title: Thrombopoietin induces tyrosine phosphorylation and activation of the Janus kinase, JAK2.
abstract: Thrombopoietin (TPO) is a recently characterized growth and differentiation factor for megakaryocytes and platelets that exerts its effects via the receptor, c-MpI. This receptor is a member of the hematopoietin receptor superfamily and is essential for megakaryocyte maturation; however, the molecular mechanisms of TPO and c-MpI action have not been elucidated. Recently, the Janus kinases have emerged as important elements in signaling via this family of receptors. In this report, we show that, in the M07e megakaryocytic cell line, which expresses c-MpI and proliferates in response to TPO, TPO induces phosphorylation of a number of substrates between 80 and 140 kD. Specifically, we show that stimulation with TPO induces the rapid tyrosine phosphorylation of a 130-kD protein that we identify as the Janus kinase, JAK2. However, no detectable tyrosine phosphorylation of JAK1, JAK3, or TYK2 was observed. TPO also induced activation of JAK2 phosphotransferase activity in vitro. Taken together, these data indicate that JAK2 likely plays a key role in TPO-mediated signal transduction.
authors.affiliation: Arthritis and Rheumatism Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892-1820, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Tortolani
authors.forename: J A
authors.initials: JA
authors.lastname: Johnston
authors.forename: C M
authors.initials: CM
authors.lastname: Bacon
authors.forename: D W
authors.initials: DW
authors.lastname: McVicar
authors.forename: A
authors.initials: A
authors.lastname: Shimosaka
authors.forename: D
authors.initials: D
authors.lastname: Linnekin
authors.forename: D L
authors.initials: DL
authors.lastname: Longo
authors.forename: J J
authors.initials: JJ
authors.lastname: O'Shea
mesh_terms: D002478:Cells, Cultured; D004789:Enzyme Activation; D006801:Humans; D053614:Janus Kinase 2; D007938:Leukemia / Q000473:pathology; D008099:Liver / Q000196:embryology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D015398:Signal Transduction; D013926:Thrombopoietin / Q000378:metabolism* / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D011518:Proto-Oncogene Proteins; D014443:Tyrosine; D013926:Thrombopoietin; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2