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Background and Aims: Ulcerative colitis [UC] is associated with excessive neutrophil infiltration and collateral tissue damage, but the link is not yet completely understood. Since c-MET receptor tyrosine kinase [MET] is required for neutrophil chemoattraction and cytotoxicity in response to its ligand hepatocyte growth factor [HGF], we aimed to identify the function of HGF-MET signalling in neutrophils in UC patients and in mice during intestinal inflammation., Methods: Serum and colonic biopsies from healthy controls and UC patients with active [Mayo endoscopic subscore 2-3] and inactive [Mayo endoscopic subscore 0-1] disease were collected to assess the level of serum and colonic HGF. Disease progression and immune cell infiltration were assessed during dextran sodium sulphate [DSS] colitis in wild-type and MRP8-Cre MET-LoxP mice., Results: Increased mucosal HGF expression was detected in patients with active UC, and in mice during the inflammatory phase of DSS colitis. Similarly, serum HGF was significantly increased in active UC patients and positively correlated with C-reactive protein and blood neutrophil counts. Flow cytometric analysis also demonstrated an upregulation of colonic MET+ neutrophils during DSS colitis. Genetic ablation of MET in neutrophils reduced the severity of DSS-induced colitis. Concomitantly, there was a decreased number of TH17 cells, which could be due to a decreased production of IL-1β by MET-deficient neutrophils., Conclusions: These data highlight the central role of neutrophilic HGF-MET signalling in exacerbating damage during intestinal inflammation. Hence, selective blockade of this pathway in neutrophils could be considered as a novel therapeutic approach in UC., (© The Author(s) 2020. Published by Oxford University Press on behalf of European Crohn’s and Colitis Organisation. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Vascular endothelial growth factor (VEGF) is a major driver of blood vessel formation. However, the signal transduction pathways culminating in the biological consequences of VEGF signaling are only partially understood. Here, we show that the Hippo pathway effectors YAP and TAZ work as crucial signal transducers to mediate VEGF-VEGFR2 signaling during angiogenesis. We demonstrate that YAP/TAZ are essential for vascular development as endothelium-specific deletion of YAP/TAZ leads to impaired vascularization and embryonic lethality. Mechanistically, we show that VEGF activates YAP/TAZ via its effects on actin cytoskeleton and that activated YAP/TAZ induce a transcriptional program to further control cytoskeleton dynamics and thus establish a feedforward loop that ensures a proper angiogenic response. Lack of YAP/TAZ also results in altered cellular distribution of VEGFR2 due to trafficking defects from the Golgi apparatus to the plasma membrane. Altogether, our study identifies YAP/TAZ as central mediators of VEGF signaling and therefore as important regulators of angiogenesis., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Recruitment of tumor-associated macrophages (TAMs) into avascular areas sustains tumor progression; however, the underlying guidance mechanisms are unknown. Here, we report that hypoxia-induced Semaphorin 3A (Sema3A) acts as an attractant for TAMs by triggering vascular endothelial growth factor receptor 1 phosphorylation through the associated holoreceptor, composed of Neuropilin-1 (Nrp1) and PlexinA1/PlexinA4. Importantly, whereas Nrp1 levels are downregulated in the hypoxic environment, Sema3A continues to regulate TAMs in an Nrp1-independent manner by eliciting PlexinA1/PlexinA4-mediated stop signals, which retain them inside the hypoxic niche. Consistently, gene deletion of Nrp1 in macrophages favors TAMs' entrapment in normoxic tumor regions, which abates their pro-angiogenic and immunosuppressive functions, hence inhibiting tumor growth and metastasis. This study shows that TAMs' heterogeneity depends on their localization, which is tightly controlled by Sema3A/Nrp1 signaling., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Hypoxia and HIFs (HIF-1α and HIF-2α) modulate innate immune responses in the setting of systemic inflammatory responses and sepsis. The HIF prolyl hydroxylase enzymes PHD1, PHD2 and PHD3 regulate the mammalian adaptive response to hypoxia; however, their significance in the innate immune response has not been elucidated. We demonstrate in this study that deficiency of PHD3 (PHD3(-/-)) specifically shortens the survival of mice subjected to various models of abdominal sepsis because of an overwhelming innate immune response, leading to premature organ dysfunction. By contrast, this phenotype was absent in mice deficient for PHD1 (PHD1(-/-)) or PHD2 (PHD2(+/-)). In vivo, plasma levels of proinflammatory cytokines were enhanced, and recruitment of macrophages to internal organs was increased in septic PHD3-deficient mice. Reciprocal bone marrow transplantation in sublethally irradiated mice revealed that enhanced susceptibility of PHD3-deficient mice to sepsis-related lethality was specifically caused by loss of PHD3 in myeloid cells. Several in vitro assays revealed enhanced cytokine production, migration, phagocytic capacity, and proinflammatory activation of PHD3-deficient macrophages. Increased proinflammatory activity of PHD3-deficient macrophages occurred concomitantly with enhanced HIF-1α protein stabilization and increased NF-κB activity, and interference with the expression of HIF-1α or the canonical NF-κB pathway blunted their proinflammatory phenotype. It is concluded that impairment of PHD3 enzyme function aggravates the clinical course of abdominal sepsis via HIF-1α- and NF-κB-mediated enhancement of the innate immune response.

Objective: To study whether Notch signaling, which regulates cell fate decisions and vessel morphogenesis, controls lymphatic development., Methods and Results: In zebrafish embryos, sprouts from the axial vein have lymphangiogenic potential because they give rise to the first lymphatics. Knockdown of delta-like-4 (Dll4) or its receptors Notch-1b or Notch-6 in zebrafish impaired lymphangiogenesis. Dll4/Notch silencing reduced the number of sprouts producing the string of parchordal lymphangioblasts; instead, sprouts connecting to the intersomitic vessels were formed. At a later phase, Notch silencing impaired navigation of lymphatic intersomitic vessels along their arterial templates., Conclusions: These studies imply critical roles for Notch signaling in the formation and wiring of the lymphatic network.

Semaphorin 3E (Sema3E) is a secreted molecule implicated in axonal path finding and inhibition of developmental and postischemic angiogenesis. Sema3E is also highly expressed in metastatic cancer cells, but its mechanistic role in tumor progression was not understood. Here we show that expression of Sema3E and its receptor Plexin D1 correlates with the metastatic progression of human tumors. Consistent with the clinical data, knocking down endogenous expression of either Sema3E or Plexin D1 in human metastatic carcinoma cells hampered their metastatic potential when injected into mice, while tumor growth was not markedly affected. Conversely, overexpression of exogenous Sema3E in cancer cells increased their invasiveness, transendothelial migration, and metastatic spreading, although it inhibited tumor vessel formation, resulting in reduced tumor growth in mice. The proinvasive and metastatic activity of Sema3E in tumor cells was dependent on transactivation of the Plexin D1-associated ErbB2/Neu oncogenic kinase. In sum, Sema3E-Plexin D1 signaling in cancer cells is crucially implicated in their metastatic behavior and may therefore be a promising target for strategies aimed at blocking tumor metastasis.

Aberrant activation of Notch receptors has been implicated in breast cancer; however, the mechanisms contributing to Notch-dependent transformation remain elusive because Notch displays dichotomous functional activities, promoting both proliferation and growth arrest. We investigated the cellular basis for the heterogeneous responses to Notch pathway activation in 3D cultures of MCF-10A mammary epithelial cells. Expression of a constitutively active Notch-1 intracellular domain (NICD) was found to induce two distinct types of 3D structures: large, hyperproliferative structures and small, growth-arrested structures with reduced cell-to-matrix adhesion. Interestingly, we found that these heterogeneous phenotypes reflect differences in Notch pathway activation levels; high Notch activity caused down-regulation of multiple matrix-adhesion genes and inhibition of proliferation, whereas low Notch activity maintained matrix adhesion and provoked a strong hyperproliferative response. Moreover, microarray analyses implicated NICD-induced p63 down-regulation in loss of matrix adhesion. In addition, a reverse-phase protein array-based analysis and subsequent loss-of-function studies identified STAT3 as a dominant downstream mediator of the NICD-induced outgrowth. These results indicate that the phenotypic responses to Notch are determined by the dose of pathway activation; and this dose affects the balance between growth-stimulative and growth-suppressive effects. This unique feature of Notch signaling provides insights into mechanisms that contribute to the dichotomous effects of Notch during development and tumorigenesis.

The topology and trafficking of receptors play a key role in their signalling capability. Indeed, receptor function is related to the microenvironment inside the cell, where specific signalling molecules are compartmentalized. The response to NGF (nerve growth factor) is strongly dependent on the trafficking of its receptor, TrkA. However, information is still scarce about the role of the cellular localization of the TrkA co-receptor, p75NTR (where NTR is neurotrophin receptor), following stimulation by NGF. It has been shown that these two receptors play a key role in epithelial tissue and in epithelial-derived tumours, where the microenvironment at the plasma membrane is defined by the presence of tight junctions. Indeed, in thyroid carcinomas, rearrangements of TrkA are frequently found, which produce TrkA mutants that are localized exclusively in the cytoplasm. We used a thyroid cellular model in which it was possible to dissect the trafficking of the two NGF receptors upon neurotrophin stimulation. In FRT (Fischer rat thyroid) cells, endogenous TrkA is localized exclusively on the basolateral surface, while transfected p75NTR is selectively distributed on the apical membrane. This cellular system enabled us to selectively stimulate either p75NTR or TrkA and to analyse the role of receptor trafficking in their signalling capability. We found that, after binding to NGF, p75NTR was co-immunoprecipitated with TrkA and was transcytosed at the basolateral membrane. We showed that the TrkA-p75NTR interaction is necessary for this relocation of p75NTR to the basolateral side. Interestingly, TrkA-specific stimulation by basolateral NGF loading also induced the TrkA-p75NTR interaction and subsequent p75NTR transcytosis at the basolateral surface. Moreover, specific stimulation of p75NTR by NGF activated TrkA and the MAPK (mitogen-activated protein kinase) pathway. Our data indicate that TrkA regulates the subcellular localization of p75NTR upon stimulation with neurotrophins, thus affecting the topology of the signal transduction molecules, driving the activation of a specific signal transduction pathway.