title: Protein tyrosine phosphatase 1B participates in the down-regulation of erythropoietin receptor signalling.
abstract: Erythropoietin (EPO) is the principal hormone regulating the proliferation of erythroid precursors and their differentiation into erythrocytes. Binding of ligand to the cell-surface EPO-R (EPO receptor) induces dimerization and JAK2 (Janus kinase 2)-mediated tyrosine phosphorylation of the receptor. Less than 1% of the EPO-Rs are displayed on the cell surface; most of the receptor molecules are retained in intracellular compartments, including the ER (endoplasmic reticulum). Using pervanadate (PV) as a potent tool to inhibit cellular PTPs (protein tyrosine phosphatases), we demonstrated previously the accumulation of mature (endoglycosidase H-resistant) tyrosine-phosphorylated EPO-R [Cohen, Altaratz, Zick, Klingmuller and Neumann (1997) Biochem. J. 327, 391-397]. In the present study, we investigated the participation of the ER-associated PTP1B in the dephosphorylation of intracellular EPO-R. We demonstrate tyrosine phosphorylation of EPO-R in BOSC-23T cells co-expressing EPO-R and the 'substrate-trapping' mutant form of PTP1B, PTP1B D181A (referred to as PTP1BD). In vivo interaction between EPO-R and PTP1B suggested that PTP1B dephosphorylates the EPO-R intracellularly. Endoglycosidase H resistance of tyrosine-phosphorylated EPO-R in cells expressing PTP1BD suggested that mature EPO-R is dephosphorylated by PTP1B. Stimulation with EPO of cells co-expressing EPO-R and either PTP1BD or PTP1B resulted in an increase or decrease respectively in phosphotyrosine EPO-R. We thus suggest that PTP1B dephosphorylates EPO-stimulated EPO-R and participates in the down-regulation cascade of EPO-mediated signal transduction.
authors.affiliation: Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel-Aviv University, Ramat Aviv, Israel.
authors.forename: Jacob
authors.initials: J
authors.lastname: Cohen
authors.forename: Liat
authors.initials: L
authors.lastname: Oren-Young
authors.forename: Ursula
authors.initials: U
authors.lastname: Klingmuller
authors.forename: Drorit
authors.initials: D
authors.lastname: Neumann
mesh_terms: D000818:Animals; D002460:Cell Line; D015536:Down-Regulation; D004921:Erythropoietin / Q000494:pharmacology; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase / Q000378:metabolism; D009154:Mutation; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases / Q000235:genetics / Q000378:metabolism*; D017467:Receptors, Erythropoietin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism
chemical_list: D017467:Receptors, Erythropoietin; D004921:Erythropoietin; D014443:Tyrosine; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D017027:Protein Tyrosine Phosphatases; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase