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Budding viral hijackers may co-opt cell machinery for the getaway

December 02, 2003

When retroviruses, like HIV, infect cells, they take over the cell's machinery to manufacture new copies of themselves. Research published this week in the top-tier open access journal, Journal of Biology, shows that to escape from cells, retroviruses may once again hijack cellular components, in this case molecules normally used to engulf material from the cell's surroundings in a pocket formed from cell membrane. The findings, offer new insights into how viruses propagate and cause disease, and how healthy cells work.

Retroviruses travel from cell to cell in 'spacecraft' surrounded by the membrane of host cells. These transporters protect the virus from attack by the immune system, as they disguise the virus as part of the body. The outer membrane of the virus particle also helps the virus to spread, as it can fuse with the membrane of other vulnerable cells.

During the construction of a virus particle, or virion, the cell membrane bulges outwards, engulfing viral components as it goes. One of the viral proteins, called Gag, is essential for this process.

Now, researchers from Columbia and Yale Universities, USA, Aijou University, South Korea and the Chinese Academy of Sciences has shown that some retroviral Gag proteins bind tightly to a host-cell protein called endophilin-2. Endophilin-2 is normally involved in the inward budding of the cell membrane, a process known as endocytosis.

Supporting the idea that this interaction is functionally relevant, the researchers found endophilin-2 inside viral particles that had budded from cells infected with Moloney-murine leukaemia virus. On further examination, they also found two other proteins involved in endocytosis, a-adaptin and clathrin, inside the virions. However, Dynamin-2, a protein that binds to endophilin-2, was not there. This suggests that the incorporation of selected proteins is unlikely to be accidental.

Endophilin-2's normal role is to increase the curvature of the cell membrane during endocytosis. Further examination of how retroviruses use endophilin-2 will not only tell us more about the normal process of endocytosis, but should also increase our knowledge of how the viruses spread from cell to cell.

The research team led by Stephen Goff write: "Endophilin could be another component that is hijacked by retroviruses to promote virion production."

BioMed Central Limited