Flavivirus biogenesis and their strategies for host immune evasion
Dengue and Zika represent two of the major mosquito-borne flaviviruses that collectively have huge health implications worldwide. Dengue infects approximately 400 million people annually, often causing severe pathologies such as vascular endothelial leakage. Zika too has emerged as a global threat with recent outbreaks linked to serious neuro-developmental complications in children and Guillain Barré syndrome in adults. Vaccines and therapeutic options for these viruses are currently unavailable, along with limited knowledge on the underlying mechanisms of pathogenesis and viral manipulation of host cell biology.
Our current research investigates mechanisms of flavivirus biogenesis, using Zika and Dengue as models, and their strategies of evading host immune responses. Infection is accompanied by upregulation of selective autophagy to hydrolyse lipid droplets, followed by massive reorganisation of the host secretory pathway, while suppressing MHC-I and II restricted antigen presentation. We apply mass spectrometry with complementary approaches in biochemistry, cell biology, immunology and virology to investigate two major aspects of flavivirus pathogenesis: mechanisms underlying their assembly/secretion, and strategies they deploy to subvert host immunity.
We have identified specific lipid droplet components that are targeted by viral proteins to induce lipophagy, and cholesterol-dependent degradation of several ER-proteins. These processes are crucial for the formation of viral replication compartments. We apply CRISPR/Cas9 mediated genetic manipulation, combined with biochemical and cell biological methods in mammalian cells to characterise genes that drive ER reorganisation and virus assembly.
Despite increased autophagy in infected cells, which in principle should enhance antigen presentation, surface expression of Major histocompatibility complex (MHC)-I and II is dramatically reduced when compared to UV-inactivated or viral dsRNA-treated cells. We investigate how viruses subvert antigen presentation in infected monocytes, to evade host immunity and drive pathogenesis. Monocytes and monocyte-derived cells prime virus-specific neutralising B- and T-cell responses, and are also major targets of Zika and Dengue replication. To determine viral interference with antigen presentation, we apply quantitative proteomics with immunology and biochemical techniques to deconstruct the multi-tiered process, and define the specific steps targeted by these viruses. We have identified several E3 ligases that are induced and copurify with MHC-I and II from Zika-infected cells. We will test whether they are co-opted by Zika to ubiquitylate and degrade, or mis-sort MHC molecules to evade host immunity.
Semin Cell Dev Biol pii: S1084-9521(18)30222-2
Cell Host Microbe. 23 (6): 819-831
Proc Natl Acad Sci USA 113(6): E705-14
Cell Host Microbe 14(5): 510-521