Figure 5. Depletion of GGpp and subsequent inhibition of geranylgeranylation blocks proteasomal degradation of the small GTPases RhoA and cdc42.

SV-589 cells were set up on day 0 at a density of 1.5 × 10⁵ cells per 60 mm dish in medium A supplemented with 5 % FCS. On day 2, cells were washed and refed identical medium supplemented with 0–10 µM (A) or 10 µM compactin (B–D). Following incubation for 24 hr at 37 °C, the cells received the identical medium in the absence or presence of 20 µM GGOH, 20 µM FOH, 10 µM MG-132, and 10 µM GGTI as indicated and incubated an addition 24 hr. Cells were then harvested for preparation of detergent-solubilized lysates that were subjected to SDS-PAGE, followed by immunoblot analysis with anti-RhoA, anti-cdc42, anti-Rap1, IgG-A9 (against reductase), and anti-calnexin. Prenylated (P) and unprenylated (U) forms of Rap1 protein are denoted by arrows.