Methylation: a regulator of HIV-1 replication?

Recent characterizations of methyl transferases as regulators of cellular processes have spurred investigations into how methylation events might influence the HIV-1 life cycle. Emerging evidence suggests that protein-methylation can positively and negatively regulate HIV-1 replication. How DNA- and RNA- methylation might impact HIV-1 is also discussed

Activation of HIV-1 expression and replication by cGMP dependent protein kinase type 1-β (PKG1β)

The effect of cGMP (cyclic GMP) dependent protein kinase 1-β (PKG1-β) and cGMP analogues on transcriptional activity and replication of human immunodeficiency virus type 1 (HIV-1) was investigated. Transfection of PKG1β expression plasmid increased expression from an HIV-1 LTR-reporter as well as from an infectious HIV-1 molecular clone, pNL4-3. Treatment of HIV-1 AD8-infected monocyte derived macrophages (MDMs) with cGMP agonists and cGMP antagonists caused respectively increased and decreased virus replication. These findings provide evidence that cGMP and PKG serve to regulate HIV-1 infection in human cells

Wip1 and p53 contribute to HTLV-1 Tax-induced tumorigenesis

BACKGROUND: Human T-cell Leukemia Virus type 1 (HTLV-1) infects 20 million individuals world-wide and causes Adult T-cell Leukemia/Lymphoma (ATLL), a highly aggressive T-cell cancer. ATLL is refractory to treatment with conventional chemotherapy and fewer than 10% of afflicted individuals survive more than 5 years after diagnosis. HTLV-1 encodes a viral oncoprotein, Tax, that functions in transforming virus-infected T-cells into leukemic cells. All ATLL cases are believed to have reduced p53 activity although only a minority of ATLLs have genetic mutations in their p53 gene. It has been suggested that p53 function is inactivated by the Tax protein. RESULTS: Using genetically altered mice, we report here that Tax expression does not achieve a functional equivalence of p53 inactivation as that seen with genetic mutation of p53 (i.e. a p53(−/−) genotype). Thus, we find statistically significant differences in tumorigenesis between Tax(+)p53(+/+)versus Tax(+)p53(−/−) mice. We also find a role contributed by the cellular Wip1 phosphatase protein in tumor formation in Tax transgenic mice. Notably, Tax(+)Wip1(−/−) mice show statistically significant reduced prevalence of tumorigenesis compared to Tax(+)Wip1(+/+) counterparts. CONCLUSIONS: Our findings provide new insights into contributions by p53 and Wip1 in the in vivo oncogenesis of Tax-induced tumors in mice

Matrin 3 is a co-factor for HIV-1 Rev in regulating post-transcriptional viral gene expression

Post-transcriptional regulation of HIV-1 gene expression is mediated by interactions between viral transcripts and viral/cellular proteins. For HIV-1, post-transcriptional nuclear control allows for the export of intron-containing RNAs which are normally retained in the nucleus. Specific signals on the viral RNAs, such as instability sequences (INS) and Rev responsive element (RRE), are binding sites for viral and cellular factors that serve to regulate RNA-export. The HIV-1 encoded viral Rev protein binds to the RRE found on unspliced and incompletely spliced viral RNAs. Binding by Rev directs the export of these RNAs from the nucleus to the cytoplasm. Previously, Rev co-factors have been found to include cellular factors such as CRM1, DDX3, PIMT and others. In this work, the nuclear matrix protein Matrin 3 is shown to bind Rev/RRE-containing viral RNA. This binding interaction stabilizes unspliced and partially spliced HIV-1 transcripts leading to increased cytoplasmic expression of these viral RNAs

Role of RNA helicases in HIV-1 replication

Viruses are replication competent genomes which are relatively gene-poor. Even the largest viruses (i.e. Herpesviruses) encode only slightly >200 open reading frames (ORFs). However, because viruses replicate obligatorily inside cells, and considering that evolution may be driven by a principle of economy of scale, it is reasonable to surmise that many viruses have evolved the ability to co-opt cell-encoded proteins to provide needed surrogate functions. An in silico survey of viral sequence databases reveals that most positive-strand and double-stranded RNA viruses have ORFs for RNA helicases. On the other hand, the genomes of retroviruses are devoid of virally-encoded helicase. Here, we review in brief the notion that the human immunodeficiency virus (HIV-1) has adopted the ability to use one or more cellular RNA helicases for its replicative life cycle

Small Molecules Targeted to a Non-Catalytic “RVxF” Binding Site of Protein Phosphatase-1 Inhibit HIV-1

HIV-1 Tat protein recruits host cell factors including CDK9/cyclin T1 to HIV-1 TAR RNA and thereby induces HIV-1 transcription. An interaction with host Ser/Thr protein phosphatase-1 (PP1) is critical for this function of Tat. PP1 binds to a Tat sequence, Q35VCF38, which resembles the PP1-binding “RVxF” motif present on PP1-binding regulatory subunits. We showed that expression of PP1 binding peptide, a central domain of Nuclear Inhibitor of PP1, disrupted the interaction of HIV-1 Tat with PP1 and inhibited HIV-1 transcription and replication. Here, we report small molecule compounds that target the “RVxF”-binding cavity of PP1 to disrupt the interaction of PP1 with Tat and inhibit HIV-1 replication. Using the crystal structure of PP1, we virtually screened 300,000 compounds and identified 262 small molecules that were predicted to bind the “RVxF”-accommodating cavity of PP1. These compounds were then assayed for inhibition of HIV-1 transcription in CEM T cells. One of the compounds, 1H4, inhibited HIV-1 transcription and replication at non-cytotoxic concentrations. 1H4 prevented PP1-mediated dephosphorylation of a substrate peptide containing an RVxF sequence in vitro. 1H4 also disrupted the association of PP1 with Tat in cultured cells without having an effect on the interaction of PP1 with the cellular regulators, NIPP1 and PNUTS, or on the cellular proteome. Finally, 1H4 prevented the translocation of PP1 to the nucleus. Taken together, our study shows that HIV- inhibition can be achieved through using small molecules to target a non-catalytic site of PP1. This proof-of-principle study can serve as a starting point for the development of novel antiviral drugs that target the interface of HIV-1 viral proteins with their host partners

Role of human immunodeficiency virus type 1 accessory genes in mother-infant transmission

The majority of AIDS cases in children occur as a result of perinatal transmission of HIV-1 at an estimated rate of 30%. However, the molecular mechanisms and viral determinants associated with perinatal transmission are not known, thus making it difficult to develop strategies for prevention and treatment of HIV-1 infection. In this study, we have investigated the role of HIV-1 accessory genes vif, vpr and vpu in maternal-fetal transmission and the kinetics of HIV-1 replication in neonatal blood mononuclear cells. While there was a high degree of conservation of vif, vpr and vpu open reading frames in mother-infant pairs' isolates, the non-transmitting mothers' showed a high frequency of defective vif and vpr open reading frames. The functional domains required for Vif, Vpr and Vpu activity were highly conserved in sequences from transmitting mothers and their infants, but were found to exhibit defects, length polymorphism and substitutions in the conserved motifs of non-transmitting mothers' isolates. There was a low degree of heterogeneity in vif and vpr sequences from transmitting mothers and their infants and non-transmitting mothers. However the non-transmitting mother sequences were less heterogeneous than transmitting mother sequences. The vpu sequences from transmitting mothers and their infants were more heterogeneous than vif and vpr sequences. Phylogenetic analysis of vif, vpr and vpu sequences revealed distinct clusters for each mother-infant pair and non-transmitting mother, indicating that the sequences from same individual or linked individuals were more closer than unrelated individuals. Furthermore, we observed that HIV-1 replicates more efficiently in immature blood lymphocytes and monocytes/macrophages cells compared to mature blood cells, suggesting that increased susceptibility of neonatal cells to productive infection could result in rapid progression to AIDS in children. In addition, there was a difference in the susceptibility of neonatal and adult blood monocytes/macrophages to primary HIV-1 isolates. Taken together, these findings suggest that accessory genes vif, vpr and vpu may play an essential role in HIV-1 transmission from mother to infants and susceptibility of neonatal monocytes/macrophages may be critical for establishing productive infection. These findings may be helpful in the developing better strategies for prevention and treatment of HIV-1 infection in children