title: Cloning and characterization of a family of proteins associated with Mpl.
abstract: Thrombopoietin (TPO) controls the formation of megakaryocytes and platelets from hematopoietic stem cells via activation of the c-Mpl receptor and multiple downstream signal transduction pathways. We used two-hybrid screening to identify new proteins that interacted with the cytoplasmic domain of Mpl, and we found a new family of proteins designated A2D (for Ataxin-2 Domain protein). The A2D are 130-kDa proteins that have three regions similar to those of Ataxin-2, the gene product causing familial type 2 spinocerebellar ataxia. A2D has several isoforms with different C-terminal domains, all produced from a single gene by alternative splicing. Northern blotting indicated that the A2D gene is widely expressed in immortalized cell lines and hematopoietic and fetal tissues. A2D proteins were constitutively associated with Mpl in vivo in human hematopoietic UT7 cells. TPO also caused the release of A2D from the activated receptor, and the phosphorylation of A2D on tyrosines residues was dependent on the Mpl C-terminal domain. Finally, A2D bound to the unstimulated erythropoietin receptor, whereas erythropoietin caused dissociation from the erythropoietin receptor, suggesting that A2D proteins are new components of the cytokine signaling system.
authors.affiliation: INSERM U363, ICGM, 27 Rue du Faubourg Saint Jacques, 75014 Paris, France.
authors.forename: Caroline
authors.initials: C
authors.lastname: Meunier
authors.forename: Didier
authors.initials: D
authors.lastname: Bordereaux
authors.forename: Francoise
authors.initials: F
authors.lastname: Porteu
authors.forename: Sylvie
authors.initials: S
authors.lastname: Gisselbrecht
authors.forename: Stany
authors.initials: S
authors.lastname: Chrétien
authors.forename: Geneviève
authors.initials: G
authors.lastname: Courtois
mesh_terms: D000595:Amino Acid Sequence; D000067528:Ataxins; D002478:Cells, Cultured; D003001:Cloning, Molecular; D006801:Humans; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D010766:Phosphorylation; D020033:Protein Isoforms; D011506:Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D018121:Receptors, Cytokine; D017467:Receptors, Erythropoietin / Q000032:analysis; D053628:Receptors, Thrombopoietin; D013926:Thrombopoietin / Q000378:metabolism / Q000494:pharmacology; D020798:Two-Hybrid System Techniques
chemical_list: D000067528:Ataxins; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms; D011506:Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D018121:Receptors, Cytokine; D017467:Receptors, Erythropoietin; D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D013926:Thrombopoietin