Misfolding of CasBrE SU is reversed by interactions with 4070A Env: implications for gammaretroviral neuropathogenesis.
Animals; Cell Line; env/*metabolism; Experimental/*virology; Gene Products; Helper Viruses/metabolism/pathogenicity/*physiology; Leukemia; Leukemia Virus; Mice; Motor Neuron Disease/*virology; Murine/metabolism/pathogenicity/*physiology; Neural Stem Cells/*virology; Protein Binding; Protein Folding; Protein Subunits/metabolism; Retroviridae Infections/*virology; Tumor Virus Infections/*virology; Virulence
BACKGROUND: CasBrE is a neurovirulent murine leukemia virus (MLV) capable of inducing paralytic disease with associated spongiform neurodegeneration. The neurovirulence of this virus has been genetically mapped to the surface expressed subunit (SU) of the env gene. However, CasBrE SU synthesized in the absence of the transmembrane subunit (TM) does not retain ecotropic receptor binding activity, indicating that folding of the receptor binding domain (RBD) requires this domain. Using a neural stem cell (NSC) based viral trans complementation approach to examine whether misfolded CasBrE SU retained neurovirulence, we observed CasBrE SU interaction with the "non-neurovirulent" amphotropic helper virus, 4070A which restored functional activity of CasBrE SU. RESULTS: Herein, we show that infection of NSCs expressing CasBrE SU with 4070A (CasES+4070A-NSCs) resulted in the redistribution of CasBrE SU from a strictly secreted product to include retention on the plasma membrane. Cell surface cross-linking analysis suggested that CasBrE SU membrane localization was due to interactions with 4070A Env. Viral particles produced from CasES+4070A-NSCS contained both CasBrE and 4070A gp70 Env proteins. These particles displayed ecotropic receptor-mediated infection, but were still 100-fold less efficient than CasE+4070A-NSC virus. Infectious center analysis showed CasBrE SU ecotropic transduction efficiencies approaching those of NSCs expressing full length CasBrE Env (CasE; SU+TM). In addition, CasBrE SU-4070A Env interactions resulted in robust ecotropic superinfection interference indicating near native intracellular SU interaction with its receptor, mCAT-1. CONCLUSIONS: In this report we provided evidence that 4070A Env and CasBrE SU physically interact within NSCs leading to CasBrE SU retention on the plasma membrane, incorporation into viral particles, restoration of mCAT-1 binding, and capacity for initiation of TM-mediated fusion events. Thus, heterotropic Env-SU interactions facilitates CasBrE SU folding events that restore Env activity. These findings are consistent with the idea that one protein conformation acts as a folding scaffold or nucleus for a second protein of similar primary structure, a process reminiscent of prion formation. The implication is that template-based protein folding may represent an inherent feature of neuropathogenic proteins that extends to retroviral Envs.
Li Ying; Lynch William P
Retrovirology
2010
2010-11
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1186/1742-4690-7-93" target="_blank" rel="noreferrer noopener">10.1186/1742-4690-7-93</a>
Postinhibitory rebound neurons and networks are disrupted in retrovirus-induced spongiform neurodegeneration.
Action Potentials/physiology; Animals; Antigens/metabolism; auditory midbrain; Calcium/metabolism; env/metabolism; Experimental/physiopathology; Gene Products; Hearing Loss/physiopathology; Inferior Colliculi/physiopathology/virology; inferior colliculus; Leukemia; Leukemia Virus; Membrane Potentials/physiology; Mice; Microglia/physiology/virology; Murine/*physiology; Neural Pathways/physiopathology; Neurodegenerative Diseases/*physiopathology; Neuroglia/physiology/virology; Neurons/*physiology/virology; Patch-Clamp Techniques; postinhibitory rebound neurons; Proteoglycans/metabolism; Retroviridae Infections/*physiopathology/virology; retrovirus; Tissue Culture Techniques; Tumor Virus Infections/*physiopathology/virology; Voltage-Sensitive Dye Imaging; voltage-sensitive dyes
Certain retroviruses induce progressive spongiform motor neuron disease with features resembling prion diseases and amyotrophic lateral sclerosis. With the neurovirulent murine leukemia virus (MLV) FrCasE, Env protein expression within glia leads to postsynaptic vacuolation, cellular effacement, and neuronal loss in the absence of neuroinflammation. To understand the physiological changes associated with MLV-induced spongiosis, and its neuronal specificity, we employed patch-clamp recordings and voltage-sensitive dye imaging in brain slices of the mouse inferior colliculus (IC), a midbrain nucleus that undergoes extensive spongiosis. IC neurons characterized by postinhibitory rebound firing (PIR) were selectively affected in FrCasE-infected mice. Coincident with Env expression in microglia and in glia characterized by NG2 proteoglycan expression (NG2 cells), rebound neurons (RNs) lost PIR, became hyperexcitable, and were reduced in number. PIR loss and hyperexcitability were reversed by raising internal calcium buffer concentrations in RNs. PIR-initiated rhythmic circuits were disrupted, and spontaneous synchronized bursting and prolonged depolarizations were widespread. Other IC neuron cell types and circuits within the same degenerative environment were unaffected. Antagonists of NMDA and/or AMPA receptors reduced burst firing in the IC but did not affect prolonged depolarizations. Antagonists of L-type calcium channels abolished both bursts and slow depolarizations. IC infection by the nonneurovirulent isogenic virus Friend 57E (Fr57E), whose Env protein is structurally similar to FrCasE, showed no RN hyperactivity or cell loss; however, PIR latency increased. These findings suggest that spongiform neurodegeneration arises from the unique excitability of RNs, their local regulation by glia, and the disruption of this relationship by glial expression of abnormal protein.
Li Ying; Davey Robert A; Sivaramakrishnan Shobhana; Lynch William P
Journal of neurophysiology
2014
2014-08
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1152/jn.00227.2014" target="_blank" rel="noreferrer noopener">10.1152/jn.00227.2014</a>
Ecotropic Murine Leukemia Virus Infection of Glial Progenitors Interferes with Oligodendrocyte Differentiation: Implications for Neurovirulence.
3T3 Cells; Animals; Cell Line; Cell Proliferation; Cell Survival; env/biosynthesis; Female; Gene Products; Leukemia Virus; Male; Mice; Motor Neuron Disease/*virology; Murine/*pathogenicity; Neural Stem Cells/*virology; Neurogenesis/*physiology; Neuroglia/*virology; Oligodendroglia/cytology/virology; Retroviridae Infections/*complications; Transgenic
UNLABELLED: Certain murine leukemia viruses (MLVs) are capable of inducing fatal progressive spongiform motor neuron disease in mice that is largely mediated by viral Env glycoprotein expression within central nervous system (CNS) glia. While the etiologic mechanisms and the glial subtypes involved remain unresolved, infection of NG2 glia was recently observed to correlate spatially and temporally with altered neuronal physiology and spongiogenesis. Since one role of NG2 cells is to serve as oligodendrocyte (OL) progenitor cells (OPCs), we examined here whether their infection by neurovirulent (FrCasE) or nonneurovirulent (Fr57E) ecotropic MLVs influenced their viability and/or differentiation. Here, we demonstrate that OPCs, but not OLs, are major CNS targets of both FrCasE and Fr57E. We also show that MLV infection of neural progenitor cells (NPCs) in culture did not affect survival, proliferation, or OPC progenitor marker expression but suppressed certain glial differentiation markers. Assessment of glial differentiation in vivo using transplanted transgenic NPCs showed that, while MLVs did not affect cellular engraftment or survival, they did inhibit OL differentiation, irrespective of MLV neurovirulence. In addition, in chimeric brains, where FrCasE-infected NPC transplants caused neurodegeneration, the transplanted NPCs proliferated. These results suggest that MLV infection is not directly cytotoxic to OPCs but rather acts to interfere with OL differentiation. Since both FrCasE and Fr57E viruses restrict OL differentiation but only FrCasE induces overt neurodegeneration, restriction of OL maturation alone cannot account for neuropathogenesis. Instead neurodegeneration may involve a two-hit scenario where interference with OPC differentiation combined with glial Env-induced neuronal hyperexcitability precipitates disease. IMPORTANCE: A variety of human and animal retroviruses are capable of causing central nervous system (CNS) neurodegeneration manifested as motor and cognitive deficits. These retroviruses infect a variety of CNS cell types; however, the specific role each cell type plays in neuropathogenesis remains to be established. The NG2 glia, whose CNS functions are only now emerging, are a newly appreciated viral target in murine leukemia virus (MLV)-induced neurodegeneration. Since one role of NG2 glia is that of oligodendrocyte progenitor cells (OPCs), we investigated here whether their infection by the neurovirulent MLV FrCasE contributed to neurodegeneration by affecting OPC viability and/or development. Our results show that both neurovirulent and nonneurovirulent MLVs interfere with oligodendrocyte differentiation. Thus, NG2 glial infection could contribute to neurodegeneration by preventing myelin formation and/or repair and by suspending OPCs in a state of persistent susceptibility to excitotoxic insult mediated by neurovirulent virus effects on other glial subtypes.
Li Ying; Dunphy Jaclyn M; Pedraza Carlos E; Lynch Connor R; Cardona Sandra M; Macklin Wendy B; Lynch William P
Journal of virology
2016
2016-01
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1128/JVI.03156-15" target="_blank" rel="noreferrer noopener">10.1128/JVI.03156-15</a>
Unique N-linked glycosylation of CasBrE Env influences its stability, processing, and viral infectivity but not its neurotoxicity.
*Protein Processing; Animals; Canavan Disease/pathology/virology; DNA Mutational Analysis; env/genetics/*metabolism; Gene Products; Glycosylation; Leukemia Virus; Mice; Murine/genetics/*pathogenicity/*physiology; Post-Translational; Virulence; Virus Replication
The envelope protein (Env) from the CasBrE murine leukemia virus (MLV) can cause acute spongiform neurodegeneration analogous to that induced by prions. Upon central nervous system (CNS) infection, Env is expressed as multiple isoforms owing to differential asparagine (N)-linked glycosylation. Because
Renszel Krystal M; Traister Russell S; Lynch William P
Journal of virology
2013
2013-08
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1128/JVI.00392-13" target="_blank" rel="noreferrer noopener">10.1128/JVI.00392-13</a>