title: Caspase-mediated cleavage of the TIAM1 guanine nucleotide exchange factor during apoptosis.
abstract: Rho family GTPases Rac and Cdc42 are pivotal regulators of apoptosis in multiple cell types. However, little is known about the mechanism by which these GTPases are regulated in response to apoptotic stimuli. Here, we demonstrate that TIAM1, a Rac-specific guanine nucleotide exchange factor, is cleaved by caspases during apoptosis. TIAM1 cleavage occurs in multiple cell lines in response to diverse apoptotic stimuli such as ceramide, Fas, and serum deprivation. Processing occurs at residue 993 of TIAM1 and removes the NH(2)-terminal of TIAM's two pleckstrin homology domains, leaving a stable fragment containing the Dbl homology and COOH-terminal pleckstrin homology domains. This leads to functional inactivation of TIAM1, as determined by failure of the cleavage product to stimulate GTP loading of Rac in vivo. Furthermore, this product is defective in signaling to two independent Rac effectors, c-Jun NH(2)-terminal kinase and serum response factor. Finally, we demonstrate that in cells treated with ceramide, cleavage of TIAM1 coincided with the inactivation of endogenous Rac. These results reveal a novel mechanism for regulating guanine nucleotide exchange factor activity and GTPase-mediated signaling pathways.
authors.affiliation: University of Pennsylvania School of Medicine, Department of Cell and Developmental Biology, 421 Curie Boulevard, Philadelphia, PA 19104-6160, USA.
authors.forename: H
authors.initials: H
authors.lastname: Qi
authors.forename: P
authors.initials: P
authors.lastname: Juo
authors.forename: J
authors.initials: J
authors.lastname: Masuda-Robens
authors.forename: M J
authors.initials: MJ
authors.lastname: Caloca
authors.forename: H
authors.initials: H
authors.lastname: Zhou
authors.forename: N
authors.initials: N
authors.lastname: Stone
authors.forename: M G
authors.initials: MG
authors.lastname: Kazanietz
authors.forename: M M
authors.initials: MM
authors.lastname: Chou
mesh_terms: D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D001798:Blood Proteins / Q000737:chemistry; D019556:COS Cells; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002518:Ceramides / Q000378:metabolism / Q000494:pharmacology; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D015151:Immunoblotting; D048031:JNK Mitogen-Activated Protein Kinases; D019169:Jurkat Cells; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009363:Neoplasm Proteins; D016716:PC12 Cells; D010750:Phosphoproteins / Q000737:chemistry; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D026362:Serum Response Factor / Q000378:metabolism; D015398:Signal Transduction; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D013997:Time Factors; D014407:Tumor Cells, Cultured; D020744:rac GTP-Binding Proteins / Q000378:metabolism
chemical_list: D001798:Blood Proteins; D002518:Ceramides; D020662:Guanine Nucleotide Exchange Factors; D009363:Neoplasm Proteins; D010750:Phosphoproteins; D011506:Proteins; D026362:Serum Response Factor; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C087334:TIAM1 protein, human; C513260:Tiam1 protein, mouse; C513259:Tiam1 protein, rat; C039077:platelet protein P47; D008156:Luciferases; D048031:JNK Mitogen-Activated Protein Kinases; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases; D020169:Caspases; D020558:GTP Phosphohydrolases; D020744:rac GTP-Binding Proteins