Granulocyte-macrophage colony-stimulating factor and erythropoietin induce tyrosine phosphorylation and activation of JAK2

Objective: In order to identify the tyrosine kinase (s) that may associate with cell proliferation.

Methods: GM-CSF/Epo responsive cell UT-7 and Epo responsive cell UT-7/Epo were used for study of tyrosine phosphorylation.

Results: The addition of GM CSF and/or Epo to the responsive cells induced rapid tyrosine phosphorylations of 145000, 130000, 80000 and 40000 cellular proteins. The tyrosine phosphorylated 130000 protein was identified as JAK2, a non receptor tyrosine kinase. GM CSF and Epo also activated its tyrosine kinase activity. Tyrosine phosphorylation and activation of JAK2 only occurred in GM-CSF and/or Epo-responsive cells.

Conclusions: JAK2 signal transduction pathway may play an important role in regulating the proliferation of hematopoietic cells induced by GM-CSF and Epo.