Although much progress has been made in the past decades, we still lack effective treatments for illness caused by several pathogens including the agents that cause the acquired immunodeficiency syndrome (AIDS), organ transplant rejection and COVID-19, i.e, the Human Immunodeficiency Virus (HIV), the Epstein-Barr Virus (EBV), and the Severe Acute Respiratory Syndrome Coronavirus Virus-2 (SARS CoV-2), respectively. Viral assembly events necessary for cell egress and the cellular machinery recruited for this process are our major research interests. All present potential targets for anti-viral drug development. These viruses synthesize structural and enzymatic proteins in the cytoplasm (HIV, SARS CoV-2) or the nucleus (EBV) and direct them to platforms within the nucleus (EBV), secretory pathway (SARS CoV-2) or on the plasma membrane (HIV) for assembly into particles. Cellular machinery is recruited to facilitate protein trafficking and ultimate egress from the periphery. The potential of viral-encoded and recruited host proteins to serve as targets for rational drug design is under investigation using tools of molecular genetics, biochemistry, cell biology and computational mathematics.
Our current research efforts include:
1. Role of cellular proteins in assembly of HIV and other members of the Retrovirus family: Use of a genetic assay for protein-protein interactions identified the endosomal sorting complex required for transport (ESCRT) factor Tsg101 as a host protein critical for assembly and release of particles formed by HIV and several other pathogens. The role of Tsg101 in trafficking of HIV proteins to the assembly site and release from the cell by budding is under study. Cellular proteins involved in the replication of other members of the Retrovirus family are also under study to understand how their protein trafficking pathways link to that used by HIV.
2. Tsg101 structure/function analysis: Understanding how viruses recruit cellular proteins to exploit host machinery is critical for devising strategies for selective interference of virus-directed functions without harm to the host. Tsg101 plays a central role in endosomal trafficking pathways through its ability to recognize a large number of participants. The 3-dimensional structure of regions of the protein is under study to identify determinants critical for directing selective virus vs host interactions.
3. Role in HIV budding of a host factor linked to cytokinesis: Viral protein engagement of Tsg101 and its recruitment to the membrane-anchored viral assembly site permits the virus to gather additional factors that function in actin cytoskeleton and membrane remodeling events and use them for viral budding. Ccdc11, a host protein that functions in cell division by recruiting one of the ESCRT proteins to the midbody between dividing cells, was found to be necessary for production of HIV particles. The role of this protein in HIV assembly is under investigation.
4. Anti-viral drug development: Through collaborations with structural biologists, medicinal chemists and computational biologists, we are developing small molecules capable of inhibiting virus production based on their interference with recruitment of Tsg101. These molecules are effective in tissue culture against a broad spectrum of pathogens including HIV-1, SARS-CoV-2, EBV, Ebola virus and Mayaro virus. The compounds are FDA-approved for other indications enabling us to propose compound repurposing as an expeditious path to anti-viral drug discovery, potentially reducing adverse effects associated with agents never before used in humans. The agents are also useful tools to investigate diverse aspects of viral replication involving ubiquitin signaling.
5. Targeting HIV-1 proteinase autoprocessing for novel drug design: Drugs targeting the mature HIV protease are an important component of current cocktails used to control virus replication. However, soon after they are administered, viral variants that are resistant to PR inhibitors are selected and rapidly emerge as the dominant form of the pathogen in the host. This seriously reduces treatment efficacy and facilitates spread of resistant forms. Our studies indicate that many drug-resistant variants express precursor forms resistant to current protease inhibitors. Studies aimed at targeting immature forms of the enzyme are underway to understand how they resist inhibition and to gain insight for improved drug design.
Watanabe SM, Strickland M, Tjandra N, Carter CA. RNA Binding Suppresses Tsg101 Recognition of Ub-Modified Gag and Facilitates Recruitment to the Plasma Membrane. Viruses. 2020 Apr 15;12(4):447. doi: 10.3390/v12040447. PMID: 32326417
Watanabe SM, Ehrlich LS, Strickland M, Li X, Soloveva V, Goff AJ, Stauft CB, Bhaduri-McIntosh S, Tjandra N, Carter C. Selective Targeting of Virus Replication by Proton Pump Inhibitors. Sci Rep. 2020 Mar 4;10(1):4003. doi: 10.1038/s41598-020-60544-y. PMID: 32132561
Takemaru L, Pandya P, Lake MW, Carter CA, Li F-Q. Investigating the role of the novel ESCRT-III recruitment factor CCDC11 in HIV budding: a potential target for anti-viral therapy. Journal of Emerging Investigators. 2020 Vol 2. 9 February www.emerginginvestigators.org