Figure 5.

Gelonin entry through a plasma membrane disruption, and not merely cell exposure to gelonin, is required for inhibition of fos expression. Coverslips containing human umbilical vein endothelial cells were scratched multiple times in two sets of perpendicular directions. During one set, gelonin was present (filled squares); during the second set, it had been washed away and was replaced with an FDx-only saline (open squares). Thus, some cells suffered disruptions in the presence of gelonin (filled squares), and this inhibitor could enter cytosol of individual cells in this population. Another subpopulation was exposed to gelonin (open squares), but direct access to cytosol was not induced until after gelonin had been removed. Such cells could take up gelonin only by other mechanisms that, theoretically, might lead to its toxic effect on protein synthesis, such as endocytosis. Then the fos and dextran intensities were determined as above for both sets of scratches.