Mitogen-activated protein kinase is involved in epidermal-growth-factor-regulated protein phosphorylation in nuclear membranes isolated from JEG-3 human choriocarcinoma cells.
The treatment of highly purified nuclear membranes isolated from JEG-3 human choriocarcinoma cells with epidermal growth factor (EGF) resulted in an increase of the receptor autophosphorylation and the phosphorylation of several other proteins, including 44-kDa, 34-kDa and 24-kDa proteins, and a decrease in the phosphorylation of a 40-kDa protein. The kinetics of phosphorylation and the use of RG-13022, a selective inhibitor of EGF-receptor kinase activity, suggested that receptor activation was necessary for the phosphorylation response of the other proteins. Tyr was exclusively phosphorylated in the EGF receptor and 24-kDa proteins, Tyr and Thr were phosphorylated in the 44-kDa protein, and Ser was phosphorylated in the 34-kDa protein and dephosphorylated in the 40-kDa protein. The molecular size, Thr/Tyr phosphorylation, immunoprecipitation and enzymatic activity towards myelin basic protein suggested that the 44-kDa protein was a mitogen-activated protein (MAP) kinase. The EGF treatment not only increased phosphorylation but also catalytic activity of MAP kinase and these increases were prevented by the addition of RG-13022. In summary, this report demonstrates that target cell nuclei contain EGF receptors, which use the MAP kinase signaling pathway.[1]References
- Mitogen-activated protein kinase is involved in epidermal-growth-factor-regulated protein phosphorylation in nuclear membranes isolated from JEG-3 human choriocarcinoma cells. Bian, L., Lei, Z., Rao, C.V. Eur. J. Biochem. (1998) [Pubmed]
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