Membrane and Actin Tethering Transitions Help IQGAP1 Coordinate GTPase and Lipid Messenger Signaling

Abstract

The coordination of lipid messenger signaling with cytoskeletal regulation is central to many organelle-specific regulatory processes. This coupling often depends on the function of multidomain scaffolds that orchestrate transient interactions among multiple signaling intermediates and regulatory proteins on organelles. The number of possible scaffold interaction partners and the ability for these interactions to occur at different timescales makes investigations of scaffold functions challenging. This work employs live cell imaging to probe how the multidomain scaffold IQ motif containing GTPase activating protein 1 (IQGAP1) coordinates the activities of proteins affecting local actin polymerization, membrane processing, and phosphoinositide signaling. Using endosomes that are confined by a local actin network as a model system, we demonstrate that IQGAP1 can transition between different actin and endosomal membrane tethered states. Fast scaffold binding/disassociation transitions are shown to be driven by interactions between C-terminal scaffold domains and Rho GTPases at the membrane. Fluctuations in these binding modes are linked to negative regulation of actin polymerization. Although this control governs core elements of IQGAP1 dynamics, actin binding by the N-terminal calponin homology domain of the scaffold is shown to help the scaffold track the temporal development of endosome membrane markers, implying actin associations bolster membrane and actin coordination. Importantly, these effects are not easily distilled purely through standard (static) co-localization analyses or traditional pathway perturbations methods and were resolved by performing dynamic correlation and multiple regression analyses of IQGAP1 scaffold mutants. Using these capabilities with pharmacological inhibition, we provide evidence that membrane tethering is dependent on the activities of the lipid kinase phosphoinositide 3-kinase in addition to the Rho GTPases Rac1 and Cdc42. Overall, these methods and results point to a scaffold tethering mechanism that allows IQGAP1 to help control the amplitude of phosphoinositide lipid messenger signaling by coordinating signaling intermediate activities with the development and disassembly of local actin cytoskeletal networks.

An Extracellular/Membrane-Bound S100P Pool Regulates Motility and Invasion of Human Extravillous Trophoblast Lines and Primary Cells

“…Immunofluorescence work using either the membrane marker Nile red [ 34 , 35 , 36 ] or the receptor integrin β1 [ 5 , 49 ] also provides strong evidence suggesting that some pools of S100P were localised near the plasma membrane. The use of the plot profiling and ROI technique is well characterised as an efficient method to evidence the colocalisation of specific complexes for both immunofluorescence and immunohistochemistry staining as well as for membrane localisation [ 50 , 51 , 52 ]. The presence of S100P close to the plasma membrane has never been reported before in the context of trophoblast cells, either in vivo or in different cell lines and primary EVT cultures.…”

SARS-CoV-2 3CLpro Main Protease Drives Cytoskeletal Reorganization and Tunnelling Nanotube Formation for Stealth Intercellular Infection

“…5a), although these proteins were not part of the 3CL pro interactome. At adherens junctions, these 3 proteins are scaffolds for large protein assemblies 45,46 that are regulated by the Rho family GTPases, Ras-related C3 botulinum toxin substrate 1 (RAC1), and cell division cycle 42 (CDC42), and their effectors, e.g., ROCK 47 . Immunofluorescence showed that the 3CL pro substrates, LASP1 (Fig.…”

“…built on IQGAP1, PLEKHA7, and cadherin-1 scaffolds encompass the zonular signalosome that orchestrates cytoskeletal organization and signalling 45,47 . Junctional rearrangement activates the zonular signalosome by perturbing protein-protein interactions and leads to translocation of IQGAP1 to the plasma membrane to coordinate phosphoinositide signalling 46 and of sequestered transcription factors to the nucleus, e.g., β-catenin and the Yes-associated protein 1 (YAP1) to activate the Wnt and Hippo signalling pathways, respectively 47 . Efficient cleavage of IQGAP1 by 3CL pro at ALH 218 ↓AAV (Fig.…”

Role of IQ Motif-Containing GTPase-Activating Proteins in Hepatocellular Carcinoma

“…Starting from the N-terminus, IQGAPs comprise a calmodulin homology domain (CHD) that mediates actin-binding ( 46 ). For instance, the interaction between the CHD of IQGAP1 and actin filaments governs the cytoskeleton modulation to facilitate actin binding and polymerization, thus further regulating cell division, cell migration, and the stability of cell-cell contacts ( 47 ). Moreover, it has been shown previously that IQGAP1 dynamically contributes to the formation of the spine head in the cultured rat hippocampal neurons through CHD ( 48 ).…”