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.

Mutations or amplification of the MET proto-oncogene are involved in the pathogenesis of several tumours1-4, which rely on the constitutive engagement of this pathway for their growth and survival1,5. However, MET is expressed not only by cancer cells but also by tumour-associated stromal cells although its precise role in this compartment is not well characterized6-11. Here, we show that MET is required for neutrophil chemoattraction and cytotoxicity in response to its ligand HGF. Met deletion in neutrophils enhances tumour growth and metastasis. This phenotype correlates with reduced neutrophil infiltration to both primary tumour and metastatic site. Similarly, Met is necessary for neutrophil transudation during colitis, skin rash or peritonitis. Mechanistically, Met is induced by tumour-derived TNF-α or other inflammatory stimuli in both mouse and human neutrophils. This induction is instrumental for neutrophil transmigration across an activated endothelium and iNOS production upon HGF stimulation. Consequently, HGF/MET-dependent nitric oxide release by neutrophils promotes cancer cell killing, which abates tumour growth and metastasis. Following systemic administration of a MET kinase inhibitor, we prove that the therapeutic benefit of MET targeting in cancer cells is partly countered by the pro-tumoural effect rising from MET blockade in neutrophils. Our work identifies an unprecedented role of MET in neutrophils, suggests a potential “Achilles’ heel” of MET-targeted therapies in cancer, and supports the rationale for evaluating anti-MET drugs in certain inflammatory diseases.

Expression of the mannose receptor (MRC1/CD206) identifies macrophage subtypes, such as alternatively activated macrophages (AAMs) and M2-polarized tumor-associated macrophages (TAMs), which are endowed with tissue-remodeling, proangiogenic, and protumoral activity. However, the significance of MRC1 expression for TAM's protumoral activity is unclear. Here, we describe and characterize miR-511-3p, an intronic microRNA (miRNA) encoded by both mouse and human MRC1 genes. By using sensitive miRNA reporter vectors, we demonstrate robust expression and bioactivity of miR-511-3p in MRC1(+) AAMs and TAMs. Unexpectedly, enforced expression of miR-511-3p tuned down the protumoral gene signature of MRC1(+) TAMs and inhibited tumor growth. Our findings suggest that transcriptional activation of Mrc1 in TAMs evokes a genetic program orchestrated by miR-511-3p, which limits rather than enhances their protumoral functions. Besides uncovering a role for MRC1 as gatekeeper of TAM's protumoral genetic programs, these observations suggest that endogenous miRNAs may operate to establish thresholds for inflammatory cell activation in tumors.

A lot of effort has been done to study how cancer cells react to low-oxygen tension, a condition known as hypoxia. Indeed, abnormal and dysfunctional blood vessels in the tumor are incapable to restore oxygenation, therefore perpetuating hypoxia, which, in turn, will fuel tumor progression, metastasis and resistance to antitumor therapies. Nevertheless, how stromal components including blood and lymphatic endothelial cells, pericytes and fibroblasts, as well as hematopoietic cells, respond to low-oxygen tension in comparison with their normoxic counterparts has been a matter of investigation in the last few years only and, to date, this field of research remains poorly understood. In general, opposing phenotypes can arise from the same stromal component when embedded in different tumor microenvironments, and, vice versa, different stromal components can have opposite reaction to the same tumor microenvironment. In this article, we will discuss the emerging link between tumor stroma and hypoxia, and how this complexity is translated at the molecular level.

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.

Plexins encode receptors for semaphorins, molecular signals guiding cell migration, and axon pathfinding. The mechanisms mediating plexin function are poorly understood. Plexin activation in adhering cells rapidly leads to retraction of cellular processes and cell rounding "cell collapse"). Here we show that, unexpectedly, this response does not require the activity of Rho-dependent kinase (ROCK) nor the contraction of F-actin cables. Interestingly, integrin-based focal adhesive structures are disassembled within minutes upon plexin activation; this is followed by actin depolymerization and, eventually, by cellular collapse. We also show that plexin activation hinders cell attachment to adhesive substrates, blocks the extension of lamellipodia, and thereby inhibits cell migration. We conclude that plexin signaling uncouples cell substrate-adhesion from cytoskeletal dynamics required for cell migration and axon extension.

Objective-The role of semaphorins in tumor progression is still poorly understood. In this study, we aimed at elucidating the regulatory role of semaphorin 3A (SEMA3A) in primary tumor growth and metastatic dissemination. Methods and Results-We used 3 different experimental approaches in mouse tumor models: (1) overexpression of SEMA3A in tumor cells, (2) systemic expression of SEMA3A following liver gene transfer in mice, and (3) tumor-targeted release of SEMA3A using gene modified Tie2-expressing monocytes as delivery vehicles. In each of these experimental settings, SEMA3A efficiently inhibited tumor growth by inhibiting vessel function and increasing tumor hypoxia and necrosis, without promoting metastasis. We further show that the expression of the receptor neuropilin-1 in tumor cells is required for SEMA3A-dependent inhibition of tumor cell migration in vitro and metastatic spreading in vivo. Conclusion-In sum, both systemic and tumor-targeted delivery of SEMA3A inhibits tumor angiogenesis and tumor growth in multiple mouse models; moreover, SEMA3A inhibits the metastatic spreading from primary tumors. These data support the rationale for further investigation of SEMA3A as an anticancer molecule. Key Words: angiogenesis Ⅲ molecular biology Ⅲ pathology Ⅲ receptors Ⅲ vascular biology Ⅲ metastasis Ⅲ neuropilin Ⅲ semaphorin Ⅲ tumor S emaphorins are a highly conserved family of molecules originally identified as axon guidance factors. 1,2 Notably, over the past few years, distinct semaphorins have been implicated in additional biological processes, including angiogenesis, immune regulation, and cancer. 3,4 See accompanying article on page 721Semaphorin function is mediated by a family of plasma membrane receptors, the plexins. 5 However, most secreted semaphorins (including semaphorin 3A [SEMA3A]) cannot bind to plexins directly; rather, they interact with plexinassociated coreceptors, namely neuropilin-1 (NP1) and neuropilin-2 (NP2). 3,5 Interestingly, NPs also bind vascular endothelial growth factor family members and associate in complex with vascular endothelial growth factor receptors, 6 playing a crucial role in angiogenesis beyond axon guidance. 3 In particular, SEMA3A signaling is fully dependent on the receptor NP1, whereas little is known about the requirement of specific plexins in its receptor complex.So far, SEMA3A has been reported to inhibit the growth of certain experimental tumors 7 and to regulate endothelial cell migration and apoptosis in vitro, 8,9 as well as arteriogenesis in the muscle, 10 skin vessel permeability, 11 and tumor angiogenesis in vivo. 12 However, the functional significance of SEMA3A signaling as a molecular target to control tumor progression is still poorly understood. Generally, tumor blood vessels display a chaotic architecture that leads to impaired tumor perfusion, elevated tissue hypoxia, and substantial cell death. It has been shown that antiangiogenic treatments targeting vascular endothelial growth factor signaling can disrupt tumor blood vessels and increase tum...

The secretome of cancer and stromal cells generates a microenvironment that contributes to tumour cell invasion and angiogenesis. Here we compare the secretome of human mammary normal and cancer-associated fibroblasts (CAFs). We discover that the chloride intracellular channel protein 3 (CLIC3) is an abundant component of the CAF secretome. Secreted CLIC3 promotes invasive behaviour of endothelial cells to drive angiogenesis and increases invasiveness of cancer cells both in vivo and in 3D cell culture models, and this requires active transglutaminase-2 (TGM2). CLIC3 acts as a glutathione-dependent oxidoreductase that reduces TGM2 and regulates TGM2 binding to its cofactors. Finally, CLIC3 is also secreted by cancer cells, is abundant in the stromal and tumour compartments of aggressive ovarian cancers and its levels correlate with poor clinical outcome. This work reveals a previously undescribed invasive mechanism whereby the secretion of a glutathione-dependent oxidoreductase drives angiogenesis and cancer progression by promoting TGM2-dependent invasion.