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Jak1 expression is required for mediating interleukin-4-induced tyrosine phosphorylation of insulin receptor
X H Chen1, B K Patel, L M Wang
1Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.
Abstract:
The Jak1, Jak2, Jak3, and Fes tyrosine kinases have been demonstrated to undergo tyrosine phosphorylation in response to interleukin (IL)-4 stimulation in different cell systems. However, it is not clear which, if any, of these kinases are responsible for initiating IL-4-induced tyrosine phosphorylation of intracellular substrates in vivo. In the present study, we have utilized a mutant Jak1-deficient HeLa cell line, E1C3, and its parental Jak1-expressing counterpart, 1D4, to analyze the role of Jak1 in mediating IL-4-induced tyrosine phosphorylation events. IL-4 treatment rapidly induced tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2 in 1D4 but not in E1C3 cells. IL-4-mediated tyrosine phosphorylation of Stat6 was pronounced in 1D4 cells, while no IL-4-induced Stat6 phosphorylation was detected in E1C3 cells. IL-4 also induced Stat6 DNA binding activity from lysates of 1D4 but not E1C3 cells utilizing a radiolabeled immunoglobulin heavy chain germline epsilon promotor sequence (Iepsilon) in an electrophoretic mobility shift assay. Reconstitution of Jak1 expression in E1C3 cells restored the ability of IL-4 to induce IRS and Stat6 tyrosine phosphorylation. These results provide evidence that Jak1 expression is required for mediating tyrosine phosphorylation and activation of crucial molecules involved in IL-4 signal transduction.
Insights
Janus kinase 1 (Jak1) is essential for interleukin-4 (IL-4) signaling. Jak1 mediates IL-4-induced tyrosine phosphorylation of key signaling molecules like insulin receptor substrates (IRS) and Stat6, crucial for cellular responses.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Interleukin-4 (IL-4) is a critical cytokine involved in immune responses.
- Several tyrosine kinases, including Janus kinase 1 (Jak1), are implicated in IL-4 signaling pathways.
- The specific role of Jak1 in initiating IL-4-induced intracellular tyrosine phosphorylation in vivo remains unclear.
Purpose of the Study:
- To investigate the role of Jak1 in mediating IL-4-induced tyrosine phosphorylation events.
- To determine if Jak1 is responsible for the phosphorylation of intracellular substrates upon IL-4 stimulation.
Main Methods:
- Utilized a Jak1-deficient HeLa cell line (E1C3) and its parental Jak1-expressing counterpart (1D4).
- Analyzed IL-4-induced tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2.
- Assessed IL-4-mediated Stat6 tyrosine phosphorylation and DNA binding activity using electrophoretic mobility shift assay.
- Restored Jak1 expression in E1C3 cells to confirm its role.
Main Results:
- IL-4 treatment induced tyrosine phosphorylation of IRS-1 and IRS-2 in Jak1-expressing cells (1D4) but not in Jak1-deficient cells (E1C3).
- Stat6 tyrosine phosphorylation and DNA binding activity in response to IL-4 were observed in 1D4 cells, but absent in E1C3 cells.
- Reconstitution of Jak1 expression in E1C3 cells restored IL-4-induced phosphorylation of IRS and Stat6.
Conclusions:
- Jak1 expression is required for IL-4-induced tyrosine phosphorylation of IRS-1, IRS-2, and Stat6.
- Jak1 plays a crucial role in initiating IL-4 signal transduction pathways.
- These findings highlight Jak1 as a key mediator of IL-4's biological effects.