Evidence for modulation of BAG3 by polyomavirus JC early protein

Abstract

Polyomavirus JC (JCV) infects oligodendrocytes and astrocytes in the brain and is the cause of the demyelinating disease progressive multifocal leukoencephalopathy (PML). In cell culture, JCV infection is characterized by severe damage to cellular DNA, which begins early in infection, and a viral cytopathic effect, which is observed late in infection. Nevertheless, these JCV-infected cells show a low level of apoptosis, at both the early and late stages of infection. This suggests that there is conflicting interplay between viral anti-apoptotic pathways that seek to optimize virus production, e.g. through T antigen (T-Ag)-p53 interaction, and cellular pro-apoptotic pathways that seek to eliminate virally infected cells. The apoptosis regulatory protein BAG3 is a member of the human Bcl-2-associated athanogene (BAG) family of proteins, which function as molecular co-chaperones through their interaction with Hsc70/Hsp70 and function in the regulation of the cellular stress response, proliferation and apoptosis. This study showed that BAG3 protein is downregulated upon JCV infection and that this effect is mediated by JCV T-Ag via repression of the BAG3 promoter. The site of action of T-Ag was mapped to an AP2 site in the BAG3 promoter, and gel shift and chromatin immunoprecipitation assays showed that T-Ag inhibited AP2 binding to this site, resulting in downregulation of BAG3 promoter expression. Using BAG3 and T-Ag expression and BAG3 siRNA, it was found that BAG3 and T-Ag had antagonistic effects on the induction of apoptosis, being anti-apoptotic and pro-apoptotic, respectively. The significance of these interactions to the JCV life cycle is discussed. INTRODUCTIONThe human polyomavirus JC (JCV) opportunistically infects the oligodendrocytes and astrocytes of the brain during development of the demyelinating disease progressive multifocal leukoencephalopathy (PML). The pathology of PML is thought to involve the destruction of oligodendrocytes, the myelin-producing cells of the brain, by lytic infection with JCV. In contrast, astrocytes do not undergo lytic infection but rather adopt a 'bizarre' morphology, yet are still productively infected as judged by the production of viral capsid protein observed by immunohistochemistry and virions observed by electron microscopy (Del Valle et al., 2008; Mázló et al., 2001). PML occurs primarily in individuals with highly suppressed immune function, especially those with human immunodeficiency virus (HIV)/AIDS (Hou & Major, 2000;Khalili et al., 2006). The JCV genome is a circular, supercoiled DNA, which is small in size (5130 bp) and has two coding regions (early and late) and a non-coding regulatory region (Frisque et al., 1984;Cole, 1996). Infection with JCV is common in childhood after which the virus becomes latent. In circumstances of severe immunosuppression, e.g. HIV/AIDS, JCV can reactivate in the central nervus system (CNS) leading to the destruction of oligodendrocytes, which produce myelin, and to PML (Hou & Major, 2000;Khalili et al., 2006).We have developed a...

Chaperone-assisted proteostasis is essential for mechanotransduction in mammalian cells

“…Affected viruses include varicella-zoster virus (VZV), 68 polyomavirus JC, 69 Epstein-Barr virus (EBV), 70 herpes simplex virus (HSV) 71 and HIV 72 . In many cases, depletion of BAG3 by small interfering RNA inhibits virus replication.…”

Bag3-Induced Autophagy Is Associated with Degradation of JCV Oncoprotein, T-Ag

“…Furthermore, T-Ag induces cell growth by interacting with cellular transcription pre-initiation complexes, binding to cellular DNA, DNA polymerase α, and ATPase-helicase [12], [13]. In a previous study we demonstrated that JCV T-Ag inhibits expression of Bag3, a member of the Bag, Bcl-2-associated athanogene) family of molecular co-chaperone proteins [14], during the course of productive viral infection of glial cells by suppressing transcription of the Bag3 promoter [15]. Bag3 was initially discovered based on its binding ability to Bcl-2 [16] and has been implicated as a modulator of cellular responses to stress by interacting with the ATPase domain of Hsc70/Hsp70, and suppressing the chaperone activity of the complex [17].…”

Deletion of thebisgene results in a marked increase in the production of corticosterone that is associated with thymic atrophy in mice

“…The prosurvival activity of Bis was supported by later studies showing that Bis is overexpressed in several types of cancer and that the downmodulation of Bis sensitizes the apoptosis of tumor cells induced by chemotherapeutic agents and proteasome inhibitors (9,32,38,39). In addition to the prosurvival activity of Bis, its induction under a variety of stresses in vitro as well as in vivo, including hypoxia and viral infections (3,4,25,31,33,40), suggests that Bis might function as an antistress protein to modulate cellular response, thereby protecting cells from unfavorable environmental stresses. Other biological functions in which Bis is involved include the promotion of differentiation as shown in promyelocytes or E19 embryonic stem cells (45), the regulation of motility migration and invasion (20,24,26), and protein quality control via the promotion of autophagy (5,13,16,19).…”