CYRI-B mediated macropinocytosis drives metastasis via lysophosphatidic acid receptor uptake.

Pancreatic ductal adenocarcinoma carries a dismal prognosis, with high rates of metastasis and few treatment options. Hyperactivation of KRAS in almost all tumours drives RAC1 activation, conferring enhanced migratory and proliferative capacity as well as macropinocytosis. Macropinocytosis is well understood as a nutrient scavenging mechanism, but little is known about its functions in trafficking of signaling receptors. We find that CYRI-B is highly expressed in pancreatic tumours in a mouse model of KRAS and p53-driven pancreatic cancer. Deletion of Cyrib (the gene encoding CYRI-B protein) accelerates tumourigenesis, leading to enhanced ERK and JNK-induced proliferation in precancerous lesions, indicating a potential role as a buffer of RAC1 hyperactivation in early stages. However, as disease progresses, loss of CYRI-B inhibits metastasis. CYRI-B depleted tumour cells show reduced chemotactic responses to lysophosphatidic acid, a major driver of tumour spread, due to impaired macropinocytic uptake of the lysophosphatidic acid receptor-1. Overall, we implicate CYRI-B as a mediator of growth and signaling in pancreatic cancer, providing new insights into pathways controlling metastasis.

Dichotomous role of the serine/threonine kinase MAP4K4 in pancreatic ductal adenocarcinoma onset and metastasis through control of AKT and ERK pathways.

MAP4K4 is a serine/threonine kinase of the STE20 family involved in the regulation of actin cytoskeleton dynamics and cell motility. It has been proposed as a target of angiogenesis and inhibitors show potential in cardioprotection. MAP4K4 also mediates cell invasion in vitro, is overexpressed in various types of cancer, and is associated with poor patient prognosis. Recently, MAP4K4 has been shown to be overexpressed in pancreatic cancer, but its role in tumour initiation, progression, and metastasis is unknown. Here, using the KrasG12D Trp53R172H Pdx1-Cre (KPC) mouse model of pancreatic ductal adenocarcinoma (PDAC), we show that deletion of Map4k4 drives tumour initiation and progression. Moreover, we report that the acceleration of tumour onset is also associated with an overactivation of ERK and AKT, two major downstream effectors of KRAS, in vitro and in vivo. In contrast to the accelerated tumour onset caused by loss of MAP4K4, we observed a reduction in metastatic burden with both the KPC model and in an intraperitoneal transplant assay indicating a major role of MAP4K4 in metastatic seeding. In summary, our study sheds light on the dichotomous role of MAP4K4 in the initiation of PDAC onset, progression, and metastatic dissemination. It also identifies MAP4K4 as a possible druggable target against pancreatic cancer spread, but with the caveat that targeting MAP4K4 might accelerate early tumorigenesis. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Collagen VI expression is negatively mechanosensitive in pancreatic cancer cells and supports the metastatic niche.

Pancreatic cancer is a deadly and highly metastatic disease, although how metastatic lesions establish is not fully understood. A key feature of pancreatic tumours is extensive fibrosis and deposition of extracellular matrix (ECM). While pancreatic cancer cells are programmed by stimuli derived from a stiff ECM, metastasis requires loss of attachment and adaptation to a softer microenvironment at distant sites. Growing evidence suggests that stiff ECM influences pancreatic cancer cell behaviour. Here, we argue that this influence is reversible and that pancreatic cancer cells can be reprogrammed upon sensing soft substrates. Using engineered polyacrylamide hydrogels with tuneable mechanical properties, we show that collagen VI is specifically upregulated in pancreatic cancer cells on soft substrates, due to a lack of integrin engagement. Furthermore, the expression of collagen VI is inversely correlated with mechanosensing and activity of YAP (also known as YAP1), which might be due to a direct or indirect effect on transcription of genes encoding collagen VI. Collagen VI supports migration in vitro and metastasis formation in vivo. Metastatic nodules formed by pancreatic cancer cells lacking Col6a1 display stromal cell-derived collagen VI deposition, suggesting that collagen VI derived from either cancer cells or the stroma is an essential component of the metastatic niche. This article has an associated First Person interview with Vasileios Papalazarou, joint first author of the paper.

Optimizing metastatic-cascade-dependent Rac1 targeting in breast cancer: Guidance using optical window intravital FRET imaging.

Assessing drug response within live native tissue provides increased fidelity with regards to optimizing efficacy while minimizing off-target effects. Here, using longitudinal intravital imaging of a Rac1-Förster resonance energy transfer (FRET) biosensor mouse coupled with in vivo photoswitching to track intratumoral movement, we help guide treatment scheduling in a live breast cancer setting to impair metastatic progression. We uncover altered Rac1 activity at the center versus invasive border of tumors and demonstrate enhanced Rac1 activity of cells in close proximity to live tumor vasculature using optical window imaging. We further reveal that Rac1 inhibition can enhance tumor cell vulnerability to fluid-flow-induced shear stress and therefore improves overall anti-metastatic response to therapy during transit to secondary sites such as the lung. Collectively, this study demonstrates the utility of single-cell intravital imaging in vivo to demonstrate that Rac1 inhibition can reduce tumor progression and metastases in an autochthonous setting to improve overall survival.

N-WASP Control of LPAR1 Trafficking Establishes Response to Self-Generated LPA Gradients to Promote Pancreatic Cancer Cell Metastasis.

Pancreatic ductal adenocarcinoma is one of the most invasive and metastatic cancers and has a dismal 5-year survival rate. We show that N-WASP drives pancreatic cancer metastasis, with roles in both chemotaxis and matrix remodeling. lysophosphatidic acid, a signaling lipid abundant in blood and ascites fluid, is both a mitogen and chemoattractant for cancer cells. Pancreatic cancer cells break lysophosphatidic acid down as they respond to it, setting up a self-generated gradient driving tumor egress. N-WASP-depleted cells do not recognize lysophosphatidic acid gradients, leading to altered RhoA activation, decreased contractility and traction forces, and reduced metastasis. We describe a signaling loop whereby N-WASP and the endocytic adapter SNX18 promote lysophosphatidic acid-induced RhoA-mediated contractility and force generation by controlling lysophosphatidic acid receptor recycling and preventing degradation. This chemotactic loop drives collagen remodeling, tumor invasion, and metastasis and could be an important target against pancreatic cancer spread.

Fam49/CYRI interacts with Rac1 and locally suppresses protrusions.

Actin-based protrusions are reinforced through positive feedback, but it is unclear what restricts their size, or limits positive signals when they retract or split. We identify an evolutionarily conserved regulator of actin-based protrusion: CYRI (CYFIP-related Rac interactor) also known as Fam49 (family of unknown function 49). CYRI binds activated Rac1 via a domain of unknown function (DUF1394) shared with CYFIP, defining DUF1394 as a Rac1-binding module. CYRI-depleted cells have broad lamellipodia enriched in Scar/WAVE, but reduced protrusion-retraction dynamics. Pseudopods induced by optogenetic Rac1 activation in CYRI-depleted cells are larger and longer lived. Conversely, CYRI overexpression suppresses recruitment of active Scar/WAVE to the cell edge, resulting in short-lived, unproductive protrusions. CYRI thus focuses protrusion signals and regulates pseudopod complexity by inhibiting Scar/WAVE-induced actin polymerization. It thus behaves like a 'local inhibitor' as predicted in widely accepted mathematical models, but not previously identified in cells. CYRI therefore regulates chemotaxis, cell migration and epithelial polarization by controlling the polarity and plasticity of protrusions.

Loss of N-WASP drives early progression in an Apc model of intestinal tumourigenesis.

N-WASP (WASL) is a widely expressed cytoskeletal signalling and scaffold protein also implicated in regulation of Wnt signalling and homeostatic maintenance of skin epithelial architecture. N-WASP mediates invasion of cancer cells in vitro and its depletion reduces invasion and metastatic dissemination of breast cancer. Given this role in cancer invasion and universal expression in the gastrointestinal tract, we explored a role for N-WASP in the initiation and progression of colorectal cancer. While deletion of N-wasp is not detectably harmful in the murine intestinal tract, numbers of Paneth cells increased, indicating potential changes in the stem cell niche, and migration up the crypt-villus axis was enhanced. Loss of N-wasp promoted adenoma formation in an adenomatous polyposis coli (Apc) deletion model of intestinal tumourigenesis. Thus, we establish a tumour suppressive role of N-WASP in early intestinal carcinogenesis despite its later pro-invasive role in other cancers. Our study highlights that while the actin cytoskeletal machinery promotes invasion of cancer cells, it also maintains normal epithelial tissue function and thus may have tumour suppressive roles in pre-neoplastic tissues. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Coordination by Cdc42 of Actin, Contractility, and Adhesion for Melanoblast Movement in Mouse Skin.

The individual molecular pathways downstream of Cdc42, Rac, and Rho GTPases are well documented, but we know surprisingly little about how these pathways are coordinated when cells move in a complex environment in vivo. In the developing embryo, melanoblasts originating from the neural crest must traverse the dermis to reach the epidermis of the skin and hair follicles. We previously established that Rac1 signals via Scar/WAVE and Arp2/3 to effect pseudopod extension and migration of melanoblasts in skin. Here we show that RhoA is redundant in the melanocyte lineage but that Cdc42 coordinates multiple motility systems independent of Rac1. Similar to Rac1 knockouts, Cdc42 null mice displayed a severe loss of pigmentation, and melanoblasts showed cell-cycle progression, migration, and cytokinesis defects. However, unlike Rac1 knockouts, Cdc42 null melanoblasts were elongated and displayed large, bulky pseudopods with dynamic actin bursts. Despite assuming an elongated shape usually associated with fast mesenchymal motility, Cdc42 knockout melanoblasts migrated slowly and inefficiently in the epidermis, with nearly static pseudopods. Although much of the basic actin machinery was intact, Cdc42 null cells lacked the ability to polarize their Golgi and coordinate motility systems for efficient movement. Loss of Cdc42 de-coupled three main systems: actin assembly via the formin FMNL2 and Arp2/3, active myosin-II localization, and integrin-based adhesion dynamics.

Loss of strumpellin in the melanocytic lineage impairs the WASH Complex but does not affect coat colour.

The five-subunit WASH complex generates actin networks that participate in endocytic trafficking, migration and invasion in various cell types. Loss of one of the two subunits WASH or strumpellin in mice is lethal, but little is known about their role in mammals in vivo. We explored the role of strumpellin, which has previously been linked to hereditary spastic paraplegia, in the mouse melanocytic lineage. Strumpellin knockout in melanocytes revealed abnormal endocytic vesicle morphology but no impairment of migration in vitro or in vivo and no change in coat colour. Unexpectedly, WASH and filamentous actin could still localize to vesicles in the absence of strumpellin, although the shape and size of vesicles was altered. Blue native PAGE revealed the presence of two distinct WASH complexes, even in strumpellin knockout cells, revealing that the WASH complex can assemble and localize to endocytic compartments in cells in the absence of strumpellin.

Loss of Scar/WAVE complex promotes N-WASP- and FAK-dependent invasion.

BACKGROUND: The Scar/WAVE regulatory complex (WRC) drives lamellipodia assembly via the Arp2/3 complex, whereas the Arp2/3 activator N-WASP is not essential for 2D migration but is increasingly implicated in 3D invasion. It is becoming ever more apparent that 2D and 3D migration utilize the actin cytoskeletal machinery differently. RESULTS: We discovered that WRC and N-WASP play opposing roles in 3D epithelial cell migration. WRC depletion promoted N-WASP/Arp2/3 complex activation and recruitment to leading invasive edges and increased invasion. WRC disruption also altered focal adhesion dynamics and drove FAK activation at leading invasive edges. We observed coalescence of focal adhesion components together with N-WASP and Arp2/3 complex at leading invasive edges in 3D. Unexpectedly, WRC disruption also promoted FAK-dependent cell transformation and tumor growth in vivo. CONCLUSIONS: N-WASP has a crucial proinvasive role in driving Arp2/3 complex-mediated actin assembly in cooperation with FAK at invasive cell edges, but WRC depletion can promote 3D cell motility.

Scar/WAVE3 contributes to motility and plasticity of lamellipodial dynamics but not invasion in three dimensions.

The Scar (suppressor of cAMP receptor)/WAVE [WASP (Wiskott-Aldrich syndrome protein) verprolin homologous] complex plays a major role in the motility of cells by activating the Arp2/3 complex, which initiates actin branching and drives protrusions. Mammals have three Scar/WAVE isoforms, which show some tissue-specific expression, but their functions have not been differentiated. In the present study we show that depletion of Scar/WAVE3 in the mammalian breast cancer cells MDA-MB-231 results in larger and less dynamic lamellipodia. Scar/WAVE3-depleted cells move more slowly but more persistently on a two-dimensional matrix and they typically only show one lamellipod. However, Scar/WAVE3 appears to have no role in driving invasiveness in a three-dimensional Matrigel™ invasion assay or a three-dimensional collagen invasion assay, suggesting that lamellipodial persistence as seen in two-dimensions is not crucial in three-dimensional environments.

Mtss1 promotes cell-cell junction assembly and stability through the small GTPase Rac1.

Cell-cell junctions are an integral part of epithelia and are often disrupted in cancer cells during epithelial-to-mesenchymal transition (EMT), which is a main driver of metastatic spread. We show here that Metastasis suppressor-1 (Mtss1; Missing in Metastasis, MIM), a member of the IMD-family of proteins, inhibits cell-cell junction disassembly in wound healing or HGF-induced scatter assays by enhancing cell-cell junction strength. Mtss1 not only makes cells more resistant to cell-cell junction disassembly, but also accelerates the kinetics of adherens junction assembly. Mtss1 drives enhanced junction formation specifically by elevating Rac-GTP. Lastly, we show that Mtss1 depletion reduces recruitment of F-actin at cell-cell junctions. We thus propose that Mtss1 promotes Rac1 activation and actin recruitment driving junction maintenance. We suggest that the observed loss of Mtss1 in cancers may compromise junction stability and thus promote EMT and metastasis.

The Arp2/3 activator WASH regulates α5ß1-integrin-mediated invasive migration.

The actin cytoskeleton provides scaffolding and physical force to effect fundamental processes such as motility, cytokinesis and vesicle trafficking. The Arp2/3 complex nucleates actin structures and contributes to endocytic vesicle invagination and trafficking away from the plasma membrane. Internalisation and directed recycling of integrins are major driving forces for invasive cell motility and potentially for cancer metastasis. Here, we describe a direct requirement for WASH and Arp2/3-mediated actin polymerisation on the endosomal membrane system for α5ß1 integrin recycling. WASH regulates the trafficking of endosomal α5ß1 integrin to the plasma membrane and is fundamental for integrin-driven cell morphology changes and integrin-mediated cancer cell invasion. Thus, we implicate WASH and Arp2/3-driven actin nucleation in receptor recycling leading to invasive motility.

Functional analysis of Dictyostelium IBARa reveals a conserved role of the I-BAR domain in endocytosis.

I-BAR (inverse-Bin/amphiphysin/Rvs)-domain-containing proteins such as IRSp53 (insulin receptor substrate of 53 kDa) associate with outwardly curved membranes and connect them to proteins involved in actin dynamics. Research on I-BAR proteins has focussed on possible roles in filopod and lamellipod formation, but their full physiological function remains unclear. The social amoeba Dictyostelium encodes a single I-BAR/SH3 (where SH3 is Src homology 3) protein, called IBARa, along with homologues of proteins that interact with IRSp53 family proteins in mammalian cells, providing an excellent model to study its cellular function. Disruption of the gene encoding IBARa leads to a mild defect in development, but filopod and pseudopod dynamics are unaffected. Furthermore, ectopically expressed IBARa does not induce filopod formation and does not localize to filopods. Instead, IBARa associates with clathrin puncta immediately before they are endocytosed. This role is conserved: human BAIAP2L2 (brain-specific angiogenesis inhibitor 1-associated protein 2-like 2) also tightly co-localizes with clathrin plaques, although its homologues IRSp53 and IRTKS (insulin receptor tyrosine kinase substrate) associate with other punctate structures. The results from the present study suggest that I-BAR-containing proteins help generate the membrane curvature required for endocytosis and implies an unexpected role for IRSp53 family proteins in vesicle trafficking.

BTB-Kelch protein Krp1 regulates proliferation and differentiation of myoblasts.

The BTB-Kelch protein Krp1 is highly and specifically expressed in skeletal muscle, where it is proposed to have a role in myofibril formation. We observed significant upregulation of Krp1 in C2 cells early in myoblast differentiation, well before myofibrillogenesis. Krp1 has a role in cytoskeletal organization and cell motility; since myoblast migration and elongation/alignment are important events in early myogenesis, we hypothesized that Krp1 is involved with earlier regulation of differentiation. Krp1 protein levels were detectable by 24 h after induction of differentiation in C2 cells and were significantly upregulated by 48 h, i.e., following the onset myogenin expression and preceding myosin heavy chain (MHC) upregulation. Upregulation of Krp1 required a myogenic stimulus as signaling derived from increased myoblast cell density was insufficient to activate Krp1 expression. Examination of putative Krp1 proximal promoter regions revealed consensus E box elements associated with myogenic basic helix-loop-helix binding. The activity of a luciferase promoter-reporter construct encompassing this 2,000-bp region increased in differentiating C2 myoblasts and in C2 cells transfected with myogenin and/or MyoD. Knockdown of Krp1 via short hairpin RNA resulted in increased C2 cell number and proliferation rate as assessed by bromodeoxyuridine incorporation, whereas overexpression of Krp1-myc had the opposite effect; apoptosis was unchanged. No effects of changed Krp1 protein levels on cell migration were observed, either by scratch wound assay or live cell imaging. Paradoxically, both knockdown and overexpression of Krp1 inhibited myoblast differentiation assessed by expression of myogenin, MEF2C, MHC, and cell fusion.

The actin-bundling protein fascin stabilizes actin in invadopodia and potentiates protrusive invasion.

Fascin is an actin-bundling protein involved in filopodia assembly and cancer invasion and metastasis of multiple epithelial cancer types. Fascin forms stable actin bundles with slow dissociation kinetics in vitro and is regulated by phosphorylation of serine 39 by protein kinase C (PKC). Cancer cells use invasive finger-like protrusions termed invadopodia to invade into and degrade extracellular matrix. Invadopodia have highly dynamic actin that is assembled by both Arp2/3 complex and formins; they also contain components of membrane trafficking machinery such as dynamin and cortactin and have been compared with focal adhesions and podosomes. We show that fascin is an integral component of invadopodia and that it is important for the stability of actin in invadopodia. The phosphorylation state of fascin at S39, a PKC site, contributes to its regulation at invadopodia. We further implicate fascin in invasive migration into collagen I-Matrigel gels and particularly in cell types that use an elongated mesenchymal type of motility in 3D. We provide a potential molecular mechanism for how fascin increases the invasiveness of cancer cells, and we compare invadopodia with invasive filopod-like structures in 3D.

Novel beta-propeller of the BTB-Kelch protein Krp1 provides a binding site for Lasp-1 that is necessary for pseudopodial extension.

Kelch-related protein 1 (Krp1) is up-regulated in oncogene-transformed fibroblasts. The Kelch repeats interact directly with the actin-binding protein Lasp-1 in membrane ruffles at the tips of pseudopodia, where both proteins are necessary for pseudopodial elongation. Herein, we investigate the molecular basis for this interaction. Probing an array of overlapping decapeptides of Rattus norvegicus (Rat) Krp1 with recombinant Lasp-1 revealed two binding sites; one ((317)YDPMENECYLT(327)) precedes the first of five Kelch repeats, and the other ((563)TEVNDIWKYEDD(574)) is in the last of the five Kelch repeats. Mutational analysis established that both binding sites are necessary for Krp1-Lasp-1 interaction in vitro and function in vivo. The crystal structure of the C-terminal domain of rat Krp1 (amino acids 289-606) reveals that both binding sites are brought into close proximity by the formation of a novel six-bladed beta-propeller, where the first blade is not formed by a Kelch repeat.

Rab25 associates with alpha5beta1 integrin to promote invasive migration in 3D microenvironments.

Here, we report a direct interaction between the beta1 integrin cytoplasmic tail and Rab25, a GTPase that has been linked to tumor aggressiveness and metastasis. Rab25 promotes a mode of migration on 3D matrices that is characterized by the extension of long pseudopodia, and the association of the GTPase with alpha5beta1 promotes localization of vesicles that deliver integrin to the plasma membrane at pseudopodial tips as well as the retention of a pool of cycling alpha5beta1 at the cell front. Furthermore, Rab25-driven tumor-cell invasion into a 3D extracellular matrix environment is strongly dependent on ligation of fibronectin by alpha5beta1 integrin and the capacity of Rab25 to interact with beta1 integrin. These data indicate that Rab25 contributes to tumor progression by directing the localization of integrin-recycling vesicles and thereby enhancing the ability of tumor cells to invade the extracellular matrix.

AP-1 differentially expressed proteins Krp1 and fibronectin cooperatively enhance Rho-ROCK-independent mesenchymal invasion by altering the function, localization, and activity of nondifferentially expressed proteins.

The transcription factor AP-1, which is composed of Fos and Jun family proteins, plays an essential role in tumor cell invasion by altering gene expression. We report here that Krp1, the AP-1 up-regulated protein that has a role in pseudopodial elongation in v-Fos-transformed rat fibroblast cells, forms a novel interaction with the nondifferentially expressed actin binding protein Lasp-1. Krp1 and Lasp-1 colocalize with actin at the tips of pseudopodia, and this localization is maintained by continued AP-1 mediated down-regulation of fibronectin that in turn suppresses integrin and Rho-ROCK signaling and allows pseudopodial protrusion and mesenchyme-like invasion. Mutation analysis of Lasp-1 demonstrates that its SH3 domain is necessary for pseudopodial extension and invasion. The results support the concept of an AP-1-regulated multigenic invasion program in which proteins encoded by differentially expressed genes direct the function, localization, and activity of proteins that are not differentially expressed to enhance the invasiveness of cells.

Invasion is a genetic program regulated by transcription factors.

The invasive and metastatic behaviour of tumours impacts crucially on the clinical management of cancer. Accordingly, it is important to understand the regulation of tumour cell invasiveness. Genetic analysis of worms, Drosophila and mice has provided evidence that invasion is a genetic pathway regulated by transcription factors that are often implicated in tumour cell invasion. Recent evidence has revealed much concerning the role of one particular transcription factor, AP1, which is involved in the regulation of a multigenic invasion program in which upregulated and downregulated genes function as invasion effectors and suppressors, respectively. Differentially expressed genes cooperatively enhance pseudopod elongation during the mesenchymal mode of invasion by altering the function, localisation and activity of non-differentially expressed proteins.