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Threonine phosphorylation diverts internalized epidermal growth factor receptors from a degradative pathway to the
1Departments of Biological Regulation and Molecular Genetics, The Weizmann Institute of Science, Rehovot 76100, Israel.
Abstract:
Transregulation of the epidermal growth factor receptor (EGFR) by protein kinase C (PKC) serves as a model for heterologous desensitization of receptor tyrosine kinases, but the underlying mechanism remained unknown. By using c-Cbl-induced ubiquitination of EGFR as a marker for transfer from early to late endosomes, we provide evidence that PKC can inhibit this process. In parallel, receptor down-regulation and degradation are significantly reduced. The inhibitory effects of PKC are mediated by a single threonine residue (threonine 654) of EGFR, which serves as a major PKC phosphorylation site. Biochemical and morphological analyses indicate that threonine-phosphorylated EGFR molecules undergo normal internalization, but instead of sorting to lysosomal degradation, they recycle back to the cell surface. In conclusion, by sorting EGFR to the recycling endosome, heterologous desensitization restrains ligand-induced down-regulation of EGFR.
Insights
Protein kinase C (PKC) desensitizes epidermal growth factor receptor (EGFR) by preventing its degradation. PKC phosphorylation at threonine 654 diverts internalized EGFR to recycling pathways, thus reducing receptor levels.
Area of Science:
- Cell biology
- Molecular signaling
Background:
- Protein kinase C (PKC) regulates receptor tyrosine kinases, including epidermal growth factor receptor (EGFR).
- The mechanism of heterologous desensitization of EGFR by PKC was previously unknown.
Purpose of the Study:
- To elucidate the mechanism by which PKC mediates heterologous desensitization of EGFR.
- To investigate the role of EGFR ubiquitination and endosomal sorting in PKC-induced desensitization.
Main Methods:
- Utilized c-Cbl-induced ubiquitination of EGFR as a marker for endosomal trafficking.
- Employed biochemical and morphological analyses to study EGFR localization and degradation.
- Investigated the role of a specific threonine residue (threonine 654) in EGFR.
Main Results:
- PKC inhibits the transfer of EGFR from early to late endosomes, a process marked by ubiquitination.
- PKC-mediated phosphorylation of EGFR at threonine 654 significantly reduces receptor down-regulation and degradation.
- Phosphorylated EGFR undergoes normal internalization but is sorted to recycling endosomes instead of lysosomal degradation.
Conclusions:
- PKC-mediated heterologous desensitization of EGFR involves sorting to recycling endosomes.
- This sorting mechanism restrains ligand-induced down-regulation of EGFR.
- Threonine 654 phosphorylation is critical for PKC's inhibitory effects on EGFR degradation.