title: Caspase 3-mediated inactivation of rac GTPases promotes drug-induced apoptosis in human lymphoma cells.
abstract: The Rac members of the Rho family GTPases control signaling pathways that regulate diverse cellular activities, including cytoskeletal organization, gene transcription, and cell transformation. Rac is implicated in apoptosis, but little is known about the mechanism by which it responds to apoptotic stimuli. Here we demonstrate that endogenous Rac GTPases are caspase 3 substrates that are cleaved in human lymphoma cells during drug-induced apoptosis. Cleavage of Rac1 occurs at two unconventional caspase 3 sites, VVGD11/G and VMVD47/G, and results in inactivation of the GTPase and effector functions of the protein (binding to the p21-activated protein kinase PAK1). Expression of caspase 3-resistant Rac1 mutants in the cells suppresses drug-induced apoptosis. Thus, proteolytic inactivation of Rac GTPases represents a novel, irreversible mechanism of Rac downregulation that allows maximal cell death following drug treatment.
authors.affiliation: Laboratory of Biochemistry, Division of Therapeutic Proteins, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892, USA. zhangb@cber.fda.gov
authors.forename: Baolin
authors.initials: B
authors.lastname: Zhang
authors.forename: Yaqin
authors.initials: Y
authors.lastname: Zhang
authors.forename: Emily
authors.initials: E
authors.lastname: Shacter
mesh_terms: D017209:Apoptosis; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D015536:Down-Regulation; D005047:Etoposide / Q000494:pharmacology; D005822:Genetic Vectors; D006801:Humans; D008223:Lymphoma / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction; D019311:Staurosporine / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D054462:p21-Activated Kinases; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D005047:Etoposide; C515903:PAK1 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D020744:rac GTP-Binding Proteins; D019311:Staurosporine