Secreted ORF8 induces monocytic pro-inflammatory cytokines through NLRP3 pathways in patients with severe COVID-19.

Despite extensive research, the specific factor associated with SARS-CoV-2 infection that mediates the life-threatening inflammatory cytokine response in patients with severe COVID-19 remains unidentified. Herein we demonstrate that the virus-encoded Open Reading Frame 8 (ORF8) protein is abundantly secreted as a glycoprotein in vitro and in symptomatic patients with COVID-19. ORF8 specifically binds to the NOD-like receptor family pyrin domain-containing 3 (NLRP3) in CD14+ monocytes to induce inflammasomal cytokine/chemokine responses including IL1ß, IL8, and CCL2. Levels of ORF8 protein in the blood correlate with severity and disease-specific mortality in patients with acute SARS-CoV-2 infection. Furthermore, the ORF8-induced inflammasome response was readily inhibited by the NLRP3 inhibitor MCC950 in vitro. Our study identifies a dominant cause of pathogenesis, its underlying mechanism, and a potential new treatment strategy for severe COVID-19.

Mechanism of STMN2 cryptic splice-polyadenylation and its correction for TDP-43 proteinopathies.

Loss of nuclear TDP-43 is a hallmark of neurodegeneration in TDP-43 proteinopathies, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). TDP-43 mislocalization results in cryptic splicing and polyadenylation of pre-messenger RNAs (pre-mRNAs) encoding stathmin-2 (also known as SCG10), a protein that is required for axonal regeneration. We found that TDP-43 binding to a GU-rich region sterically blocked recognition of the cryptic 3' splice site in STMN2 pre-mRNA. Targeting dCasRx or antisense oligonucleotides (ASOs) suppressed cryptic splicing, which restored axonal regeneration and stathmin-2-dependent lysosome trafficking in TDP-43-deficient human motor neurons. In mice that were gene-edited to contain human STMN2 cryptic splice-polyadenylation sequences, ASO injection into cerebral spinal fluid successfully corrected Stmn2 pre-mRNA misprocessing and restored stathmin-2 expression levels independently of TDP-43 binding.

An integrin αEß7-dependent mechanism of IgA transcytosis requires direct plasma cell contact with intestinal epithelium.

Efficient IgA transcytosis is critical for the maintenance of a homeostatic microbiota. In the canonical model, locally-secreted dimeric (d)IgA reaches the polymeric immunoglobulin receptor (pIgR) on intestinal epithelium via simple diffusion. A role for integrin αE(CD103)ß7 during transcytosis has not been described, nor its expression by intestinal B cell lineage cells. We found that αE-deficient (αE-/-) mice have a luminal IgA deficit, despite normal antibody-secreting cells (ASC) recruitment, local IgA production and increased pIgR expression. This deficit was not due to dendritic cell (DC)-derived retinoic acid (RA) nor class-switching defects, as stool from RAG-/- mice reconstituted with αE-/- B cells was also IgA deficient. Flow cytometric, ultrastructural and transcriptional profiling showed that αEß7-expressing ASC represent an undescribed subset of terminally-differentiated intestinal plasma cells (PC) that establishes direct cell to cell contact with intestinal epithelium. We propose that IgA not only reaches pIgR through diffusion, but that αEß7+ PC dock with E-cadherin-expressing intestinal epithelium to directly relay IgA for transcytosis into the intestinal lumen.

Cephalopod-inspired optical engineering of human cells.

Although many animals have evolved intrinsic transparency for the purpose of concealment, the development of dynamic, that is, controllable and reversible, transparency for living human cells and tissues has remained elusive to date. Here, by drawing inspiration from the structures and functionalities of adaptive cephalopod skin cells, we design and engineer human cells that contain reconfigurable protein-based photonic architectures and, as a result, possess tunable transparency-changing and light-scattering capabilities. Our findings may lead to the development of unique biophotonic tools for applications in materials science and bioengineering and may also facilitate an improved understanding of a wide range of biological systems.

AMP-activated protein kinase fortifies epithelial tight junctions during energetic stress via its effector GIV/Girdin.

Loss of epithelial polarity impacts organ development and function; it is also oncogenic. AMPK, a key sensor of metabolic stress stabilizes cell-cell junctions and maintains epithelial polarity; its activation by Metformin protects the epithelial barrier against stress and suppresses tumorigenesis. How AMPK protects the epithelium remains unknown. Here, we identify GIV/Girdin as a novel effector of AMPK, whose phosphorylation at a single site is both necessary and sufficient for strengthening mammalian epithelial tight junctions and preserving cell polarity and barrier function in the face of energetic stress. Expression of an oncogenic mutant of GIV (cataloged in TCGA) that cannot be phosphorylated by AMPK increased anchorage-independent growth of tumor cells and helped these cells to evade the tumor-suppressive action of Metformin. This work defines a fundamental homeostatic mechanism by which the AMPK-GIV axis reinforces cell junctions against stress-induced collapse and also provides mechanistic insight into the tumor-suppressive action of Metformin.

Activation of Gαi at the Golgi by GIV/Girdin imposes finiteness in Arf1 signaling.

A long-held tenet of heterotrimeric G protein signal transduction is that it is triggered by G protein-coupled receptors (GPCRs) at the PM. Here, we demonstrate that Gi is activated in the Golgi by GIV/Girdin, a non-receptor guanine-nucleotide exchange factor (GEF). GIV-dependent activation of Gi at the Golgi maintains the finiteness of the cyclical activation of ADP-ribosylation factor 1 (Arf1), a fundamental step in vesicle traffic in all eukaryotes. Several interactions with other major components of Golgi trafficking-e.g., active Arf1, its regulator, ArfGAP2/3, and the adaptor protein ß-COP-enable GIV to coordinately regulate Arf1 signaling. When the GIV-Gαi pathway is selectively inhibited, levels of GTP-bound Arf1 are elevated and protein transport along the secretory pathway is delayed. These findings define a paradigm in non-canonical G protein signaling at the Golgi, which places GIV-GEF at the crossroads between signals gated by the trimeric G proteins and the Arf family of monomeric GTPases.

GIV/girdin links vascular endothelial growth factor signaling to Akt survival signaling in podocytes independent of nephrin.

Podocytes are critically involved in the maintenance of the glomerular filtration barrier and are key targets of injury in many glomerular diseases. Chronic injury leads to progressive loss of podocytes, glomerulosclerosis, and renal failure. Thus, it is essential to maintain podocyte survival and avoid apoptosis after acute glomerular injury. In normal glomeruli, podocyte survival is mediated via nephrin-dependent Akt signaling. In several glomerular diseases, nephrin expression decreases and podocyte survival correlates with increased vascular endothelial growth factor (VEGF) signaling. How VEGF signaling contributes to podocyte survival and prevents apoptosis remains unknown. We show here that Gα-interacting, vesicle-associated protein (GIV)/girdin mediates VEGF receptor 2 (VEGFR2) signaling and compensates for nephrin loss. In puromycin aminonucleoside nephrosis (PAN), GIV expression increased, GIV was phosphorylated by VEGFR2, and p-GIV bound and activated Gαi3 and enhanced downstream Akt2, mammalian target of rapamycin complex 1 (mTORC1), and mammalian target of rapamycin complex-2 (mTORC2) signaling. In GIV-depleted podocytes, VEGF-induced Akt activation was abolished, apoptosis was triggered, and cell migration was impaired. These effects were reversed by introducing GIV but not a GIV mutant that cannot activate Gαi3. Our data indicate that after PAN injury, VEGF promotes podocyte survival by triggering assembly of an activated VEGFR2/GIV/Gαi3 signaling complex and enhancing downstream PI3K/Akt survival signaling. Because of its important role in promoting podocyte survival, GIV may represent a novel target for therapeutic intervention in the nephrotic syndrome and other proteinuric diseases.

ARH directs megalin to the endocytic recycling compartment to regulate its proteolysis and gene expression.

Receptors internalized by endocytosis can return to the plasma membrane (PM) directly from early endosomes (EE; fast recycling) or they can traffic from EE to the endocytic recycling compartment (ERC) and recycle from there (slow recycling). How receptors are sorted for trafficking along these two pathways remains unclear. Here we show that autosomal recessive hypercholesterolemia (ARH) is required for trafficking of megalin, a member of the LDL receptor family, from EE to the ERC by coupling it to dynein; in the absence of ARH, megalin returns directly to the PM from EE via the connecdenn2/Rab35 fast recycling pathway. Binding of ARH to the endocytic adaptor AP-2 prevents fast recycling of megalin. ARH-mediated trafficking of megalin to the ERC is necessary for γ-secretase mediated cleavage of megalin and release of a tail fragment that mediates transcriptional repression. These results identify a novel mechanism for sorting receptors for trafficking to the ERC and link ERC trafficking to regulated intramembrane proteolysis (RIP) and expression of megalin.

The PDZ protein GIPC regulates trafficking of the LPA1 receptor from APPL signaling endosomes and attenuates the cell's response to LPA.

Lysophosphatidic acid (LPA) mediates diverse cellular responses through the activation of at least six LPA receptors--LPA(1-6,) but the interacting proteins and signaling pathways that mediate the specificity of these receptors are largely unknown. We noticed that LPA(1) contains a PDZ binding motif (SVV) identical to that present in two other proteins that interact with the PDZ protein GIPC. GIPC is involved in endocytic trafficking of several receptors including TrkA, VEGFR2, lutropin and dopamine D2 receptors. Here we show that GIPC binds directly to the PDZ binding motif of LPA(1) but not that of other LPA receptors. LPA(1) colocalizes and coimmunoprecipitates with GIPC and its binding partner APPL, an activator of Akt signaling found on APPL signaling endosomes. GIPC depletion by siRNA disturbed trafficking of LPA(1) to EEA1 early endosomes and promoted LPA(1) mediated Akt signaling, cell proliferation, and cell motility. We propose that GIPC binds LPA(1) and promotes its trafficking from APPL-containing signaling endosomes to EEA1 early endosomes and thus attenuates LPA-mediated Akt signaling from APPL endosomes.

Gαs promotes EEA1 endosome maturation and shuts down proliferative signaling through interaction with GIV (Girdin).

The organization of the endocytic system into biochemically distinct subcompartments allows for spatial and temporal control of the strength and duration of signaling. Recent work has established that Akt cell survival signaling via the epidermal growth factor receptor (EGFR) occurs from APPL early endosomes that mature into early EEA1 endosomes. Less is known about receptor signaling from EEA1 endosomes. We show here that EGF-induced, proliferative signaling occurs from EEA1 endosomes and is regulated by the heterotrimeric G protein Gαs through interaction with the signal transducing protein GIV (also known as Girdin). When Gαs or GIV is depleted, activated EGFR and its adaptors accumulate in EEA1 endosomes, and EGFR signaling is prolonged, EGFR down-regulation is delayed, and cell proliferation is greatly enhanced. Our findings define EEA1 endosomes as major sites for proliferative signaling and establish that Gαs and GIV regulate EEA1 but not APPL endosome maturation and determine the duration and strength of proliferative signaling from this compartment.

Human hematopoietic stem/progenitor cells modified by zinc-finger nucleases targeted to CCR5 control HIV-1 in vivo.

CCR5 is the major HIV-1 co-receptor, and individuals homozygous for a 32-bp deletion in CCR5 are resistant to infection by CCR5-tropic HIV-1. Using engineered zinc-finger nucleases (ZFNs), we disrupted CCR5 in human CD34(+) hematopoietic stem/progenitor cells (HSPCs) at a mean frequency of 17% of the total alleles in a population. This procedure produces both mono- and bi-allelically disrupted cells. ZFN-treated HSPCs retained the ability to engraft NOD/SCID/IL2rgamma(null) mice and gave rise to polyclonal multi-lineage progeny in which CCR5 was permanently disrupted. Control mice receiving untreated HSPCs and challenged with CCR5-tropic HIV-1 showed profound CD4(+) T-cell loss. In contrast, mice transplanted with ZFN-modified HSPCs underwent rapid selection for CCR5(-/-) cells, had significantly lower HIV-1 levels and preserved human cells throughout their tissues. The demonstration that a minority of CCR5(-/-) HSPCs can populate an infected animal with HIV-1-resistant, CCR5(-/-) progeny supports the use of ZFN-modified autologous hematopoietic stem cells as a clinical approach to treating HIV-1.

Major O-glycans in the spores of two microsporidian parasites are represented by unbranched manno-oligosaccharides containing alpha-1,2 linkages.

Protein glycosylation in microsporidia, a fungi-related group comprising exclusively obligate intracellular parasitic species, is still poorly documented. Here, we have studied glycoconjugate localization and glycan structures in spores of Encephalitozoon cuniculi and Antonospora locustae, two distantly related microsporidians invading mammalian and insect hosts, respectively. The polar sac-anchoring disc complex or polar cap, an apical element of the sporal invasion apparatus, was strongly periodic acid-thiocarbohydrazide-Ag proteinate-positive. Mannose-binding lectins reacted with the polar cap and recognized several bands (from 20 to 160 kDa) on blots of E. cuniculi protein extracts. Physicochemical analyses provided the first determination of major glycostructures in microsporidia. O-linked glycans were demonstrated to be linear manno-oligosaccharides containing up to eight alpha1, 2-linked mannose residues, thus resembling those reported in some fungi such as Candida albicans. No N-linked glycans were detected. The data are in accordance with gene-based prediction of a minimal O-mannosylation pathway. Further identification of individual mannoproteins should help in the understanding of spore germination mechanism and host-microsporidia interactions.

An improved procedure for Percoll gradient separation of sporogonial stages in Encephalitozoon cuniculi (Microsporidia).

Intracellular development of microsporidian parasites comprises a proliferative phase (merogony) followed by a differentiation phase (sporogony) leading to the release of resistant spores. Sporogony implies, successively, meront-to-sporont transformation, sporont division into sporoblasts, and sporogenesis. We report a procedure improving the separation of sporogonial stages of Encephalitozoon cuniculi, a species that develops inside parasitophorous vacuoles of mammalian cells. Supernatants of E. cuniculi-infected Madin-Darby canine kidney cell cultures provided a large number of parasites mixed with host-cell debris. This material was gently homogenized in phosphate-buffered saline containing 0.05% saponin and 0.05% Triton X-100 then filtered through glass wool columns. Centrifugation of the filtrate on 70% Percoll-0.23 M sucrose gradient gave a reproducible pattern of bands at different densities. Transmission electron microscopy showed that three of the four collected fractions were free of visible contaminants. Corresponding prominent cell stages were early sporoblasts (fraction B), late sporoblasts plus immature spores (fraction C), and mature spores (fraction D). Further centrifugation of the lightest fraction (A) on 30% Percoll-0.23 M sucrose gradient generated a sporont-rich fraction (A2). First analysis of proteins from fractions A2 and D by two-dimensional gel electrophoresis suggested a potential use of the described method for proteomic profiling.

Proteolytic activity in Encephalitozoon cuniculi sporogonial stages: predominance of metallopeptidases including an aminopeptidase-P-like enzyme.

A fraction enriched in spore precursor cells (sporoblasts) of the microsporidian Encephalitozoon cuniculi, an intracellular parasite of mammals, was obtained by Percoll gradient centrifugation. Soluble extracts of these cells exhibited proteolytic activity towards azocasein, with an alkaline optimum pH range (9-10). Prevalence of some metallopeptidases was supported by the stimulating effect of Ca2+, Mg2+, Mn2+ and Zn2+ ions, and inhibition by two chelating agents (EDTA and 1,10-phenanthroline), a thiol reductant (dithiothreitol) and two aminopeptidase inhibitors (bestatin and apstatin). Zymographic analysis revealed four caseinolytic bands at about 76, 70, 55 and 50 kDa. Mass spectrometry of tryptic peptides from one-dimensional gel slices identified a cytosol (leucine) aminopeptidase homologue (M17 family) in 50-kDa band and an enzyme similar to aminopeptidase P (AP-P) of cytosolic type (M24B subfamily) in 70-kDa band. Multiple sequence alignments showed conservation of critical residues for catalysis and metal binding. A long insertion in a common position was found in AP-P sequences from E. cuniculi and Nosema locustae, an insect-infecting microsporidian. The expression of cytosolic AP-P in sporogonial stages of microsporidia may suggest a key role in the attack of proline-containing peptides as a prerequisite to long-duration biosynthesis of structural proteins destined to the sporal polar tube.