MAPK scaffold IQGAP1 binds the EGF receptor and modulates its activation
Dean E McNulty1, Zhigang Li, Colin D White
1Proteomic and Biological Mass Spectrometry Laboratory, GlaxoSmithKline, Collegeville, Pennsylvania 19426, USA.
The Journal of Biological Chemistry
|February 26, 2011
Summary
IQGAP1 acts as a scaffold, linking Epidermal Growth Factor Receptor (EGFR) to downstream signaling. This study reveals IQGAP1
Area of Science:
- Cellular Biology
- Molecular Signaling
- Cancer Research
Background:
- Epidermal Growth Factor (EGF) signaling is crucial for cell growth and is mediated by the Epidermal Growth Factor Receptor (EGFR).
- IQGAP1 is a known scaffold protein involved in the MAPK cascade, regulating B-Raf, MEK, and ERK activation.
- Previous work indicated EGF cannot activate B-Raf without IQGAP1, but the link between IQGAP1 and EGFR was unclear.
Purpose of the Study:
- To elucidate the mechanism by which IQGAP1 connects B-Raf to EGFR in cellular signaling pathways.
- To investigate the functional interaction between IQGAP1 and EGFR in response to EGF stimulation.
- To determine the role of IQGAP1 phosphorylation at Ser(1443) in EGFR activation.
Main Methods:
- Co-immunoprecipitation and co-localization assays to study EGFR and IQGAP1 interaction.
- In vitro binding assays using purified IQGAP1 and EGFR domains.
- Mass spectrometry to identify EGF-induced phosphorylation sites on IQGAP1.
- Pharmacological inhibition and siRNA knockdown of EGFR, PKC, and PKCα.
- Analysis of EGF-stimulated EGFR phosphorylation in IQGAP1-null cells and reconstituted cells.
Main Results:
- EGFR and IQGAP1 co-localize and directly associate, an interaction sensitive to Ca(2+) and calmodulin.
- EGF stimulation induces IQGAP1 phosphorylation at Ser(1443), dependent on EGFR and PKC signaling.
- IQGAP1-null cells exhibit attenuated EGF-stimulated EGFR tyrosine phosphorylation, which is restored by wild-type IQGAP1 and enhanced by an S1443D mutant.
Conclusions:
- IQGAP1 directly interacts with EGFR, modulating its activation.
- IQGAP1 phosphorylation at Ser(1443) is a key event in EGF-induced EGFR signaling.
- IQGAP1 plays a critical role in linking EGFR to downstream MAPK pathway activation.
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