Role for RhoB and PRK in the suppression of epithelial cell transformation by farnesyltransferase inhibitors

Abstract

Recent genetic investigations have established that RhoB gain-of-function is sufficient to mediate the antitransforming effects of farnesyltransferase inhibitors (FTIs) in H-Ras-transformed fibroblast systems. In this study, we addressed the breadth and mechanism of RhoB action in epithelial cells transformed by oncoproteins which are themselves insensitive to FTI inactivation. Rat intestinal epithelial (RIE) cells transformed by activated K-Ras or Rac1 were highly sensitive to FTI-induced actin reorganization and growth inhibition, despite the inability of FTI to block prenylation of either K-Ras or Rac1. Ectopic expression of the geranylgeranylated RhoB isoform elicited in cells by FTI treatment phenocopied these effects. Analysis of RhoB effector domain mutants pointed to a role for PRK, a Rho effector kinase implicated in the physiological function of RhoB in intracellular receptor trafficking, and these findings were supported further by experiments in a fibroblast system. We propose that FTIs recruit the antioncogenic RhoB protein in the guise of RhoB-GG to interfere with signaling by pro-oncogenic Rho proteins, possibly by sequestering common exchange factors or effectors such as PRK that are important for cell transformation.

Inhibition of Geranylgeranylation Mediates the Effects of 3-Hydroxy-3-methylglutaryl (HMG)-CoA Reductase Inhibitors on Microglia

“…51 for a recent review). It is possible that the pathways leading to cytoskeletal versus gene regulation diverge at the very beginning of the isoprenylation step and that different members of the Rho family initiate different cascades (52)(53)(54)(55)(56)(57)(58)(59)(60)(61).…”

RhoB facilitates c-Myc turnover by supporting efficient nuclear accumulation of GSK-3

“…Generation of recombinant retroviruses has been described previously that a hemagglutinin antigen epitope (HA)-tagged RhoB-WT cDNA or RhoB-GG cDNA was subcloned into the replication-incompetent retroviral vector MSCVpac, which includes a puromycin selection marker (Zeng et al, 2003). Recombinant MSCVpac viruses were packaged by standard methods in Phoenix cells.…”

Narciclasine, a plant growth modulator, activates Rho and stress fibers in glioblastoma cells

“…It has been shown that oligodendrocyte lineage transcription factor 2 inhibits the motility of a certain human glial tumor cell line by activating RhoA (22). This may explain the selective antitumor activity of farnesyl transferase inhibitors, which, although originally designed to attenuate the action of Ras proteins, are now believed to act including in glioblastoma multiforme cells at least in part by activating Rho (40)(41)(42). Conversely, metastatic tumors whose cells invade using a rounded, amoeboid movement are clearly susceptible to Rho inhibition (39).…”

“…Once in the cytosol, the cell-penetrating moiety is released, thereby allowing C3 transferase to freely diffuse intracellularly and inactive RhoA, RhoB, and RhoC but not related GTPases such as Cdc42 or Rac1. C3 transferase inhibits Rho proteins by ADP ribosylation on Asn 41 in the effector binding domain of the GTPase. Cells were then lysed and RhoA activity was measured by the RhoA G-LISA Activation Assay (TebuBio) or alternatively cells were stained for F-actin.…”