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Integrins are transmembrane receptors that, upon activation, bind extracellular ligands and link them to the actin filament (F-actin) cytoskeleton to mediate cell adhesion and migration. Cytoskeletal forces in migrating cells generated by polymerization- or contractility-driven “retrograde flow” of F-actin from the cell leading edge have been hypothesized to mediate integrin activation for ligand binding. This predicts that these forces should align and orient activated, ligand-bound integrins at the leading edge. Here, polarization-sensitive fluorescence microscopy of GFP-αVβ3 integrins in fibroblasts shows that integrins are coaligned in a specific orientation within focal adhesions (FAs) in a manner dependent on binding immobilized ligand and a talin-mediated linkage to the F-actin cytoskeleton. These findings, together with Rosetta modeling, suggest that integrins in FA are coaligned and may be highly tilted by cytoskeletal forces. Thus, the F-actin cytoskeleton sculpts an anisotropic molecular scaffold in FAs, and this feature may underlie the ability of migrating cells to sense directional extracellular cues.

Galectin-1 (Gal-1) is involved in several pathological activities associated with tumor progression and chemoresistance, however, the role and molecular mechanism of Gal-1 activity in hepatocellular carcinoma (HCC) epithelial–mesenchymal transition (EMT) and sorafenib resistance remain enigmatic. In the present study, forced Gal-1 expression promoted HCC progression and sorafenib resistance. Gal-1 elevated α v β 3-integrin expression, leading to AKT activation. Moreover, Gal-1 overexpression induced HCC cell EMT via PI3K/AKT cascade activation. Clinically, our data revealed that Gal-1 overexpression is correlated with poor HCC survival outcomes and sorafenib response. These data suggest that Gal-1 may be a potential therapeutic target for HCC and a biomarker for predicting response to sorafenib treatment.

Key Points Coxiella burnetii is a Gram-negative obligate intracellular bacterial pathogen that is the aetiological agent of Q fever, which manifests as both acute and chronic infections. The infection is a zoonosis that is most often transmitted by aerosolized dry, contaminated soil or animal products. Genetic differences between C. burnetii isolates from acute and chronic infections have led to the hypothesis that pathotype-specific virulence exists. After inhalation by a host, C. burnetii invades and replicates within alveolar macrophages without alerting the innate immune system and has therefore been described as a stealth pathogen. Inside macrophages, the bacterium replicates within a compartment that is very similar to a phagolysosome, termed the Coxiella -containing vacuole (CCV). C. burnetii has a type IV secretion system that resembles the Dot/Icm (defect in organelle trafficking/intracellular multiplication) system of Legionella pneumophila and is necessary for pathogenesis. C. burnetii encodes homologues for 24 of the 27 L. pneumophila Dot/Icm proteins, and four C. burnetii Dot/Icm genes can actually complement homologous mutations in the L. pneumophila system, lending strength to the conjecture that these systems are structurally and functionally similar. Establishment and maintenance of the CCV is dependent on protein production by C. burnetii . Although the identity of the virulence factors involved are unknown, new evidence suggests that most are effectors secreted by the type IV secretion system. The recent development of axenic media to grow C. burnetii has enabled the development of genetic tools to identify virulence factors. These developments have started a new era of research for C. burnetii , and Koch's postulates can now be tested for the first time. The obligate intracellular bacterium Coxiella burnetii causes both acute and chronic zoonotic infections. Here, Samuel and colleagues discuss the recent technological advances that have facilitated a deeper understanding of the molecular mechanisms of C. burnetii pathogenesis, including host cell invasion and modulation by virulence factors exported through the type IV Dot/Icm secretion system. The agent of Q fever, Coxiella burnetii , is an obligate intracellular bacterium that causes acute and chronic infections. The study of C. burnetii pathogenesis has benefited from two recent fundamental advances: improved genetic tools and the ability to grow the bacterium in extracellular media. In this Review, we describe how these recent advances have improved our understanding of C. burnetii invasion and host cell modulation, including the formation of replication-permissive Coxiella -containing vacuoles. Furthermore, we describe the Dot/Icm (defect in organelle trafficking/intracellular multiplication) system, which is used by C. burnetii to secrete a range of effector proteins into the host cell, and we discuss the role of these effectors in remodelling the host cell.

IGF1 plays a critical role in cell proliferation and survival. Previous studies show that IGF1 binds to integrin αvβ3 and induces αvβ3-IGF1-IGF1R ternary complex formation. However, how IGF1 binding to αvβ3 leads to IGF1R activation is unclear. Previous studies showed that Gα13, a guanine nucleotide-binding protein of the G12 class of Gα proteins, binds to the integrin β3 tail through the EEE motif upon fibrinogen binding to integrin αIIbβ3 and induces RhoA activation. We discovered that the EEE/AAA mutation of the β3 tail inhibited IGF1-induced cell survival, suggesting that Gα13 binding to the β3 tail is required for IGF1 signaling. Since RhoA activation may not be directly involved in IGF1R activation, we studied if Gα13 binds to molecules other than RhoA. Since Gα13 binds to several cytoplasmic tyrosine kinases, we studied if Gα13 binds to the IGF1R kinase by a docking simulation. The simulation predicted that Gα13 binds to the IGF1R kinase through a new binding site. Mutating the predicted Gα13 binding site in the IGF1R kinase (residues 1020-1022) or the predicted IGF1R kinase binding site in Gα13 (residues 260-279) inhibited Gα13 binding to the IGF1R kinase, which is consistent with the docking model. Notably, the Gα13(260-279A) mutant inhibited IGF1-induced cell survival. We propose that IGF1 binding to αvβ3 induces Gα13 binding to the β3 tail and subsequent Gα13 binding to the IGF1R kinase, leading to IGF1R activation. Interestingly, Gα13(260-279A) mutation inhibited cell survival due to a constitutively active Gα13(Q226L) mutant. We propose that Gα13(Q226L) induces its effect by binding to the IGF1R kinase. We propose that the Gα13 binding site of the IGF1R kinase or the IGF1R binding site in Gα13 may be a novel therapeutic target.

Background We have previously shown that in pancreatic ductal adenocarcinoma (PDA) cells, the glycolytic enzyme alpha-enolase (ENO1) also acts as a plasminogen receptor and promotes invasion and metastasis formation. Moreover, ENO1 silencing in PDA cells induces oxidative stress, senescence and profoundly modifies PDA cell metabolism. Although anti-ENO1 antibody inhibits PDA cell migration and invasion, little is known about the role of ENO1 in regulating cell-cell and cell-matrix contacts. We therefore investigated the effect of ENO1 silencing on the modulation of cell morphology, adhesion to matrix substrates, cell invasiveness, and metastatic ability. Methods The membrane and cytoskeleton modifications that occurred in ENO1-silenced (shENO1) PDA cells were investigated by a combination of confocal microscopy and atomic force microscopy (AFM). The effect of ENO1 silencing was then evaluated by phenotypic and functional experiments to identify the role of ENO1 in adhesion, migration, and invasion, as well as in senescence and apoptosis. The experimental results were then validated in a mouse model. Results We observed a significant increase in the roughness of the cell membrane due to ENO1 silencing, a feature associated with an impaired ability to migrate and invade, along with a significant downregulation of proteins involved in cell-cell and cell-matrix adhesion, including alpha v/beta 3 integrin in shENO1 PDA cells. These changes impaired the ability of shENO1 cells to adhere to Collagen I and IV and Fibronectin and caused an increase in RGD-independent adhesion to vitronectin (VN) via urokinase plasminogen activator receptor (uPAR). Binding of uPAR to VN triggers integrin-mediated signals, which result in ERK1-2 and RAC activation, accumulation of ROS, and senescence. In shENO1 cancer cells, the use of an anti-uPAR antibody caused significant reduction of ROS production and senescence. Overall, a decrease of in vitro and in vivo cell migration and invasion of shENO1 PDA cells was observed. Conclusion These data demonstrate that ENO1 promotes PDA survival, migration, and metastasis through cooperation with integrins and uPAR.

Ovarian carcinoma is the fifth common cause of cancer death in women, despite advanced therapeutic approaches. αvβ3 integrin, a plasma membrane receptor, binds thyroid hormones (L-thyroxine, T4; 3,5,3’-triiodo-L-thyronine, T3) and is overexpressed in ovarian cancer. We have demonstrated selective binding of fluorescently labeled hormones to αvβ3-positive ovarian cancer cells but not to integrin-negative cells. Physiologically relevant T3 (1 n M ) and T4 (100 n M ) concentrations in OVCAR-3 (high αvβ3) and A2780 (low αvβ3) cells promoted αv and β3 transcription in association with basal integrin levels. This transcription was effectively blocked by RGD (Arg–Gly–Asp) peptide and neutralizing αvβ3 antibodies, excluding T3-induced β3 messenger RNA, suggesting subspecialization of T3 and T4 binding to the integrin receptor pocket. We have provided support for extracellular regulated kinase (ERK)-mediated transcriptional regulation of the αv monomer by T3 and of β3 monomer by both hormones and documented a rapid (30–120 min) and dose-dependent (0.1–1000 n M ) ERK activation. OVCAR-3 cells and αvβ3-deficient HEK293 cells treated with αvβ3 blockers confirmed the requirement for an intact thyroid hormone-integrin interaction in ERK activation. In addition, novel data indicated that T4, but not T3, controls integrin's outside-in signaling by phosphorylating tyrosine 759 in the β3 subunit. Both hormones induced cell proliferation (cell counts), survival (Annexin-PI), viability (WST-1) and significantly reduced the expression of genes that inhibit cell cycle ( p21, p16 ), promote mitochondrial apoptosis ( Nix , PUMA ) and tumor suppression ( GDF-15 , IGFBP-6), particularly in cells with high integrin expression. At last, we have confirmed that hypothyroid environment attenuated ovarian cancer growth using a novel experimental platform that exploited paired euthyroid and severe hypothyroid serum samples from human subjects. To conclude, our data define a critical role for thyroid hormones as potent αvβ3-ligands, driving ovarian cancer cell proliferation and suggest that disruption of this axis may present a novel treatment strategy in this aggressive disease.

In zebrafish, brain lymphatic endothelial cells (BLECs) are essential for meningeal angiogenesis and cerebrovascular regeneration. Although epidermal growth factor-like domain 7 (Egfl7) has been reported to act as a pro-angiogenic factor, its roles in lymphangiogenesis remain unclear. Here, we show that Egfl7 is expressed in both blood and lymphatic endothelial cells. We generate an egfl7 cq180 mutant with a 13-bp-deletion in exon 3 leading to reduced expression of Egfl7. The egfl7 cq180 mutant zebrafish exhibit defective formation of BLEC bilateral loop-like structures, although trunk and facial lymphatic development remains unaffected. Moreover, while the egfl7 cq180 mutant displays normal BLEC lineage specification, the migration and proliferation of these cells are impaired. Additionally, we identify integrin αvβ3 as the receptor for Egfl7. αvβ3 is expressed in the CVP and sprouting BLECs, and blocking this integrin inhibits the formation of BLEC bilateral loop-like structures. Thus, this study identifies a role for Egfl7 in BLEC development that is mediated through the integrin αvβ3. Although epidermal growth factor-like domain 7 (Egfl7) is known to play a pro-angiogenic role in zebrafish, its contribution to brain lymphangiogenesis remains less clear. Here, the authors demonstrate that Egfl7 is dispensable for brain lymphatic endothelial cell specification, but not their migration and proliferation.

EOC cells are shed from the primary tumor and survive the transit in ascites to colonize at metastatic sites. In EOC cell transfectants, a constitutively active αvß3 with unclasped TMD conferred anoikis resistance via prosurvival signaling implicating the activation of the EGF‐R, FAK, src, PKB/Akt, and Erk, compared with rapid onset of apoptosis by a signaling‐incompetent αvß3 with associated TMD. Epithelial ovarian cancer involves the shedding of single tumor cells or spheroids from the primary tumor into ascites, followed by their survival, and transit to the sites of metastatic colonization within the peritoneal cavity. During their flotation, anchorage‐dependent epithelial‐type tumor cells gain anoikis resistance, implicating integrins, including αvß3. In this study, we explored anoikis escape, cisplatin resistance, and prosurvival signaling as a function of the αvß3 transmembrane conformational activation state in cells suspended in ascites. A high‐affinity and constitutively signaling‐competent αvß3 variant, which harbored unclasped transmembrane domains, was found to confer delayed anoikis onset, enhanced cisplatin resistance, and reduced cell proliferation in ascites or 3D‐hydrogels, involving p27kip upregulation. Moreover, it promoted EGF‐R expression and activation, prosurvival signaling, implicating FAK, src, and PKB/Akt. This led to the induction of the anti‐apoptotic factors Bcl‐2 and survivin suppressing caspase activation, compared to a signaling‐incapable αvß3 variant displaying firmly associated transmembrane domains. Dissecting the mechanistic players for αvß3‐dependent survival and peritoneal metastasis of ascitic ovarian cancer spheroids is of paramount importance to target their anchorage independence by reversing anoikis resistance and blocking αvß3‐triggered prosurvival signaling.

Malaria-causing Plasmodium sporozoites are deposited in the dermis by the bite of an infected mosquito and move by gliding motility to the liver where they invade and develop within host hepatocytes. Although extracellular interactions between Plasmodium sporozoite ligands and host receptors provide important guidance cues for productive infection and are good vaccine targets, these interactions remain largely uncharacterized. Thrombospondin-related anonymous protein (TRAP) is a parasite cell surface ligand that is essential for both gliding motility and invasion because it couples the extracellular binding of host receptors to the parasite cytoplasmic actinomyosin motor; however, the molecular nature of the host TRAP receptors is poorly defined. Here, we use a systematic extracellular protein interaction screening approach to identify the integrin αvβ3 as a directly interacting host receptor for Plasmodium falciparum TRAP. Biochemical characterization of the interaction suggests a two-site binding model, requiring contributions from both the von Willebrand factor A domain and the RGD motif of TRAP for integrin binding. We show that TRAP binding to cells is promoted in the presence of integrin-activating proadhesive Mn2+ ions, and that cells genetically targeted so that they lack cell surface expression of the integrin αv-subunit are no longer able to bind TRAP. P. falciparum sporozoites moved with greater speed in the dermis of Itgb3-deficient mice, suggesting that the interaction has a role in sporozoite migration. The identification of the integrin αvβ3 as the host receptor for TRAP provides an important demonstration of a sporozoite surface ligand that directly interacts with host receptors.

Tumor metastasis is the leading cause of cancer-associated mortality. Unfortunately, the underlying mechanism of metastasis is poorly understood. Expression of legumain (LGMN), an endo-lysosomal cysteine protease, positively correlates with breast cancer metastatic progression and poor prognosis. Here, we report that LGMN is secreted in the zymogen form by motile breast cancer cells. Through binding to cell surface integrin αvβ3 via an RGD motif, the autocrine pro-LGMN activates FAK-Src-RhoA signaling in cancer cells and promotes cancer cell migration and invasion independent of LGMN protease activity. Either silencing LGMN expression or mutationally abolishing pro-LGMN‒αvβ3 interaction significantly inhibits cancer cell migration and invasion in vitro and breast cancer metastasis in vivo. Finally, we developed a monoclonal antibody against LGMN RGD motif, which blocks pro-LGMN‒αvβ3 binding, and effectively suppresses cancer cell migration and invasion in vitro and breast cancer metastasis in vivo. Thus, disruption of pro-LGMN‒integrin αvβ3 interaction may be a potentially promising strategy for treating breast cancer metastasis.