BBS Faculty Member - Priscilla Yang

Priscilla Yang

Department of Microbiology and Molecular Genetics

Harvard Medical School
New Research Building, Room 930
77 Avenue Louis Pasteur
Boston, MA 02115
Tel: 617-432-5415
Fax: 617-432-5418
Lab Members: 6 postdoctoral fellows, 1 technician
Visit my lab page here.

My research group is focused equally on basic and applied research goals. First, we are basic scientists studying the molecular mechanisms whereby viruses replicate themselves and cause disease. Second, we use our understanding of molecular mechanism to discover and validate novel antiviral targets and approaches that can complement traditional antiviral drug discovery efforts. While my laboratory is grounded primarily in the study of dengue virus and hepatitis C virus (HCV), we also investigate the applicability of our inhibitors and antiviral strategies to other viral pathogens. As a chemist and virologist, I have prioritized opportunities in which chemical tools can be used to investigate questions that may have not been accessible using more conventional virological methods. This has included 1) the use of novel screening and profiling platforms to identify host factors with functions in dengue virus replication; 2) the use of medicinal chemistry to develop small molecules as mechanistic probes of dengue virus entry, translation, genome replication, and assembly and tool compounds for pharmacological validation of antiviral targets in vitro and in vivo; 3) the use of chemoproteomic profiling methods to identify virus-induced changes in host protein function (rather than host gene expression); and 4) the use of analytical and biophysical chemistry approaches to study the relationship between specific lipid structure and function in viral processes.

Development of a novel screening platform and its use to identify dengue virus host factors and small molecule inhibitors of dengue virus replication
Knowledge of the molecular mechanisms for viral processes and the viral and host factors involved is a necessary foundation for developing rational antiviral strategies. To identify host factors required for dengue virus (DV) replication and inhibitors of DV, we first developed a novel screening platform that enables detection of inhibitors affecting any step in the DV infection cycle. We used this platform to perform the first phenotypic small molecule and RNAi screens against DV and have on-going efforts developing novel assays suitable for low- and high-throughput assays against specific targets and viral processes.

Discovery and Validation of Existing Drugs as Potent Inhibitors of Dengue Virus
Due to DV’s high mutation rate and the limited financial resources available for anti-DV drug development, we have hypothesized that host-targeted antivirals may have advantages over direct-acting antivirals. First, drug resistance may be less of an issue due to the absence of a direct genetic pathway to resistance. Second, host-targeted antivirals may be leveraged against other related viral pathogens that have evolved utilizing similar host factors or pathways. Third, opportunities to repurpose or rescue existing drugs may expedite development of clinically useful anti-DV agents. Fourth, functionally well-annotated drugs can also be chemical probes aiding in the identification of host factors and pathways that are critical for specific viral processes. Despite the recent popularity of these ideas, they remain to be proven. To put our rationale for host-targeted antiviral drug discovery to the test, we followed up on dasatinib, saracatinib, and 4-hydroxyphenylretinamide (4-HPR), three drugs that have been FDA-approved or advanced to late stages of clinical testing and that we identified as anti-DV compounds in our inhibitor screens. In addition to providing concrete examples that help validate the rationale for host-targeted antivirals, our elucidation of the virological mechanisms of action of these agents and examination of their host targets and potential resistance mechanisms have laid the foundation for translational efforts to repurpose these drugs as much-needed antivirals.

The Dengue Virus E Protein and Mechanisms for Inhibiting Its Function
To complement our interest in host-targeted antivirals, we have investigated the development of agents that act via viral targets other than the viral protease and polymerase, the two classical antiviral targets which have been heavily pursued by many other groups in both industry and academia. The E protein exists as a prefusion dimer on the surface of mature virions and mediates multiple steps in DV entry. Membrane fusion during entry is coupled to structural reorganization of E as postfusion trimers upon exposure to acidic pH. Although E decreases the energy of activation for membrane fusion, it is not a classical catalyst in the sense of having a well-defined active site in which specific bond formation or scission occurs. Moreover, it is unclear how many of the 180 copies of E on the virion surface must be occupied by inhibitor to prevent the biological event of membrane fusion. We have developed cyanohydrazone and disubstituted pyrimidine compounds that bind to the prefusion E dimer inhibit DV entry by blocking membrane fusion. We are now using these compounds as tools to study E’s catalytic mechanism of action, to elucidate effective modes for inhibiting its biological function, and to assess potential pathways to resistance. In addition to understanding the fundamental biochemistry in this system, this work is important for understanding E as a potential drug target.

Structure and function of lipids in viral replication
Despite the critical function of host lipids in viral replication, very little is known about the chemical composition of lipid membranes utilized by specific viruses and the relationship between lipid structure and biochemical function in viral processes. We have been investigating the interaction of viruses with host lipids within a framework of three related hypotheses: (1) that every virus has a molecular selectivity for given specific lipids; (2) that viruses perturb host metabolism in ways increase the steady-state abundance of lipids needed for optimal replication; and (3) that we exploit a virus’s dependence on host lipids and host lipid metabolism to selectively inhibit viral pathogens. Using mass spectrometry-based lipidomic profiling, we have identified specific lipid molecules that are rare in uninfected cells and whose steady-state abundance increases by an order of magnitude in the presence of virus. In one example, we have shown that hepatitis C virus (HCV) causes a greater than ten-fold increase in steady-state desmosterol. Inhibition of desmosterol synthesis causes a major inhibition of viral replication that is rescued upon addition of exogenous desmosterol but not upon the addition of cholesterol. Studies to elucidate the mechanisms whereby HCV affects desmosterol homeostasis and desmosterol functions in HCV replication are currently underway. Since these desmosterol and cholesterol differ by the presence of a single carbon-carbon double bond, this system presents a novel system in which to investigate how even subtle differences in lipid structure can affect function and have a profound effect on biological processes.

Last Update: 7/27/2015


For a complete listing of publications click here.



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