title: Investigating TrkA expression in canine appendicular osteosarcoma.
abstract: BACKGROUND
  The tropomyosin-related kinase A (TrkA) proto-oncogene encodes for a receptor that binds with high affinity to the neurotrophin ligand, nerve growth factor (NGF). Intracellular signaling mediated by the TrkA/NGF axis orchestrates neuronal cell differentiation, mitogenesis, and survival. Interestingly, TrkA also is expressed by bone forming cells, and its signaling promotes antiapoptotic effects in actively dividing osteoblasts.
  
  
  OBJECTIVE
  In canine immortalized cell lines and naturally occurring tumor samples, osteosarcoma (OSA) cells will express TrkA. In canine OSA cell lines, TrkA signaling will promote cell mitogenesis and survival.
  
  
  METHODS
  In vitro, TrkA expression in canine OSA cell lines was assessed by reverse transcriptase-polymerase chain reaction, flow cytometry, and immunocytochemistry. In vitro, the involvement of TrkA-mediated signaling for cell mitogenesis and survival were investigated with commercially available assays. In vivo, TrkA expression was evaluated in primary tumors and pulmonary metastases with immunocytochemistry and immunohistochemistry, respectively.
  
  
  RESULTS
  In vitro, canine OSA cells expressed TrkA mRNA and protein. Ligation of TrkA with exogenous NGF did not induce mitogenesis. Blockade of TrkA signaling with either a protein kinase inhibitor or NGF-neutralizing antibody induced apoptosis of canine OSA cell lines. In vivo, the majority (10/15) of canine OSA primary tumors and pulmonary metastases (9/12) expressed TrkA protein.
  
  
  CONCLUSIONS
  Canine OSA cells express TrkA, and its signaling protects against apoptosis. Most dogs with spontaneously arising OSA express TrkA within their primary tumors and pulmonary metastatic lesions, warranting further investigations with TrkA antagonists as a novel treatment option for canine OSA.
authors.affiliation: Department of Veterinary Clinical Medicine, University of Illinois at Urbana-Champaign, Urbana, IL 61802-4714, USA. t-fan@uiuc.edu
authors.forename: T M
authors.initials: TM
authors.lastname: Fan
authors.forename: A M
authors.initials: AM
authors.lastname: Barger
authors.forename: I T
authors.initials: IT
authors.lastname: Sprandel
authors.forename: R L
authors.initials: RL
authors.lastname: Fredrickson
mesh_terms: D000818:Animals; D017209:Apoptosis; D045744:Cell Line, Tumor; D004283:Dog Diseases / Q000378:metabolism*; D004285:Dogs; D005121:Extremities / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D008175:Lung Neoplasms / Q000556:secondary; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D012516:Osteosarcoma / Q000378:metabolism* / Q000473:pathology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D009419:Nerve Tissue Proteins; D011494:Protein Kinases