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Evidence that farnesyltransferase inhibitors suppress Ras transformation by interfering with Rho activity
P F Lebowitz1, J P Davide, G C Prendergast
1Wistar Institute, University of Pennsylvania, Philadelphia 19104, USA.
Abstract:
Small-molecule inhibitors of the housekeeping enzyme farnesyltransferase (FT) suppress the malignant growth of Ras-transformed cells. Previous work suggested that the activity of these compounds reflected effects on actin stress fiber regulation rather than Ras inhibition. Rho proteins regulate stress fiber formation, and one member of this family, RhoB, is farnesylated in vivo. Therefore, we tested the hypothesis that interference with RhoB was the principal basis by which the peptidomimetic FT inhibitor L-739,749 suppressed Ras transformation. The half-life of RhoB was found to be approximately 2 h, supporting the possibility that it could be functionally depleted within the 18-h period required by L-739,749 to induce reversion. Cell treatment with L-739,749 disrupted the vesicular localization of RhoB but did not effect the localization of the closely related RhoA protein. Ras-transformed Rat1 cells ectopically expressing N-myristylated forms of RhoB (Myr-rhoB), whose vesicular localization was unaffected by L-739,749, were resistant to drug treatment. The protective effect of Myr-rhoB required the integrity of the RhoB effector domain and was not due to a gain-of-function effect of myristylation on cell growth. In contrast, Rat1 cells transformed by a myristylated Ras construct remained susceptible to growth inhibition by L-739,749. We concluded that Rho is necessary for Ras transformation and that FT inhibitors suppress the transformed phenotype at least in part by direct or indirect interference with Rho, possibly with RhoB itself.
Insights
Farnesyltransferase (FT) inhibitors suppress Ras-transformed cell growth by interfering with Rho proteins, particularly RhoB. This interference disrupts cellular processes, reversing malignant transformation.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Small-molecule inhibitors of farnesyltransferase (FT) are known to suppress malignant growth in Ras-transformed cells.
- Previous research suggested these inhibitors' effects on actin stress fiber regulation, not directly on Ras.
- Rho proteins, including RhoB, are involved in stress fiber formation and are farnesylated in vivo.
Purpose of the Study:
- To investigate if interference with RhoB is the primary mechanism by which the FT inhibitor L-739,749 suppresses Ras transformation.
- To determine the role of Rho proteins in Ras-mediated cell transformation.
Main Methods:
- Assessed the half-life of RhoB to evaluate functional depletion potential.
- Examined the effect of L-739,749 on the cellular localization of RhoB and RhoA.
- Utilized Ras-transformed Rat1 cells expressing N-myristylated RhoB (Myr-rhoB) to assess resistance to L-739,749.
- Tested Ras-transformed Rat1 cells with a myristylated Ras construct for susceptibility to L-739,749.
Main Results:
- RhoB has a half-life of approximately 2 hours, allowing for functional depletion.
- L-739,749 treatment disrupted RhoB's vesicular localization but not RhoA's.
- Cells expressing Myr-rhoB were resistant to L-739,749, indicating RhoB's importance.
- This protective effect of Myr-rhoB depended on its effector domain integrity.
- Ras-transformed cells with myristylated Ras remained susceptible to L-739,749 growth inhibition.
Conclusions:
- Rho proteins are essential for Ras-mediated cell transformation.
- Farnesyltransferase inhibitors suppress the transformed phenotype, at least partially, through interference with Rho proteins, potentially RhoB.
- The study highlights a novel mechanism for FT inhibitors in cancer therapy by targeting Rho signaling pathways.