The WW domain of IQGAP1 binds directly to the p110α catalytic subunit of PI 3-kinase
A Jane Bardwell1, Madhuri Paul1, Kiku C Yoneda1
1University of California Irvine, Irvine, California, United States.
Abstract:
IQGAP1 is a multi-domain cancer-associated protein that serves as a scaffold protein for multiple signaling pathways. Numerous binding partners have been found for the calponin homology, IQ and GAP-related domains in IQGAP1. Identification of a binding partner for its WW domain has proven elusive, however, even though a cell-penetrating peptide derived from this domain has marked anti-tumor activity. Here, using in vitro binding assays with human proteins and co-precipitation from human cells, we show that the WW domain of human IQGAP1 binds directly to the p110α catalytic subunit of phosphoinositide 3-kinase (PI3K). In contrast, the WW domain does not bind to ERK1/2, MEK1/2, or the p85α regulatory subunit of PI3K when p85α is expressed alone. However, the WW domain is able to bind to the p110α/p85α heterodimer when both subunits are co-expressed, as well as to the mutationally activated p110α/p65α heterodimer. We present a model of the structure of the IQGAP1 WW domain, and experimentally identify key residues in the hydrophobic core and beta strands of the WW domain that are required for binding to p110α. These findings contribute to a more precise understanding of IQGAP1-mediated scaffolding, and of how IQGAP1-derived therapeutic peptides might inhibit tumorigenesis.
Insights
Researchers identified that the IQGAP1 protein's WW domain binds to phosphoinositide 3-kinase (PI3K) p110α. This discovery advances understanding of cancer-associated protein scaffolding and potential anti-tumor peptide therapies.
Area of Science:
- Molecular Biology
- Cancer Research
- Protein Interactions
Background:
- IQGAP1 is a cancer-associated scaffold protein involved in multiple signaling pathways.
- While binding partners for most IQGAP1 domains are known, the WW domain's partner remained elusive.
- A peptide from the IQGAP1 WW domain shows significant anti-tumor activity.
Purpose of the Study:
- To identify the binding partner of the IQGAP1 WW domain.
- To elucidate the interaction between IQGAP1 and phosphoinositide 3-kinase (PI3K).
- To understand the structural basis for the IQGAP1 WW domain-PI3K interaction.
Main Methods:
- In vitro binding assays using human proteins.
- Co-precipitation experiments from human cells.
- Structural modeling of the IQGAP1 WW domain.
Main Results:
- The IQGAP1 WW domain directly binds to the p110α catalytic subunit of PI3K.
- Binding occurs with the p110α/p85α heterodimer and activated p110α/p65α heterodimer, but not p85α alone.
- Key residues in the IQGAP1 WW domain's hydrophobic core and beta strands crucial for p110α binding were identified.
Conclusions:
- The IQGAP1 WW domain directly interacts with the p110α subunit of PI3K.
- This interaction is specific and depends on the heterodimeric state of PI3K.
- Findings provide insights into IQGAP1 scaffolding and potential therapeutic strategies targeting IQGAP1-derived peptides for cancer treatment.
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