The adenovirus E3 10.4K and 14.5K proteins, which function to prevent cytolysis by tumor necrosis factor and to down-regulate the epidermal growth factor receptor, are localized in the plasma membrane.

The adenovirus type 2 and 5 E3 10,400- and 14,500-molecular-weight (10.4K and 14.5K) proteins are both required to protect some cell lines from lysis by tumor necrosis factor and to down-regulate the epidermal growth factor receptor. We have shown previously that both 10.4K and 14.5K are integral membrane proteins and that 14.5K is phosphorylated and O glycosylated. The 10.4K protein coimmunoprecipitates with 14.5K, indicating that the two proteins function as a complex. Here we show, using immunofluorescence and two different cell surface-labeling techniques, that both proteins are localized in the plasma membrane. In addition, we show that trafficking of each protein to the plasma membrane depends on concomitant expression of the other protein. Finally, neither protein could be immunoprecipitated from conditioned media, indicating that neither is secreted. Taken together, these results suggest that the plasma membrane is the site at which 10.4K and 14.5K function to inhibit cytolysis by tumor necrosis factor and to down-regulate the epidermal growth factor receptor.