title: Protein disulfide isomerase blocks CEBPA translation and is up-regulated during the unfolded protein response in AML.
abstract: Deregulation of the myeloid key transcription factor CEBPA is a common event in acute myeloid leukemia (AML). We previously reported that the chaperone calreticulin is activated in subgroups of AML patients and that calreticulin binds to the stem loop region of the CEBPA mRNA, thereby blocking CEBPA translation. In this study, we screened for additional CEBPA mRNA binding proteins and we identified protein disulfide isomerase (PDI), an endoplasmic reticulum (ER) resident protein, to bind to the CEBPA mRNA stem loop region. We found that forced PDI expression in myeloid leukemic cells in fact blocked CEBPA translation, but not transcription, whereas abolishing PDI function restored CEBPA protein. In addition, PDI protein displayed direct physical interaction with calreticulin. Induction of ER stress in leukemic HL60 and U937 cells activated PDI expression, thereby decreasing CEBPA protein levels. Finally, leukemic cells from 25.4% of all AML patients displayed activation of the unfolded protein response as a marker for ER stress, and these patients also expressed significantly higher PDI levels. Our results indicate a novel role of PDI as a member of the ER stress-associated complex mediating blocked CEBPA translation and thereby suppressing myeloid differentiation in AML patients with activated unfolded protein response (UPR).
authors.affiliation: Department of Medical Oncology, University Hospital and University of Berne, Berne, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Haefliger
authors.forename: Christiane
authors.initials: C
authors.lastname: Klebig
authors.forename: Kerstin
authors.initials: K
authors.lastname: Schaubitzer
authors.forename: Julian
authors.initials: J
authors.lastname: Schardt
authors.forename: Nikolai
authors.initials: N
authors.lastname: Timchenko
authors.forename: Beatrice U
authors.initials: BU
authors.lastname: Mueller
authors.forename: Thomas
authors.initials: T
authors.lastname: Pabst
mesh_terms: D015153:Blotting, Western; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D037282:Calreticulin / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015973:Gene Expression Regulation, Leukemic; D018922:HL-60 Cells; D006801:Humans; D047468:Immunoprecipitation; D015470:Leukemia, Myeloid, Acute / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D014176:Protein Biosynthesis; D019704:Protein Disulfide-Isomerases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020298:U937 Cells; D056811:Unfolded Protein Response / Q000502:physiology*; D015854:Up-Regulation
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; C515848:CEBPA protein, human; D037282:Calreticulin; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D019704:Protein Disulfide-Isomerases