Biology subjects

Casanova, J. E.

Publications and source records attributed to Casanova, J. E..

4 recordsLinked to original sources

bioRxiv2026

Lipid transfer protein ORP3 mediates lysosomal repair via LC3B and ubiquitin-TAK1-p38

Lysosomal membrane damage triggers a multi-stage repair response essential for cellular homeostasis. Here we identify the oxysterol-binding protein-related protein ORP3 as a critical mediator of late-stage lysosomal membrane repair. Following lysosomal damage induced by L-leucine-leucine methyl ester (LLOME) or cationic amphiphilic drugs (CADs), ORP3 is phosphorylated and recruited to ER-lysophagosome contact sites via a signaling cascade initiated by lysosomal membrane ubiquitination, TAK1, p38 MAPK, and, to a lesser extent, IKK. p38-dependent phosphorylation promotes direct interaction between ORP3 and LC3B, which together with PI(4,5)P2 binding, is required for autophagic lysosome recruitment. ORP3 depletion impairs late-stage lysosomal recovery, elevates lysosomal lipid peroxidation, and reduces cell survival. A lipid transfer-deficient ORP3 mutant fails to restore lysosome function despite normal recruitment, indicating that ER-to-lysophagosome transfer of phosphatidylcholine by ORP3 is functionally required. ORP3 activity is subsequently terminated by VCP/p97-mediated deubiquitination of lysosomes. These findings define ORP3 as a MAPK regulated lipid transfer protein during the late autophagic phase of the endolysosomal damage response. SummaryLysosomal membrane damage triggers ubiquitination that activates a TAK1-p38 signaling cascade, phosphorylating the lipid transfer protein ORP3 and recruiting it to damaged lysosomes via LC3B interaction. ORP3-mediated phosphatidylcholine transfer from the ER is essential for late-stage lysosomal repair and cell survival. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=121 SRC="FIGDIR/small/731146v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@b00f0borg.highwire.dtl.DTLVardef@abd2ecorg.highwire.dtl.DTLVardef@a491a2org.highwire.dtl.DTLVardef@552616_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2023

Phosphorylation of the inner core oligosaccharide of lipopolysaccharide mediates recognition and phagocytosis of Gram-negative bacteria by Brain Angiogenesis Inhibitor 1 (BAI1)

Recognition of lipopolysaccharide (LPS) is critical for host defense against Gram-negative bacteria and the regulation of local inflammatory responses at the host-microbial interface. We have previously shown that the adhesion G-protein-coupled receptor (aGPCR) BAI1 acts as a phagocytic pattern recognition receptor (PRR) that selectively recognizes Gram-negative bacteria through a series of five Type I thrombospondin repeats (TSRs) in its extracellular domain. Unlike Toll-like receptor 4 (TLR4), which recognizes the hydrophobic lipid A region of LPS, the BAI1 TSRs bind the core oligosaccharide of canonical LPS structures (1). In this study, we report that BAI1 requires the phosphorylated inner core L-glycero-d-manno-heptose moiety of LPS for recognition, in the context of intact, live bacteria. Mutant strains of Salmonella enterica serovar Typhimurium or E. coli BW25113 K-12 that fail to phosphorylate the inner core oligosaccharide, specifically heptose I, are not recognized by BAI1. Phosphorylation of inner core oligosaccharides is critical for membrane stability and function and is conserved across most Gram-negative species, thus allowing BAI1 to recognize a broad range of organisms.

microbiology↗

bioRxiv2021

The ARF GAPs ELMOD1 and ELMOD3 act at the Golgi and Cilia to Regulate Ciliogenesis and Ciliary Protein Traffic

ELMODs are a family of three mammalian paralogs that display GTPase activating protein (GAP) activity towards a uniquely broad array of ADP-ribosylation factor (ARF) family GTPases that includes ARF-like (ARL) proteins. ELMODs are ubiquitously expressed in mammalian tissues, highly conserved across eukaryotes, and ancient in origin, being present in the last eukaryotic common ancestor. We described functions of ELMOD2 in immortalized mouse embryonic fibroblasts (MEFs) in the regulation of cell division, microtubules, ciliogenesis, and mitochondrial fusion. Here, using similar strategies with the paralogs ELMOD1 and ELMOD3, we identify novel functions and locations of these cell regulators and compare them to those of ELMOD2, allowing determination of functional redundancy among the family members. We found strong similarities in phenotypes resulting from deletion of either Elmod1 or Elmod3 and marked differences from those arising in Elmod2 deletion lines. Deletion of either Elmod1 or Elmod3 results in the decreased ability of cells to form primary cilia, loss of a subset of proteins from cilia, and accumulation of some ciliary proteins at the Golgi, predicted to result from compromised traffic from the Golgi to cilia. These phenotypes are reversed upon expression of activating mutants of either ARL3 or ARL16, linking their roles to ELMOD1/3 actions. Thus, we believe that ELMOD1 and ELMOD3 perform multiple functions in cells, most prominently linked to ciliary biology and Golgi-ciliary traffic, and likely acting from more than one cellular location.

cell biology↗

bioRxiv2019

Calcium-stimulated disassembly of focal adhesions mediated by an ORP3/IQSec1 complex

Coordinated assembly and disassembly of integrin-mediated focal adhesions (FAs) is essential for cell migration. Many studies have shown that FA disassembly requires Ca2+ influx, however our understanding of this process remains incomplete. Here we show that Ca2+ influx via STIM1/Orai1 calcium channels, which cluster near FAs, leads to activation of the GTPase Arf5 via the Ca2+-activated GEF IQSec1, and that both IQSec1 and Arf5 activation are essential for adhesion disassembly. We further show that IQSec1 forms a complex with the lipid transfer protein ORP3, and that Ca2+ influx triggers PKC-dependent translocation of this complex to ER/plasma membrane contact sites adjacent to FAs. In addition to allosterically activating IQSec1, ORP3 also extracts PI4P from the PM, in exchange for phosphatidylcholine. ORP3-mediated lipid exchange is also important for FA turnover. Together, these findings identify a new pathway that links calcium influx to FA turnover during cell migration.

cell biology↗