title: Mammalian target of rapamycin pathway activation is associated to RET mutation status in medullary thyroid carcinoma.
abstract: BACKGROUND
  The genetic pathways involved in medullary thyroid carcinomas (MTC), except for RET mutations, are largely unknown, as is the detailed mapping of proteins activated as a consequence of RET tyrosine kinase phosphorylation.
  
  
  OBJECTIVE
  The present study was designed to screen for the presence of mutations in other genes downstream to RET activation and to detect the activation patterns of a panel of intracellular regulators of cell growth.
  
  
  METHODS
  Forty-nine cases of MTC were analyzed for mutations in RET, BRAF, N-, H-, and K-RAS, and phosphatidylinositol-3 (PI3) kinase genes. Immunohistochemical analysis was performed using antibodies against several intracellular transducers. The effect of mammalian target of rapamycin (mTOR) inhibition was assessed in vitro onto TT cells by means of methyl thiazolyl tetrazolium and Western blot assays.
  
  
  RESULTS
  BRAF, K-, H-, and N-RAS, and PI3 kinase mutations were absent in all cases examined. Germline RET mutations were detected in 20% of cases overall, whereas somatic RET mutations represented 53% of sporadic tumors. RET mutational status was associated to age, presence of multifocal tumors, and nodal status, but not disease outcome. Protein expression of markers investigated was highly heterogeneous, with a strong association between phospho-mTOR, phospho-AKT, and phospho-p70S6K, positively correlated to the presence of germline RET mutations. Moreover, selective mTOR inhibition affected cell proliferation of RET-mutant TT cells.
  
  
  CONCLUSIONS
  Taken together, our findings indicate that mTOR intracellular signaling pathway is functionally activated in MTC with a preferential expression in cases with germline RET mutations; genes downstream to RET tyrosine kinase such as BRAF, RAS isoforms, and PI3 kinase are not mutated in MTC.
authors.affiliation: Department of Clinical and Biological Sciences, University of Turin, San Luigi Hospital, 10043 Orbassano, Turin, Italy.
authors.forename: Ida
authors.initials: I
authors.lastname: Rapa
authors.forename: Enrico
authors.initials: E
authors.lastname: Saggiorato
authors.forename: Daniela
authors.initials: D
authors.lastname: Giachino
authors.forename: Nicola
authors.initials: N
authors.lastname: Palestini
authors.forename: Fabio
authors.initials: F
authors.lastname: Orlandi
authors.forename: Mauro
authors.initials: M
authors.lastname: Papotti
authors.forename: Marco
authors.initials: M
authors.lastname: Volante
mesh_terms: D000328:Adult; D018276:Carcinoma, Medullary / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010766:Phosphorylation; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism; D051096:Proto-Oncogene Proteins c-ret / Q000235:genetics* / Q000378:metabolism; D012189:Retrospective Studies; D015398:Signal Transduction / Q000235:genetics*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000235:genetics* / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D058570:TOR Serine-Threonine Kinases; D018631:ras Proteins