Thrombopoietin induces tyrosine phosphorylation and activation of the Janus kinase, JAK2

P. Justin Tortolani, James A. Johnston, Chris M. Bacon, Daniel W. McVicar, Akihiro Shimosaka, Diana Linnekin, Dan L. Longo, John J. O'Shea

Research output: Contribution to journalArticlepeer-review

86 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)3444-3451
Number of pages8
Issue number12
StatePublished - Jun 15 1995
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Immunology
  • Hematology
  • Cell Biology


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