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Mechanism of biological synergy between cellular Src and epidermal growth factor receptor
D A Tice1, J S Biscardi, A L Nickles
1Box 441, Department of Microbiology and Cancer Center, University of Virginia Health Sciences Center, Charlottesville, VA 22908, USA.
Abstract:
Overexpression of both cellular Src (c-Src) and the epidermal growth factor receptor (EGFR) occurs in many of the same human tumors, suggesting that they may functionally interact and contribute to the progression of cancer. Indeed, in murine fibroblasts, overexpression of c-Src has been shown to potentiate the mitogenic and tumorigenic capacity of the overexpressed EGFR. Potentiation correlated with the ability of c-Src to physically associate with the activated EGFR and the appearance of two unique in vivo phosphorylations on the receptor (Tyr-845 and Tyr-1101). Using stable cell lines of C3H10T1/2 murine fibroblasts that contain kinase-deficient (K-) c-Src and overexpressed wild-type EGFR, we show that the kinase activity of c-Src is required for both the biological synergy with the receptor and the phosphorylations on the receptor, but not for the association of c-Src with the receptor. In transient transfection assays, not only epidermal growth factor but also serum- and lysophosphatidic acid-induced DNA synthesis was ablated in a dominant-negative fashion by a Y845F mutant of the EGFR, indicating that c-Src-induced phosphorylation of Y845 is critical for the mitogenic response to both the EGFR and a G protein-coupled receptor (lysophosphatidic acid receptor). Unexpectedly, the Y845F mutant EGFR was found to retain its full kinase activity and its ability to activate the adapter protein SHC and extracellular signal-regulated kinase ERK2 in response to EGF, demonstrating that the mitogenic pathway involving phosphorylation of Y845 is independent of ERK2-activation. The application of these findings to the development of novel therapeutics for human cancers that overexpress c-Src and EGFR is discussed.
Insights
Cellular Src (c-Src) kinase activity is essential for its synergistic potentiation of the epidermal growth factor receptor (EGFR) in cancer progression. Phosphorylation of EGFR at Tyr-845 by c-Src is critical for mitogenic signaling, independent of ERK2 activation.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- Overexpression of cellular Src (c-Src) and epidermal growth factor receptor (EGFR) is common in human tumors.
- c-Src potentiates EGFR's mitogenic and tumorigenic capacity, correlating with physical association and specific EGFR phosphorylations (Tyr-845, Tyr-1101).
Purpose of the Study:
- To investigate the role of c-Src kinase activity in EGFR potentiation and identify key phosphorylation sites.
- To elucidate the signaling pathways downstream of c-Src-mediated EGFR phosphorylation.
Main Methods:
- Utilized stable murine fibroblast cell lines with kinase-deficient c-Src and overexpressed wild-type EGFR.
- Employed transient transfection assays with EGFR mutants (Y845F) to assess signaling pathways.
Main Results:
- c-Src kinase activity, not just its association, is required for EGFR potentiation and receptor phosphorylations.
- EGFR Tyr-845 phosphorylation by c-Src is critical for mitogenic responses to EGF and lysophosphatidic acid.
- EGFR Y845F mutant retained kinase activity and activated SHC/ERK2, indicating a distinct mitogenic pathway.
Conclusions:
- c-Src kinase activity is crucial for its oncogenic synergy with EGFR.
- EGFR phosphorylation at Tyr-845 by c-Src mediates critical mitogenic signaling independent of the SHC/ERK pathway.
- Findings offer insights for developing targeted therapies for cancers co-overexpressing c-Src and EGFR.