Viral infection is war between virus and host waged at the molecular level. The Chandran Lab seeks to uncover the detailed battle plans for the first phase of this conflict, in which viruses invade host cells to gain access to the cytoplasm, where the resources necessary for constructing new viruses are located. We study highly pathogenic emerging viruses for which no treatments are currently available. Our current efforts are focused on filoviruses (e.g., Ebola virus and Marburg virus) and hantaviruses (e.g., Sin Nombre virus). Insights into how viruses exploit their hosts yield targets for development of antiviral treatments, and we vigorously explore such opportunities through wide-ranging collaborations.
ID'ing the players: discovering host molecules required for viral invasion
Using comprehensive loss-of-function genetic screens in haploid cells, we are discovering critical host factors required for viral invasion. One of our major finds is Niemann-Pick C1 (NPC1), which we subsequently showed to be an essential receptor for filovirus entry. We have also uncovered components of cellular membrane trafficking pathways. We propose that these pathways are required to deliver filoviruses to lysosomes, from which the virus may escape into the cytoplasm. (Also see 'Working Model')
Deciphering the role of NPC1 in filovirus invasion
The discovery of a central role for NPC1 in filovirus entry promises to revolutionize our understanding of the filovirus infection cycle, in vivo viral pathogenesis, and the ecology and natural history of filovirus infections. Not least, NPC1 provides a new target for the development of anti-filovirus therapeutics.
Here are some questions we are currently exploring:
1. Why is NPC1 required for filovirus entry? Our working hypothesis is that NPC1 induces structural changes in the viral glycoprotein that drive fusion of viral and endosomal lipid bilayers and bring about viral escape into the host cytoplasm.
2. What role does NPC1 play in filovirus in vivo pathogenesis? In collaboration with Steve Walkley’s lab at Einstein, and John Dye’s group at USAMRIID, we are asking if NPC1 is required for filovirus multiplication in vivo and for filovirus hemorrhagic fever.
3. How does the virus-NPC1 interaction influence filovirus host range, interspecies transmission, and virus-host coevolution?
4. Can antivirals targeting NPC1 be developed? With an industry partner, we are working to find small molecules that target NPC1 and block its capacity to support filovirus infection.
5. How do endosomal cysteine proteases mediate filovirus entry? We are using a combination of approaches to test our working hypothesis, which is that cleavage of the filovirus glycoprotein by cathepsins L and B acts in concert with NPC1 interaction to trigger viral membrane fusion.
6. What additional host factors and pathways are required for filovirus entry? We have identified additional endosomal host factors, including multiprotein complexes that are involved in the biogenesis and trafficking of specific endosomal compartments. We are exploring the roles of these endosomal factors in filovirus entry
7. What is the cascade of structural transformations in the viral glycoprotein that drives filovirus entry? In collaboration with Jon Lai’s lab at Einstein, we are using state-of-the-art synthetic antibody repertoires and phage display technology to develop monoclonal antibodies that bind to different conformational states of the filovirus glycoprotein and illuminate new frames in our molecular movie of viral entry.