Ras has traditionally been regarded as a positive regulator and therapeutic target due to its role in cell proliferation, but recent findings indicate a more nuanced role in cell migration, where suppressed Ras activity can unexpectedly promote migration. To clarify this complexity, we systematically modulate Ras activity using various RasGEF and RasGAP proteins and assess their effects on migration dynamics. Leveraging optogenetics, we assess the immediate, non-transcriptional effects of Ras signaling on migration. Local RasGEF recruitment to the plasma membrane induces protrusions and new fronts to effectively guide migration, even in the absence of GPCR/G-protein signaling whereas global recruitment causes immediate cell spreading halting cell migration. Local RasGAP recruitment suppresses protrusions, generates new backs, and repels cells whereas global relocation either eliminates all protrusions to inhibit migration or preserves a single protrusion to maintain polarity. Consistent local and global increases or decreases in signal transduction and cytoskeletal activities accompany these morphological changes. Additionally, we performed cortical tension measurements and found that RasGEFs generally increase cortical tension while RasGAPs decrease it. Our results reveal a biphasic relationship between Ras activity and cellular dynamics, reinforcing our previous findings that optimal Ras activity and cortical tension are critical for efficient migration. Significance:This study challenges the traditional view of Ras as solely a positive regulator of cell functions by controlling of gene expression. Using optogenetics to rapidly modulate Ras activity in Dictyostelium , we demonstrate a biphasic relationship between Ras activity and migration: both excessive and insufficient Ras activity impair cell movement. Importantly, these effects occur rapidly, independent of transcriptional changes, revealing the mechanism by which Ras controls cell migration. The findings suggest that optimal Ras activity and cortical tension are crucial for efficient migration, and that targeting Ras in cancer therapy should consider the cell's initial state, aiming to push Ras activity outside the optimal range for migration. This nuanced understanding of the role of Ras in migration has significant implications for developing more effective cancer treatments, as simply inhibiting Ras might inadvertently promote metastasis in certain contexts.

Ras has traditionally been regarded as a positive regulator and therapeutic target due to its role in cell proliferation, but recent findings indicate a more nuanced role in cell migration, where suppressed Ras activity can unexpectedly promote migration. To clarify this complexity, we systematically modulate Ras activity using various RasGEF and RasGAP proteins and assess their effects on migration dynamics. Leveraging optogenetics, we assess the immediate, nontranscriptional effects of Ras signaling on migration. Local RasGEF recruitment to the plasma membrane induces protrusions and new fronts to effectively guide migration, even in the absence of GPCR/G-protein signaling, whereas global recruitment causes immediate cell spreading halting cell migration. Local RasGAP recruitment suppresses protrusions, generates new backs, and repels cells, whereas global relocation either eliminates all protrusions to inhibit migration or preserves a single protrusion to maintain polarity. Consistent local and global increases or decreases in signal transduction and cytoskeletal activities accompany these morphological changes. Additionally, we performed cortical tension measurements and found that Ras activity is regulated by guanine nucleotide exchange factors generally increase cortical tension while Ras activity is regulated by GTPase-activating proteins decrease it. Our results reveal a biphasic relationship between Ras activity and cellular dynamics, reinforcing our previous findings that optimal Ras activity and cortical tension are critical for efficient migration.

Although glycolysis is traditionally considered a cytosolic reaction, here we show that glycolytic enzymes propagate as self-organized waves on the membrane/cortex of human cells. Altering these waves led to corresponding changes in glycolytic activity, ATP production, and dynamic cell behaviors, impacting energy-intensive processes such as macropinocytosis and protein synthesis. Mitochondria were absent from the waves, and inhibiting oxidative phosphorylation (OXPHOS) had minimal effect on ATP levels or cellular dynamics. Synthetic membrane recruitment of individual glycolytic enzymes increased cell motility and co-recruited additional enzymes, suggesting assembly of glycolytic multi-enzyme complexes in the waves. Remarkably, wave activity and glycolytic ATP levels increased in parallel across human mammary epithelial and other cancer cell lines with higher metastatic potential. Cells with stronger wave activity relied more on glycolysis than on OXPHOS for ATP. These results reveal a distinct subcellular compartment for enriched local glycolysis at the cell periphery and suggest a mechanism that coordinates energy production with cellular state, potentially explaining the Warburg effect.

Symmetry breaking is a fundamental process that underlies key cellular behaviors such as cell polarity and migration, but the mechanism - how a uniform plasma membrane spontaneously transitions to an asymmetric state - is still unknown. Here in this study, using a combination of Dictyostelium amoeba, multiple mammalian leukocytes, and human cancer cells and 3D organoid systems, we monitored the localization dynamics of RasGTP and PIP5K, dissected the effects of eliminating, conditionally increasing, or optogenetically manipulating membrane PIP5K levels, screened for key regulators of Ras activation, and tracked single-molecules of PIP5K. Our data converge on a core biochemical circuit involving mutually inhibitory interactions between PIP5K and RasGTP that is both necessary and sufficient for symmetry breaking. The process is initiated by stochastic, localized Ras activation coupled with a decrease in the lifetime of the association of PIP5K with the membrane. A resulting localized reduction in PI(4,5)P2 facilitates the recruitment of a RasGEF to the corresponding domain, amplifying RasGTP production through a positive feedback loop. Dissociated PIP5K relocates to other membrane regions, where it suppresses Ras activation. These events separate the membrane into distinct active and inactive zones, even when receptor inputs or cytoskeletal activities are absent. This same core biochemical circuit controls the spatial organization of downstream PI3K/Akt/Rac signaling and actin/actomyosin activities, which generate the localized protrusions to define polarity and migration mode. While many models have been forwarded to explain polarity or symmetry breaking, the PIP5K-Ras mutually inhibitory bistable circuit we present here is the first universal molecular mechanism to explain the initiation of asymmetry as well as subsequent polarity and migration.

Cell adhesion to the substrate influences a variety of cell behaviors and its proper regulation is essential for migration, although details of the molecular pathways regulating cell adhesion during migration are lacking. Rap1 is a small GTPase that regulates adhesion in mammalian cells, as well as in Dictyostelium discoideum social amoeba, which is an established model for studying directed cell migration. In Dictyostelium, Rap1 controls adhesion via its effects on adhesion mediator talin and Ser/Thr kinase Phg2, which inhibits myosin II function. Kinase responsive to stress B (KrsB), a homologue of mammalian tumor suppressor MST1/2 and Drosophila Hippo, also regulates cell adhesion and migration, although the molecular mechanism of KrsB action is not understood. Because KrsB has been shown to interact with active Rap1 by mass spectroscopy, we investigated the genetic interaction between Rap1 and KrsB. Cells lacking KrsB have increased adhesion to the substrate, which leads to reduced movement. Expression of constitutively active Rap1 G12V increased cell spreading and adhesion even in the absence of KrsB, suggesting that Rap1 does not require KrsB to mediate cell adhesion. In contrast, KrsB activation requires Rap1 since dominant-negative Rap1 S17N impaired KrsB phosphorylation, which has been previously shown to be necessary for KrsB activity and its function in adhesion. Even though Rap1 did not require KrsB for its function in adhesion, KrsB negatively regulates Rap1 function as seen by increased cortical localization of active Rap1 in KrsB-null cells. Consistently, Rap1 S17N completely reversed the overadhesive phenotype of KrsB-null cells. Furthermore, chemoattractant-induced activation of downstream effectors of Rap1, TalB and Phg2, was increased in the absence of KrsB. Taken together, these findings suggest that Rap1 leads to activation of KrsB, which inhibits Rap1 and its downstream targets, shutting off adhesion. The existence of a negative feedback loop between Rap1 and KrsB may contribute to the dynamic regulation of cell adhesion that is necessary for rapid amoeboid-type migration.

SummaryGlycolysis has traditionally been thought to take place in the cytosol but we observed the enrichment of glycolytic enzymes in propagating waves of the cell cortex in human epithelial cells. These waves reflect excitable Ras/PI3K signal transduction and F-actin/actomyosin networks that drive cellular protrusions, suggesting that localized glycolysis at the cortex provides ATP for cell morphological events such as migration, phagocytosis, and cytokinesis. Perturbations that altered cortical waves caused corresponding changes in enzyme localization and ATP production whereas synthetic recruitment of glycolytic enzymes to the cell cortex enhanced cell spreading and motility. Interestingly, the cortical waves and ATP levels were positively correlated with the metastatic potential of cancer cells. The coordinated signal transduction, cytoskeletal, and glycolytic waves in cancer cells may explain their increased motility and their greater reliance on glycolysis, often referred to as the Warburg effect.

Ras has been extensively studied as a promoter of cell proliferation, whereas few studies have explored its role in migration. To investigate the direct and immediate effects of Ras activity on cell motility or polarity, we focused on RasGAPs, C2GAPB in Dictyostelium amoebae and RASAL3 in HL-60 neutrophils and macrophages. In both cellular systems, optically recruiting the respective RasGAP to the cell front extinguished pre-existing protrusions and changed migration direction. However, when these respective RasGAPs were recruited uniformly to the membrane, cells polarized and moved more rapidly, whereas targeting to the back exaggerated these effects. These unexpected outcomes of attenuating Ras activity naturally had strong, context-dependent consequences for chemotaxis. The RasGAP-mediated polarization depended critically on myosin II activity and commenced with contraction at the cell rear, followed by sustained mTORC2-dependent actin polymerization at the front. These experimental results were captured by computational simulations in which Ras levels control front- and back-promoting feedback loops. The discovery that inhibiting Ras activity can produce counterintuitive effects on cell migration has important implications for future drug-design strategies targeting oncogenic Ras. Lin, Pal, et al. report a role for localized activation of Ras activity in promoting cell polarity and motility.

Studies in the model systems, Dictyostelium amoebae and HL-60 neutrophils, have shown that local Ras activity directly regulates cell motility or polarity. Localized Ras activation on the membrane is spatiotemporally regulated by its activators, RasGEFs, and inhibitors, RasGAPs, which might be expected to create a stable ‘front’ and ‘back’, respectively, in migrating cells. Focusing on C2GAPB in amoebae and RASAL3 in neutrophils, we investigated how Ras activity along the cortex controls polarity. Since existing gene knockout and overexpression studies can be circumvented, we chose optogenetic approaches to assess the immediate, local effects of these Ras regulators on the cell cortex. In both cellular systems, optically targeting the respective RasGAPs to the cell front extinguished existing protrusions and changed the direction of migration, as might be expected. However, when the expression of C2GAPB was induced globally, amoebae polarized within hours. Furthermore, within minutes of globally recruiting either C2GAPB in amoebae or RASAL3 in neutrophils, each cell type polarized and moved more rapidly. Targeting the RasGAPs to the cell backs exaggerated these effects on migration and polarity. Overall, in both cell types, RasGAP-mediated polarization was brought about by increased actomyosin contractility at the back and sustained, localized F-actin polymerization at the front. These experimental results were accurately captured by computational simulations in which Ras levels control front and back feedback loops. The discovery that context-dependent Ras activity on the cell cortex has counterintuitive, unanticipated effects on cell polarity can have important implications for future drug-design strategies targeting oncogenic Ras.

Abstract Tumors preferentially metabolize glucose anaerobically through glycolysis with lower ATP production efficiency rather than aerobically even when oxygen is available. This was reported by Otto Warburg 100 years ago, yet the mechanism is hitherto not well-understood. Glycolysis is canonically thought to occur only in cytosol; if and how it is regulated by the actin cytoskeletal network is controversial. I found that, in epithelial cells, 6 of the 9 glycolytic enzymes (HK, PFK, ALDO, GAPDH, ENO, and PK, others not tested) are enriched at newly formed LifeAct labeled waves and protrusions, where mitochondria are barely detected by Mito-Tracker. The application of glycolysis inhibitors but not oxidative phosphorylation inhibitors abolishes cell migration. These results indicate that cells rely on the local ATP production from glycolysis enriched in the cortical waves and protrusions to move. We visualized and measured glycolysis production in confocal and TIRF microscopes using a series of biosensors for ATP, NADH/NAD+ ratio, and pyruvate. We then found glycolysis was enhanced by perturbations that increase wave formation such as EGF/Insulin stimulation or recruiting ActA to membrane, and reduced by wave decrease from PI3K inhibition, hyper- and hypo-osmotic shock, or F-actin assembly inhibition. This suggests that enriching glycolytic enzymes on waves results in higher glycolysis production. We do not think the changes of glycolysis by wave perturbations are merely due to direct regulation on glycolytic enzymes by canonical signaling pathways (e.g., Ras-PI3K-AKT), since ActA recruitment or F-actin inhibition does not lead to acute changes in these signaling pathways but mainly causes the assembly or disassembly of the F-actin/glycolytic waves. These findings together lead to our new theory that energy production from glycolysis is enhanced by recruiting the glycolytic enzymes to the waves and protrusions on the cell cortex. This is potentially paradigm-shifting because for many decades glycolysis - one of the two major ways in a cell to produce ATP - has been thought to only occur in cytosol. Interestingly, we also found glycolytic enzymes enriched in F-actin labeled protrusions of Dictyostelium cells, which indicates that this can possibly be an evolutionally conserved mechanism. Additionally, we investigated non-cancer MCF-10A cells (M1) and a series of M1-derived cancer cell lines (M2 - M4) with increased metastatic index and cancer malignancy, and found a sequential increase in actin wave and glycolysis activities from M1 to M4 cells. Cancer cells such as M3 had a larger drop in glycolysis than non-cancer parental M1 cells upon wave inhibition. These results provide a new explanation for the Warburg effect that increased cortical waves in cancer cells will accelerate and improve glycolysis, which will not only greatly contribute to our understanding of cancer but also the design of new interventions. Citation Format: Huiwang David Zhan, Jane Borleis, Chris Janetopoulos, Peter Devreotes. Glycolysis is enriched to propagating waves in cell cortex as a new mechanism for cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 288.

Ras signaling is typically associated with cell growth, but not direct regulation of motility or polarity. By optogenetically targeting different nodes in the Ras/PI3K/Akt network in differentiated human HL-60 neutrophils, we abruptly altered protrusive activity, bypassing the chemoattractant receptor/G-protein network. First, global recruitment of active KRas4B/HRas isoforms or a RasGEF, RasGRP4, immediately increased spreading and random motility. Second, activating Ras at the cell rear generated new protrusions, reversed pre-existing polarity, and steered sustained migration in neutrophils or murine RAW 264.7 macrophages. Third, recruiting a RasGAP, RASAL3, to cell fronts extinguished protrusions and changed migration direction. Remarkably, persistent RASAL3 recruitment at stable fronts abrogated directed migration in three different chemoattractant gradients. Fourth, local recruitment of the Ras-mTORC2 effector, Akt, in neutrophils or Dictyostelium amoebae generated new protrusions and rearranged pre-existing polarity. Overall, these optogenetic effects were mTORC2-dependent but relatively independent of PI3K. Thus, receptor-independent, local activations of classical growth-control pathways directly control actin assembly, cell shape, and migration modes.

Functions of Ras oncogenes and their downstream effectors are typically associated with cell proliferation and growth control while their role in immune cell migration has been largely unexplored. Although Ras-mediated signaling cascades have been implicated in immune response, there is no conclusive evidence to show local activation of these pathways on the plasma membrane directly regulates cell motility or polarity. Using spatiotemporally precise, cryptochrome-based optogenetic systems in human neutrophils, we abruptly altered protrusive activity, bypassing the chemoattractant-sensing receptor/G-protein network. First, global recruitment of active KRas4B/HRas isoforms or the guanine nucleotide exchange factor, RasGRP4, immediately increased spreading and random motility in neutrophils. Second, creating Ras activity at the cell rear generated new protrusions at the site and reversed pre-existing polarity, similar to the effects of steep chemoattractant gradients. Third, recruiting GTPase activating protein, RASAL3, at cell fronts abrogated existing protrusions and changed the direction of motility whereas dynamically inhibiting nascent fronts stopped migration completely. Fourth, combining pharmacological inhibition studies with optogenetics revealed that mTorC2 is more important than PI3K for Ras-mediated polarity and migration. Finally, local recruitment of Ras-mTorC2 effector, Akt, also generated new protrusions, rearranged pre-existing polarity, and triggered migration, even in absence of PI3K signaling. We propose that actin assembly, cell shape, and migration modes in immune cells are promptly controlled by rapid, local activities of established components of classical growth-control pathways independently of receptor activation.

Download This Paper Open PDF in Browser Add Paper to My Library Share: Permalink Using these links will ensure access to this page indefinitely Copy URL Actuation of Single Downstream Nodes in Growth Factor Network Mediates Neutrophil Guidance Developmental Cell 71 Pages Posted: 9 Dec 2022 Publication Status: Under Review See all articles by Dhiman PalDhiman PalJohns Hopkins University - Center for Cell DynamicsTatsat BanerjeeJohns Hopkins University - Center for Cell DynamicsYiyan LinJohns Hopkins University - Center for Cell DynamicsJane BorleisJohns Hopkins University - Center for Cell DynamicsPeter N. DevreotesJohns Hopkins University - Center for Cell Dynamics More... Abstract Functions of Ras oncogenes and their downstream effectors are typically associated with cell proliferation and growth control while their role in mammalian cell migration has been largely unexplored. Although Ras-mediated signaling cascades have been implicated in immune response, there is no evidence showing that local activation of these pathways directly regulates cell motility or polarity. By establishing optogenetic systems to trigger multiple different individual network nodes in human neutrophils, we were able to abruptly alter protrusive activity, bypassing the chemoattractant-sensing receptor/G-protein network. First, global recruitment of active KRas4B/HRas isoforms or the guanine nucleotide exchange factor, RasGRP4, immediately increased spreading and random motility in neutrophils. Second, creating Ras activity at the cell rear generated new protrusions at the site and reversed pre-existing polarity. Third, recruiting GTPase activating protein, RASAL3, at cell fronts abrogated existing protrusions and changed the direction of motility whereas dynamically inhibiting nascent fronts stopped migration completely. Fourth, combining pharmacological inhibition studies with optogenetics revealed that mTorC2 is more important than PI3K for Ras-mediated polarity and migration. Finally, local recruitment of Ras-mTorC2 effector, Akt, also generated new protrusions, rearranged pre-existing polarity, and triggered migration, even in absence of PI3K signaling. We propose that actin assembly, cell shape, and migration modes in neutrophils are controlled by spontaneous, receptor-independent local activations of downstream components of classical growth-control pathways. Note: Funding Information: This work was supported by NIH grant R35 GM118177 (to PND), DARPA HR0011-16-C-0139 (to PAI and PND), AFOSR MURI FA95501610052 (to PND), as well as NIH grant S10 OD016374 (to S Kuo of the JHU Microscope Facility). Declaration of Interests: The authors declare no competing interests. Keywords: biochemical excitability, cancer, leukocytes, inflammation, optogenetics Suggested Citation: Suggested Citation Pal, Dhiman and Banerjee, Tatsat and Lin, Yiyan and Borleis, Jane and Devreotes, Peter N., Actuation of Single Downstream Nodes in Growth Factor Network Mediates Neutrophil Guidance. Available at SSRN: https://ssrn.com/abstract=4295347 This version of the paper has not been formally peer reviewed. Dhiman Pal Johns Hopkins University - Center for Cell Dynamics Tatsat Banerjee Johns Hopkins University - Center for Cell Dynamics ( email ) Yiyan Lin Johns Hopkins University - Center for Cell Dynamics ( email ) Jane Borleis Johns Hopkins University - Center for Cell Dynamics ( email ) Peter N. Devreotes (Contact Author) Johns Hopkins University - Center for Cell Dynamics ( email ) Download This Paper Open PDF in Browser Please enable JavaScript to view the comments powered by Disqus. 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The model organism Dictyostelium discoideum has greatly facilitated our understanding of the signal transduction and cytoskeletal pathways that govern cell motility. Cell-substrate adhesion is downstream of many migratory and chemotaxis signaling events. Dictyostelium cells lacking the tumor suppressor PTEN show strongly impaired migratory activity and adhere strongly to their substrates. We reasoned that other regulators of migration could be obtained through a screen for overly adhesive mutants. A screen of restriction enzyme-mediated integration mutagenized cells yielded numerous mutants with the desired phenotypes, and the insertion sites in 18 of the strains were mapped. These regulators of adhesion and motility mutants have increased adhesion and decreased motility. Characterization of seven strains demonstrated decreased directed migration, flatness, increased filamentous actin-based protrusions, and increased signal transduction network activity. Many of the genes share homology to human genes and demonstrate the diverse array of cellular networks that function in adhesion and migration.

Signal transduction pathways activated by chemoattractants have been extensively studied, but little is known about the events mediating responses to mechanical stimuli. We discovered that acute mechanical perturbation of cells triggered transient activation of all tested components of the chemotactic signal transduction network, as well as actin polymerization. Similarly to chemoattractants, the shear flow-induced signal transduction events displayed features of excitability, including the ability to mount a full response irrespective of the length of the stimulation and a refractory period that is shared with that generated by chemoattractants. Loss of G protein subunits, inhibition of multiple signal transduction events, or disruption of calcium signaling attenuated the response to acute mechanical stimulation. Unlike the response to chemoattractants, an intact actin cytoskeleton was essential for reacting to mechanical perturbation. These results taken together suggest that chemotactic and mechanical stimuli trigger activation of a common signal transduction network that integrates external cues to regulate cytoskeletal activity and drive cell migration.

Asymmetric protein localization is essential for cell polarity and migration. We report a novel protein, Callipygian (CynA), which localizes to the lagging edge before other proteins and becomes more tightly restricted as cells polarize; additionally, it accumulates in the cleavage furrow during cytokinesis. CynA protein that is tightly localized, or "clustered," to the cell rear is immobile, but when polarity is disrupted, it disperses throughout the membrane and responds to uniform chemoattractant stimulation by transiently localizing to the cytosol. These behaviors require a pleckstrin homology-domain membrane tether and a WD40 clustering domain, which can also direct other membrane proteins to the back. Fragments of CynA lacking the pleckstrin homology domain, which are normally found in the cytosol, localize to the lagging edge membrane when coexpressed with full-length protein, showing that CynA clustering is mediated by oligomerization. Cells lacking CynA have aberrant lateral protrusions, altered leading- edge morphology, and decreased directional persistence, whereas those overexpressing the protein display exaggerated features of polarity. Consistently, actin polymerization is inhibited at sites of CynA accumulation, thereby restricting protrusions to the opposite edge. We suggest that the mutual antagonism between CynA and regions of responsiveness creates a positive feedback loop that restricts CynA to the rear and contributes to the establishment of the cell axis.