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Subsets of epidermal growth factor receptors during activation and endocytosis
D R Emlet1, D K Moscatello, L B Ludlow
1Department of Pharmacology, Kimmel Cancer Institute, Philadelphia, Pennsylvania 19107, USA.
Abstract:
Mutation of the autophosphorylation sites of receptor protein-tyrosine kinases alters ligand dependent internalization and down-regulation, indicating a critical role for these sites in receptor processing. Currently, no differences in receptor processing based on an individual autophosphorylation site have been defined. By using a glutathione S-transferase fusion protein containing the src homology 2 domains of phospholipase C-gamma1 to specifically recognize tyrosine 992 on the EGF receptor (Tyr(P)992), we have found differences in this subpopulation of receptors. Following EGF stimulation, the number of Tyr(P)992 receptors increased 2-fold over receptors identified by an antibody that recognizes activated EGF receptors (alpha-Act. EGFR) in A431 cells. Confocal fluorescence microscopy showed that Tyr(P)992 receptors underwent endocytosis at a slower rate and did not rapidly concentrate in juxtanuclear bodies. Tyr(P)992 receptors were associated with more SOS, Ras-GTPase activating protein, phosphatidylinositol 3-kinase, and SHPTP2/syp, but less Grb2, than receptors in the general population, and these receptors were more heavily phosphorylated than the general population of active receptors. These findings suggest that autophosphorylation status is relevant to the endocytosis, degradation, and effector molecule interaction of individual EGF receptors. Further investigations based on phosphorylation status should provide new insights into how receptor protein-tyrosine kinase signaling is regulated.
Insights
Phosphorylation of specific sites on EGF receptors influences their processing and signaling. This study identifies distinct behaviors of Tyr(P)992 receptors, impacting endocytosis and effector interactions.
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- Receptor protein-tyrosine kinases (RTKs) play crucial roles in cellular signaling.
- Autophosphorylation sites on RTKs are critical for receptor processing, including internalization and down-regulation.
- Previous studies have not differentiated receptor processing based on individual autophosphorylation sites.
Purpose of the Study:
- To investigate differences in epidermal growth factor receptor (EGFR) processing based on the phosphorylation status of specific sites.
- To characterize the endocytosis, degradation, and effector interactions of EGFR phosphorylated at tyrosine 992 (Tyr(P)992).
Main Methods:
- Utilized a glutathione S-transferase fusion protein with phospholipase C-gamma1 SH2 domains to specifically detect Tyr(P)992 EGFR.
- Employed confocal fluorescence microscopy to track receptor localization and endocytosis.
- Analyzed the association of Tyr(P)992 EGFR with downstream signaling molecules (SOS, Grb2, PI3K, etc.).
Main Results:
- The population of Tyr(P)992 receptors increased twofold compared to generally activated EGFR (alpha-Act. EGFR) after EGF stimulation in A431 cells.
- Tyr(P)992 receptors exhibited slower endocytosis and delayed concentration in juxtanuclear bodies.
- These receptors showed altered associations with signaling proteins, including increased SOS, PI3K, and SHPTP2/syp, but decreased Grb2, and higher overall phosphorylation levels.
Conclusions:
- Autophosphorylation status significantly influences the endocytosis, degradation, and effector molecule interactions of individual EGFRs.
- Phosphorylation-dependent differences in EGFR processing suggest a regulatory mechanism for RTK signaling.
- Further research into phosphorylation-specific receptor behavior can yield deeper insights into RTK signaling regulation.