Mechanism of biological synergy between cellular Src and epidermal growth factor receptor

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 C3H10T 1 ⁄2 murine fibroblasts that contain kinase-deficient (K؊) c-Src and overexpressed wildtype 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.Considerable evidence has accumulated in recent years to suggest that cellular Src (c-Src) and members of the epidermal growth factor (EGF) receptor (EGFR) family are critical elements in the etiology of multiple human cancers. Both kinases are found overexpressed in many of the same types of tumors, including glioblastomas and carcinomas of the colon, breast, and lung (1-4), raising the question of whether they functionally interact to promote the growth of these malignancies. In breast cancer, overexpression of EGFR family members is estimated to occur in 60% or more of the cases (5), and overexpression of the family member HER2͞NEU, has been associated with a poor prognosis for the disease (6). Recent reports have also described overexpression of c-Src in a significant majority of patients with breast cancer, a frequency that approaches 100% (1). Studies to assess the oncogenic potential of each kinase have shown that the EGFR is tumorigenic when overexpressed in cultured fibroblasts and activated by ligand (7,8), but overexpression of c-Src alone is insufficient for malignant transformation (9, 10).A possible role for c-Src in tumorigenesis was revealed when it was demonstrated in C3H10T 1 ⁄2 murine fibroblasts that co-overexpression of c-Src and the EGFR resulted in a synergistic increase in EGF-ind...

EGF-independent activation of cell-surface EGF receptors harboring mutations found in gefitinib-sensitive lung cancer

“…As shown in Figure 3a, the relative degree of phosphorylation at tyrosines 845, 992, 1045 and 1068 was indistinguishable in WT and mutated EGFR, with-and without EGF. We saw no evidence for the selective phosphorylation of tyrosine 845 (primarily a Src phosphorylation site Tice et al, 1999)) reported for the L834R EGFR in mouse mammary epithelial cells , or for enhanced autophosphorylation of Y992 or Y1068 reported for L834R and DL723-P729insS in the same study . Similarly, we could not reproduce the increased Y1045 phosphorylation reported by Chen et al (2006) for EGFR mutants expressed in the H1299 NSCLC cell line.…”

Transactivation of the epidermal growth factor receptor in responses to myocardial stress and cardioprotection

“…Distinct from other receptor kinases, phosphorylation of the kinase activation segment of EGFR is not required for activation (Gotoh et al, 1992;Tice et al, 1999). Instead, ligand-activated kinase domains form an asymmetric dimer: ligand (EGF, TGF, HB-EGF) independently binds with low affinity to extracellular domains I and III (LR1, LR2) of ErbB1, inducing a conformational change that facilitates high affinity binding to both domains ( Figure 1).…”

Translationally controlled tumor protein induces human breast epithelial cell transformation through the activation of Src

“…In addition to cell proliferation, Src also regulates other cellular functions, including cell adhesion, motility and invasion, which change the cell behavior, ultimately contributing to the tumor progression and metastasis (Yeatman, 2004). It has been suggested that direct phosphorylation of the Tyr845 residue of EGFR by Src is a necessary component of Src's role in tumorigenesis (Tice et al, 1999;Ishizawar and Parsons, 2004). Thus, a downstream signaling pathway activated by Src seems to have an essential role in tumor progression.…”