title: Examination of the coordinate effects of Pseudomonas aeruginosa ExoS on Rac1.
abstract: Exoenzyme S (ExoS) is a bifunctional toxin directly translocated into eukaryotic cells by the Pseudomonas aeruginosa type III secretory (TTS) process. The amino-terminal GTPase-activating (GAP) activity and the carboxy-terminal ADP-ribosyltransferase (ADPRT) activity of ExoS have been found to target but exert opposite effects on the same low-molecular-weight G protein, Rac1. ExoS ADP-ribosylation of Rac1 is cell line dependent. In HT-29 human epithelial cells, where Rac1 is ADP-ribosylated by TTS-ExoS, Rac1 was activated and relocalized to the membrane fraction. Arg66 and Arg68 within the GTPase-binding region of Rac1 were identified as preferred sites of ExoS ADP-ribosylation. The modification of these residues by ExoS would be predicted to interfere with Rac1 inactivation and explain the increase in active Rac1 caused by ExoS ADPRT activity. Using ExoS-GAP and ADPRT mutants to examine the coordinate effects of the two domains on Rac1 function, limited effects of ExoS-GAP on Rac1 inactivation were evident in HT-29 cells. In J774A.1 macrophages, where Rac1 was not ADP-ribosylated, ExoS caused a decrease in the levels of active Rac1, and this decrease was linked to ExoS-GAP. Using immunofluorescence staining of Rac1 to understand the cellular basis for the targeting of ExoS ADPRT activity to Rac1, an inverse relationship was observed between Rac1 plasma membrane localization and Rac1 ADP-ribosylation. The results obtained from these studies have allowed the development of a model to explain the differential targeting and coordinate effects of ExoS GAP and ADPRT activity on Rac1 within the host cell.
authors.affiliation: Department of Microbiology, Immunology and Cell Biology, Robert C. Byrd Health Sciences Center, PO Box 9177, West Virginia University, Morgantown, WV 26506-9177, USA.
authors.forename: Claudia L
authors.initials: CL
authors.lastname: Rocha
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Rucks
authors.forename: Deanne M
authors.initials: DM
authors.lastname: Vincent
authors.forename: Joan C
authors.initials: JC
authors.lastname: Olson
mesh_terms: D036002:ADP Ribose Transferases / Q000502:physiology*; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D001427:Bacterial Toxins; D016466:CHO Cells; D002460:Cell Line; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D006224:Cricetinae; D005455:Fluorescent Antibody Technique; D019073:HT29 Cells; D006801:Humans; D019169:Jurkat Cells; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000201:enzymology*; D051381:Rats; D014709:Vero Cells; D054462:p21-Activated Kinases; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D001427:Bacterial Toxins; D000246:Adenosine Diphosphate Ribose; D036002:ADP Ribose Transferases; C444820:exoenzyme S; C515903:PAK1 protein, human; C515905:Pak1 protein, mouse; C515906:Pak1 protein, rat; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020744:rac GTP-Binding Proteins