Effects of cell cycle status on early events in retroviral replication

Foamy viruses are a member of the spumavirus subfamily of retroviruses with unique mechanisms of virus replication. Foamy virus replication is cell cycle dependent; however, the genome is found in the nuclei of cells arrested in the G 1 /S phase. Despite the presence of genome in the nuclei of growth-arrested cells, there is no viral gene expression, thus explaining its dependency on cell cycle. This report shows that the foamy virus genome remains unintegrated in G 1 /S phase-arrested cells. The foamy virus genome is detected by confocal microscopy in the nuclei of both dividing and growth-arrested cells. Alu PCR revealed foamy virus-specific DNA amplification from genomic DNA isolated in cycling cells at 24 h postinfection. In arrested cells no foamy virus DNA band was detected in cells harvested at 1 or 7 days after infection, and a very faint band that is significantly less than DNA amplified from cycling cells was observed at day 15. After these cells were arrested at the G 1 /S phase for 1, 7, or 15 days they were allowed to cycle, at which time foamy virus-specific DNA amplification was readily observed. Taken together, these results suggest that the foamy virus genome persists in nondividing cells without integrating. We have also established evidence for the first time that the foamy virus genome and Gag translocation into the nucleus are dependent on integrase in cycling cells, implicating the role of integrase in transport of the preintegration complex into the nucleus. Furthermore, despite the presence of a nuclear localization signal sequence in Gag, we observed no foamy virus Gag importation into the nucleus in the absence of integrase.

Section: Discussionmentioning

confidence: 99%

The Foamy Virus Genome Remains Unintegrated in the Nuclei of G₁/S Phase-Arrested Cells, and Integrase Is Critical for Preintegration Complex Transport into the Nucleus

Tian

Nadeau

et al. 2010

“…The physiological status of host cells has an enormous influence on the outcome of retrovirus infection (19,43). For example, cells that exit from the cell cycle are not susceptible to infections by many retroviruses.…”

Section: The Ability Of Human Immunodeficiency Virus (Hiv) To Infect mentioning

confidence: 99%

Cellular Restriction Targeting Viral Capsids Perturbs Human Immunodeficiency Virus Type 1 Infection of Nondividing Cells

Yamashita

Emerman

2009

The ability of human immunodeficiency virus (HIV) to infect nondividing cells is a fundamental property by which HIV replicates in critical target cells, such as macrophages and resting CD4+ T cells. Recent studies have revealed that the capsid (CA) protein is a dominant factor that determines retrovirus infectivity in nondividing cells, and several mutations in HIV type 1 (HIV-1) CA abrogate the ability of HIV-1 to infect nondividing cells. We present evidence for a connection between cellular restriction against viral capsids and the resistance of nondividing cells to retrovirus infection. TRIM proteins that are able to target incoming viral capsids restrict HIV-1 more potently in nondividing cells than in dividing cells, thus rendering HIV-1 infection dependent on cell division. Moreover, cyclophilin A, another cellular protein that binds to HIV-1 CA, regulates HIV-1 infection of nondividing cells. Together, these data demonstrate the importance of capsid-binding cellular proteins in the control of the cell cycle independence of HIV-1. We propose that cellular restrictions to retroviral infections are themselves cell cycle dependent.

“…For most retroviral PICs, access to the nucleus takes place during cell division and the concomitant breakdown of the nuclear envelope. In contrast, the members of the lentivirus and alpharetrovirus subfamilies are able to productively infect nondividing cells, or cells arrested in the G 1 phase of the cell cycle, indicating that lentiviral and alpharetroviral PICs are able to traverse an intact nuclear envelope (37,48,80).The pathway and mechanism by which the lentiviral PIC crosses the nuclear envelope of an interphase cell are not clearly defined. Some components of the PIC have been hypothesized to confer a karyophilic property to the complex by bridging an interaction between the complex and cellular nuclear import factors (reviewed in reference 83).…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Integrase Interacts with Nucleoporin NUP153 To Mediate the Nuclear Import of Human Immunodeficiency Virus Type 1

Woodward

Prakobwanakit²,

Mosessian³

et al. 2009

100

The ability to traverse an intact nuclear envelope and productively infect nondividing cells is a salient feature of human immunodeficiency virus type 1 (HIV-1) and other lentiviruses, but the viral factors and mechanism of nuclear entry have not been defined. Partitioning of the eukaryotic genome into a separate cellular compartment is important for the regulation of cellular events, ranging from gene expression to cell cycle progression and cell activation. Controlling access to the genome may also serve to provide genetic stability and function as a potential deterrent to invading pathogens. Indeed, for many viruses that replicate in the nucleus, the nuclear envelope represents a significant barrier to establishing a productive infection. Circumvention and appropriation of nuclear import factors and pathways are strategies that viruses use to gain access to the nucleus (44).For retroviruses, nuclear import of the viral genome for the purpose of integration is a critical step in the viral life cycle (15). After cell entry and uncoating, the newly reverse transcribed viral genome exists with viral and host cell proteins in a large nucleoprotein complex termed the preintegration complex (PIC), which represents the subviral particle imported to the nucleus (reviewed in references 54 and 83). For most retroviral PICs, access to the nucleus takes place during cell division and the concomitant breakdown of the nuclear envelope. In contrast, the members of the lentivirus and alpharetrovirus subfamilies are able to productively infect nondividing cells, or cells arrested in the G 1 phase of the cell cycle, indicating that lentiviral and alpharetroviral PICs are able to traverse an intact nuclear envelope (37,48,80).The pathway and mechanism by which the lentiviral PIC crosses the nuclear envelope of an interphase cell are not clearly defined. Some components of the PIC have been hypothesized to confer a karyophilic property to the complex by bridging an interaction between the complex and cellular nuclear import factors (reviewed in reference 83). The identity or nature of such a factor is unknown, but viral integrase (IN) is a likely candidate due to its own karyophilic property and close association with the PIC (17, 47). In addition to IN, viral proteins matrix (MA) and Vpr, as well as the reverse transcription intermediate cDNA flap, are viral factors that have been studied for their role in PIC nuclear import. However, viruses mutated for both MA and Vpr are still capable of infecting nondividing cells (41, 51), and a definitive role for the cDNA flap in the nuclear import of the complex remains to be demonstrated (31, 56). More recently, the viral capsid protein (CA) has been reported to be the primary determinant for the nuclear import of human immunodeficiency virus type 1 (HIV-1) (30,100,102,103). However, a role for CA in nuclear import may reflect the importance of the proper uncoating of the core particle prior to nuclear translocation (101) as opposed to that of a mechanism for movement of the complex acr...