title: Thermostable direct hemolysin diminishes tyrosine phosphorylation of epidermal growth factor receptor through protein kinase C dependent mechanism.
abstract: BACKGROUND
  Adequate evidence mounts to the fact that several bacteria and their toxins have protective or curative roles in colorectal cancers. Thermostable direct hemolysin (TDH), produced by Vibrio parahaemolyticus, down regulates cell proliferation in colon carcinoma cell lines. TDH induces Ca2+ influx from an extracellular environment accompanied by protein kinase C phosphorylation. Activated protein kinase C inhibits the tyrosine kinase activity of epidermal growth factor receptor (EGFR), the rational target of anti-colorectal cancer therapy.
  
  
  METHODS
  Immunoblotting analyses were performed to ascertain protein kinase C activation, EGFR status, EGFR phosphorylation and mitogen activated protein kinase (MAPK) activity. Flow cytometry analysis and ELISA reconfirmed tyrosine phosphorylation of EGFR and ERK activations, respectively. PKC-α siRNA knockdown was done to corroborate the involvement of PKC-α in the undertaken study.
  
  
  RESULTS
  Our study showed the translocation of PKC-α from cytosol to the membrane fraction in colon carcinoma cell lines on incubation with TDH. The EGFR tyrosine kinase activity exhibited a down regulation on TDH treatment which involved PKC-α, as confirmed by siRNA knockdown. Also ERK phosphorylation occurred on PKC-α activation.
  
  
  CONCLUSIONS
  TDH activated PKC-α down regulates EGFR tyrosine kinase activity by MEK dependent mechanism involving MAPK.
  
  
  CONCLUSIONS
  In this study we have seen that TDH has an implication in EGFR based therapeutic approach in colorectal cancer via PKC mediated mechanism.
authors.affiliation: National Institute of Cholera and Enteric Diseases, Scheme-XM, Beliaghata, Kolkata, India.
authors.forename: Poulomee
authors.initials: P
authors.lastname: Karmakar
authors.forename: Manoj K
authors.initials: MK
authors.lastname: Chakrabarti
mesh_terms: D001427:Bacterial Toxins / Q000494:pharmacology; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D004768:Enterotoxins / Q000494:pharmacology*; D004797:Enzyme-Linked Immunosorbent Assay; D066246:ErbB Receptors / Q000378:metabolism*; D005434:Flow Cytometry; D006460:Hemolysin Proteins / Q000494:pharmacology*; D006801:Humans; D047468:Immunoprecipitation; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D051571:Protein Kinase C-alpha / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects*; D014443:Tyrosine / Q000378:metabolism
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D006460:Hemolysin Proteins; D034741:RNA, Small Interfering; C068489:thermostable direct hemolysin; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; C512478:EGFR protein, human; D066246:ErbB Receptors; D051571:Protein Kinase C-alpha; D020928:Mitogen-Activated Protein Kinases