• OTUB1 prevents lethal hepatocyte necroptosis through stabilization of c-IAP1 during murine liver inflammation.

      Koschel, Josephin; Nishanth, Gopala; Just, Sissy; Harit, Kunjan; Kröger, Andrea; Deckert, Martina; Naumann, Michael; Schlüter, Dirk; HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany. (Springer Nature, 2021-03-12)
      In bacterial and sterile inflammation of the liver, hepatocyte apoptosis is, in contrast to necroptosis, a common feature. The molecular mechanisms preventing hepatocyte necroptosis and the potential consequences of hepatocyte necroptosis are largely unknown. Apoptosis and necroptosis are critically regulated by the ubiquitination of signaling molecules but especially the regulatory function of deubiquitinating enzymes (DUBs) is imperfectly defined. Here, we addressed the role of the DUB OTU domain aldehyde binding-1 (OTUB1) in hepatocyte cell death upon both infection with the hepatocyte-infecting bacterium Listeria monocytogenes (Lm) and D-Galactosamine (DGal)/Tumor necrosis factor (TNF)-induced sterile inflammation. Combined in vivo and in vitro experiments comprising mice lacking OTUB1 specifically in liver parenchymal cells (OTUB1LPC-KO) and human OTUB1-deficient HepG2 cells revealed that OTUB1 prevented hepatocyte necroptosis but not apoptosis upon infection with Lm and DGal/TNF challenge. Lm-induced necroptosis in OTUB1LPC-KO mice resulted in increased alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) release and rapid lethality. Treatment with the receptor-interacting serine/threonine-protein kinase (RIPK) 1 inhibitor necrostatin-1s and deletion of the pseudokinase mixed lineage kinase domain-like protein (MLKL) prevented liver damage and death of infected OTUB1LPC-KO mice. Mechanistically, OTUB1 reduced K48-linked polyubiquitination of the cellular inhibitor of apoptosis 1 (c-IAP1), thereby diminishing its degradation. In the absence of OTUB1, c-IAP1 degradation resulted in reduced K63-linked polyubiquitination and increased phosphorylation of RIPK1, RIPK1/RIPK3 necrosome formation, MLKL-phosphorylation and hepatocyte death. Additionally, OTUB1-deficiency induced RIPK1-dependent extracellular-signal-regulated kinase (ERK) activation and TNF production in Lm-infected hepatocytes. Collectively, these findings identify OTUB1 as a novel regulator of hepatocyte-intrinsic necroptosis and a critical factor for survival of bacterial hepatitis and TNF challenge.
    • The role of the poly(A) tract in the replication and virulence of tick-borne encephalitis virus.

      Asghar, Naveed; Lee, Yi-Ping; Nilsson, Emma; Lindqvist, Richard; Melik, Wessam; Kröger, Andrea; Överby, Anna K; Johansson, Magnus; Helmholtz Centre for infection research. Inhoffenstr. 7. 38124 Braunschweig, Germany. (2016-12-16)
      The tick-borne encephalitis virus (TBEV) is a flavivirus transmitted to humans, usually via tick bites. The virus causes tick-borne encephalitis (TBE) in humans, and symptoms range from mild flu-like symptoms to severe and long-lasting sequelae, including permanent brain damage. It has been suggested that within the population of viruses transmitted to the mammalian host, quasispecies with neurotropic properties might become dominant in the host resulting in neurological symptoms. We previously demonstrated the existence of TBEV variants with variable poly(A) tracts within a single blood-fed tick. To characterize the role of the poly(A) tract in TBEV replication and virulence, we generated infectious clones of Torö-2003 with the wild-type (A)3C(A)6 sequence (Torö-6A) or with a modified (A)3C(A)38 sequence (Torö-38A). Torö-38A replicated poorly compared to Torö-6A in cell culture, but Torö-38A was more virulent than Torö-6A in a mouse model of TBE. Next-generation sequencing of TBEV genomes after passaging in cell culture and/or mouse brain revealed mutations in specific genomic regions and the presence of quasispecies that might contribute to the observed differences in virulence. These data suggest a role for quasispecies development within the poly(A) tract as a virulence determinant for TBEV in mice.
    • SARS-CoV-2 neutralizing human recombinant antibodies selected from pre-pandemic healthy donors binding at RBD-ACE2 interface.

      Bertoglio, Federico; Meier, Doris; Langreder, Nora; Steinke, Stephan; Rand, Ulfert; Simonelli, Luca; Heine, Philip Alexander; Ballmann, Rico; Schneider, Kai-Thomas; Roth, Kristian Daniel Ralph; et al. (NPG, 2021-03-11)
      COVID-19 is a severe acute respiratory disease caused by SARS-CoV-2, a new recently emerged sarbecovirus. This virus uses the human ACE2 enzyme as receptor for cell entry, recognizing it with the receptor binding domain (RBD) of the S1 subunit of the viral spike protein. We present the use of phage display to select anti-SARS-CoV-2 spike antibodies from the human naïve antibody gene libraries HAL9/10 and subsequent identification of 309 unique fully human antibodies against S1. 17 antibodies are binding to the RBD, showing inhibition of spike binding to cells expressing ACE2 as scFv-Fc and neutralize active SARS-CoV-2 virus infection of VeroE6 cells. The antibody STE73-2E9 is showing neutralization of active SARS-CoV-2 as IgG and is binding to the ACE2-RBD interface. Thus, universal libraries from healthy human donors offer the advantage that antibodies can be generated quickly and independent from the availability of material from recovering patients in a pandemic situation.