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Anti-epidermal growth factor receptor monoclonal antibodies affecting signal transduction
H A Reins1, G Steinhilber, B Freiberg
1Friedrich-Miescher-Laboratorium der Max-Planck-Gesellschaft, Tuebingen, Federal Republic of Germany.
Abstract:
Monoclonal antibodies prepared against tyrosine phosphorylated epidermal growth factor receptor (EGFR) were tested for their effects on transmembrane signal transduction in A431 tumor cells. Monoclonal antibodies (mab) defined by SDS-sensitive epitopes, i.e., epitopes with conformational specificity, were most effective. Mab 5-125 reacting with a site of the extracellular EGFR domain blocked EGF-binding and cell proliferation in vitro, as well as tumor growth in vivo. However, this mab appeared not to be internalized upon binding to EGFR and did not trigger EGFR autophosphorylation. In contrast, mab 5-D43, also defined by an SDS-sensitive epitope and reacting with an extracellular EGFR site, did not block EGF binding but was readily internalized after binding to EGFR of untreated A431 cells. This mab induced EGFR tyrosine phosphorylation in cell lysates and tyrosine-specific autophosphorylation of insolubilized EGFR immune complexes. Cell growth in vitro was greatly stimulated in the presence of mab 5-D43. Since interaction of mab 5-D43 with EGFR induced most EGF-specific functions, although it did not bind to the EGF-specific site of EGFR, we have to assume that binding of mab 5-D43 to EGFR induced a conformational shift that activated the cytoplasmic EGFR kinase site. On the other hand, activation and/or accessibility of the EGFR kinase site could be blocked by mab 1-594, which is defined by an SDS-insensitive protein epitope of the cytoplasmic EGFR domain. Blocking of the EGFR kinase site by mab 1-594 also abolished EGF-induced tyrosine phosphorylation of endogenous cellular substrates with molecular masses of 145, 97, 85, 37, and 32 kDa, as well as of exogenous substrates such as GAT copolymer.
Insights
Monoclonal antibodies targeting the epidermal growth factor receptor (EGFR) can modulate its signaling. Specific antibodies that induce conformational changes in EGFR activate its kinase, promoting cell growth and signal transduction.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- The epidermal growth factor receptor (EGFR) is crucial for cell growth and survival.
- Dysregulation of EGFR signaling is implicated in various cancers.
- Understanding how antibodies interact with EGFR is key to developing targeted therapies.
Purpose of the Study:
- To investigate the effects of monoclonal antibodies (mabs) against tyrosine-phosphorylated EGFR on transmembrane signal transduction.
- To determine how different antibody epitopes influence EGFR activity and downstream signaling pathways.
Main Methods:
- Generation of monoclonal antibodies against tyrosine-phosphorylated EGFR.
- Testing antibody effects on EGF binding, cell proliferation, and tumor growth in A431 cells.
- Analysis of antibody internalization, EGFR autophosphorylation, and substrate phosphorylation.
Main Results:
- SDS-sensitive epitope-specific mabs were most effective in modulating EGFR signaling.
- Mab 5-125 blocked EGF binding and proliferation but was not internalized and did not induce autophosphorylation.
- Mab 5-D43, while not blocking EGF binding, was internalized, induced EGFR autophosphorylation, and stimulated cell growth, suggesting a conformational change activating the kinase.
Conclusions:
- Antibodies targeting specific extracellular epitopes of EGFR can induce conformational changes that activate its intracellular kinase domain.
- Antibody-mediated activation of EGFR signaling can promote cell proliferation.
- Antibody 1-594, targeting a cytoplasmic epitope, blocked EGFR kinase activity and downstream substrate phosphorylation, highlighting the importance of the kinase site.