 with BU, an aminopeptidase which trims peptides before their presentation by HLA class I at the cell surface, which suggests that ERAP2-dependent peptide presentation by HLA-A29 drives the pathogenesis of BU. However, it remains poorly understood whether the effects of ERAP2 on the HLA-A29 peptidome are distinct from its effect on other HLA allotypes. To address this, we focused on the effects of ERAP2 on the immunopeptidome in patient-derived antigen presenting cells. Using complementary HLA-A29-based and pan-class I immunopurifications, isotope-labelled naturally processed and presented HLA-bound peptides were sequenced by mass spectrometry. We show that the effects of ERAP2 on the N-terminus of ligands of HLA-A29 are shared across endogenous HLA allotypes, but discover and replicate that one peptide motif generated in the presence of ERAP2 is specifically bound by HLA-A29. This motif can be found in the amino acid sequence of putative autoantigens. We further show evidence for internal sequence specificity for ERAP2 imprinted in the immunopeptidome. These results reveal that ERAP2 can generate an HLA-A29-specific antigen repertoire, which supports that antigen presentation is a key disease pathway in BU.

immunology↗

bioRxiv2019

Discovery and Optimization of Inhibitors for the Pup Proteasome System in Mycobacterium tuberculosis

Tuberculosis is a global health problem with the existence and spreading of multidrug resistant and extensive drug resistant strains. The development of new drugs for tuberculosis that inhibit different activities than the current drugs is thus urgent. The prokaryotic ubiquitin like protein proteasome system is an attractive target for the development of new drugs. Using a Pup-based fluorogenic substrate, we screened for inhibitors of Dop, a depupylase, and identified I-OMe-Tyrphostin AG538 (1) and Tyrphostin AG53 (2). The hits were validated and determined to be fast reversible non-ATP competitive inhibitors. The SAR was established by testing 27 synthesized analogs of 1 and 2. Several of the synthesized compounds also inhibited the depupylation of a native substrate, FabD[~]Pup. Importantly, the pupylation and depupylation activities of PafA, the sole Pup ligase in M. tuberculosis, was also inhibited by some of these compounds. With the identification of the first described lead compounds for Dop and PafA inhibition, this study shows that high throughput screening can be a successful strategy for this purpose.

microbiology↗