title: Incorporation of ortho- and meta-tyrosine into cellular proteins leads to erythropoietin-resistance in an erythroid cell line.
abstract: OBJECTIVE
  Erythropoietin-resistance is an unsolved concern in the treatment of renal anaemia. We aimed to investigate the possible role of ortho- and meta-tyrosine - the hydroxyl free radical products of L-phenylalanine - in the development of erythropoietin-resistance.
  
  
  METHODS
  TF-1 erythroblast cell line was used. Cell concentration was determined on day 1; 2 and 3 by two independent observers simultaneously in Bürker cell counting chambers. Protein concentration was determined with colorimetric method. Para-, ortho- and meta-tyrosine levels were measured using reverse phase-HPLC with fluorescence detection. Using Western blot method activating phosphorylation of STAT5 and ERK1/2 were investigated.
  
  
  RESULTS
  We found a time- and concentration-dependent decrease of erythropoietin-induced proliferative activity in case of ortho- and meta-tyrosine treated TF-1 erythroblasts, compared to the para-tyrosine cultured cells. Decreased erythropoietin-response could be regained with a competitive dose of para-tyrosine. Proteins of erythroblasts treated by ortho- or meta-tyrosine had lower para-tyrosine and higher ortho- or meta-tyrosine content. Activating phosphorylation of ERK and STAT5 due to erythropoietin was practically prevented by ortho- or meta-tyrosine treatment.
  
  
  CONCLUSIONS
  According to this study elevated ortho- and meta-tyrosine content of erythroblasts may lead to the dysfunction of intracellular signaling, resulting in erythropoietin-hyporesponsiveness.
authors.affiliation: 2nd Department of Medicine and Nephrological Center, University of Pécs, Pécs, Hungary.
authors.forename: Esztella
authors.initials: E
authors.lastname: Mikolás
authors.forename: Szilárd
authors.initials: S
authors.lastname: Kun
authors.forename: Boglárka
authors.initials: B
authors.lastname: Laczy
authors.forename: Gergő A
authors.initials: GA
authors.lastname: Molnár
authors.forename: Eszter
authors.initials: E
authors.lastname: Sélley
authors.forename: Tamás
authors.initials: T
authors.lastname: Kőszegi
authors.forename: István
authors.initials: I
authors.lastname: Wittmann
mesh_terms: D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D004351:Drug Resistance; D000068817:Epoetin Alfa; D041905:Erythroid Cells / Q000187:drug effects*; D004921:Erythropoietin / Q000494:pharmacology*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D011506:Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D050799:STAT5 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D011506:Proteins; D011994:Recombinant Proteins; D050799:STAT5 Transcription Factor; D004921:Erythropoietin; D014443:Tyrosine; D000068817:Epoetin Alfa