Large T Antigen Promotes JC Virus Replication in G2-arrested Cells by Inducing ATM- and ATR-mediated G2 Checkpoint Signaling

Abstract

The human polyomavirus JC virus (JCV) 2 is the causative agent of progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease of the central nervous system. JCV infection usually occurs during childhood, but remains subclinical. However, opportunistic reactivation of JCV results in the development of PML in individuals with a compromised immune system, such as those with acquired immunodeficiency syndrome (AIDS) or advanced-stage malignant tumors, or those recently having undergone organ transplantation with immunosuppressive therapy (1). There is currently no effective or specific therapy for PML, even though the incidence of this condition is increasing with the growing number of individuals with AIDS.JCV is a small virus with a double-stranded DNA genome that encodes early proteins (large T antigen, small t antigen, and TЈ antigen) and late proteins (VP1, VP2, VP3, and agnoprotein) (2). The entry of JCV into the nucleus of an infected cell is followed by transcription of the early genes and the production of large T antigen (TAg). The replication of JCV DNA progresses in association with the accumulation of TAg, which subsequently stimulates transcription of late genes and represses that of the early genes (3). JCV TAg shares 72% amino acid sequence identity with TAg of simian virus 40 (SV40), another primate polyomavirus, and, like SV40 TAg, it is necessary for replication of the viral genome as a result of its DNA binding and helicase activities. The replication of polyomaviruses also requires DNA replication proteins of the host cell, such as DNA polymerase ␣, topoisomerases, and replication protein A (RPA) (4, 5), with such host cell factors being thought to serve as determinants of host specificity (6).The utilization of such cellular proteins requires that polyomaviruses replicate in a phase of the cell cycle in which they are available. Polyomavirus TAg thus modulates cellular signaling pathways to induce quiescent cells to enter S phase, in which cellular DNA is replicated (7). A key event in this process is the interaction of TAg with members of the retinoblastoma protein family, which results in inactivation of retinoblastoma protein and in consequent progression of the cell cycle (8). Moreover, polyomaviruses are thought to take advantage of the DNA damage response to enhance viral replication. SV40 lytic infection thus triggers the DNA damage checkpoint, resulting in a bypass of mitosis and additional replication of cellular and viral DNA (9), and murine polyomavirus-infected cells accumulate in S and G 2 phases (10). Replication of viral DNA in cells *

The human JC polyomavirus (JCPyV): virological background and clinical implications

“…Similar to the original findings for SV40, LTag binding to the retinoblastoma pRB family proteins modulates the activity and abundance of host cell transcription factors (47). LTag also counteracts the p53-mediated apoptosis which would be caused by accumulating DNA fragments and metabolic exhaustion, as reviewed elsewhere (48), and shifts the cell into a proliferative G2/S state by activating ATM-and ATR-mediated pathways (49). The sTag is a cytoplasmic protein of 172 aa.…”

Merkel Cell Polyomavirus Large T Antigen Disrupts Host Genomic Integrity and Inhibits Cellular Proliferation

“…Studies of other polyomaviruses implicate the DDR machinery in replication and monomeric resolution of viral genomes, as well as repair of cellular DNA damage caused by the viruses (59,60).…”

Human glial chimeric mice reveal astrocytic dependence of JC virus infection

“…Polyoma viral replication requires S-phase progression on the part of infected host cells. In particular, previous studies had revealed that JCV genome replication may be facilitated by virally induced cell cycle arrest in G2, prior to the G2/M transition (23). In light of the apparent delay in viral replication in human oligodendroglia, relative to astrocytes and GPCs, we next asked whether infected astrocytes and oligodendrocytes differ in their efficiency of S/G2 traversal.…”

“…Because p53 is phosphorylated at Ser15 when DNA damage is detected, phospho-p53(Ser15) expression may be used as a marker of DNA damage, as well as its associated cell cycle arrest at G2/M (23)(24)(25). We found that a significantly higher proportion of T-Ag + astrocytes coexpressed phospho-p53(Ser15) than did uninfected T-Ag -cells ( + glia in the corpus callosum of a human glial chimeric Rag2 -/-Mbp shi/shi mouse 12 weeks after type 1A (Mad-1) JCV infection showed the predominant white matter spread of virus in these mice, which manifested both oligodendrocytic and astrocytic infection (compare with the Rag1 -/-section in C).…”