Revisiting G3BP1 as a RasGAP binding protein: sensitization of tumor cells to chemotherapy by the RasGAP 317-326 sequence does not involve G3BP1

• Published in: PloS one 2011-12, Vol.6 (12), p.e29024
• Main Authors: Annibaldi, Alessandro, Dousse, Aline, Martin, Sophie, Tazi, Jamal, Widmann, Christian
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino acids; Animals; Antigens; Apoptosis; Apoptosis - drug effects; Binding; Biochemistry, Molecular Biology; Biology; c-Myc protein; Cancer; Carrier Proteins - metabolism; Caspase; Caspase-3; Cell Line, Tumor; Chemotherapy; Cisplatin; Cricetinae; DNA Helicases; Drug Resistance, Neoplasm - drug effects; Enzymes; Glycerol; Granular materials; Humans; Leukemia; Life Sciences; Medicine; Messenger RNA; Mice; mRNA stability; Mutagens - pharmacology; Myc protein; Passengers; Peptide Fragments - chemistry; Peptide Fragments - pharmacology; Peptides; Physiology; Poly-ADP-Ribose Binding Proteins; Protein Binding; Proteins; ras GTPase-Activating Proteins - chemistry; ras GTPase-Activating Proteins - metabolism; RNA Helicases; RNA Recognition Motif Proteins; Signaling; Surveillance; Tumor cells; Tumors
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0029024

RasGAP is a multifunctional protein that controls Ras activity and that is found in chromosomal passenger complexes. It also negatively or positively regulates apoptosis depending on the extent of its cleavage by caspase-3. RasGAP has been reported to bind to G3BP1 (RasGAP SH3-domain-binding protein 1), a protein regulating mRNA stability and stress granule formation. The region of RasGAP (amino acids 317-326) thought to bind to G3BP1 corresponds exactly to the sequence within fragment N2, a caspase-3-generated fragment of RasGAP, that mediates sensitization of tumor cells to genotoxins. While assessing the contribution of G3BP1 in the anti-cancer function of a cell-permeable peptide containing the 317-326 sequence of RasGAP (TAT-RasGAP₃₁₇₋₃₂₆), we found that, in conditions where G3BP1 and RasGAP bind to known partners, no interaction between G3BP1 and RasGAP could be detected. TAT-RasGAP₃₁₇₋₃₂₆ did not modulate binding of G3BP1 to USP10, stress granule formation or c-myc mRNA levels. Finally, TAT-RasGAP₃₁₇₋₃₂₆ was able to sensitize G3BP1 knock-out cells to cisplatin-induced apoptosis. Collectively these results indicate that G3BP1 and its putative RasGAP binding region have no functional influence on each other. Importantly, our data provide arguments against G3BP1 being a genuine RasGAP-binding partner. Hence, G3BP1-mediated signaling may not involve RasGAP.