Conditional activation of Janus kinase (JAK) confers factor independence upon interleukin-3-dependent cells. Essential role of Ras in JAK-triggered mitogenesis.
Cytokines play crucial roles in the growth and differentiation of hematopoietic cells. They bind to specific cell membrane receptors that usually do not possess intrinsic protein-tyrosine kinase activity. Janus kinases (JAKs) are cytoplasmic protein-tyrosine kinases that physically interact with intracellular domains of the cytokine receptors and have been implicated in playing important roles in signal transduction triggered by the cytokine-cytokine receptor interaction. However, it is still uncertain whether JAK activation alone suffices to induce cell proliferation. In this work, we modified Tyk2, a member of the JAK family, by adding a membrane localization sequence and a chemical dimerizer (coumermycin)-dependent dimerization sequence. The modified Tyk2 was activated in a coumermycin-dependent manner, and the activated Tyk2 conferred cytokine independence upon interleukin-3-dependent pro-B lymphoid cells. This cytokine-independent proliferation was completely inhibited by dominant-negative Ras. These results indicate that activation of JAK through membrane-proximal dimerization is sufficient to induce cell cycle progression and that Ras is essentially involved in JAK-triggered mitogenesis.[1]References
- Conditional activation of Janus kinase (JAK) confers factor independence upon interleukin-3-dependent cells. Essential role of Ras in JAK-triggered mitogenesis. Mizuguchi, R., Hatakeyama, M. J. Biol. Chem. (1998) [Pubmed]
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