LA JOLLA, CALIF. Dec. 11, 1999 -- A new technique developed by Salk scientists allows the first glimpse of HIV inside a living cell and shows how the virus advances toward its ultimate target, the nucleus.
"After it penetrates the cell's surface, HIV must reach the nucleus before it can really set up headquarters and produce more virus," said Tom Hope, a Salk assistant professor and leader of the study. "But virtually nothing was known about how it got there. Now we have a candidate vehicle."
Hope and his colleagues devised a method of tracking HIV's movements using a fluorescent tag and a recently developed deconvolution microscope that enables them to scrutinize living cells in three dimensions.
"Essentially, we can make a time-lapse video of the virus," said Hope, who is presenting the work Dec. 15, 1999 at the American Society for Cell Biology meeting in Washington, D.C.
The Salk researchers found that HIV appears to skim along the infected cell's microtubules, molecular "tent poles" that form what is commonly referred to as the cell's skeleton. In their experiments, the viral protein Vpr is labeled with a tag, green fluorescent protein (GFP) derived from bioluminescent jellyfish.
"We see the green lights gliding along in a straight line and moving toward the nucleus fairly rapidly," said Hope. "This led us to believe the virus might be attaching to something solid, rather than diffusing through the cytoplasm or being transported in vesicles."
Hope and his colleagues used the drug taxol, which "locks" microtubules. Then they broke the cells apart and examined the microtubules. Sure enough, they found fluorescent tags clinging to the structures.
"The findings indicate that, like herpes and adenoviruses, HIV hitches a ride on the cell's backbone," said Hope. "If we could obstruct this step, we'd have a good candidate for a drug to block HIV infection."
First author of the study is David McDonald, a postdoctoral fellow in Hope's laboratory. The study was done in collaboration with Marie A. Vodicka and Michael Emerman at the Fred Hutchinson Cancer Research Center in Seattle, Wash. The study, titled "HIV Travels on Microtubules to Reach the Nucleus of Infected Cells," was supported by the National Institutes of Health.
The Salk Institute for Biological Studies, located in La Jolla, Calif., is an independent nonprofit institution dedicated to fundamental discoveries in the life sciences, the improvement of human health and conditions, and the training of future generations of researchers. The Institute was founded in 1960 by Jonas Salk, M.D., with a gift of land from the City of San Diego and the financial support of the March of Dimes Birth Defects Foundation.
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