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.

Journal of Cell Science 1724 including cell-adhesion molecule L1 (Castellani and Rougon, 2002) and the receptor tyrosine kinases (RTKs) VEGFR2 (Toyofuku et al., 2004), erythroblastic leukemia viral oncogene homolog 2 (ErbB2) (Swiercz et al., 2004), off-track kinase (OTK) (Winberg et al., 2001) and Met (also known as HGFR) (Giordano et al., 2002). In the immune system, CD72 and Tim2 (T-cell immunoglobulin and mucin domain-containing protein 2) were found to interact functionally (although with low affinity) with the transmembrane semaphorins SEMA4D and SEMA4A, respectively (Kumanogoh et al., 2002;Kumanogoh et al., 2000). Recently, other ligands for NPs have also been described, including fibroblast growth factor 2 (FGF2) (West et al., 2005), hepatocyte growth factor (HGF) (Sulpice et al., 2008) and galectin-1 (Gal-1) (Hsieh et al., 2008). In addition, NPs were recently observed to form complexes with additional cell-surface receptors, including Met (Matsushita et al., 2007), β1 integrin (Fukasawa et al., 2007) and transforming growth factor-β1 (TGF-β1) (Glinka and Prud'homme, 2008) (for reviews see Neufeld and Kessler, 2008;Pellet-Many et al., 2008).In addition to their function in a range of basic cellular processes, recent studies have shown that semaphorin-mediated signals might also play important regulatory functions in cancer . On one side, tumor progression and metastatic dissemination depend on intrinsic properties of cancer cells, such as survival, self-renewal and the ability to migrate and overcome tissue barriers (invasiveness). On the other side, the tumor stroma -which includes endothelial cells, fibroblasts and cells of the immune system -is engaged in active molecular crosstalk with cancer cells. For example, blood-and lymph-vessel angiogenesis, together with inflammatory and immunosuppressive responses, further promotes cancer-cell survival, migration and invasion, as well as initiation of the metastatic cascade. In this Commentary, we review the current knowledge on the emerging role of semaphorin signals in controlling these 'two sides of a coin' -that is, the tumor-cell intrinsic alterations, and the crosstalk between cancer cells and other cells of the tumor microenvironment. In addition, the implications of semaphorin signaling in tumor progression will be discussed. . Of the vertebrate semaphorins, those in classes 4, 5 and 6 are transmembrane proteins, whereas those in class 7 are membrane-anchored via glycophosphatidylinositol (GPI). Class-3 secreted semaphorins have C-terminal basic-charged sequences, which are required for binding to neuropilins. Several class-3 semaphorins and SEMA4D have been shown to undergo regulatory cleavage by furins or metalloproteases. Class-5 semaphorins are distinguished by thrombospondin repeats. Several semaphorins also contain immunoglobulin-like domains. (B) Neuropilins are transmembrane receptors that are characterized by two complement-like (CUB) domains (also called the a1 and a2 domains), two FV/FVIII coagulation factor-like domains (also called the...

MicroRNAs (miRNA) are a recently identified class of noncoding, endogenous, small RNAs that regulate gene expression, mainly at the translational level. These molecules play critical roles in several biological processes, such as cell proliferation and differentiation, development, and aging. It is also known that miRNAs play a role in human cancers where they can act either as oncogenes, down-regulating tumor suppressor genes, or as onco-suppressors, targeting molecules critically involved in promotion of tumor growth. One of such molecules is the tyrosine kinase receptor for hepatocyte growth factor, encoded by the MET oncogene. The MET receptor promotes a complex biological program named ''invasive growth'' that results from stimulation of cell motility, invasion, and protection from apoptosis. This oncogene is deregulated in many human tumors, where its most frequent alteration is overexpression. In this work, we have identified three miRNAs (miR-34b, miR-34c, and miR199a*) that negatively regulate MET expression. Inhibition of these endogenous miRNAs, by use of antagomiRs, resulted in increased expression of MET protein, whereas their exogenous expression in cancer cells blocked MET-induced signal transduction and the execution of the invasive growth program, both in cells expressing normal levels of MET and in cancer cells overexpressing a constitutively active MET. Moreover, we show that these same miRNAs play a role in regulating the MET-induced migratory ability of melanomaderived primary cells. In conclusion, we have identified miRNAs that behave as oncosuppressors by negatively targeting MET and might thus provide an additional option to inhibit this oncogene in tumors displaying its deregulation.

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...