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Activation of c-fos gene expression by a kinase-deficient epidermal growth factor receptor
E R Eldredge1, G M Korf, T A Christensen
1Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota 55905.
Abstract:
The intrinsic tyrosine kinase activity of the epidermal growth factor receptor (EGFR) has been shown to be responsible for many of the pleiotropic intracellular effects resulting from ligand stimulation [W.S. Chen, C.S. Lazar, M. Poenie, R.Y. Tsien, G.N. Gill, and M.G. Rosenfeld, Nature (London) 328:820-823, 1987; A.M. Honegger, D. Szapary, A. Schmidt, R. Lyall, E. Van Obberghen, T.J. Dull, A. Ulrich, and J. Schlessinger, Mol. Cell. Biol. 7:4568-4571, 1987]. Recently, however, it has been shown that addition of ligand to cells expressing kinase-defective EGFR mutants can result in the phosphorylation of mitogen-activated protein kinase (R. Campos-González and J.R. Glenney, Jr., J. Biol. Chem. 267:14535-14538, 1992; E. Selva, D.L. Raden, and R.J. Davis, J. Biol. Chem. 268:2250-2254, 1993), as well as stimulation of DNA synthesis (K.J. Coker, J.V. Staros, and C.A. Guyer, Proc. Natl. Acad. Sci. USA 91:6967-6971, 1994). Moreover, mitogen-activated protein kinase has been shown to phosphorylate the transcription factor p62TCF in vitro, leading to enhanced ternary complex formation between p62TCF, p67SRF, and the c-fos serum response element (SRE) [H. Gille, A.D. Sharrocks, and P.E. Shaw, Nature (London) 358:414-417, 1992]. On the basis of these observations, we have investigated the possibility that the intrinsic tyrosine kinase activity of the EGFR may not be necessary for transcriptional activation mediated via p62TCF. Here, we demonstrate that a kinase-defective EGFR mutant can signal ligand-induced expression of c-fos protein and that a significant component of this induction appears to be mediated at the transcriptional level. Investigation of transcriptional activation mediated by the c-fos SRE shows that this response is impaired by mutations in the SRE which eliminate binding of p62(TCF). These data indicate that information inherent in the structure of the EGFR can be accessed by ligand stimulation independent of the receptor's catalytic kinase function.
Insights
Epidermal growth factor receptor (EGFR) kinase activity is not essential for ligand-induced c-fos expression. Kinase-defective EGFR mutants can activate transcription via p62TCF, independent of catalytic function.
Area of Science:
- Cellular signaling
- Molecular biology
- Signal transduction
Background:
- Epidermal growth factor receptor (EGFR) tyrosine kinase activity mediates many intracellular effects upon ligand stimulation.
- Recent studies show kinase-defective EGFR mutants can still activate mitogen-activated protein kinase and DNA synthesis.
- Mitogen-activated protein kinase phosphorylates transcription factor p62TCF, enhancing complex formation with p67SRF and the c-fos serum response element (SRE).
Purpose of the Study:
- To investigate if EGFR's intrinsic tyrosine kinase activity is required for transcriptional activation mediated by p62TCF.
- To determine if a kinase-defective EGFR mutant can signal ligand-induced c-fos protein expression.
- To examine the role of transcriptional regulation in this process.
Main Methods:
- Utilized kinase-defective EGFR mutants.
- Assessed ligand-induced c-fos protein expression.
- Investigated transcriptional activation via the c-fos SRE.
- Introduced mutations into the SRE to disrupt p62(TCF) binding.
Main Results:
- A kinase-defective EGFR mutant demonstrated the ability to signal ligand-induced c-fos protein expression.
- A significant portion of this induction was mediated at the transcriptional level.
- Mutations in the SRE that prevent p62(TCF) binding impaired the transcriptional response.
Conclusions:
- EGFR's catalytic kinase function is not necessary for initiating transcriptional activation via p62TCF.
- Ligand stimulation can access information within the EGFR structure independently of its kinase activity.
- This suggests alternative signaling pathways downstream of EGFR activation.