Geranylgeranyltransferase I inhibitors target RalB to inhibit anchorage-dependent growth and induce apoptosis and RalA to inhibit anchorage-independent growth.

Abstract

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.

• Authors: Samuel C Falsetti, De-an Wang, Hairuo Peng, Dora Carrico, Adrienne D Cox, Channing J Der, Andrew D Hamilton, Saïd M Sebti
• Journal: Molecular and cellular biology (Mol Cell Biol) Vol. 27 Issue 22 Pg. 8003-14 (Nov 2007) ISSN: 1098-5549 [Electronic] United States
• PMID: 17875936 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• BIRC5 protein, human
• CDKN1B protein, human
• Enzyme Inhibitors
• Inhibitor of Apoptosis Proteins
• Intracellular Signaling Peptides and Proteins
• Microtubule-Associated Proteins
• Neoplasm Proteins
• Protein Isoforms
• Ralb protein, human
• Survivin
• Cyclin-Dependent Kinase Inhibitor p27
• Alkyl and Aryl Transferases
• geranylgeranyltransferase type-I
• RALA protein, human
• ral GTP-Binding Proteins

Topics

• Alkyl and Aryl Transferases (antagonists & inhibitors, metabolism)
• Animals
• Apoptosis (physiology)
• Cell Adhesion (physiology)
• Cell Line
• Cyclin-Dependent Kinase Inhibitor p27
• Enzyme Inhibitors (metabolism)
• Humans
• In Situ Nick-End Labeling
• Inhibitor of Apoptosis Proteins
• Intracellular Signaling Peptides and Proteins (genetics, metabolism)
• Microtubule-Associated Proteins (genetics, metabolism)
• Mutagenesis, Site-Directed
• Neoplasm Proteins (genetics, metabolism)
• Protein Isoforms (genetics, metabolism)
• Protein Prenylation
• Survivin
• ral GTP-Binding Proteins (genetics, metabolism)