Involvement of human topoisomerase II isoforms in HIV-1 reverse transcription

The hypoxia-regulated ectonucleotidase CD73 is a host determinant of HIV latency

Deciphering the mechanisms underlying viral persistence is critical to achieving a cure for human immunodeficiency virus (HIV) infection. Here, we implement a systems approach to discover molecular signatures of HIV latently infected CD4+ T cells, identifying the immunosuppressive, adenosine-producing ectonucleotidase CD73 as a key surface marker of latent cells. Hypoxic conditioning, reflecting the lymphoid tissue microenvironment, increases the frequency of CD73+ CD4+ T cells and promotes HIV latency. Transcriptomic profiles of CD73+ CD4+ T cells favor viral quiescence, immune evasion, and cell survival. CD73+ CD4+ T cells are capable of harboring a functional HIV reservoir and reinitiating productive infection ex vivo. CD73 or adenosine receptor blockade facilitates latent HIV reactivation in vitro, mechanistically linking adenosine signaling to viral quiescence. Finally, tissue imaging of lymph nodes from HIV-infected individuals on antiretroviral therapy reveals spatial association between CD73 expression and HIV persistence in vivo. Our findings warrant development of HIV-cure strategies targeting the hypoxia-CD73-adenosine axis.

Noncytotoxic functions of killer cell granzymes in viral infections

Cytotoxic lymphocytes produce granules armed with a set of 5 serine proteases (granzymes (Gzms)), which, together with the pore-forming protein (perforin), serve as a major defense against viral infections in humans. This granule-exocytosis pathway subsumes a well-established mechanism in which target cell death is induced upon perforin-mediated entry of Gzms and subsequent activation of various (apoptosis) pathways. In the past decade, however, a growing body of evidence demonstrated that Gzms also inhibit viral replication and potential reactivation in cell death–independent manners. For example, Gzms can induce proteolysis of viral or host cell proteins necessary for the viral entry, release, or intracellular trafficking, as well as augment pro-inflammatory antiviral cytokine response. In this review, we summarize current evidence for the noncytotoxic mechanisms and roles by which killer cells can use Gzms to combat viral infections, and we discuss the potential thereof for the development of novel therapies.

The RNA-Binding Proteins SRP14 and HMGB3 Control HIV-1 Tat mRNA Processing and Translation During HIV-1 Latency

HIV-1 Tat protein is essential for virus production. RNA-binding proteins that facilitate Tat production may be absent or downregulated in resting CD4+ T-cells, the main reservoir of latent HIV in people with HIV (PWH) on antiretroviral therapy (ART). In this study, we examined the role of Tat RNA-binding proteins on the expression of Tat and control of latent and productive infection. Affinity purification coupled with mass spectrometry analysis was used to detect binding partners of MS2-tagged tat mRNA in a T cell-line model of HIV latency. The effect of knockdown and overexpression of the proteins of interest on Tat transactivation and translation was assessed by luciferase-based reporter assays and infections with a dual color HIV reporter virus. Out of the 243 interactions identified, knockdown of SRP14 (Signal Recognition Particle 14) negatively affected tat mRNA processing and translation as well as Tat-mediated transactivation, which led to an increase in latent infection. On the other hand, knockdown of HMGB3 (High Mobility Group Box 3) resulted in an increase in Tat transactivation and translation as well as an increase in productive infection. Footprinting experiments revealed that SRP14 and HMGB3 proteins bind to TIM-TAM, a conserved RNA sequence-structure in tat mRNA that functions as a Tat IRES modulator of tat mRNA. Overexpression of SRP14 in resting CD4+ T-cells from patients on ART was sufficient to reverse HIV-1 latency and induce virus production. The role of SRP14 and HMGB3 proteins in controlling HIV Tat expression during latency will be further assessed as potential drug targets.

Topoisomerase II β Gene Specific siRNA Delivery by Nanoparticles Prepared with c-ter Apotransferrin and its Effect on HIV-1 Replication

Topoisomerase II beta (Topo IIβ) is one of the two isoforms of type II topoisomerases present in higher eukaryotes. This 180 kDa nuclear protein involves in different cellular processes like transcription, recombination, etc., apart from its normal topological functions. Previously, we have reported the association of this isoform along with the other isoform topoisomerase II alpha (Topo IIα) with HIV-1 reverse transcription complex and the downregulation of Topo IIβ expression resulted in incomplete reverse transcription. In this study, we have tested the Topo IIβ specific siRNA delivery using protein nanoparticles prepared with c-terminal domine of transferrin (c-ter) for the first time. Results show that, c-ter nanoparticles resemble apotransferrin nanoparticles in drug holding capability and drug delivery but with small in size. Topo IIβ specific siRNA delivered in the form of c-ter nanoformulation resulted in knockdown of Topo IIβ expression for the prolonged periods and which intern resulted in decreased viral replication of HIV-1.

Development of pyridine dicoumarols as potent anti HIV-1 leads, targeting HIV-1 associated topoisomeraseIIβ kinase

Aim: A structural study of a series of pyridine dicoumarol derivatives with potential activity against a novel Topoisomerase IIβ kinase which was identified in the HIV-1 viral lysate, compounds were designed and synthesized based on a 3D-QSAR study. Materials & methods: Based on QSAR model we have designed and synthesized a series of pyridine dicoumarol derivatives and characterized by spectral studies, all the molecules are biologically evaluated by kinase assay, cytotoxicity assay, ELISA and PCR method. Result: We demonstrated the achievement of water soluble disodium pyridine dicoumarate derivatives showing high anti-HIV-1 activity (IC50 <25 nM) which provides a crucial point for further development of pyridine dicoumarol series as HIV-1-associated topoisomerase IIβ kinase inhibitors for clinical application against AIDS. Conclusion: A new class of anti-HIV-1 lead compounds have been designed and tested. Further studies would result in development of  novel and potential drugs.

Topoisomerase IIβ and its role in different biological contexts

Topoisomerase IIβ is a type II DNA topoisomerase that was reported to be expressed in all mammalian cells but abundantly expressed in cells that have undergone terminal differentiation to attain a post mitotic state. Enzymatically it catalyzes ATP-dependent topological changes of double stranded DNA, while as a protein it was reported to be associated with several factors in promoting cell growth, migration, DNA repair and transcription regulation. The cellular roles of topoisomerase IIβ are very less understood compared to its counterpart topoisomerase IIα. This review discusses origin of Topoisomerase II beta, its structure, activities reported in vitro and in vivo along with implications in cellular processes namely transcription, DNA repair, neuronal development, aging, HIV-infection and cancer.

Granzyme M: behind enemy lines

The granule-exocytosis pathway is the major mechanism via which cytotoxic lymphocytes eliminate virus-infected and tumor cells. In this pathway, cytotoxic lymphocytes release granules containing the pore-forming protein perforin and a family of serine proteases known as granzymes into the immunological synapse. Pore-formation by perforin facilitates entry of granzymes into the target cell, where they can activate various (death) pathways. Humans express five different granzymes, of which granzymes A and B have been most extensively characterized. However, much less is known about granzyme M (GrM). Recently, structural analysis and advanced proteomics approaches have determined the primary and extended specificity of GrM. GrM functions have expanded over the past few years: not only can GrM efficiently induce cell death in tumor cells, it can also inhibit cytomegalovirus replication in a noncytotoxic manner. Finally, a role for GrM in lipopolysaccharide-induced inflammatory responses has been proposed. In this review, we recapitulate the current status of GrM expression, substrate specificity, functions, and inhibitors.