It may be possible to slow down the evolution of influenza viruses, according to a new study.
Researchers from the Massachusetts Institute of Technology (MIT) have found that the flu viruses’ rapid evolution relies partially on its ability to hijack some of the cellular machinery of the infected host cell—specifically a group of proteins called chaperones that help other proteins fold into the correct shape.
In the study, when viruses were unable to get help from the chaperones they did not evolve as rapidly as when they did get help, and the specific evolutionary trajectories followed by individual flue proteins depend on host chaperone activities.
The researchers believe that interfering with host cell chaperones could help prevent flu viruses from becoming drug and vaccine resistant.
“It’s relatively easy to make a drug that kills a virus or an antibody that stops a virus from propagating but it’s very hard to make one that the virus doesn’t promptly escape from once you start using it,” Matthew Shoulders, the Whitehead Career Development Associate Professor of Chemistry at MIT, said in a statement. “Our data suggest that, at some point in the future, targeting host chaperones might restrict the ability of a virus to evolve and allow us to kill viruses before they become drug resistant.”
Flu viruses carry eight genome segments encoded by RNA.
Of particular interest to flu researchers is the gene for the hemagglutinin protein, which is displayed on the surface of the viral envelope and interacts with cells of the infected host.
While most flu vaccines target this protein, they have to be updated every year to keep up with the protein’s ability to evolve quickly.
“Viral proteins are known to interact with host chaperones, so we suspected that this interplay could have a major impact on what evolutionary pathways are available to the virus,” Shoulders said.
The researchers generated one set of cells with low protein-folding activity by inhibiting a key chaperone protein called heat shock protein 90 (Hsp90).
They also used chemical genetic methods in another set of cells to enhance the levels of numerous chaperone proteins and create a cellular environment with high protein-folding activity.
After infecting both sets of cells—as well as a group of cells with normal chaperone levels—with a strain of flu, the researchers allowed the virus to evolve for nearly 200 generations and found that the virus evolved faster in the cells with higher chaperone levels.
“This finding suggests that influenza will acquire new traits that might be beneficial for it faster when you have the heat shock response activated and slower when you have key chaperones inhibited,” Shoulders said.
The researchers also found specific proteins that tend to become more mutated in cells with more chaperones, including the hemagglutinin protein and an enzyme called PA that is a type of RNA polymerase that helps the virus copy its genes. They also identified specific amino acids within the proteins that are morel likely to become mutated in different protein-folding environments.
By targeting these proteins, researchers hope to delay viral evolution and decelerate escape from existing drugs and vaccines.
The researchers also said that other viruses including HIV, may evolve in a similar fashion.
“We can recapitulate environmental pressures like antiviral drugs in the lab, in the context of different host protein-folding environments and see whether there’s a big impact,” Shoulders said. “Our data suggest that there’s going to be, but we have to actually test it out.”