Pur-Alpha Induces JCV Gene Expression and Viral Replication by Suppressing SRSF1 in Glial Cells

Abstract

ObjectivePML is a rare and fatal demyelinating disease of the CNS caused by the human polyomavirus, JC virus (JCV), which occurs in AIDS patients and those on immunosuppressive monoclonal antibody therapies (mAbs). We sought to identify mechanisms that could stimulate reactivation of JCV in a cell culture model system and targeted pathways which could affect early gene transcription and JCV T-antigen production, which are key steps of the viral life cycle for blocking reactivation of JCV. Two important regulatory partners we have previously identified for T-antigen include Pur-alpha and SRSF1 (SF2/ASF). SRSF1, an alternative splicing factor, is a potential regulator of JCV whose overexpression in glial cells strongly suppresses viral gene expression and replication. Pur-alpha has been most extensively characterized as a sequence-specific DNA- and RNA-binding protein which directs both viral gene transcription and mRNA translation, and is a potent inducer of the JCV early promoter through binding to T-antigen.Methods and ResultsPur-alpha and SRSF1 both act directly as transcriptional regulators of the JCV promoter and here we have observed that Pur-alpha is capable of ameliorating SRSF1-mediated suppression of JCV gene expression and viral replication. Interestingly, Pur-alpha exerted its effect by suppressing SRSF1 at both the protein and mRNA levels in glial cells suggesting this effect can occur independent of T-antigen. Pur-alpha and SRSF1 were both localized to oligodendrocyte inclusion bodies by immunohistochemistry in brain sections from patients with HIV-1 associated PML. Interestingly, inclusion bodies were typically positive for either Pur-alpha or SRSF1, though some cells appeared to be positive for both proteins.ConclusionsTaken together, these results indicate the presence of an antagonistic interaction between these two proteins in regulating of JCV gene expression and viral replication and suggests that they play an important role during viral reactivation leading to development of PML.

PURA , the gene encoding Pur-alpha, member of an ancient nucleic acid-binding protein family with mammalian neurological functions

“…Under certain immunosuppressive conditions, however, JCV undergoes genetic changes in its non-coding replication/transcription control region and gains the ability to infect oligodendrocytes in the brain (Johnson et al, 2015). In this case Pura acts by altering both gene expression (Chen et al, 1995; Krachmarov et al, 1996; Gallia et al, 1998; White et al, 2009; Sariyer et al, 2016) and replication of JCV (Chen et al, 1995; Krachmarov et al, 1996; Wortman et al, 2000; Daniel et al, 2001; Reiss and Khalili, 2003; Daniel et al, 2004). The types of immune suppression activating JCV in glial cells include HIV-1 infection.…”

Regulation of Polyomavirus Transcription by Viral and Cellular Factors

“…Several cellular factors that regulate JCPyV transcription have been discovered since the 1990s; the readers are referred to a review containing a visual overview of the binding sites of these transcription factors in the viral NCRR [ 78 ]. Tst-1, YB-1, c-Jun, NF-1, C/EBPβ, Spi-B, SRSF1 (also known as SF2/ASF) and the DNA- and RNA-binding factor Pur-α are among the key cellular factors found to bind the 98-bp repeat enhancer elements within the JCPyV NCRR [ 79 , 80 , 81 , 82 , 83 , 84 ]. Tst-1 stimulates transcription of both JCPyV early and late genes via its DNA-binding activity [ 79 ].…”

“…Additionally, SRSF1 acts as a potent repressor of JCPyV gene expression by binding to the viral promoter. In order to circumvent this viral transcriptional repression, both the viral LT protein and Pur-α inhibit SRSF1 at the transcriptional level [ 82 , 83 ]. Pur-α also represses SRSF1 at the protein level, and is able to induce the viral early promoter after binding to LT [ 82 , 83 ].…”

“…In order to circumvent this viral transcriptional repression, both the viral LT protein and Pur-α inhibit SRSF1 at the transcriptional level [ 82 , 83 ]. Pur-α also represses SRSF1 at the protein level, and is able to induce the viral early promoter after binding to LT [ 82 , 83 ]. Interestingly, SRSF1 also suppresses LT expression in JCPyV-transformed cell lines [ 84 ].…”

Understanding Progressive Multifocal Leukoencephalopathy Risk in Multiple Sclerosis Patients Treated with Immunomodulatory Therapies: A Bird’s Eye View

“…T-antigen, in turn, can suppress the expression of SRSF1 through interactions with the SRSF1 promoter ( 167 ). SRSF1 suppression can also be mediated by the DNA- and RNA-binding protein, Pur-alpha, through its activation of T-antigen expression and direct inhibition of SRSF1 gene expression ( 168 ). Soluble factors secreted by immune cells, such as cytokines, can tip the balance in favor of SRSF1 and suppress JCV replication.…”