title: Externalization of host cell protein kinase C during enteropathogenic Escherichia coli infection.
abstract: Enteropathogenic Escherichia coli (EPEC) is a common cause of diarrhea in children in developing countries. Protein kinase C (PKC), a serine- and threonine-directed protein kinase, is rapidly activated following EPEC infection and this is accompanied by its translocation to a membrane-bound location where it is tightly bound to phosphatidylserine (PS). EPEC infection causes host cell death, one of whose features is externalization of PS. We hypothesized that externalization of PS would be accompanied by externalization of PKC as well. We report that EPEC infection triggers the externalization of PKC to the outer surface of the host cell. Ecto-PKC remains firmly tethered to the cell but can be released by incubation with peptide or protein substrates for the enzyme. Ecto-PKC is intact and biologically active and able to phosphorylate protein substrates on the surface of the host cell. Phosphorylation of whole EPEC bacteria or EPEC-secreted proteins could not be detected. Externalization of PKC could be reproduced by the combination of an apoptotic stimulus (ultraviolet (UV) irradiation) and phorbol myristate acetate (PMA), a procedure which resulted in externalization of >25% of the total cellular content of PKC-alpha. In the presence of ATP, ecto-PKC inhibited UV-induced cell shrinkage, membrane blebbing, and propidium iodide uptake but not the activation of caspases 3 and 7. This is the first report that expression of an ecto-protein kinase is altered by a microbial pathogen and the first to note that externalization of PKC can accompany apoptosis.
authors.affiliation: Department of Medicine, University at Buffalo, Buffalo, NY, USA. jcrane@acsu.buffalo.edu
authors.forename: J K
authors.initials: JK
authors.lastname: Crane
authors.forename: C M
authors.initials: CM
authors.lastname: Vezina
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D001422:Bacterial Adhesion / Q000187:drug effects / Q000528:radiation effects; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D004926:Escherichia coli / Q000254:growth & development* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014466:Ultraviolet Rays; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D029968:Escherichia coli Proteins; D047428:Protein Kinase Inhibitors; D000255:Adenosine Triphosphate; D011494:Protein Kinases; C034454:ectoprotein kinase; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; D013755:Tetradecanoylphorbol Acetate; D000077191:Wortmannin