High Affinity for Farnesyltransferase and Alternative Prenylation Contribute Individually to K-Ras4B Resistance to Farnesyltransferase Inhibitors

Farnesyltransferase inhibitors (FTIs) block Ras farnesylation, subcellular localization and activity, and inhibit the growth of Ras-transformed cells. Although FTIs are ineffective against K-Ras4B, the Ras isoform most commonly mutated in human cancers, they can inhibit the growth of tumors containing oncogenic K-Ras4B, implicating other farnesylated proteins or suggesting distinct functions for farnesylated and for geranylgeranylated K-Ras, which is generated when farnesyltransferase is inhibited. In addition to bypassing FTI blockade through geranylgeranylation, K-Ras4B resistance to FTIs may also result from its higher affinity for farnesyltransferase. Using chimeric Ras proteins containing all combinations of Ras background, CAAX motif, and K-Ras polybasic domain, we show that either a polybasic domain or an alternatively prenylated CAAX renders Ras prenylation, Ras-induced Elk-1 activation, and anchorage-independent cell growth FTI-resistant. The polybasic domain alone increases the affinity of Ras for farnesyltransferase, implying independent roles for each K-Ras4B sequence element in FTI resistance. Using microarray analysis and colony formation assays, we confirm that K-Ras function is independent of the identity of the prenyl group and, therefore, that FTI inhibition of K-Ras transformed cells is likely to be independent of K-Ras inhibition. Our results imply that relevant FTI targets will lack both polybasic and potentially geranylgeranylated methionine-CAAX motifs

Transforming Activity of the Rho Family GTPase, Wrch-1, a Wnt-regulated Cdc42 Homolog, Is Dependent on a Novel Carboxyl-terminal Palmitoylation Motif

Wrch-1 is a Rho family GTPase that shares strong sequence and functional similarity with Cdc42. Like Cdc42, Wrch-1 can promote anchorage-independent growth transformation. We determined that activated Wrch-1 also promoted anchorage-dependent growth transformation of NIH 3T3 fibroblasts. Wrch-1 contains a distinct carboxyl-terminal extension not found in Cdc42, suggesting potential differences in subcellular location and function. Consistent with this, we found that Wrch-1 associated extensively with plasma membrane and endosomes, rather than with cytosol and perinuclear membranes like Cdc42. Like Cdc42, Wrch-1 terminates in a CAAX tetrapeptide (where C is cysteine, A is aliphatic amino acid, and X is any amino acid) motif (CCFV), suggesting that Wrch-1 may be prenylated similarly to Cdc42. Most surprisingly, unlike Cdc42, Wrch-1 did not incorporate isoprenoid moieties, and Wrch-1 membrane localization was not altered by inhibitors of protein prenylation. Instead, we showed that Wrch-1 is modified by the fatty acid palmitate, and pharmacologic inhibition of protein palmitoylation caused mislocalization of Wrch-1. Most interestingly, mutation of the second cysteine of the CCFV motif (CCFV > CSFV), but not the first, abrogated both Wrch-1 membrane localization and transformation. These results suggest that Wrch-1 membrane association, subcellular localization, and biological activity are mediated by a novel membrane-targeting mechanism distinct from that of Cdc42 and other isoprenylated Rho family GTPases

Zoledronic acid treatment impairs protein geranyl-geranylation for biological effects in prostatic cells

BACKGROUND: Nitrogen-containing bisphosphonates (N-BPs) have been designed to inhibit osteoclast-mediated bone resorption. However, it is now accepted that part of their anti-tumor activities is related to interference with the mevalonate pathway. METHODS: We investigated the effects of zoledronic acid (ZOL), on cell proliferation and protein isoprenylation in two tumoral (LnCAP, PC-3,), and one normal established (PNT1-A) prostatic cell line. To assess if inhibition of geranyl-geranylation by ZOL impairs the biological activity of RhoA GTPase, we studied the LPA-induced formation of stress fibers. The inhibitory effect of ZOL on geranyl geranyl transferase I was checked biochemically. Activity of ZOL on cholesterol biosynthesis was determined by measuring the incorporation of (14)C mevalonate in cholesterol. RESULTS: ZOL induced dose-dependent inhibition of proliferation of all the three cell lines although it appeared more efficient on the untransformed PNT1A. Whatever the cell line, 20 μM ZOL-induced inhibition was reversed by geranyl-geraniol (GGOH) but neither by farnesol nor mevalonate. After 48 hours treatment of cells with 20 μM ZOL, geranyl-geranylation of Rap1A was abolished whereas farnesylation of HDJ-2 was unaffected. Inhibition of Rap1A geranyl-geranylation by ZOL was rescued by GGOH and not by FOH. Indeed, as observed with treatment by a geranyl-geranyl transferase inhibitor, treatment of PNT1-A cells with 20 μM ZOL prevented the LPA-induced formation of stress fibers. We checked that in vitro ZOL did not inhibit geranyl-geranyl-transferase I. ZOL strongly inhibited cholesterol biosynthesis up to 24 hours but at 48 hours 90% of this biosynthesis was rescued. CONCLUSION: Although zoledronic acid is currently the most efficient bisphosphonate in metastatic prostate cancer management, its mechanism of action in prostatic cells remains unclear. We suggest in this work that although in first intention ZOL inhibits FPPsynthase its main biological actitivity is directed against protein Geranylgeranylation

Protein farnesyltransferase in embryogenesis, adult homeostasis, and tumor development

Protein farnesyltransferase (FTase) is an enzyme responsible for posttranslational modification of proteins carrying a carboxy-terminal CaaX motif. Farnesylation allows substrates to interact with membranes and protein targets. Using gene-targeted mice, we report that FTase is essential for embryonic development, but dispensable for adult homeostasis. Six-month-old FTase-deficient mice display delayed wound healing and maturation defects in erythroid cells. Embryonic fibroblasts lacking FTase have a flat morphology and reduced motility and proliferation rates. Ablation of FTase in two ras oncogene-dependent tumor models has no significant consequences for tumor initiation. However, elimination of FTase during tumor progression had a limited but significant inhibitory effect. These results should help to better understand the role of protein farnesylation in normal tissues and in tumor development.This work was supported by grants from the V Framework Programme of the European Union (QLK3-1999-00875) to M.B. and from the Ministerio de Ciencia y Tecnologia (SAF2001-0058) and Fondo de Investigación Sanitaria (00/0109) to J.V. P.D. was supported by the Association pour la Recherche contre le Cancer (ARC). P.J.C. was supported by NIH grant GM46372. N.M. was supported by a BEFI Fellowship from the Fondo de Investigación Sanitaria. The CNIO is partially supported by the RTICCC (Red de Centros de Cáncer; FIS C03/10

Zoledronic acid treatment impairs protein geranyl-geranylation for biological effects in prostatic cells-5

<p><b>Copyright information:</b></p><p>Taken from "Zoledronic acid treatment impairs protein geranyl-geranylation for biological effects in prostatic cells"</p><p>BMC Cancer 2006;6():60-60.</p><p>Published online 15 Mar 2006</p><p>PMCID:PMC1434759.</p><p>Copyright © 2006 Goffinet et al; licensee BioMed Central Ltd.</p> to the medium for 2 hours more. Sterols were separated by thin layer chromatography (silica gel F/ethyl acetate). [C]-Cholesterol was revealed and quantified by autoradiography with Phophorimager(Molecular Dynamics)

Zoledronic acid treatment impairs protein geranyl-geranylation for biological effects in prostatic cells-3

<p><b>Copyright information:</b></p><p>Taken from "Zoledronic acid treatment impairs protein geranyl-geranylation for biological effects in prostatic cells"</p><p>BMC Cancer 2006;6():60-60.</p><p>Published online 15 Mar 2006</p><p>PMCID:PMC1434759.</p><p>Copyright © 2006 Goffinet et al; licensee BioMed Central Ltd.</p> (0.5 μM, 8–10 Ci/mmol) incorporation into a mutant form of H-ras with a geranyl-geranylation CAXX box. The level of prenylation is expressed as a percentage of maximum incorporation of [H]-prenyl, as determined by allowing the uninhibited reaction to go to completion. : Western-blot analysis; PC-3 cells are treated by vehicle, ZOL 20 μM; ZOL 20 μM + FOH 10 μM; ZOL 20 μM + GGOH 10 μM

Zoledronic acid treatment impairs protein geranyl-geranylation for biological effects in prostatic cells-0

<p><b>Copyright information:</b></p><p>Taken from "Zoledronic acid treatment impairs protein geranyl-geranylation for biological effects in prostatic cells"</p><p>BMC Cancer 2006;6():60-60.</p><p>Published online 15 Mar 2006</p><p>PMCID:PMC1434759.</p><p>Copyright © 2006 Goffinet et al; licensee BioMed Central Ltd.</p>nd D3, cells were treated by vehicle or increasing doses of zoledronate (ZOL: 5, 10, 15, 20 μM). At D5, the cells were fixed with TCA and stained with 0.4% sulforhodamine. Staining intensity was quantified at 540 nm. Results are expressed as the ratio OD/ODof three independent assays each performed six times. Error bars indicate inter-assay mean ± 1 SD. * indicates a significant difference versus non-treated cells (p < 0.01). PC3 PNT1A LNCa