4-Phenylbutyrate Attenuates the ER Stress Response and Cyclic AMP Accumulation in DYT1 Dystonia Cell Models

Dystonia is a neurological disorder in which sustained muscle contractions induce twisting and repetitive movements or abnormal posturing. DYT1 early-onset primary dystonia is the most common form of hereditary dystonia and is caused by deletion of a glutamic acid residue (302/303) near the carboxyl-terminus of encoded torsinA. TorsinA is localized primarily within the contiguous lumen of the endoplasmic reticulum (ER) and nuclear envelope (NE), and is hypothesized to function as a molecular chaperone and an important regulator of the ER stress-signaling pathway, but how the mutation in torsinA causes disease remains unclear. Multiple lines of evidence suggest that the clinical symptoms of dystonia result from abnormalities in dopamine (DA) signaling, and possibly involving its down-stream effector adenylate cyclase that produces the second messenger cyclic adenosine-3′, 5′-monophosphate (cAMP). Here we find that mutation in torsinA induces ER stress, and inhibits the cyclic adenosine-3′, 5′-monophosphate (cAMP) response to the adenylate cyclase agonist forskolin. Both defective mechanins are corrected by the small molecule 4-phenylbutyrate (4-PBA) that alleviates ER stress. Our results link torsinA, the ER-stress-response, and cAMP-dependent signaling, and suggest 4-PBA could also be used in dystonia treatment. Other pharmacological agents known to modulate the cAMP cascade, and ER stress may also be therapeutic in dystonia patients and can be tested in the models described here, thus supplementing current efforts centered on the dopamine pathway

Insights on the trafficking and retro-translocation of glycosphingolipid-binding bacterial toxins

Some bacterial toxins and viruses have evolved the capacity to bind mammalian glycosphingolipids to gain access to the cell interior, where they can co-opt the endogenous mechanisms of cellular trafficking and protein translocation machinery to cause toxicity. Cholera toxin (CT) is one of the best-studied examples, and is the virulence factor responsible for massive secretory diarrhea seen in cholera. CT enters host cells by binding to monosialotetrahexosylganglioside (GM1 gangliosides) at the plasma membrane where it is transported retrograde through the trans-Golgi network (TGN) into the endoplasmic reticulum (ER). In the ER, a portion of CT, the CT-A1 polypeptide, is unfolded and then “retro-translocated” to the cytosol by hijacking components of the ER associated degradation pathway (ERAD) for misfolded proteins. CT-A1 rapidly refolds in the cytosol, thus avoiding degradation by the proteasome and inducing toxicity. Here, we highlight recent advances in our understanding of how the bacterial AB5 toxins induce disease. We highlight the molecular mechanisms by which these toxins use glycosphingolipid to traffic within cells, with special attention to how the cell senses and sorts the lipid receptors. We also discuss several new studies that address the mechanisms of toxin unfolding in the ER and the mechanisms of CT A1-chain retro-translocation to the cytosol

Remodeling of the Intestinal Brush Border Underlies Adhesion and Virulence of an Enteric Pathogen

ABSTRACT Intestinal colonization by Vibrio parahaemolyticus—the most common cause of seafood-borne bacterial enteritis worldwide—induces extensive disruption of intestinal microvilli. In orogastrically infected infant rabbits, reorganization of the apical brush border membrane includes effacement of some microvilli and marked elongation of others. All diarrhea, inflammation, and intestinal pathology associated with V. parahaemolyticus infection are dependent upon one of its type 3 secretion systems (T3SS2); however, translocated effectors that directly mediate brush border restructuring and bacterial adhesion are not known. Here, we demonstrate that the effector VopV is essential for V. parahaemolyticus intestinal colonization and therefore its pathogenicity, that it induces effacement of brush border microvilli, and that this effacement is required for adhesion of V. parahaemolyticus to enterocytes. VopV contains multiple functionally independent and mechanistically distinct domains through which it disrupts microvilli. We show that interaction between VopV and filamin, as well as VopV’s previously noted interaction with actin, mediates enterocyte cytoskeletal reorganization. VopV’s multipronged approach to epithelial restructuring, coupled with its impact on colonization, suggests that remodeling of the epithelial brush border is a critical step in pathogenesis

Identification of host cell factors required for intoxication through use of modified cholera toxin

We describe a novel labeling strategy to site-specifically attach fluorophores, biotin, and proteins to the C terminus of the A1 subunit (CTA1) of cholera toxin (CTx) in an otherwise correctly assembled and active CTx complex. Using a biotinylated N-linked glycosylation reporter peptide attached to CTA1, we provide direct evidence that ∼12% of the internalized CTA1 pool reaches the ER. We also explored the sortase labeling method to attach the catalytic subunit of diphtheria toxin as a toxic warhead to CTA1, thus converting CTx into a cytolethal toxin. This new toxin conjugate enabled us to conduct a genetic screen in human cells, which identified ST3GAL5, SLC35A2, B3GALT4, UGCG, and ELF4 as genes essential for CTx intoxication. The first four encode proteins involved in the synthesis of gangliosides, which are known receptors for CTx. Identification and isolation of the ST3GAL5 and SLC35A2 mutant clonal cells uncover a previously unappreciated differential contribution of gangliosides to intoxication by CTx.Fundação para a Ciência e a Tecnologia (Fellowship

Mechanism for Adhesion G Protein-Coupled Receptor GPR56-Mediated RhoA Activation Induced By Collagen III Stimulation

GPR56 is a member of the adhesion G protein-coupled receptor (GPCR) family. Despite the importance of GPR56 in brain development, where mutations cause a devastating human brain malformation called bilateral frontoparietal polymicrogyria (BFPP), the signaling mechanism(s) remain largely unknown. Like many other adhesion GPCRs, GPR56 is cleaved via a GPCR autoproteolysis-inducing (GAIN) domain into N- and C-terminal fragments (GPR56N and GPR56C); however, the biological significance of this cleavage is elusive. Taking advantage of the recent identification of a GPR56 ligand and the presence of BFPP-associated mutations, we investigated the molecular mechanism of GPR56 signaling. We demonstrate that ligand binding releases GPR56N from the membrane-bound GPR56C and triggers the association of GPR56C with lipid rafts and RhoA activation. Furthermore, one of the BFPP-associated mutations, L640R, does not affect collagen III-induced lipid raft association of GPR56. Instead, it specifically abolishes collagen III-mediated RhoA activation. Together, these findings reveal a novel signaling mechanism that may apply to other members of the adhesion GPCR family

The Recycling and Transcytotic Pathways for IgG Transport by FcRn are Distinct and Display an Inherent Polarity

The Fc receptor FcRn traffics immunoglobulin G (IgG) in both directions across polarized epithelial cells that line mucosal surfaces, contributing to host defense. We show that FcRn traffics IgG from either apical or basolateral membranes into the recycling endosome (RE), after which the actin motor myosin Vb and the GTPase Rab25 regulate a sorting step that specifies transcytosis without affecting recycling. Another regulatory component of the RE, Rab11a, is dispensable for transcytosis, but regulates recycling to the basolateral membrane only. None of these proteins affect FcRn trafficking away from lysosomes. Thus, FcRn transcytotic and recycling sorting steps are distinct. These results are consistent with a single structurally and functionally heterogeneous RE compartment that traffics FcRn to both cell surfaces while discriminating between recycling and transcytosis pathways polarized in their direction of transport

IRE1β negatively regulates IRE1α signaling in response to endoplasmic reticulum stress

IRE1β is an ER stress sensor uniquely expressed in epithelial cells lining mucosal surfaces. Here, we show that intestinal epithelial cells expressing IRE1β have an attenuated unfolded protein response to ER stress. When modeled in HEK293 cells and with purified protein, IRE1β diminishes expression and inhibits signaling by the closely related stress sensor IRE1α. IRE1β can assemble with and inhibit IRE1α to suppress stress-induced XBP1 splicing, a key mediator of the unfolded protein response. In comparison to IRE1α, IRE1β has relatively weak XBP1 splicing activity, largely explained by a nonconserved amino acid in the kinase domain active site that impairs its phosphorylation and restricts oligomerization. This enables IRE1β to act as a dominant-negative suppressor of IRE1α and affect how barrier epithelial cells manage the response to stress at the host–environment interface

Language, Gender and Power Relations: A Study of Power Structure in Dholuo Dirges

This paper examines the image of women emanating from the Luo dirges and their implications in gender relations. It identifies the expressions and idioms used in Luo dirges, describe the gender biased expressions in these linguistic items and show how the terms both reflect and structure power relations between the females and males in the said community. It provides a case study of the relationship between language and gender in dholuo by providing linguistic evidence of sexist ideology reflected in the vocabulary and expressions associated with women. It, in particular, aims to demonstrate the role that language plays in the social categorization and cultural evaluation of power in Luo community, and the extent to which patterns of language use is reflective of Luo social structure, cultural values of inequality and oppression, and sustenance of the existing gender arrangements. It will achieve this through an analysis of the imagery embodied in the language used in Luo dirges. The hypothesis underlying the study is that language has been used to project a negative image of women and sustain patriarchy. This paper provides data on gender discrimination in language and how language reflects social structures and patterns in the society. It shows the impact of language in the society and how it can promote discrimination as well as mirror the injustices in our societies. It shades light on how language in literature plays a major role as far as structuring patterns in the society and socialising members of a society in to the structure is concerned. Keywords: Luo, Dirges, Gender, Languag

On-chip photonic memory elements employing phase-change materials

Open Access Article - Wiley OnlineOpenPhase-change materials integrated into nanophotonic circuits provide a flexible way to realize tunable optical components. Relying on the enormous refractive-index contrast between the amorphous and crystalline states, such materials are promising candidates for on-chip photonic memories. Nonvolatile memory operation employing arrays of microring resonators is demonstrated as a route toward all-photonic chipscale information processing...Deutsche Forschungsgemeinschaft (DFG)Engineering and Physical Sciences Research Council (EPSRC)NSF Materials World Networ