title: PTK6 Potentiates Gemcitabine-Induced Apoptosis by Prolonging S-phase and Enhancing DNA Damage in Pancreatic Cancer.
abstract: Protein Tyrosine Kinase 6 (PTK6) is a non-receptor-type tyrosine kinase known to be expressed in various cancers, including pancreatic cancer. The role of PTK6 in cancer chemoresistance remains unclear. Therefore, it was hypothesized that PTK6 mechanistically regulates gemcitabine resistance in pancreatic cancer. Gemcitabine treatment stimulated endogenous PTK6 overexpression in MIAPaCa2 and Panc1 cells. PTK6 gene silencing increased cell survival after gemcitabine treatment and decreased apoptosis, whereas PTK6 overexpression decreased cell survival and increased apoptosis. Selection for gemcitabine resistance revealed substantially lower PTK6 expression in the gemcitabine-resistant subclones compared with the parental lines, while restoring PTK6 rescued gemcitabine sensitivity. Gemcitabine induced phosphorylation of H2AX (γ-H2AX) and ataxia-telangiectasia mutated kinase (pATM), specific markers for DNA double-strand breaks. Both gemcitabine-induced phosphorylation of H2AX and ATM were reduced by PTK6 knockdown and increased by PTK6 overexpression. PTK6 overexpression also increased the S-phase fraction 48 hours after gemcitabine treatment. Although gemcitabine activated both caspase-8 (CASP8) and caspase-9 (CASP9), the effect of PTK6 on gemcitabine-induced apoptosis required CASP8 but not CASP9. In mouse xenografts, PTK6 overexpression in subcutaneous tumors attenuated tumor growth after gemcitabine treatment. In conclusion, PTK6 prolongs S-phase and increases the ability of gemcitabine to cause DNA damage in vitro and in vivo.
  
  
  CONCLUSIONS
  PTK6 affects cell cycle and DNA damage, thus making it an important therapeutic target to improve the outcomes of patients with pancreatic cancer.
authors.affiliation: Department of Surgery, Michigan State University, College of Human Medicine, Lansing, Michigan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ono
authors.affiliation: Department of Surgery, Michigan State University, College of Human Medicine, Lansing, Michigan.
authors.forename: Marc D
authors.initials: MD
authors.lastname: Basson
authors.affiliation: Department of Surgery, Michigan State University, College of Human Medicine, Lansing, Michigan. Hiromichi.Ito@hc.msu.edu.
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Ito
mesh_terms: D000818:Animals; D017209:Apoptosis; D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002453:Cell Cycle; D045744:Cell Line, Tumor; D002470:Cell Survival; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000737:chemistry; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006657:Histones / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000378:metabolism*; D009368:Neoplasm Transplantation; D010190:Pancreatic Neoplasms / Q000188:drug therapy* / Q000235:genetics*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D016196:S Phase; D000093542:Gemcitabine
chemical_list: C468783:H2AX protein, human; D006657:Histones; D009363:Neoplasm Proteins; D003841:Deoxycytidine; D011505:Protein-Tyrosine Kinases; C088375:PTK6 protein, human; C000598269:Ptk6 protein, mouse; D064007:Ataxia Telangiectasia Mutated Proteins; D053181:Caspase 8; D053453:Caspase 9; D000093542:Gemcitabine