Borna Disease Virus Phosphoprotein Binds a Neurite Outgrowth Factor, Amphoterin/HMG-1

Abstract

The Borna disease virus (BDV) p24 phosphoprotein is an abundant protein in BDV-infected cultured cells and animal brains. Therefore, there is a possibility that binding of the p24 protein to cellular factor(s) induces functional alterations of infected neural cells in the brain. To identify a cellular protein(s) that interacts with BDV p24 protein, we performed far-Western blotting with extracts from various cell lines. Using recombinant p24 protein as a probe, we detected a 30-kDa protein in all cell lines examined. Binding between the 30-kDa and BDV p24 proteins was also demonstrated using BDV p24 affinity and ion-exchange chromatography columns. Microsequence analysis of the purified 30-kDa protein revealed that its N terminus showed complete homology with rat amphoterin protein, which is a neurite outgrowth factor abundant in the brain during development. Mammalian two-hybrid and immunoprecipitation analyses also confirmed that amphoterin is a specific target for the p24 protein in vivo. Furthermore, we showed that infection by BDV, as well as purified p24 protein in the medium, significantly decreased cell process outgrowth of cells grown on laminin, indicating the functional inhibition of amphoterin by interaction with the p24 protein. Immunohistochemical analysis revealed decreased levels of amphoterin protein at the leading edges of BDV-infected cells. Moreover, the expression of the receptor for advanced glycation end products, of which the extracellular moiety is a receptor for amphoterin, was not significantly activated in BDV-infected cells during the process of extension, suggesting that the secretion of amphoterin from the cell surface is inhibited by the binding of the p24 protein. These results suggested that BDV infection may cause direct damage in the developing brain by inhibiting the function of amphoterin due to binding by the p24 phosphoprotein.Borna disease virus (BDV) is the prototype of a new family, Bornaviridae, within the nonsegmented negative-strand RNA viruses, the Mononegavirales (12, 45), which is characterized by low productivity, neurotropism, and nuclear localization for transcription and replication (8). Although BDV was originally described as an agent of nonpurulent encephalomyelitis in horses in Germany (40), BDV infection has now been found in a wide range of vertebrate species, including sheep, cattle, cats, and ostriches (6,28,40). Recent epidemiological studies have suggested that BDV infection also occurs in humans and that it may be related to certain psychiatric diseases (7,13,22,27,43). Human BDV was isolated from the peripheral blood granulocyte cell fraction of a psychiatric patient (35). Furthermore, we have also demonstrated BDV infection in the brain of a schizophrenic patient with a very recent onset of disease (32).BDV shows noncytolytic replication in cultured cells. However, neonatal rats infected with BDV develop persistent infection and show developmental disturbances affecting specific areas of the brain (4,9,14,19,42). Neonatal BDV infection also result...

Enhanced Neurovirulence of Borna Disease Virus Variants Associated with Nucleotide Changes in the Glycoprotein and L Polymerase Genes

“…In CRP5-infected rats with or without encephalitis, rapid degeneration of pyramidal neurons in the CA3/4 region of the hippocampus was observed, a clear departure from the typically protracted hippocampal dentate gyrus damage usually observed following CRP3 infection (9). Thus, these studies demonstrate that in the Lewis rat, CRNP5 infection causes a significantly different disease phenotype than CRP3 infection, whether due to direct virus cytopathic effect, neuroimmune responses (8,26,36,45), or other pathogenic processes (e.g., the inhibition of the function of amphoterin, a neurite outgrowth-promoting adhesive factor, or the indication of neurotrophins) (27,58).…”

Glial expression of Borna disease virus phosphoprotein induces behavioral and neurological abnormalities in transgenic mice

“…Intriguingly, we have recently found that BDV P directly interacts with a neurite outgrowth factor, HMGB1, and inhibits its function in cultured neuronal cells (18). Considering the roles of HMGB1 in neurite outgrowth, cell migration, and cellular survival in developing brains (19), it is also possible that P can affect neuronal development by inhibiting HMGB1 function in glial cells.…”

“…Here we use transgenic mice expressing the phosphoprotein (P) of BDV in the CNS to understand the linkage between CNS virus infection and neurobehavioral disorders, as well as to elucidate the molecular nature of BDV neuropathogenesis. The P is abundantly expressed in infected animal brains and interferes with a multifunctional protein, HMGB1, in neuronal cells (18,19), suggestive of a neurotropic effect of this protein in the infected CNS. We demonstrate that BDV P transgenic mice develop behavioral abnormalities resembling those in BDV-infected animals, and that the transgenic brains show severe neurobiological disturbances linked to neurobehavioral disorders.…”

Borna Disease Virus Phosphoprotein Represses p53-Mediated Transcriptional Activity by Interference with HMGB1

“…In a recent study, it was revealed that BDV P binds directly to a multifunctional protein, HMGB1 (also called amphoterin or HMG-1), and inhibits its function in cultured neural cells (30). A line of evidence has suggested that HMGB1 plays important roles not only in the neurite outgrowth of neurons but also in cell survival through interaction with its cellular receptor, RAGE (receptor for advanced glycation end products) (36).…”