Ariel - Volume 4 Number 6

Editors David A. Jacoby Eugenia Miller Tom Williams Associate Editors Paul Bialas Terry Burt Michael Leo Gail Tenikat Editor Emeritus and Business Manager Richard J. Bonnano Movie Editor Robert Breckenridge Staff Richard Blutstein Mary F. Buechler J.D. Kanofsky Rocket Weber David Maye

Intracellular Bacteria Encode Inhibitory SNARE-Like Proteins

Pathogens use diverse molecular machines to penetrate host cells and manipulate intracellular vesicular trafficking. Viruses employ glycoproteins, functionally and structurally similar to the SNARE proteins, to induce eukaryotic membrane fusion. Intracellular pathogens, on the other hand, need to block fusion of their infectious phagosomes with various endocytic compartments to escape from the degradative pathway. The molecular details concerning the mechanisms underlying this process are lacking. Using both an in vitro liposome fusion assay and a cellular assay, we showed that SNARE-like bacterial proteins block membrane fusion in eukaryotic cells by directly inhibiting SNARE-mediated membrane fusion. More specifically, we showed that IncA and IcmG/DotF, two SNARE-like proteins respectively expressed by Chlamydia and Legionella, inhibit the endocytic SNARE machinery. Furthermore, we identified that the SNARE-like motif present in these bacterial proteins encodes the inhibitory function. This finding suggests that SNARE-like motifs are capable of specifically manipulating membrane fusion in a wide variety of biological environments. Ultimately, this motif may have been selected during evolution because it is an efficient structural motif for modifying eukaryotic membrane fusion and thus contribute to pathogen survival

The diagnosis and management of idiosyncratic drug‐induced liver injury

Drug‐induced liver injury (DILI) is an uncommon but important cause of liver disease that can arise after exposure to a multitude of drugs and herbal and dietary supplements. The severity of idiosyncratic DILI varies from mild serum aminotransferase elevations to the development of severe liver injury that can progress to acute liver failure resulting in death or liver transplantation within days of DILI onset. Chronic liver injury that persists for more than 6 months after DILI onset is also becoming increasingly recognized in up to 20% of DILI patients. Host demographic (age, gender, race), clinical and laboratory features at DILI onset have been associated with the severity and outcome of liver injury in DILI patients. In addition to cessation of the suspect drug, other medical interventions including the use of N‐acetylcysteine and corticosteroids in selected patients have shown some clinical benefit, but additional prospective studies are needed. A number of promising diagnostic, prognostic and mechanistic serum and genetic biomarkers may help improve our understanding of the pathogenesis and treatment of idiosyncratic DILI.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147192/1/liv13931.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147192/2/liv13931_am.pd

SNARE Protein Mimicry by an Intracellular Bacterium

Many intracellular pathogens rely on host cell membrane compartments for their survival. The strategies they have developed to subvert intracellular trafficking are often unknown, and SNARE proteins, which are essential for membrane fusion, are possible targets. The obligate intracellular bacteria Chlamydia replicate within an intracellular vacuole, termed an inclusion. A large family of bacterial proteins is inserted in the inclusion membrane, and the role of these inclusion proteins is mostly unknown. Here we identify SNARE-like motifs in the inclusion protein IncA, which are conserved among most Chlamydia species. We show that IncA can bind directly to several host SNARE proteins. A subset of SNAREs is specifically recruited to the immediate vicinity of the inclusion membrane, and their accumulation is reduced around inclusions that lack IncA, demonstrating that IncA plays a predominant role in SNARE recruitment. However, interaction with the SNARE machinery is probably not restricted to IncA as at least another inclusion protein shows similarities with SNARE motifs and can interact with SNAREs. We modelled IncA's association with host SNAREs. The analysis of intermolecular contacts showed that the IncA SNARE-like motif can make specific interactions with host SNARE motifs similar to those found in a bona fide SNARE complex. Moreover, point mutations in the central layer of IncA SNARE-like motifs resulted in the loss of binding to host SNAREs. Altogether, our data demonstrate for the first time mimicry of the SNARE motif by a bacterium

Prevention of cultured rat stellate cell transformation and endothelin-B receptor upregulation by retinoic acid

1. Physiologically, perisinusoidal hepatic stellate cells (HSC) are quiescent and store retinoids. During liver injury and in cell culture, HSC transform into proliferating myofibroblast-like cells that express α-smooth muscle actin (α-sma) and produce excessive amounts of extracellular matrix. During transformation (also known as activation), HSC are depleted of the retinoid stores, and their expression of the endothelin-1 (ET-1) system is increased. ET-1 causes contraction of transformed HSC and is implicated in their proliferation and fibrogenic activity. In order to understand the association between retinoids, ET-1 and the activation of HSC, we investigated the effect of 13-cis-retinoic acid on the transformation of cultured HSC and the expression of ET-1 system. 2. HSC derived from normal rat liver were maintained for 10–12 days in a medium supplemented with 5% serum and containing 2.5 μM retinoic acid without or with 50 nM ET-1 (ETA+ETB agonist) or sarafotoxin S6c (ETB agonist). In another set of experiments, cells treated for 10–12 days with vehicle (ethanol) or retinoic acid were challenged with ET-1 or sarafotoxin S6c, and various determinations were made at 24 h. 3. Retinoic acid inhibited transformation and proliferation of HSC as assessed by morphological characteristics, expression of α-sma, bromodeoxyuridine incorporation and cell count. Retinoic acid also prevented upregulation of ETB receptors without affecting ET-1 or ETA expression. Total protein synthesis ([(3)H]leucine incorporation), collagen α types I mRNA expression and collagen synthesis ([(3)H]proline incorporation) were lower in retinoic acid-treated cells. Although ET-1-treated cells were morphologically similar to the control cells, their expression of α-smooth muscle actin was significantly inhibited. The presence of retinoic acid in the medium during treatment with ET-1 caused further reduction in the expression of α-smooth muscle actin. ET-1 and sarafotoxin S6c stimulated total protein synthesis in vehicle- and retinoic acid-treated cells, but collagen synthesis only in the latter. 4. These results showing prevention of HSC activation and negative regulation of ETB receptor expression in them by retinoic acid may have important pathophysiologic implications