Citations

Chronic hepatitis B (CHB), a major global public health burden, is characterized by the presence of high circulating levels of non-infectious subviral particles (SVPs). These SVPs are mainly composed of small hepatitis B surface antigen (SHBs) and are associated with a dysfunctional HBV-specific immune response. Previous studies exploring the cellular mechanisms and molecular pathways by which SVPs are secreted from hepatocytes have utilized either non-hepatic cells or whole-genome HBV-integrated hepatoma cell lines in which SHBs can also be secreted as a component of the virion envelope. In this study, we provide a detailed examination of SHBs trafficking using biochemical approaches coupled with high-resolution confocal microscopy and live-cell imaging via a novel fluorophore-tagged SHBs probe in both HepG2 and primary human hepatocytes stably expressing SHBs. Our results provide evidence that SHBs utilize a modified ER-Golgi secretory pathway with transit from the ER to the multivesicular body and lysosomal/late endosomal compartments. Importantly, we identified the autophagy adapters ATG5 and LC3B, and the ER-phagy protein atlastin 3 (ATL3), central to mediating SHBs secretion. These findings suggest that SHBs is trafficked through a non-canonical path for secretion and provides new potential therapeutic targets for the treatment of CHB.

Introduction Increasing publication of fraudulent clinical trials poses a serious threat to evidence-based medicine. In the VITALITY Study I, we demonstrated that contamination by retracted trials significantly distorts evidence synthesis. The upcoming VITALITY Study II will take a step further and investigate how such problematic evidence undermines the credibility of guideline recommendations. Methods and analyses The VITALITY Study II will adopt a retrospective cohort design and will be structured as three work packages (WPs). To start with, a cohort of clinical practice guidelines (CPGs) that were contaminated by retracted trials and/or meta-analyses that included retracted trials will be established based on forward citation searching (WP1). Then, recommendations from these CPGs that used evidence from retracted trials and/or meta-analyses that synthesised these retracted trials will be re-evaluated after removing such problematic evidence, in terms of both the direction and strength of effect sizes (WP2). Finally, the subsequent impact on patient outcomes attributable to distorted recommendations will be estimated on a hypothetical population, measured by the number of expected benefit loss and the number of expected harm increment per 100 000 patients (WP3). Ethics and dissemination Formal ethical approval is not necessary for this study as it does not involve human or animal participants, nor does it involve the collection of primary data. We will disseminate the findings through publication in peer-reviewed journals and, whenever possible, presentations at academic conferences.

It is well established that many tumor types possess defective autophagic pathways. Several studies have reported that the transmembrane, autophagic lipid scramblase ATG9B is altered in multiple cancers, suggesting that this dysregulation could contribute to oncogenesis. Therefore, the goal of this study was to define the cellular distribution of ATG9B in two different tumor cell types and to provide insights into its cellular function. Surprisingly, we found that ATG9B shows a modest association with autophagic structures and exhibits a unique and prominent localization to mitochondria, in contrast to its related form ATG9A. Upon expression of tagged ATG9B forms, this mitochondrial distribution was accompanied by aberrant changes in mitochondrial morphology as well as a reduction in the mitochondrial membrane potential and the release of mtDNA. Few indicators for ATG9B-dependent mitophagy were noted. Instead, ATG9B overexpression led to pronounced apoptotic cell death as assessed by a variety of indicators. Further, we find that the N-terminal sequence of ATG9B acts as a mitochondrial targeting domain and that expression of this peptide alone can induce apoptotic cell death. These findings provide new insights into a putative cellular localization and function for ATG9B.

Rab32 is a small GTPase and molecular switch implicated in vesicular trafficking. Rab32 is also an A-Kinase Anchoring Protein (AKAP), which anchors cAMP-dependent Protein Kinase (PKA) to specific subcellular locations and specifies PKA phosphorylation of nearby substrates. Surprisingly, we found that a form of Rab32 deficient in PKA binding (Rab32 L188P) relocalized away from the Golgi apparatus and induced a marked disruption in Golgi organization, assembly, and dynamics. Although Rab32 L188P did not cause a global defect in PKA activity, our data indicate that Rab32 facilitates the phosphorylation of a specific PKA substrate. We uncovered a direct interaction between Rab32 and the adaptor protein optineurin (OPTN), which regulates Golgi dynamics. Further, our data indicate that optineurin is phosphorylated by PKA at Ser342 in a Rab32-dependent manner. Critically, blocking phosphorylation at OPTN Ser342 leads to Golgi fragmentation, and a phospho-mimetic version of OPTN rescues Golgi defects induced by Rab32 L188P. Finally, Rab32 AKAP function and OPTN phosphorylation are required for Golgi repositioning during cell migration, contributing to tumor cell invasion. Together, these data reveal a role for Rab32 in regulating Golgi dynamics through PKA-mediated phosphorylation of OPTN.

ABSTRACT The large GTPase dynamin is a mechanoenzyme that participates in the scission of nascent vesicles from the plasma membrane. Recently, dynamin has been demonstrated to associate with the Golgi apparatus in mammalian cells by morphological and biochemical methods. Additional studies using a well characterized, cell-free assay have supported these findings by demonstrating a requirement for dynamin function in the formation of clathrin-coated, and non-clathrin-coated vesicles from the trans-Golgi network (TGN). In this study, we tested if dynamin participates in Golgi function in living cells through the expression of a dominant negative dynamin construct (K44A). Cells co-transfected to express this mutant dynamin and a GFP-tagged Golgi resident protein (TGN38) exhibit Golgi structures that are either compacted, vesiculated, or tubulated. Electron microscopy of these mutant cells revealed large numbers of Golgi stacks comprised of highly tubulated cisternae and an extraordinary number of coated vesicle buds. Cells expressing mutant dynamin and GFP-tagged VSVG demonstrated a marked retention (8- to 11-fold) of the nascent viral G-protein in the Golgi compared to control cells. These observations in living cells are consistent with previous morphological and in vitro studies demonstrating a role for dynamin in the formation of secretory vesicles from the TGN.

Currently, the hepatocellular trafficking pathways that are used by the hepatitis B virus (HBV) during viral infection and shedding are poorly defined. It is known that the HBV uses late endosomal and multivesicular body (MVB) compartments for assembly and release. The intraluminal vesicles (ILVs) generated within MVBs have also been implicated in the late synthesis stages of a variety of pathogenic viruses. We recently observed that the HBV within infected hepatocytes appears to associate with the tetraspanin protein CD63, known to be a prominent and essential component of ILVs. Immunofluorescence microscopy of HBV‐expressing cells showed that CD63 colocalized with HBV proteins (large hepatitis B surface antigens [LHBs] and hepatitis B core) and labeled an exceptionally large number of secreted extracellular vesicles of uniform size. Small interfering RNA (siRNA)–mediated depletion of CD63 induced a substantial accumulation of intracellular LHBs protein but did not alter the levels of either intracellular or extracellular HBV DNA, nor pregenomic RNA. Consistent with these findings, we found that markedly less LHBs protein was associated with the released HBV particles from CD63 siRNA‐treated cells. Importantly, the HBV viral particles that were shed from CD63‐depleted cells were substantially less infective than those collected from control cells with normal CD63 levels. Conclusion: These findings implicate the tetraspanin protein CD63 as a marker and an important component in the formation and release of infectious HBV particles.

Dyn2 and α-actinin 4 interact directly to regulate invasive cell migration and the stabilization of invadopodia. Intriguingly, this is specific for α-actinin 4, and not the highly related protein α-actinin 1. These findings elucidate a novel mechanism of regulating cell migration, with important implications for invasive tumor cells.

ABSTRACT Epithelial cells, such as liver-resident hepatocytes, rely heavily on the Rab family of small GTPases to perform membrane trafficking events that dictate cell physiology and metabolism. Not surprisingly, disruption of several Rab proteins can manifest in metabolic diseases or cancer. Rab32 is expressed in many secretory epithelial cells but its role in cellular metabolism is virtually unknown. In this study, we find that Rab32 associates with lysosomes and regulates proliferation and cell size of Hep3B hepatoma and HeLa cells. Specifically, we identify that Rab32 supports the mechanistic target of rapamycin complex 1 (mTORC1) signaling under basal and amino acid-stimulated conditions. Consistent with inhibited mTORC1, an increase in nuclear TFEB localization and lysosome biogenesis is also observed in Rab32-depleted cells. Finally, we find that Rab32 interacts with mTOR kinase, and that loss of Rab32 reduces the association of mTOR and mTORC1 pathway proteins with lysosomes, suggesting that Rab32 regulates lysosomal mTOR trafficking. In summary, these findings suggest that Rab32 functions as a novel regulator of cellular metabolism through supporting mTORC1 signaling. This article has an associated First Person interview with the first author of the paper.

Background and Aims Hepatocytes play a central role in storage and utilization of fat by the liver. Selective breakdown of lipid droplets (LDs) by autophagy (also called lipophagy) is a key process utilized to catabolize these lipids as an energy source. How the autophagic machinery is selectively targeted to LDs, where it mediates membrane engulfment and subsequent degradation, is unclear. Recently, we have reported that two distinct GTPases, the mechanoenzyme, dynamin2 (Dyn2), and the small regulatory Rab GTPase, Rab10, work independently at distinct steps of lipophagy in hepatocytes. Approach and Results In an attempt to understand how these proteins are regulated and recruited to autophagic organelles, we performed a nonbiased biochemical screen for Dyn2‐binding partners and found that Dyn2 actually binds Rab10 directly through a defined effector domain of Rab10 and the middle domain of Dyn2. These two GTPases can be observed to interact transiently on membrane tubules in hepatoma cells and along LD‐centric autophagic membranes. Most important, we found that a targeted disruption of this interaction leads to an inability of cells to trim tubulated cytoplasmic membranes, some of which extend from lipophagic organelles, resulting in LD accumulation. Conclusions This study identifies a functional, and direct, interaction between Dyn2 and a regulatory Rab GTPase that may play an important role in hepatocellular metabolism.

Abstract Background: The fastest growing cause of cancer related death is hepatocellular carcinoma (HCC), in part due to the rising prevalence of nonalcoholic steatohepatitis (NASH). HCC cases are expected to increase during 2015-2030. Cholecystokinin (CCK), blood levels are increased in those consuming high fat diets and CCK receptors have been identified in normal liver, fibroblasts, and immune cells. Hypothesis: We hypothesize that CCK receptor blockade could decrease NASH and prevent HCC in a mouse model.Methods: We examined whether CCK receptor blockade with proglumide could decrease NASH in the choline deficient ethionine supplemented (CDE)-diet mouse model. Two cohorts of Female C57BL/6 mice (N=65) mice were examined: (1) a preventive study in which mice were treated for 12 and 18 weeks to determine if proglumide could prevent NASH and HCC and (2) a ‘reversal study’ in which histologic and biochemical NASH was induced on a 75% CDE high fat diet for 12 weeks followed by treatment with proglumide for 6 weeks (until week 18) while remaining on the CDE diet to determine if CCK-receptor blockade could reverse NASH once established. Control mice received the same high fat diet with choline and half received proglumide therapy. Results: Alanine aminotransferase, aspartate aminotransferases, and bilirubin were increased in mice on the CDE/Regular (untreated water) diet and these values returned to near normal with proglumide therapy in the prevention study and also reversed after NASH was established. Histologic scoring showed significant decreased inflammation, fibrosis and steatosis in mice on the high fat CDE diet when treated with proglumide. 35% of the mice (N=23) at week 18 developed HCC or dysplastic nodules on the CDE diet while none of the mice in the CDE/proglumide prevention (N=15) or reversal therapy groups (N=15) had HCC. Mice on the lard-control diet had fatty livers at week 18 but no evidence of NASH histologically or biochemically and no HCC. Fibrosis was decreased in mice treated with proglumide as evidence by Masson’s trichrome stain and Western blot for FAP. Gene expression of the liver’s collagen-4, TGFβR11, PDGH-Rβ, and collagen-1α1 as determined by qRT-PCR decreased with proglumide treatment. Control diet fed mice had normal serum tests and fibrosis biomarkers. Conclusion: This data supports our novel hypothesis that CCK receptors play a role in NASH-associated HCC. CCK receptor blockade decreased histologic and biochemical evidence of NASH and prevented HCC. Since proglumide has already been tested in human subjects for peptic ulcer disease decades ago and is known to be orally bioavailable, results of our study could easily be translated into a clinical trial in human subjects to improve NASH to prevent HCC. Supported by AGA Research Foundation, Ruesch Foundation, and a grant from NIH, TL1TR001431 Citation Format: Martha D. Gay, Victor Ciofoaia, Sandeep Nadella, Hong Cao, Matthew Huber, Robin D. Tucker, Narayan Shivapurkar, Bhaskar Kallakury, Alexander H. Kroemer, Jill P. Smith. Cholecystokinin receptor antagonist proglumide reverses nonalcoholic steatohepatitis and prevents hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2728.