Gene: EGFR maps to 7p13-q22, contains 26 exons, and covers approximately 110 kb (Kondo I. and Shimizu N., 1983; Haley J. et al., 1987). Its promoter region contains neither a "TATA box" nor a "CAAT box," and has an extremely high G+C content (88%)(Ishii S. et al., 1985).
mRNA: size: 10.5-kb. A ~6.0-kb band has also been described (Ullrich A. et al., 1984).
Protein: a 170-kDa cell membrane receptor. It consists of an extracellular domain with high cysteine content and N-linked glycosylation, a single and short transmembrane domain, and a cytoplasmic domain exhibiting a protein tyrosine kinase (PTK) activity. Binding of EGF to EGFR results in receptor dimerization with itself or other members of the Erb-B transmembrane PTK family (
Erb-B2, -B3, -B4. For a review on ErbB proteins, see
Tzahar E. and Yarden Y, 1998), resulting in activation with autophosphorylation of the PTK domain. EGFR is physically and functionnally associated with
Src proto-oncogene family PTK, including p60
src. This association is believed to be an integral part of the signaling events in breast cancer cells mediated by the EGFR and contributes to proliferation and survival of these cells.
In contrast to normal human breast, EGFR is not detectable in all breast carcinomas. The incidence of positivity (by binding assays and immunohistochemistry is frequently 30-40%. The expression of EGFR by these tumors is frequently associated with high tumour grade, elevated growth fraction, an inverse relationship with oestrogen receptor, poor response to endocrine therapy, and reduced survival. The failure to respond to endocrine therapy is seen for both ER negative/EGFR positive and ER positive/EGFR positive tumours, suggesting that EGFR could have a role in the progression of breast cancers to hormone independence (Walker R.A. and Dearing S.J., 1999).
Cell lines:
- High levels of low-affinity EGFR were found in the
estrogen receptor (ER) negative breast cancer cell (BCC) lines MDA-MB-231 and Hs578T, while low levels of high-affinity EGFR were found in the
ER positive BCC lines MCF-7, T-47D, ZR-75-1 (Roos W. et al., 1986).
- Treatment of
estrogen receptor (ER) positive BCC with antisense
ER RNA led to decreased
ER expression followed, after 6-12h, by a four-fold increase in EGFR mRNA levels. Thus, the level of expression of
ER could influence expression of EGFR in BCC (de Fazio A. et al., 1997). On the other hand, overexpression of EGFR in ZR-75 BCC did not induce a hormone-independent phenotype (Valverius E.M. et al., 1990).
- MDA-MB-468 BCC overexpress the EGFR and exhibit a functional TGFalpha-EGFR autocrine pathway. Loss of EGFR expression following stable transfection with an antisense EGFR cDNA containing plasmid was shown to down-regulate type I cAMP-dependent protein kinase (PKAI) expression with acquisition of cell growth resistance to the PKAI inhibitor 8-Cl-cAMP. Thus, PKAI expression and function could be controlled by a TGFalpha-EGFR autocrine pathway in BCC overexpressing the EGFR (Ciardiello F. et al., 1998).
- It was demonstrated that fusion proteins composed of Heparin-binding epidermal growth factor (HBEGF) and the plant ribosome-inactivating protein saporin (SAP) exhibit targeting specificity and cytotoxicity that may be of therapeutic value in treating a variety of EGFR-bearing malignancies (Chandler L.A. et al., 1998).
- NS2T2A1 are epithelial cells derived from a normal human breast-epithelial-cell culture transformed by SV40-T Ag. They have a high level of EGFR, TGFalpha, amphiregulin and of thymidine-kinase activity associated with tumorigenic potential in nude mice. The monoclonal antibody MAb 425, which blocks ligands interaction with EGFR, reduced by more than 90% anchorage-independent growth of NS2T2A1 cells. Another anti-EGFR MAb, 528, reduced to 25% of controls the mean tumor mass after NS2T2A1 grafting in mice. Anti-sense RNA expression of EGFR in these cells confirmed the importance of this receptor in tumor progression, since it reduced significantly the tumor volume and tumor weight of NS2T2A1 cells to 16% of those in mock-transfected control cells (Ma L. et al., 1998).
- A RT-PCR assay using EGFR primers was developed and evaluated for the detection of circulating micrometastases in the blood of breast cancer patients. Total RNA was extracted from breast cancer cell lines and from the blood of 23 control individuals and 37 breast cancer patients. EGFR RNA was identified from the blood of 4 of 18 (22%) metastatic breast cancer patients, 0 of 6 locally recurrent breast cancer patients, 0 of 13 adjuvant breast cancer patients, and 0 of 23 controls (P = 0.03, metastatic versus control). The 18 metastatic breast cancer patients all had progressive disease at the time of blood sampling. The identity of the four EGFR-positive bands was confirmed by Southern blotting. The presence of RT-PCR positivity for EGFR was not a treatment-related phenomenon, because three of the four EGFR-positive patients were not receiving treatment at the time of blood collection. It was concluded that RT-PCR for EGFR is a sensitive and specific method for the detection of circulating micrometastases in a proportion of patients with metastatic breast cancer (Leitzel K. et al., 1998).
- Irradiation (2 Gy) of MDA-MB-231 BCC caused immediate primary activations (0-10 min) of the EGFR and the mitogen-activated protein kinase (MAPK) and c-Jun NH(2)-terminal kinase (JNK) pathways, which were surprisingly followed by later prolonged secondary activations (90-240 min). It was shown that the secondary activation of the EGFR and the MAPK and JNK pathways was dependent on radiation-induced cleavage and autocrine action of TGFalpha. Disruption of the TGFalpha-EGFR-MAPK signaling module could represent a strategy to decrease carcinoma cell growth and survival after irradiation (Dent P. et al., 1999).
Tumors:
- By RT-PCR, EGFR mRNA was found in 88 of 94 (93%) primary breast tumors (Falette N. et al., 1994). EGFR protein was found in 45% of patients in a review of 40 different studies with a combined total of 5232 breast tumors (Klijn G.G.M. et al., 1992).
- Epidermal growth factor receptor (EGFR)-associated protein tyrosine kinase (PTK) complexes have vital anti-apoptotic functions in human breast cancer cells. It has been shown that targeting the naturally occurring PTK inhibitor genistein to the EGFR-associated PTK complexes using the EGF-Genistein (Gen) conjugate triggers rapid apoptotic cell death in human breast cancer cells and abrogates their
in vitro clonogenic growth. EGF-Gen treatment was also able to reduce the growth rate of breast cancer xenografts in mice (Uckun F.M. et al., 1998).
- In a study of 64 invasive breast carcinomas, EGFR mRNA and EGFR protein were detected in 66% and 36% of cases, respectively. EGFR protein had a strong correlation to lack of
estrogen receptor (ER) and high histological grade. The presence of EGFR protein was strongly correlated with more intense labelling for EGFR mRNA. The
ER negative/
progesterone receptor negative carcinomas showed the full range of EGFR mRNA labelling. It was postulated that oestrogen or oestrogen regulated proteins are involved in regulation of EGFR mRNA and protein (Walker R.A. and Dearing S.J., 1999).
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