Fig. 6. Expression of the RhoB-binding HR1 domain from PRK1 overcomes the FTI-induced block on EGF-receptor degradation. Cells were transiently transfected with a HA-tagged HR1 domain construct from PRK1/PKN. Cells were starved overnight in the absence or presence of FTI and then stimulated with 100 ng/ml EGF for 2 hours. Cells were fixed and stained for endogenous EGF receptor and for expression of the HR1 construct. Cells were imaged by confocal microscopy, and the mean fluorescence signal for the EGF receptor within a fixed area was determined from 30 cells for each condition. Error bars represent standard error of the mean (s.e.m.) (n=3; 30 cells each experiment). The negation of the FTI induced block of EGF receptor by expression of the HR1 domain was found to be significant by the Student's t-test (P<0.001).