title: RHEX, a novel regulator of human erythroid progenitor cell expansion and erythroblast development.
abstract: Ligation of erythropoietin (EPO) receptor (EPOR) JAK2 kinase complexes propagates signals within erythroid progenitor cells (EPCs) that are essential for red blood cell production. To reveal hypothesized novel EPOR/JAK2 targets, a phosphotyrosine (PY) phosphoproteomics approach was applied. Beyond known signal transduction factors, 32 new targets of EPO-modulated tyrosine phosphorylation were defined. Molecular adaptors comprised one major set including growth factor receptor-bound protein 2 (GRB2)-associated binding proteins 1-3 (GAB1-3), insulin receptor substrate 2 (IRS2), docking protein 1 (DOK1), Src homology 2 domain containing transforming protein 1 (SHC1), and sprouty homologue 1 (SPRY1) as validating targets, and SPRY2, SH2 domain containing 2A (SH2D2A), and signal transducing adaptor molecule 2 (STAM2) as novel candidate adaptors together with an ORF factor designated as regulator of human erythroid cell expansion (RHEX). RHEX is well conserved in Homo sapiens and primates but absent from mouse, rat, and lower vertebrate genomes. Among tissues and lineages, RHEX was elevated in EPCs, occurred as a plasma membrane protein, was rapidly PY-phosphorylated >20-fold upon EPO exposure, and coimmunoprecipitated with the EPOR. In UT7epo cells, knockdown of RHEX inhibited EPO-dependent growth. This was associated with extracellular signal-regulated kinase 1,2 (ERK1,2) modulation, and RHEX coupling to GRB2. In primary human EPCs, shRNA knockdown studies confirmed RHEX regulation of erythroid progenitor expansion and further revealed roles in promoting the formation of hemoglobinizing erythroblasts. RHEX therefore comprises a new EPO/EPOR target and regulator of human erythroid cell expansion that additionally acts to support late-stage erythroblast development.
authors.affiliation: COBRE Center of Excellence in Stem Cell Biology and Regenerative Medicine, Maine Medical Center Research Institute, Scarborough ME, 04074.
authors.forename: Rakesh
authors.initials: R
authors.lastname: Verma
authors.affiliation: COBRE Center of Excellence in Stem Cell Biology and Regenerative Medicine, Maine Medical Center Research Institute, Scarborough ME, 04074.
authors.forename: Su
authors.initials: S
authors.lastname: Su
authors.affiliation: COBRE Center of Excellence in Stem Cell Biology and Regenerative Medicine, Maine Medical Center Research Institute, Scarborough ME, 04074.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: McCrann
authors.affiliation: Affymax, Inc., Palo Alto, CA 94304.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Green
authors.affiliation: Affymax, Inc., Palo Alto, CA 94304.
authors.forename: Karen
authors.initials: K
authors.lastname: Leu
authors.affiliation: Affymax, Inc., Palo Alto, CA 94304.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Young
authors.affiliation: Affymax, Inc., Palo Alto, CA 94304.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Schatz
authors.affiliation: Cell Signaling Technology, Inc., Danvers, MA 01923.
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Silva
authors.affiliation: Cell Signaling Technology, Inc., Danvers, MA 01923.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Stokes
authors.affiliation: COBRE Center of Excellence in Stem Cell Biology and Regenerative Medicine, Maine Medical Center Research Institute, Scarborough ME, 04074 wojchd@mmc.org.
authors.forename: Don M
authors.initials: DM
authors.lastname: Wojchowski
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D004900:Erythroblasts / Q000166:cytology* / Q000502:physiology*; D015672:Erythroid Precursor Cells / Q000166:cytology* / Q000502:physiology*; D004920:Erythropoiesis / Q000502:physiology; D004921:Erythropoietin / Q000502:physiology*; D055785:Gene Knockdown Techniques; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism; D008969:Molecular Sequence Data; D040901:Proteomics; D017467:Receptors, Erythropoietin / Q000502:physiology; D015398:Signal Transduction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C554270:EPO protein, human; C000592506:RHEX protein, human; D017467:Receptors, Erythropoietin; D004921:Erythropoietin; C507924:JAK2 protein, human; D053614:Janus Kinase 2
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