Innate immunity and viral evasion
If a virus attacks us, our immune system registers this attack and starts a whole chain of reactions. Messengers initiate the release of cellular proteins, through which our cells prevent the spread of viruses – known as antiviral factors. However, some viruses have developed very effective strategies against these antiviral factors, so that the self-protection mechanism of the cells is ultimately insufficient to defend against the infection. Wanted: new antiviral factors which can fight off even these viruses – of which HIV is one.
Characterization of the secretory glycoprotein 90K/LGALS3BP as an antiviral restriction factor
DFG Collaborative Research Centre 900 Chronic Infections: "Microbial Persistence and its Control"
After recognition of pathogen-associated molecular patterns (PAMPs) by infected cells, interferons are synthesized, secreted and bind the interferon receptor on neighboring cells to „alarm“ them from an upcoming virus invasion. Binding induces a signaling cascade that ultimately results in synthesis of several interferon-stimulated genes, so-called ISGs (“interferon-stimulated genes”). ISGs comprise many antiviral genes, including those encoding APOBEC3G, a cellular deaminase which hypermutates the viral genome, or Tetherin, which prevents release of mature virions from the producer cell´s surface. Another ISG is lgals3bp, which encodes for the cellular glycoprotein 90K. Previous work of our group demonstrated the antiviral potency of 90K against HIV. Specifically, 90K reduces the infectivity of newly assembled virions by interfering with the viral incorporation of HIV Envelope proteins (Lodermeyer et al., Retrovirology 2013).
We are now focusing on the elucidation of the antiviral mechanism. Using truncated versions of 90K, we plan to define which domains/regions within 90K are essential and sufficient for its antiviral function. In parallel, 90K orthologs from non-human species, which share a high degree of homology with human 90K, but differ in their antiviral capability, are useful tools for the elucidation of the antiviral mechanism. Further, they shed light on the evolutionary conservation of 90K´s antiviral function. Finally, we test whether 90K acts antivirally against other enveloped viruses. The long-term perspective is to pave avenues towards a new antiviral treatment strategy.
A novel approach for eradicating HIV
Gilead Infectiology Programme 2016 (Cooperation with Prof. Georg Behrens, MHH)
Latently infected cells produce no viral products and remain invisible to the immune system. A “shock and kill” strategy of transcription induction (“shock”) with subsequent cell elimination (“kill”) has been proposed to reduce or even eradicate the HIV-1 reservoir. While reactivation of HIV-1 from the reservoir (shock) is mostly pursued by pharmacological interventions such as histone deacytelase inhibitors (HDACi), the elimination of cells which are in the process of reactivation (kill) is believed to be best achieved by immune-mediated mechanisms. Our proposed experiments are crucial to confirm autophagy as novel therapeutic targets in cells with incomplete reactivation of provirus.
Our project provides an alternative to the predominantly immune-based strategies. The project has the potential to identify novel cellular pathways for efficient reduction of the HIV reservoir. An important translational aspect is that we focus on available and licensed compounds for rapid evaluation in patients/animal models if proven effective in the preclinical evaluation.
Characterisation of the cGAS-mediated DNA-sensing signaling in HIV infected T-cells
DFG Priority Programme 1923, "Innate Sensing and Restriction of Retroviruses"
Upon HIV-1 infection of T-cells, viral DNA can be sensed by the cytosolic DNA sensor cGAS. In cocultures with macrophages, HIV-1 Env-mediated membrane fusion pores allow the horizontal transfer of the cGAS product and cyclic dinucleotide cGAMP to macrophages, where it activates STING-dependent expression of antiviral cytokines and effector molecules (Xu und Ducroux et al., Cell Host & Microbe 2016). In monocultures of T-cells and macrophages, HIV-1 prevents or counteracts activation of this cellular defense mechanism. In contrast to the situation in macrophages, our understanding of the reasons for the lack of a detectable type I IFN response in HIV-1-infected T-cells is limited.
In this project, we address the effectiveness of the cGAS-mediated DNA sensing pathway in primary T-cells and try to unravel potential explanations for the lack of IFN induction in this important HIV-1 target cell type.