Semaphorin

Objective—To characterize the role of a vascular-expressed class 3 semaphorin (semaphorin 3G [Sema3G]). Methods and Results—Semaphorins have been identified as axon guidance molecules. Yet, they have more recently also been characterized as attractive and repulsive regulators of angiogenesis. Through a transcriptomic screen, we identified Sema3G as a molecule of angiogenic endothelial cells. Sema3G-deficient mice are viable and exhibit no overt vascular phenotype. Yet, LacZ expression in the Sema3G locus revealed intense arterial vascular staining in the angiogenic vasculature, starting at E9.5, which was detectable throughout adolescence and downregulated in adult vasculature. Sema3G is expressed as a full-length 100-kDa secreted molecule that is processed by furin proteases to yield 95- and a 65-kDa Sema domain–containing subunits. Full-length Sema3G binds to NP2, whereas processed Sema3G binds to NP1 and NP2. Expression profiling and cellular experiments identified autocrine effe...

Semaphorins are a large family of secreted and membrane-associated proteins necessary for wiring of the brain. Semaphorin 5A (SEMA5A) acts as a bifunctional guidance cue, exerting both attractive and inhibitory effects on developing axons. Previous studies have suggested that SEMA5A could be a susceptibility gene for autism spectrum disorders (ASDs). We first identified a de novo translocation t(5;22)(p15.3;q11.21) in a patient with ASD and intellectual disability (ID). At the translocation breakpoint on chromosome 5, we observed a 861-kb deletion encompassing the end of the SEMA5A gene. We delineated the breakpoint by NGS and observed that no gene was disrupted on chromosome 22. We then used Sanger sequencing to search for deleterious variants affecting SEMA5A in 142 patients with ASD. We also identified two independent heterozygous variants located in a conserved functional domain of the protein. Both variants were maternally inherited and predicted as deleterious. Our genetic screens identified the first case of a de novo SEMA5A microdeletion in a patient with ASD and ID. Although our study alone cannot formally associate SEMA5A with susceptibility to ASD, it provides additional evidence that Semaphorin dysfunction could lead to ASD and ID. Further studies on Semaphorins are warranted to better understand the role of this family of genes in susceptibility to neurodevelopmental disorders.

In vertebrates, class 3 semaphorins (SEMA3) control axon behaviour by binding to neuronal cell surface receptors composed of a ligand binding subunit termed neuropilin (NRP) and a signal transduction subunit of the A-type plexin family (PLXNA). We have determined the ...

Loss of heterozygosity on human chromosome 3p21.3 is a frequent occurrence in many tumor types. In a previous study, our laboratory demonstrated that an 80-kb P1 clone from chromosome 3 suppresses the tumorigenicity of the mouse fibrosarcoma cell line A9. Two cDNAs corresponding to genes encoded on this P1 clone, semaphorin 3F (SEMA3F) and N23, were tested for their effects on in vitro and in vivo growth characteristics after transfection into mouse A9 cells. Transfection of SEMA3F cDNA resulted in complete loss of tumorigenicity in nude mice, whereas transfection of N23 had no effect. Moreover, SEMA3F also functioned to block apoptosis of transfected A9 cells treated with Taxol or Adriamycin. The human ovarian adenocarcinoma cell line HEY showed a similar result as A9 cells, but the small cell lung cancer line GLC45 was unaffected by expression of SEMA3F.

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. 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. In sum, both systemic and tumor-targeted delivery of SEMA3A inhibits tumor angiogenesis and tumor growth in multipl...

Blood vessels and neurons share guidance cues and cell-surface receptors to control their behaviour during embryogenesis. The transmembrane protein NRP1 (neuropilin 1) is present on both blood vessels and nerves and binds two structurally diverse ligands, the class 3 semaphorin ...

Neural crest cells (NCCs) are highly motile embryonic stem cells that delaminate from the neuroectoderm early during vertebrate embryogenesis and differentiate at defined target sites into various essential cell types. To reach their targets, NCCs follow 1 of 3 sequential pathways that correlate ...

Blood vessels and neurons share guidance cues and cell-surface receptors to control their behaviour during embryogenesis. The transmembrane protein NRP1 (neuropilin 1) is present on both blood vessels and nerves and binds two structurally diverse ligands, the class 3 semaphorin SEMA3A and an isoform of the vascular endothelial growth factor VEGF-A termed VEGF165 (VEGF164 in mice). In vitro, SEMA3A competes with VEGF164 for binding to NRP1 to modulate the migration of endothelial cells and neuronal progenitors. It was therefore hypothesized that NRP1 signalling controls neurovascular co-patterning by integrating competing VEGF164 and SEMA3A signals. However, SEMA3A, but not VEGF164, is required for axon patterning of motor and sensory nerves, and, vice versa, VEGF164 rather than SEMA3A is required for blood vessel development. Ligand competition for NRP1 therefore does not explain neurovascular congruence. Instead, these ligands control different aspects of neurovascular patterning t...

Growth and survival of chronic B-cell tumors are favored by the malignant cell's capacity to respond to selected microenvironmental stimuli provided by nontumoral bystander cells. To investigate which mechanisms operate in these crosstalks and whether they are malignancy-related or reproduce the mechanisms used by normal B cells we have studied the expression and functional role of semaphorin CD100 (now called Sema4D) in chronic lymphocytic leukemia (CLL) cells and normal CD5+ B cells. We demonstrate here that (1) leukemic and normal CD5+ B lymphocytes uniformly express CD100; (2) the CD100 high-affinity receptor Plexin-B1 is expressed by bone marrow stromal cells, follicular dendritic cells, and activated T lymphocytes, and is thus available to CD100+ lymphocytes in different specific microenvironments; and (3) upon interaction between CD100 and Plexin-B1 both CLL and normal CD5+ B cells increase their proliferative activity and extend their life span. These findings establish ...

The aim of this study was to evaluate the promoter methylation status and loss of heterozygosity (LOH) of the SEMA3B in non-small cell lung cancers (NSCLCs). We analyzed the methylation status of semaphorin 3B (SEMA3B) promoter and LOH at 3p21.3 in eight NSCLC cell lines and 27 primary tumors. Hypermethylation of SEMA3B was found in 50% of the cell lines and 41% of the primary tumors studied. The presence of hypermethylation was statistically associated with loss of SEMA3B expression in both cell lines (P = 0.02) and primary tumors (P < 0.01). There was no correlation between SEMA3B and tumor stage. On the other hand, the correlation between SEMA3B methylation status and LOH at 3p21.3 was significant (P = 0.02). Notably, 7 of 8 tumors with both hypermethylation and LOH of SEMA3B showed the absence of the expression. Treatment with 5-AZAC restored SEMA3B expression in NSCLC cell line. These results indicate that SEMA3B gene alterations may play a important role in the malignant tr...

Plexins are transmembrane high-affinity receptors for semaphorins, regulating cell guidance, motility, and invasion. Functional evidences implicate semaphorin signals in cancer progression and metastasis. Yet, it is largely unknown whether plexin genes are genetically altered in human tumors. We performed a comprehensive gene copy analysis and mutational profiling of all nine members of the plexin gene family (plexinome), in melanomas and pancreatic ductal adenocarcinomas (PDACs), which are characterized by high metastatic potential and poor prognosis. Gene copy analysis detected amplification of PLXNA4 in melanomas, whereas copy number losses of multiple plexin genes were seen in PDACs. Somatic mutations were detected in PLXNA4, PLXNB3, and PLXNC1; providing the first evidence that these plexins are mutated in human cancer. Functional assays in cellular models revealed that some of these missense mutations result in loss of plexin function. For instance, c.1613G>A, p.R538H mutation in the extracellular domain of PLXNB3 prevented binding of the ligand Sema5A. Moreover, although PLXNA4 signaling can inhibit tumor cell migration, the mutated c.5206C>T, p.H1736Y allele had lost this activity. Our study is the first systematic analysis of the “plexinome” in human tumors, and indicates that multiple mutated plexins may be involved in cancer progression. Hum Mutat 30,1–8, 2009. © 2009 Wiley-Liss, Inc.