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Functional studies on the EGF receptor with an antibody that recognizes the intracellular portion of the receptor
Abstract:
An antibody against the human epidermal growth factor receptor (EGF), capable of activating its tyrosine kinase has been produced. Antibody 2913 recognizes only the cytoplasmic portion of the EGF receptor in A431 carcinoma cells, in normal human fibroblasts, and in a variety of other human tumor cell lines (Xu, Y.-A., Richert, N., Ito, S., Merlino, G. T., and Pastan, I. (1984) Proc. Natl. Acad. Sci. U. S. A. 81, 7308-7313). Indirect immunofluorescence and electron microscopy show that the antibody binds to intact cells only after membrane permeabilization. Moreover the antibody immunoprecipitates the v-erb-B gene product in avian myeloblastosis virus-infected cells but does not recognize the secreted form (105 kDa) of the A431 cell EGF receptor which lacks the cytoplasmic domain. Antibody 2913 activates the EGF receptor kinase in solubilized A431 membranes causing autophosphorylation on tyrosine residues only. Tryptic peptide maps suggest that antibody 2913 and EGF stimulate phosphorylation of the same amino acid residues. By electron microscopy, the cytoplasmic portion of the receptor was followed throughout its endocytotic pathway. The results show that the kinase domain is rapidly degraded in lysosomes with no accumulation in the cytoplasm or in the nucleus.
Insights
A novel antibody activates the epidermal growth factor receptor (EGF-R) tyrosine kinase. This antibody targets the EGF-R cytoplasmic domain, leading to its degradation in lysosomes.
Area of Science:
- Molecular Biology
- Cell Biology
- Immunology
Background:
- The human epidermal growth factor receptor (EGF-R) is a key regulator of cell growth and is often dysregulated in cancer.
- Understanding the function and regulation of the EGF-R tyrosine kinase is crucial for developing targeted therapies.
Purpose of the Study:
- To produce and characterize a novel antibody against the human epidermal growth factor receptor (EGF-R).
- To investigate the functional consequences of antibody-mediated activation of the EGF-R tyrosine kinase.
- To elucidate the intracellular fate of the EGF-R kinase domain following antibody engagement.
Main Methods:
- Production and characterization of a specific antibody (2913) targeting the cytoplasmic portion of EGF-R.
- Indirect immunofluorescence and electron microscopy for cellular localization studies.
- Immunoprecipitation assays to identify protein interactions.
- Kinase assays to assess receptor activation and autophosphorylation.
- Tryptic peptide mapping to compare signaling pathways.
Main Results:
- Antibody 2913 specifically recognizes the cytoplasmic domain of EGF-R in various human cell lines.
- The antibody activates the EGF-R tyrosine kinase, inducing autophosphorylation on tyrosine residues.
- Antibody 2913 and EGF stimulate phosphorylation at the same sites, suggesting a shared signaling mechanism.
- Electron microscopy revealed rapid degradation of the EGF-R kinase domain in lysosomes after endocytosis.
Conclusions:
- Antibody 2913 serves as a valuable tool for studying EGF-R function and signaling.
- Antibody-induced activation of EGF-R leads to its lysosomal degradation, offering insights into receptor regulation.
- The findings contribute to understanding the cellular trafficking and turnover of activated receptor tyrosine kinases.