Reverse transcription of viral RNA and the subsequent integration of reverse transcripts are the classical early events of the HIV-1 life-cycle. Simultaneously, abundant unintegrated DNAs (uDNAs), are formed in cells ubiquitously. The uDNAs either undergo recombination or degradation or persist inactively for long periods in the nucleus as future resources. Among them, 2-LTR circles are considered a dead-end for viral spread. Their contribution to the HIV-1 infection is still poorly understood. Nevertheless, the preintegration transcription of the aberrant DNAs and the consequent alterations of cellular factors have already been reported. Since the major fate of the viral genome is to persist as episomal DNA, precise characterization is required for studying the biology of HIV-1. This review compiles the biochemical and genetic updates on uDNA in the HIV-1 life cycle and could provide direction to further study of their roles in HIV-1 replication and application in HIV-1 pathogenesis.
Retroviruses must integrate their cDNA into the host genome to generate proviruses. Viral DNA-protein complexes interact with cellular proteins and produce pre-integration complexes, which carry the viral genome and cross the nuclear pore channel to enter the nucleus and integrate viral DNA into host chromosomal DNA. If the reverse transcripts fail to integrate, linear or circular DNA species such as 1-and 2-long terminal repeats are generated. Such complexes encounter numerous cellular proteins in the cytoplasm, which restrict viral infection and protect the nucleus. To overcome host cell defenses, the pathogens have evolved several evasion strategies. Viral proteins often contain nuclear localization signals, allowing entry into the nucleus. Among more than 1000 proteins identified as required for HIV infection by RNA interference screening, karyopherins, cleavage and polyadenylation specific factor 6, and nucleoporins have been predominantly studied. This review discusses current opinions about the synergistic relationship between the viral and cellular factors involved in nuclear import, with focus on the unveiled mysteries of the host-pathogen interaction, and highlights novel approaches to pinpoint therapeutic targets.
Transportin 3 (TNPO3) is a member of the importin-ß superfamily proteins. Despite numerous studies, the exact molecular mechanism of TNPO3 in retroviral infection is still controversial. Here, we provide evidence for the role and mechanism of TNPO3 in the replication of prototype foamy virus (PFV). Our findings revealed that PFV infection was reduced 2-fold by knockdown (KD) of TNPO3. However, late stage of viral replication including transcription, translation, viral assembly, and release was not influenced. The differential cellular localization of PFV integrase (IN) in KD cells pinpointed a remarkable reduction of viral replication at the nuclear import step. We also found that TNPO3 interacted with PFV IN but not with Gag, suggesting that IN-TNPO3 interaction is important for nuclear import of PFV pre-integration complex. Our report enlightens the mechanism of PFV interaction with TNPO3 and support ongoing research on PFV as a promising safe vector for gene therapy.
The foamy viruses are currently considered essential for development as vectors for gene delivery. Previous studies demonstrated that prototype foamy virus (PFV) can infect and replicate prevalently in a variety of cell types for its exclusive replication strategy. However, the virus-host interaction, especially PFV-transportin3 (TNPO3), is still poorly understood. In our investigation of the role of TNPO3 in PFV infection, we found lower virus production in TNPO3 knockdown (KD) cells compared with wild-type 293T cells. PCR analysis revealed that viral DNAs were mostly altered to circular forms: both 1-long terminal repeat (1-LTR) and 2-LTR in TNPO3 KD cells. We therefore suggest that TNPO3 is required for successful PFV replication, at least at/after the nuclear entry step of viral DNA. These findings highlight the obscure mysteries of PFV-host interaction and the requirement of TNPO3 for productive infection of PFV in 293T cells.
The aim of the present study was to isolate and investigate the genetic heterogeneities in single circulating tumour cells (CTCs) from patients with colorectal carcinoma (CRC). Twenty-eight single CTCs were collected from eight patients with CRC using a negative immunomagnetic enrichment method. After validation with glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene expression in 3 colon cancer cell lines, a panel of 19 genes were used to analyse the single CTCs (n = 28), primary colorectal carcinoma tissues (n = 8) and colon carcinoma cells (n = 6) using real-time qPCR. Genetic heterogeneities were assessed by comparing gene expression profiles of single CTCs from the different patients and in the same patient, respectively. Genetic profiling of the single CTCs showed extensive heterogeneities of the selected genes among the CTCs. Hierarchical clustering analyses exhibited two clusters of CTCs with differentially expressed genes, which highlighted different modifications from the primary carcinomas. Further, the genetic heterogeneities were observed between different patients or in the same patient. Finally, AKT1 expression was significantly (p = 0.0129) higher in single CTCs from CRC of advanced pathological stages (III or IV) CRC than in CTCs from CRC of early stages (I or II). Our findings suggest that single-cell genetic analysis can monitor the genetic heterogeneities and guide the personalised therapeutic targets in clinical sectors.
Integrase-binding domain (IBD) is a critical region on the lens epithelium-derived growth factor (LEDGF/p75) protein that specifically interacts with human immunodeficiency virus type 1 integrase (HIV-1 IN). In this study, we expressed and purified the IBD, and utilized in endonucleolytic assay and strand transfer assay to investigate whether IBD improve enzymatic activities of HIV-1 IN. Our results showed that IBD along with HIV-1 IN increased the strand transfer activity but not the endonucleolytic activity. Furthermore, our results showed that IBD induced efficient integration of the donor DNA into the target DNA to create half-site integration and full-site integration using plasmid as target DNA. Therefore, it is suggested that LEDGF-IBD itself might be able to increase viral infectivity by enhancing the strand transfer activities of HIV-1 IN and accelerating integration of viral cDNA into cellular chromosomal DNA.
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