title: The mechanistic target for rapamycin pathway is related to the phosphorylation score for estrogen receptor-α in human breast tumors in vivo.
abstract: BACKGROUND
  A phosphorylation score for estrogen receptor-alpha (ERα), called P7 score, was shown previously to be an independent prognostic factor in breast cancer patients treated with tamoxifen. Since mechanistic target of rapamycin (mTOR) activation is implicated in resistance to endocrine therapy in breast cancer we determined whether mechanistic target of rapamycin complex 1 (mTORC1) activation, measured by phosphorylation on S2448 (p-mTOR), was associated with the P7-score and/or clinical outcome in the same cohort.
  
  
  METHODS
  mTOR phosphorylation status was determined at S2448 residue in vivo by immunohistochemistry in a cohort of more than 400 well-characterized ERα positive breast tumors. MCF7 cells were treated with estrogen and activation of mTOR pathway was determined by Western blotting.
  
  
  RESULTS
  Contrary to earlier reports, p-mTOR expression, measured by immunohistochemistry, was negatively associated with size and nodal status. Additionally, p-S2448 mTOR expression was positively correlated with p-S118- ERα, p-S167-ERα and p-S282-ERα but negatively correlated with p-T311- ERα. Consistent with these, p-S2448 mTOR was negatively associated with P7-score and was significantly associated with overall survival (OS) (hazard ratio (HR) = 0.61, P = 0.028, 95% confidence interval (CI) 0.39 to 0.95, n = 337) and relapse-free survival (HR = 0.58, P = 0.0032, 95% CI 0.41 to 0.83, n = 337) following univariate but not multivariate analysis. Furthermore, we show that estrogen can regulate phosphorylation of mTOR and its down stream target p70S6 kinase. Additionally, recombinant mTOR can phosphorylate ERα in vitro.
  
  
  CONCLUSIONS
  These data suggest that in breast tumors where there is intact estrogen regulated signaling, mTOR is regulated by estrogen and therefore associated with an increased likelihood of responsiveness to endocrine therapy.
authors.forename: Anuraag
authors.initials: A
authors.lastname: Shrivastav
authors.forename: Mary
authors.initials: M
authors.lastname: Bruce
authors.forename: Danira
authors.initials: D
authors.lastname: Jaksic
authors.forename: Tarek
authors.initials: T
authors.lastname: Bader
authors.forename: Srinivas
authors.initials: S
authors.lastname: Seekallu
authors.forename: Carla
authors.initials: C
authors.lastname: Penner
authors.forename: Zoann
authors.initials: Z
authors.lastname: Nugent
authors.forename: Peter
authors.initials: P
authors.lastname: Watson
authors.forename: Leigh
authors.initials: L
authors.lastname: Murphy
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000401:mortality; D045744:Cell Line, Tumor; D018572:Disease-Free Survival; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004789:Enzyme Activation; D047628:Estrogen Receptor alpha / Q000378:metabolism*; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D061986:MCF-7 Cells; D000076222:Mechanistic Target of Rapamycin Complex 1; D008875:Middle Aged; D046912:Multiprotein Complexes / Q000096:biosynthesis / Q000378:metabolism*; D010766:Phosphorylation; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000096:biosynthesis / Q000378:metabolism*; D013629:Tamoxifen / Q000627:therapeutic use*; D016896:Treatment Outcome
chemical_list: D018931:Antineoplastic Agents, Hormonal; C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; D004967:Estrogens; D046912:Multiprotein Complexes; D013629:Tamoxifen; D000076222:Mechanistic Target of Rapamycin Complex 1; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases