Tumor Cell Invadopodia: Invasive Protrusions that Orchestrate Metastasis

hMENA is a key regulator in endothelin-1/β-arrestin1-induced invadopodial function and metastatic process

Discovering new targets and novel determinants of metastatic spread is an unmet need in ovarian cancer, which is plagued by high rates of recurrence. Endothelin-1 receptors (ET-1R), belonging to the G-protein–coupled receptor family, represent important targets critically involved in malignant progression. Here we identify a mechanistic link between ET-1R and the actin regulatory protein hMENA/hMENAΔv6 through the specific interaction with the multifunctional protein β-arrestin1 (β-arr1), which initiates signaling cascades as part of the molecular complex crucial for invadopodial maturation and malignant dissemination. Targeting ET-1R by using macitentan, a Food and Drug Administration-approved antipulmonary arterial hypertension drug, can impair the β-arr1–mediated signaling network controlling ovarian cancer progression and therefore represents a therapeutic option for ovarian cancer patients.

Aberrant activation of endothelin-1 receptors (ET-1R) elicits pleiotropic effects relevant for tumor progression. The network activated by this receptor might be finely, spatially, and temporarily orchestrated by β-arrestin1 (β-arr1)–driven interactome. Here, we identify hMENA, a member of the actin-regulatory protein ENA/VASP family, as an interacting partner of β-arr1, necessary for invadopodial function downstream of ET-1R in serous ovarian cancer (SOC) progression. ET-1R activation by ET-1 up-regulates expression of hMENA/hMENAΔv6 isoforms through β-arr1, restricted to mesenchymal-like invasive SOC cells. The interaction of β-arr1 with hMENA/hMENAΔv6 triggered by ET-1 leads to activation of RhoC and cortactin, recruitment of membrane type 1-matrix metalloprotease, and invadopodia maturation, thereby enhancing cell plasticity, transendothelial migration, and the resulting spread of invasive cells. The treatment with the ET-1R antagonist macitentan impairs the interaction of β-arr1 with hMENA and inhibits invadopodial maturation and tumor dissemination in SOC orthotopic xenografts. Finally, high ET_AR/hMENA/β-arr1 gene expression signature is associated with a poor prognosis in SOC patients. These data define a pivotal function of hMENA/hMENAΔv6 for ET-1/β-arr1–induced invadopodial activity and ovarian cancer progression.

Identification of a membrane-less compartment regulating invadosome function and motility

Depletion of liprin-α1, ERC1 or LL5 scaffolds inhibits extracellular matrix degradation by invasive cells. These proteins co-accumulate near invadosomes in NIH-Src cells, identifying a novel invadosome–associated compartment distinct from the core and adhesion ring of invadosomes. Depletion of either protein perturbs the organization of invadosomes without influencing the recruitment of MT1-MMP metalloprotease. Liprin-α1 is not required for de novo formation of invadosomes after their disassembly by microtubules and Src inhibitors, while its depletion inhibits invadosome motility, thus affecting matrix degradation. Fluorescence recovery after photobleaching shows that the invadosome–associated compartment is dynamic, while correlative light immunoelectron microscopy identifies bona fide membrane–free invadosome–associated regions enriched in liprin-α1, which is virtually excluded from the invadosome core. The results indicate that liprin-α1, LL5 and ERC1 define a novel dynamic membrane-less compartment that regulates matrix degradation by affecting invadosome motility.

Chemotherapy-induced metastasis: mechanisms and translational opportunities

Tumors often overcome the cytotoxic effects of chemotherapy through either acquired or environment-mediated drug resistance. In addition, signals from the microenvironment obfuscate the beneficial effects of chemotherapy and may facilitate progression and metastatic dissemination. Seminal mediators in chemotherapy-induced metastasis appear to be a wide range of hematopoietic, mesenchymal and immune progenitor cells, originating from the bone marrow. The actual purpose of these cells is to orchestrate the repair response to the cytotoxic damage of chemotherapy. However, these repair responses are exploited by tumor cells at every step of the metastatic cascade, ranging from tumor cell invasion, intravasation and hematogenous dissemination to extravasation and effective colonization at the metastatic site. A better understanding of the mechanistic underpinnings of chemotherapy-induced metastasis will allow us to better predict which patients are more likely to exhibit pro-metastatic responses to chemotherapy and will help develop new therapeutic strategies to neutralize chemotherapy-driven prometastatic changes.

Phosphoinositide 5-phosphatase activities control cell motility in glioblastoma: Two phosphoinositides PI(4,5)P2 and PI(3,4)P2 are involved

Inositol polyphosphate 5-phosphatases or phosphoinositide 5-phosphatases (PI 5-phosphatases) are enzymes that can act on soluble inositol phosphates and/or phosphoinositides (PIs). Several PI 5-phosphatases have been linked to human genetic diseases, in particular the Lowe protein or OCRL which is mutated in the Lowe syndrome. There are 10 different members of this family and 9 of them can use PIs as substrate. One of these substrates, PI(3,4,5)P3 binds to specific PH domains and recruits as effectors specific proteins to signaling complexes. Protein kinase B is one target protein and activation of the kinase will have a major impact on cell proliferation, survival and cell metabolism. Two other PIs, PI(4,5)P2 and PI(3,4)P2, are produced or used as substrates of PI 5-phosphatases (OCRL, INPP5B, SHIP1/2, SYNJ1/2, INPP5K, INPP5J, INPP5E). The inositol lipids may influence many aspects of cytoskeletal organization, lamellipodia formation and F-actin polymerization. PI 5-phosphatases have been reported to control cell migration, adhesion, polarity and cell invasion particularly in cancer cells. In glioblastoma, reducing SHIP2 expression can positively or negatively affect the speed of cell migration depending on the glioblastoma cell type. The two PI 5-phosphatases SHIP2 or SKIP could be localized at the plasma membrane and can reduce either PI(3,4,5)P3 or PI(4,5)P2 abundance. In the glioblastoma 1321 N1 cells, SHIP2 controls plasma membrane PI(4,5)P2 thereby participating in the control of cell migration.

Localized Lysosome Exocytosis Helps Breach Tissue Barriers

Cell invasion across basement membrane barriers is important in both normal development and cancer metastasis. In this issue of Developmental Cell, Naegeli et al. (2017) identify a mechanism for breaching basement membranes. Localized lysosome exocytosis fuels generation of large, invasive cellular protrusions that expand tiny basement membrane openings.

Rac3 regulates breast cancer invasion and metastasis by controlling adhesion and matrix degradation

The initial step of metastasis is the local invasion of tumor cells into the surrounding tissue. Invadopodia are actin-based protrusions that mediate the matrix degradation necessary for invasion and metastasis of tumor cells. We demonstrate that Rac3 GTPase is critical for integrating the adhesion of invadopodia to the extracellular matrix (ECM) with their ability to degrade the ECM in breast tumor cells. We identify two pathways at invadopodia important for integrin activation and delivery of matrix metalloproteinases: through the upstream recruiter CIB1 as well as the downstream effector GIT1. Rac3 activity, at and surrounding invadopodia, is controlled by Vav2 and βPIX. These guanine nucleotide exchange factors regulate the spatiotemporal dynamics of Rac3 activity, impacting GIT1 localization. Moreover, the GTPase-activating function of GIT1 toward the vesicular trafficking regulator Arf6 GTPase is required for matrix degradation. Importantly, Rac3 regulates the ability of tumor cells to metastasize in vivo. The Rac3-dependent mechanisms we show in this study are critical for balancing proteolytic activity and adhesive activity to achieve a maximally invasive phenotype.

Emerging roles for LPP in metastatic cancer progression

LIM domain containing proteins are important regulators of diverse cellular processes, and play pivotal roles in regulating the actin cytoskeleton. Lipoma Preferred Partner (LPP) is a member of the zyxin family of LIM proteins that has long been characterized as a promoter of mesenchymal/fibroblast cell migration. More recently, LPP has emerged as a critical inducer of tumor cell migration, invasion and metastasis. LPP is thought to contribute to these malignant phenotypes by virtue of its ability to shuttle into the nucleus, localize to adhesions and, most recently, to promote invadopodia formation. In this review, we will examine the mechanisms through which LPP regulates the functions of adhesions and invadopodia, and discuss potential roles of LPP in mediating cellular responses to mechanical cues within these mechanosensory structures.