Ras and signal transducer and activator of transcription (STAT) are essential and sufficient downstream components of Janus kinases in cell proliferation.
Cytokines exert their activities in cell growth and differentiation by binding specific cell membrane receptors. Janus kinases (JAKs) are cytoplasmic protein tyrosine kinases that physically interact with intracellular domains of the cytokine receptors and they play crucial roles in transducing signals triggered by the cytokine-receptor interaction. We have previously shown that conditional activation of JAK through membrane-proximal dimerization confers cytokine-independence on interleukin-3 (IL-3)-dependent Ba / F3 lymphoid cells and that the cytokine-independent proliferation is completely inhibited by dominant negative Ras. In this work, we demonstrate that ectopic expression of a dominant negative form of Stat5, a major signal transducer and activator of transcription (STAT) expressed in Ba / F3 cells, also inhibits JAK-triggered mitogenesis. In contrast, overexpression of constitutively active Ras or conditional activation of Stat5 by chemical dimerization fails to confer cytokine-independence. However, concomitant activation of ectopic Ras and Stat5 molecules in Ba / F3 cells suffices for cell proliferation in the absence of IL-3. Our results indicate that Ras and STAT are essential and sufficient components of JAK-triggered mitogenesis. Our findings further indicate that the cytokine signal bifurcates into Ras and STAT pathways following JAK activation.
Mizuguchi
R
R
Department of Viral Oncology, Cancer Institute, Japanese Foundation for Cancer Research, 1-37-1 Kami-Ikebukuro, Toshima-ku, Tokyo 170-8455, Japan.
Noto
S
S
Yamada
M
M
Ashizawa
S
S
Higashi
H
H
Hatakeyama
M
M
D000818:Animals; D002455:Cell Division / Q000502:physiology*; D002460:Cell Line / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000502:physiology*; D019281:Dimerization; D004789:Enzyme Activation; D005822:Genetic Vectors; D051379:Mice; D008894:Milk Proteins; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases; D011506:Proteins / Q000502:physiology*; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D053634:TYK2 Kinase; D015534:Trans-Activators / Q000502:physiology*; D014162:Transfection
D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011506:Proteins; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D011505:Protein-Tyrosine Kinases; D053634:TYK2 Kinase; C499356:Tyk2 protein, mouse; D016283:Proto-Oncogene Proteins p21(ras)