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Molecular identification and properties of two cell surface receptors playing roles in mitogenesis and epigenesis
Abstract:
Studies leading to the identification of cell surface receptor macromolecules which specifically recognize a hormone, epidermal growth factor (EGF), or gp70, the coat antigen of the C-type RNA tumor viruses, have been described. EGF receptors are internalized and processed by lysosomal protease action after interaction of receptor and EGF. Other hormones, which resemble EGF in their ability to trigger mitogenesis in cultured cells, interact with the EGF receptor in a yet to be defined, but probably indirect way, decreasing the number of EGF binding sites on the cell surface. The evidence at this point indicates that these hormones interact with EGF receptors through the communal utilization of a shared cellular mechanism for internalization of their receptors and the EGF receptors. The receptor for gp70 is not internalized in response to gp70 binding, but is instead shed into the medium by cultured cells. This receptor protein BPgp70 has now been isolated and purified to apparent homogeneity. Antibodies to BPgp70 completely block gp70 binding to cells at low concentration, indicating that BPgp70 is the physiological receptor for gp70.
Insights
Researchers identified cell surface receptors for epidermal growth factor (EGF) and gp70. Unlike EGF receptors, the gp70 receptor (BPgp70) is shed from cells, not internalized, and antibodies to BPgp70 block gp70 binding.
Area of Science:
- Cell biology
- Molecular biology
- Virology
Background:
- Cell surface receptors mediate cellular responses to external stimuli.
- Epidermal growth factor (EGF) and gp70 (a C-type RNA tumor virus antigen) bind to specific cell surface receptors.
- EGF receptor interactions involve internalization and lysosomal processing.
Purpose of the Study:
- To identify and characterize cell surface receptors for EGF and gp70.
- To elucidate the distinct mechanisms of receptor processing following ligand binding.
- To confirm the identity and function of the gp70 receptor.
Main Methods:
- Ligand binding assays to study receptor interactions.
- Cellular internalization and processing studies.
- Protein isolation, purification, and antibody generation for BPgp70.
Main Results:
- EGF receptors are internalized and degraded after EGF binding.
- Other mitogenic hormones indirectly affect EGF receptor binding, likely via shared internalization pathways.
- The gp70 receptor (BPgp70) is shed into the medium upon gp70 binding.
- Purified BPgp70 and antibodies against it confirm its role as the physiological gp70 receptor.
Conclusions:
- Distinct mechanisms govern the processing of EGF and gp70 receptors.
- BPgp70 is the specific cell surface receptor for gp70 and is released from the cell.
- Understanding these receptor dynamics is crucial for cell signaling and viral interactions.