Borna Disease Virus Nucleoprotein Interacts with the Cdc2-Cyclin B1 Complex

Abstract

Transition from G 2 to M phase, a cell cycle checkpoint, is regulated by the Cdc2-cyclin B1 complex. Here, we report that persistent infection with Borna disease virus (BDV), a noncytolytic RNA virus infecting the central nervous system, results in decelerated proliferation of infected host cells due to a delayed G 2 -to-M transition. Persistent BDV-infected rat fibroblast cells showed reduced proliferation compared to uninfected cells. In pull-down assays we observed an interaction of the viral nucleoprotein with the Cdc2-cyclin B1 complex. Transfection of the viral nucleoprotein but not of the phosphoprotein also results in decelerated proliferation. This phenomenon was found in BDV-susceptible primary rat fibroblast cells and also in primary mouse cells, which are not susceptible to BDV infection. This is the first evidence that the noncytolytic Borna disease virus can manipulate host cell functions via interaction of the viral nucleoprotein with mitotic entry regulators. BDV preferentially infects and persists in nondividing neurons. The present report could give an explanation for this selective choice of host cell by BDV.Cell division of eukaryotic cells is a highly regulated process. One round of cell division requires accurate duplication of DNA during S phase of the cell cycle and proper segregation of duplicated chromosomes during mitosis. Progression through the cell cycle is mediated by the activation of members of a highly conserved family of protein kinases, the cyclindependent kinases (termed CdkЈs or CdcЈs) (22). Activation of a Cdk requires binding to a specific regulatory subunit, termed a cyclin. These Cdk-cyclin complexes function as universal cell cycle regulators, each controlling a specific transition to the next phase in the cell cycle.The initiation of mitosis in vertebrate cells is triggered by the cyclin-dependent protein kinase Cdk1, also known as Cdc2. The activation of Cdc2 begins with the binding of cyclin B1, whose level gradually increases during S and G 2 phases. The Cdc2-cyclin B1 complex remains in an inactive state before mitosis by phosphorylation of Cdc2 at Thr14 and Tyr15. At the end of G 2 , these residues are dephosphorylated by the phosphatase Cdc25C, and the active Cdc2-cyclin B1 complex is then competent to initiate the events of mitosis (19,20,30).It is well known that many DNA viruses interact with the cell cycle machinery, since they are dependent on the DNA synthesis enzymes for viral replication (reviewed in reference 16). In contrast, little is known about the interference of RNA viruses with cell cycle checkpoints, where our knowledge is almost exclusively based on investigations of human immunodeficiency virus (reviewed in reference 5). In addition, it was recently reported that reovirus, a cytolytic, nonenveloped, double-stranded RNA virus, inhibits cellular proliferation by inducing G 2 cell cycle arrest (25).Borna disease virus (BDV), a noncytolytic single-stranded RNA virus, is the only known member of the Bornaviridae, in the order Mononegavirales. BDV is...

Constitutive Activation of the Transcription Factor NF-κB Results in Impaired Borna Disease Virus Replication

“…Therefore, it is tempting to speculate that BDV avoids the infection of neurons with active NF-B during the early phase of infection to ensure effective virus spread and, most obviously, viral persistence. In contrast, at the peak of BDV infection, at about day 21 p.i., BDV infectivity and NF-B activity were found in the same regions of the brain, indicating that the inhibitory effect of BDV on NF-B activity can be overcome in vivo, most probably due to the activation of various cytokines that function as potent NF-B activators in the brain, such as interleukin-1 (38).…”

“…The fact that NF-B promotes neuronal activity or differentiation seems contradictory to the biology of BDV. Recently, we reported that BDV prefers slow proliferative host cells and that BDV is able to reduce the host cell cycle by interfering with the Cdc2/cyclin B1 complex (38). Therefore, it is tempting to speculate that BDV avoids the infection of neurons with active NF-B during the early phase of infection to ensure effective virus spread and, most obviously, viral persistence.…”

“…It has been shown that BDV infection interferes with the activation of the Raf/MEK/ERK signaling cascade and that the blockade of this pathway results in reduced viral spread (21,37). Furthermore, it has been demonstrated that the interaction of the viral nucleoprotein with the Cdc2/cyclin B1 complex results in prolongation of the G 2 phase (38).…”

Roseoloviruses manipulate host cell cycle

“…The cell cycle is controlled by complex interactions that are not yet fully understood. In a number of instances, G2 arrest has been linked to the inhibition or delay in the activation of the Cdk1/cyclin B1 kinase activity [28]. Another mechanism is the interference with mitotic progression.…”

Persistent Borna Disease Virus Infection Confers Instability of HSP70 mRNA in Glial Cells during Heat Stress

“…Furthermore, we have demonstrated that BDV phosphoprotein (P) specifically interacts with a multifunctional protein, HMGB1 (high-mobility group box 1 protein), and interferes with its functions in persistently infected neural cells (19,54). More recently, interaction between BDV nucleoprotein (N) and the Cdc2-cyclin B1 complex has been reported to induce decelerated proliferation of infected rat fibroblast cells (36). These findings suggest that although BDV infection appears to be noncytolytic, persistent infection might widely induce functional fragility in infected CNS cells, leading to neurological abnormalities.…”