THE NONSTRUCTURAL GLYCOPROTEIN OF ROTAVIRUS AFFECTS INTRACELLULAR CALCIUM LEVELS

Rotavirus infection of monkey kidney cells has been reported to result in a significant increase in the concentration of intracellular calci um. This increase in intracellular calcium was associated with viral p rotein synthesis and cytopathic effects in infected cells. We tested t he effect of individual rotavirus proteins on intracellular calcium co ncentrations in insect Spodoptera frugiperda (Sf9) cells. Insect cells were infected with wild-type baculovirus or baculovirus recombinants that contained an individual rotavirus gene. The cells were harvested at different times postinfection, and the intracellular calcium concen tration was measured by using fura-2 as a fluorescent calcium indicato r. We found that the concentration of intracellular calcium was increa sed nearly fivefold in infected Sf9 cells that expressed the nonstruct ural glycoprotein (NSP4) of group A rotavirus, and this increase in in tracellular calcium concentration coincided with NSP4 expression. A si milar result was observed in insect cells expressing NSP4 from a group B rotavirus, suggesting the conservation of this function among rotav irus groups. Expression of the other 10 rotavirus proteins or of wild- type baculovirus proteins in Sf9 cells did not significantly increase intracellular calcium levels. These results suggest that the nonstruct ural glycoprotein NSP4 is responsible for the increase in cytosolic ca lcium observed in rotavirus-infected cells.