Biology subjects

Bos, E.

Publications and source records attributed to Bos, E..

5 recordsLinked to original sources

bioRxiv2026

Selectivity and dynamics of VAP family tether exchange across membrane contact sites

To integrate diverse cellular function and coordinate homeostasis, the endoplasmic reticulum (ER) communicates with all other intracellular compartments through physical interfaces termed membrane contact sites (MCSs). Given the sheer diversity of possible MCS pairings, how the ER discriminates between simultaneously available binding partners remains unclear. To explore this, we performed comparative endogenous contact site mapping for three closely related VAP family tethers and uncovered a unique set of FFAT motif selectivity and MCS footprints for each: VAPA at mitochondria and TGN, VAPB at mitochondria and peroxisomes, and MOSPD2 at mature endosomes, lysosomes and lipid droplets. In line with their MCS selectivity profiles, co-depletion of VAPA and VAPB, but not MOSPD2, caused systemic breakdown in mitochondrial integrity, while silencing of MOSPD2 alone was sufficient to disrupt the organization and transport of (endo)lysosomes. Unexpectedly, coincident loss of VAPA and VAPB instigated ER contact site rewiring by redirecting endogenous MOSPD2 to the collapsing mitochondrial network. Our findings define hierarchies of ER contact site formation and reveal compensation mechanisms exploited by cells to safeguard organelle homeostasis and crosstalk.

cell biology↗

bioRxiv2026

VAPB and its binding partner AKAP11 promote lipid droplet degradation

The endoplasmic reticulum (ER) is the master regulator of various cellular processes. To achieve its diverse functions, the ER interacts with other organelles at membrane contact sites, regions where organelles are brought into proximity. Most ER membrane contact sites are facilitated by the ER-resident VAP proteins. To address the role of VAP proteins in regulating cellular lipid homeostasis, we performed a targeted lipidomic screen after silencing individual VAPs. The loss of VAPB increases cellular levels of neutral lipids stored in lipid droplets (LDs). The increase in neutral lipids is reflected in the size, number and motility of LDs, and is due to the impaired degradation of these organelles. VAPB requires its contact site forming ability to regulate LDs, prompting the identification of protein kinase A (PKA) anchor AKAP11 as a VAPB interaction partner in regulating LD degradation and dynamics. Collectively, our findings identify a role for the ER-resident VAPB-AKAP11 interaction and PKA activity in regulating LD homeostasis. SummaryThe ER-resident membrane contact site protein VAPB and its interaction partner AKAP11 regulate lipid droplet size and motility by mediating neutral lipid degradation. VAPB requires its ability to form membrane contact sites and interact with AKAP11, protein kinase A anchor protein, for mediating lipid droplet homeostasis. This paper uncovers a role for VAPB-AKAP11-PKA axis in regulating the homeostasis of lipid droplets.

cell biology↗

bioRxiv2024

Cell-Surface RNA Associates with Heparan Sulfate and RNA-Binding Proteins to Modulate Receptor-Ligand Interactions

Recent discoveries have shown the presence of RNA molecules on the cell surface, defying the traditional view that RNA only functions intracellularly. However, it is not well understood how cell-surface RNA (csRNA) is stably present on the plasma membrane and what functions it performs. We answer the pressing questions in the emerging field by taking integrated omic-wide approaches and multiple orthogonal validatory methods. Firstly, we exploited the RNA-sensing ability of TLR7 as a specific recombinant probe to detect csRNA. Coupling it with a genome-wide CRISPR-Cas9-knockout screening, we identified heparan sulfate (HS) as a crucial factor for RNA presentation on cells. Using the TLR7 probe, cell surface proximity labelling revealed that these HS-associated csRNAs (hepRNAs) are in vicinity with a plethora of RNA-binding proteins. The compelling observation led us to a molecular model where HS, RNA and RBP form ternary complexes at cell surface. A photochemical RNA-protein crosslinking technology termed SCOOPS were then established to validate the termolecular model in a TLR7-orthogonal manner. Moreover, enabled by SCOOPS, we unveiled identities of hepRNA using next-generation sequencing, and identified traits in RNA primary structures that facilitate HS association. We further show that hepRNA binds to killer cell immunoglobulin-like receptor 2DL5 (KIR2DL5), recruiting the protein to cell surface and potentially enhancing receptor-ligand interactions. Our findings provide a foundation for exploring how cell-surface ribonucleoproteins contribute to immune modulation.

molecular biology↗

bioRxiv2024

Correlating Protein Aggregate Structure with Cellular Function in Differentiated Muscle Cells: Discriminating Pathogenic from Non-Pathogenic Forms

Ageing has a major adverse impact on maintaining cellular proteostasis and age-related dysregulation leads to an increase in protein aggregation. Equivalently, the accumulation of aggregated proteins accelerates proteostasis impairment. Accumulation of protein aggregates and impaired proteostasis are hallmarks of ageing-associated neuromuscular disorders and tissue degeneration is predominantly in post-mitotic muscle and neuronal cells. A short alanine expansion mutation in the Poly(A) binding protein nuclear 1 (PABPN1) causes Oculopharyngeal muscular dystrophy (OPMD), a rare age-associated protein aggregation myopathy. PABPN1 is a vital RNA-binding protein but OPMD pathology is limited to skeletal muscles connected to nuclear aggregates. In contrast to the mutant PABPN1, the wild-type PABPN1 forms age-associated non-pathogenic aggregates. We generated an inducible muscle cell models for mutant and wild-type PABPN1 protein aggregation. By combining four different, but complementary, imaging modalities, covering micro- to nanoscale resolutions, we were able to characterise differences in structure and dynamics between pathogenic and non-pathogenic PABPN1 aggregates in differentiated muscle cells. These data allowed us to correlate the structure of aggregates to cellular function, providing important insights into how aggregates lead to cell dysfunction in post-mitotic cells. Graphical summary O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=159 SRC="FIGDIR/small/591067v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@22870corg.highwire.dtl.DTLVardef@d0616borg.highwire.dtl.DTLVardef@abe34dorg.highwire.dtl.DTLVardef@d7f359_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2022

Vimentin intermediate filaments organize organellar architecture in response to ER stress

Compartmentalization of organelles in space and time affects their functional state and enables higher order regulation of essential cellular processes. How organellar residence is maintained in a defined area of the cell remains poorly understood. In this study, we uncover a new role for intermediate filaments in the maintenance of organellar architecture and dynamics, which is executed through a functional connection between Vimentin and the ER-embedded ubiquitin ligase ring finger protein 26 (RNF26). While the ubiquitin ligase function of RNF26 promotes perinuclear positioning of endolysosomes, its catalytically inactive mutant I382R preferentially binds Vimentin through the RNF26 C-terminal tail. Loss of either RNF26 or Vimentin redistributes endolysosomes throughout the cytosol and mobilizes ER membranes from the perinuclear ER towards the periphery. Furthermore, RNF26 and Vimentin control changes in ER morphology and organelle compartmentalization during ER stress. Collectively, we define a new function for Vimentin-containing intermediate filaments as anchors of a dynamic interplay between the ER and endosomes, critical to the integrity of the perinuclear ER and corresponding perinuclear endosomal cloud during homeostatic and stress conditions. SynopsisThe perinuclear area hosts a wide variety of cellular organelles, and their interaction with the ER governs essential cellular processes. To spatiotemporally organize endosomes and ER in the perinuclear region, the ER-embedded E3 ubiquitin ligase RNF26 interacts with Vimentin to physically link the perinuclear ER membrane with the intermediate filament cytoskeleton. As a result, Vimentin ensures perinuclear RNF26 retention, which in turn controls the perinuclear location of ER membranes and endosomes, which can be affected during stressed conditions. O_LIVimentin interacts with inactive RNF26 in the ER membrane C_LIO_LIRNF26 by virtue of the Vimentin interaction controls perinuclear organization of ER membranes and the endosomal system C_LIO_LIVimentin immobilizes ER membranes in the perinuclear area C_LIO_LIVimentin and RNF26 compartmentalize organelles in the perinuclear region during ER stress C_LIO_LIWe define a new function of Vimentin intermediate filaments in the control of the perinuclear endosomal and ER organization C_LI

cell biology↗