Home » Key Scientific Articles » Structural basis for activation of trimeric Gi proteins by multiple growth factor receptors via GIV/Girdin

Structural basis for activation of trimeric Gi proteins by multiple growth factor receptors via GIV/Girdin

Significance Statement

This work defines the structural and biochemical basis for activation of G proteins by growth factor receptor tyrosine kinases (RTKs), and thereby, helps define a new paradigm in signal transduction. It also sheds light on the observed promiscuity and versatility of GIV as a signal transducer, i.e., its ability to integrate signals downstream of multiple RTKs in a variety of cells during diverse cellular processes, e.g., cancer invasion, angiogenesis, epithelial wound healing, insulin response and cellular autophagy etc., all via G protein intermediates. By demonstrating that GIV’s SH2-like domain is intrinsically disordered in quiescent cells and stably folded only upon encountering phosphotyrosine ligands on cytoplasmic tails of activated RTKs, this work qualifies GIV as a member of a rapidly expanding group of intrinsically unstructured proteins that play key roles in cell-signaling, regulation and cancer, where coupled folding and binding is a common mechanism. Finally, we provide evidence that the RTK:GIV interface, and more specifically, GIV’s SH2-like domain is an effective and attractive target for anti-cancer therapy because it is sensitive to disruption and effectively uncouples GIV from multiple RTKs. Thus, it is tempting to speculate that small molecules against GIV’s SH2-like domain have the potential of being both selective and broad– i.e., selectively inhibit GIV-dependent growth factor signaling.

Figure Legend: Structural basis for how GIV, a non-receptor GEF for trimeric Gi, forms a novel platform for G protein activation by growth factor RTKs, thereby, defining a novel paradigm in signal transduction.

 Top: Schematic of two major signaling pathways and their downstream pathways are shown. The concept of activation of RTKs by GPCR/G proteins (Red arrow) is widely-accepted and supported by in-depth mechanistic insights, but the concept of activation of G proteins by RTKs (Green arrow) has typically been met with skepticism. Current work defines GIV as a novel platform for crosstalk between RTKs and G proteins and provides a structural basis for such function. Bottom: Schematic of various functional domains in GIV. The C-terminus of GIV features a unique coexisten of  a GEF (red) and a SH2 (blue) domain. Numbers represent amino acids. The GEF domain of GIV is required for assembly of GIV:Gi signaling interface (red arrow), which activates Gi. The newly defined SH2 domain is essential for GIV to recognize and bind ligand-activated RTKs like EGFR, thereby assembling the RTK:GIV signaling interface (blue arrow; current work). It is this coexistence of G protein-activating-GEF and RTK-binding-SH2 domains in-tandem within GIV’s C-terminus, which allows for convergence of two pathways on a common platform.

Structural basis for activation of trimeric Gi proteins by multiple growth factor receptors via GIV/Girdin. Global Medical Discovery

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Journal Reference

Lin C1, Ear J1, Midde K1, Lopez-Sanchez I1, Aznar N1, Garcia-Marcos M2, Kufareva I3, Abagyan R3, Ghosh P4. Mol Biol Cell. 2014;25(22):3654-71.

Show Affiliations

1Department of Medicine, University of California, San Diego, School of Medicine, CA 92093.

2Department of Cellular and Molecular Medicine, University of California, San Diego, School of Medicine, CA 92093.

3Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA 92093.

4Department of Medicine, University of California, San Diego, School of Medicine, CA 92093. Email: [email protected]

 

Abstract 

A long-standing issue in the field of signal transduction is to understand the cross-talk between receptor tyrosine kinases (RTKs) and heterotrimeric G proteins, two major and distinct signaling hubs that control eukaryotic cell behavior. Although stimulation of many RTKs leads to  activation of trimeric G proteins, the molecular mechanisms behind this phenomenon remain elusive. We discovered a unifying mechanism that allows GIV/Girdin, a bona fide metastasis-related protein and a guanine-nucleotide exchange factor (GEF) for Gαi, to serve as a direct platform for multiple RTKs to activate Gαi proteins. Using a combination of homology modeling, protein-protein interaction, and kinase assays, we demonstrate that a stretch of ∼110 amino acids within GIV C-terminus displays structural plasticity that allows folding into a SH2-like domain in the presence of phosphotyrosine ligands. Using protein-protein interaction assays, we demonstrated that both SH2 and GEF domains of GIV are required for the formation of a ligand-activated ternary complex between GIV, Gαi, and growth factor receptors and for activation of Gαi after growth factor stimulation. Expression of a SH2-deficient GIV mutant (Arg 1745→Leu) that cannot bind RTKs impaired all previously demonstrated functions of GIV-Akt enhancement, actin remodeling, and cell migration. The mechanistic and structural insights gained here shed light on the long-standing questions surrounding RTK/G protein cross-talk, set a novel paradigm, and characterize a unique pharmacological target for uncoupling GIV-dependent signaling downstream of multiple oncogenic RTKs.

© 2014 Lin, Ear, et al. This article is distributed by The American Society for Cell Biology under license from the author(s).

Go To Mol. Biol. Cell