The coordinating role of IQGAP1 in the regulation of local, endosome-specific actin networks

Samson, Edward B.; Tsao, David; Zimak, Jan; McLaughlin, Robert T.; Trenton, Nicholaus J.; Mace, Emily M.; Schweikhard, Volker; Diehl, Michael R.

doi:10.1242/bio.022624

Cited by 8 publications

(7 citation statements)

References 55 publications

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“…1C, right bottom),. It is possible that these cytosolic interactions occur in endosomes and/or lysosomes as IQGAP1 is known to localize to endosomes [21]. A similar interaction between IQGAP1 and PIPKIγ is also seen in NIH 3T3 fibroblasts and a liver cancer cell line HepG2 (Fig.…”

Section: Iqgap1 Associates With Pipkiγmentioning

confidence: 70%

IQGAP1 connects phosphoinositide signaling to cytoskeletal reorganization

Yerramilli

Ross

Lindberg³

et al. 2019

Preprint

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IQGAP1 is a multi-domain protein that acts as a scaffold for multiple signaling pathways. IQGAP1 generates the lipid messenger PI(3,4,5)P 3 by scaffolding the phosphoinositide kinases PIPKIs and PI3K.The dynamics of this scaffolding protein complex in intact, living cells are unknown. Here, we delineate the role of IQGAP1 in PI(3,4,5)P 3 -mediated signaling in live cells under basal and stimulated conditions using fluorescence lifetime imaging microscopy. We demonstrate that IQGAP1 interacts strongly with PIPKIγ at intracellular entities and on the plasma membrane, and scaffolds PI3K and PIPKIγ in response to physiological changes. Additionally, we show that IQGAP1 scaffolds phosphoinositides with PI3K, PIPKIγ and EGFR, and forms clusters upon cell stimulation with epidermal growth factor. Importantly, we show that IQGAP1 connects PI(3,4,5)P 3 -mediated signaling and cytoskeletal signaling pathways by binding PIPKIγ in proximity of the cytoskeletal proteins talin and Cdc42. Our results support a model in which IQGAP1 mediates crosstalk between phosphoinositide signaling and the cytoskeleton to promote directed cell movement. IQGAP1 connects PI signaling to cytoskeletal reorganization

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Section: Iqgap1 Associates With Pipkiγmentioning

confidence: 70%

IQGAP1 connects phosphoinositide signaling to cytoskeletal reorganization

Yerramilli

Ross

Lindberg³

et al. 2019

Preprint

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“…To do so, we employed IQGAP1-positive sorting endosomes as an experimental model as the micron size, basal confinement, low mobility, and relatively short lifetime ($1 h) of these compartments make them highly amenable to temporal imaging analyses. Again, we have previously shown that IQGAP1 intensities correlate negatively with actin at high frequencies because of the temporal relationship between transient scaffold disassociation and growth of the actin networks that surround and confine endosomes to the basal cortex of polarized epithelial MCF10A cells (26). To further characterize this apparent negative actin regulation and to probe potential coupling to other membrane development and signaling processes, we first performed a series of live cell imaging experiments to identify and characterize the temporal hierarchy of actin regulatory proteins and PI lipid species that function within the compartments.…”

Section: Resultsmentioning

confidence: 85%

“…Live cell imaging analyses indicate that the mechanism underlying IQGAP1 localization to these compartments is multifaceted and involves combinations of positive (supportive) and negative (inhibitory) interactions with actin and other protein or membrane components of the endosomal compartment. Moreover, dynamic correlation analyses indicate these interactions occur at different timescales, yielding nonmonotonic, frequency-dependent localization behaviors and scaffold/actin intensity correlations (26). For example, IQGAP1 and actin intensities tend to rise and fall together over long timescales (>10 min) as compartments assembled and disassembled.…”

Section: Introductionmentioning

confidence: 99%

“…Our group recently demonstrated that IQGAP1 participates in a local regulatory network that controls the assembly and disassembly of actin networks that surround and confine sorting endosomes to the basal cortex of polarized epithelial cells (26). Live cell imaging analyses indicate that the mechanism underlying IQGAP1 localization to these compartments is multifaceted and involves combinations of positive (supportive) and negative (inhibitory) interactions with actin and other protein or membrane components of the endosomal compartment.…”

Section: Introductionmentioning

confidence: 99%

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

Trenton

McLaughlin

Bellamkonda

et al. 2020

Biophysical Journal

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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.

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“…On average the duration of IQGAP1-mediated pauses was 20.6 ± 1.9 (SE) s, regardless of concentration (Figure 1I). Thus, IQGAP1 performs two actin-related activities: 1) it bundles actin filaments (Figure 1C) 34,38,[41][42][43] , and 2) it reduces overall actin filament assembly by transiently pausing elongation at the filament plus-end (Figure 1D-I).…”

Section: Iqgap1 Bundles and Temporarily Pauses Actin Filament Elongat...mentioning

confidence: 99%

Coordination of actin plus-end dynamics by IQGAP1, formin, and capping protein

Pimm

Marcin

Haarer

et al. 2023

Preprint

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Cell processes require precise regulation of actin polymerization at filament plus ends to execute normal functions. The detailed mechanisms used to control filament assembly at plus ends in the presence of diverse and often opposing regulators is not clear. Here we explore and identify residues important for the plus-end related activities of IQGAP1. In multi-wavelength TIRF assays, we directly visualize dimers of IQGAP1, mDia1, and capping protein (CP) on filament ends alone and as a multicomponent end binding complex. IQGAP1 promotes the turnover of end-binding proteins, reducing the dwell times of CP, mDia1, or mDia1-CP "decision complexes" by 8-18-fold. Loss of these activities in cells disrupts actin filament arrays, morphology, and migration. Together, our results reveal a new role for IQGAP1 in promoting protein turnover on filament ends and provide new insights into how actin assembly is regulated in cells.

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The coordinating role of IQGAP1 in the regulation of local, endosome-specific actin networks

Cited by 8 publications

References 55 publications

IQGAP1 connects phosphoinositide signaling to cytoskeletal reorganization

IQGAP1 connects phosphoinositide signaling to cytoskeletal reorganization

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

Coordination of actin plus-end dynamics by IQGAP1, formin, and capping protein

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