A variety of environmental stresses, such as osmotic shock, UV radiati
on, and heat shock, or the proinflammatory cytokines tumor necrosis fa
ctor-alpha and interleukin-1 reportedly induce activation of c-Jun ami
no-terminal kinases (JNK), which are usually activated by SEK1/MKK4. W
e report here that the hematopoietic cytokines interleukin-3 (IL-3), e
rythropoietin (Epo), and thrombopoietin (Tpo), which regulate growth a
nd differentiation of hematopoietic progenitor cells, erythroids, and
megakaryocytes/platelets, respectively, also activate a JNK signaling
cascade. In-gel kinase assay as well as in vitro kinase assay clearly
showed that IL-3, Epo, and Tpo rapidly and transiently activated both
JNK1 and JNK2 in IL-3-, Epo-, or Tpo-dependent mouse hematopoietic pro
genitor cells, However, immunoblot analysis and in vitro kinase assay
showed that neither phosphorylation nor activation of SEK1/MKK4 was in
duced by IL-3, Epo, or Tpo stimulation, Therefore, we concluded that t
he JNK signaling cascade plays an important role not only in stress re
sponses and proinflammatory cytokine actions but also in hematopoietic
cytokine actions and that hematopoietic cytokines may activate the JN
Ks through a kinase other than SEK1/MKK4, as previously suggested for
stress-activated cells. (C) 1997 by The American Society of Hematology
.