Geranylgeranyltransferase I inhibitors target RalB to inhibit anchorage-dependent growth and induce apoptosis and RalA to inhibit anchorage-independent growth.
Geranylgeranyltransferase I inhibitors (GGTIs) are presently undergoing advanced preclinical studies and have been shown to disrupt oncogenic and tumor survival pathways, to inhibit anchorage-dependent and -independent growth, and to induce apoptosis. However, the geranylgeranylated proteins that are targeted by GGTIs to induce these effects are not known. Here we provide evidence that the Ras-like small GTPases RalA and RalB are exclusively geranylgeranylated and that inhibition of their geranylgeranylation mediates, at least in part, the effects of GGTIs on anchorage-dependent and -independent growth and tumor apoptosis. To this end, we have created the corresponding carboxyl-terminal mutants that are exclusively farnesylated and verified that they retain the subcellular localization and signaling activities of the wild-type geranylgeranylated proteins and that Ral GTPases do not undergo alternative prenylation in response to GGTI treatment. By expressing farnesylated, GGTI-resistant RalA and RalB in Cos7 cells and human pancreatic MiaPaCa2 cancer cells followed by GGTI-2417 treatment, we demonstrated that farnesylated RalB, but not RalA, confers resistance to the proapoptotic and anti-anchorage-dependent growth effects of GGTI-2417. Conversely, farnesylated RalA but not RalB expression renders MiaPaCa2 cells less sensitive to inhibition of anchorage-independent growth. Furthermore, farnesylated RalB, but not RalA, inhibits the ability of GGTI-2417 to suppress survivin and induce p27(Kip1) protein levels. We conclude that RalA and RalB are important, functionally distinct targets for GGTI-mediated tumor apoptosis and growth inhibition.
Falsetti
Samuel C
SC
Drug Discovery Program, The H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida, USA.
Wang
De-an
DA
Peng
Hairuo
H
Carrico
Dora
D
Cox
Adrienne D
AD
Der
Channing J
CJ
Hamilton
Andrew D
AD
Sebti
Saïd M
SM
D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002448:Cell Adhesion / Q000502:physiology*; D002460:Cell Line; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D020287:In Situ Nick-End Labeling; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D017368:Protein Prenylation; D000077022:Survivin; D020725:ral GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
C107489:BIRC5 protein, human; C436291:CDKN1B protein, human; D004791:Enzyme Inhibitors; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D020033:Protein Isoforms; C483163:Ralb protein, human; D000077022:Survivin; D050760:Cyclin-Dependent Kinase Inhibitor p27; D019883:Alkyl and Aryl Transferases; C083291:geranylgeranyltransferase type-I; C492198:RALA protein, human; D020725:ral GTP-Binding Proteins