SMAD proteins of oligodendroglial cells regulate transcription of JC virus early and late genes coordinately with the Tat protein of human immunodeficiency virus type 1

Abstract

JC virus (JCV) is the aetiological agent of progressive multifocal leukoencephalopathy (PML), a fatal, demyelinating disease of the brain affecting people with AIDS. Although immunosuppression is involved in infection of the brain by JCV, a direct influence of human immunodeficiency virus type 1 (HIV-1) has also been established. The Tat protein of HIV-1 has been implicated in activation of the cytokine transforming growth factor (TGF)-β in HIV-1-infected cells and in stimulating JCV gene transcription and DNA replication in oligodendroglia, the primary central nervous system cell type infected by JCV in PML. This study demonstrated that Tat can cooperate with SMAD proteins, the intracellular effectors of TGF-β, at the JCV DNA control region (CR) to stimulate JCV gene transcription. Tat stimulated JCV early gene transcription in KG-1 oligodendroglial cells when expressed via transfection or added exogenously. Using chromatin immunoprecipitation, it was shown that exogenous Tat enhanced binding of SMAD2, -3 and -4 and their binding partner Fast1 to the JCV CR in living cells. When SMAD2, -3 and -4 were expressed together, Tat, expressed from plasmid pTat, stimulated transcription from both early and late gene promoters, with the early promoter exhibiting stimulation of >100-fold. Tat, SMAD4 and JCV large T-antigen were all visualized in oligodendroglial cells at the border of an active PML lesion in the cerebral frontal lobe. These results revealed a positive reinforcement system in which the SMAD mediators of the TGF-β system act cooperatively with Tat to stimulate JCV gene transcription.

Transforming Growth Factor β-Induced Reactivation of Epstein-Barr Virus Involves Multiple Smad-Binding Elements Cooperatively Activating Expression of the Latent-Lytic SwitchBZLF1Gene

“…TGF-␤ may contribute to the reactivation of other human DNA viruses as well. For example, like EBV, the human neurotropic polyomavirus JC virus sometimes can replicate to high levels in patients immunosuppressed by HIV/AIDS, with high TGF-␤ levels inducing JC virus-infected cells to produce infectious virus (18,61,68). Likewise, BK virus, another human polyomavirus, is frequently reactivated following kidney transplantation and immunosuppressant drug therapy (2).…”

Functions of Tat: the versatile protein of human immunodeficiency virus type 1

“…In addition to the modulation of HIV-1 genes, Tat has been reported to upregulate a number of non-HIV viral genes, resulting in virus activation (Gorrill et al, 2006;Stettner et al, 2009). In a number of carcinogenic viruses, such as human papillomavirus (HPV) and KS-associated herpesvirus (KSHV) this activation could result in neoplasia (Aoki & Tosato, 2004;Turner & Palefsky, 1998), this is discussed below.…”

“…For example, Tat has been shown to upregulate the expression levels of a number of cytokines, the HIV-1 co-receptor CCR5 and the interleukin-2 (IL-2) receptor (CD25) in HIV-1-infected cells (Mayol et al, 2007;Stettner et al, 2009;Zheng et al, 2005). Tat also downregulates several genes, such as the gene encoding major histocompatibility complex (MHC) class I (Matsui et al, 1996).…”

“…Tat has been shown to activate the cytokine transforming growth factor (TGF)-b in HIV-1-infected cells and to stimulate JCV gene transcription and DNA replication in oligodendrocytes, myelin producing cells of the central nervous system (CNS). In vitro studies have indicated that Tat stimulates transcription from both early and late gene promoters of JCV (Stettner et al, 2009). …”

“…In addition to the regulatory roles of HIV-1 Tat in the transactivation of virus genes, Tat has been implicated as a modulator of expression levels of a number of cellular genes (Li et al, 2005;Stettner et al, 2009). For example, Tat has been shown to upregulate the expression levels of a number of cytokines, the HIV-1 co-receptor CCR5 and the interleukin-2 (IL-2) receptor (CD25) in HIV-1-infected cells (Mayol et al, 2007;Stettner et al, 2009;Zheng et al, 2005).…”