Semaphorin-3A and Semaphorin-3F Work Together to Repel Endothelial Cells and to Inhibit Their Survival by Induction of Apoptosis

Abstract

Semaphorin-3A (sema3A) is a neuropilin-1 (np1) agonist. It inhibits the binding of the 165-amino acid form of VEGF (VEGF 165 ) to np1 and was reported to inhibit angiogenesis as a result. However, we find that sema3A concentrations that inhibit the mitogenic effects of VEGF 165 do not inhibit VEGF 165 -induced phosphorylation of VEGF receptor-2 (VEGFR-2). Furthermore, sema3A inhibits the biological effects of VEGF 121 , a VEGF form that does not bind to neuropilins and basic fibroblast growth factor, a growth factor whose activity, unlike that of VEGF, is not inhibited by small interfering RNA directed against np1. Therefore, the mechanism by which sema3A inhibits VEGF 165 activity does not depend on competition with VEGF 165 for binding to np1. Sema3A induced rapid disappearance of focal contacts followed by collapse of the actin cytoskeleton in human umbilical vein-derived endothelial cells. HEK293 cells expressing sema3A repel human endothelial cells and at high concentrations induce their death by apoptosis. Furthermore, sema3A inhibited the formation of tubes from endothelial cells in an in vitro angiogenesis assay. Similar effects are induced by the neuropilin-2 (np2) agonist sema3F. These inhibitory effects are abrogated by small interfering RNAs directed against np1 or np2, respectively. The anti-proliferative effects of sema3A and sema3F are additive when the semaphorins are added as pure proteins. However, when sema3A and sema3F were co-expressed in HEK293 cells their pro-apoptotic and cell repellant activities appeared to be synergistic. These observations suggest that combinations of sema3A and sema3F may be able to inhibit tumor angiogenesis more effectively than single semaphorins.

Semaphorin signaling in angiogenesis, lymphangiogenesis and cancer

“…However, recent reports have shown that Sema3s and VEGF use different domains on Nrp1 for binding [40]. Consistent with a separate function of Sema3A on Nrp1, Sema3A increases vascular permeability, inhibits endothelial cell proliferation, and induces apoptosis even in the absence of VEGF [34,41], suggesting Sema3A activates its own signaling routes. Interestingly, Sema3A impairs endothelial cell adhesion and migration by inhibiting integrin function [32].…”

“…Sema3A regulates endothelial cell migration and survival in vitro [33,34], and tumor-induced angiogenesis in vivo [35]. The information emerging from the analysis of Sema3A null mice and mutant mice lacking Sema3A-Nrp1 signaling suggests that Sema3A may not be required for the early stages of developmental angiogenesis, but rather that Sema3A contributes to the reshaping of the vasculature to form a mature vascular network, such as that in the heart and brain [32,36,37].…”

Pulmonary Epithelial Neuropilin-1 Deletion Enhances Development of Cigarette Smoke–induced Emphysema

“…Because epithelial cells are the primary source of VEGF in lung lavage, an alternative explanation linking conditional epithelial Nrp1 deletion and decreased lavage VEGF concentrations in CS-exposed CCSPrtTA/tetO-Cre/Nrp1 flox/flox mice could be that enhanced epithelial cell death decreases VEGF production. Furthermore, although several investigators have demonstrated that the effects of Nrp1 on cell proliferation and death may depend on how this receptor modulates the balance between VEGF and Sema3 signaling (17,26), other studies also demonstrate that Nrp1 may alter cell survival independent of its effects on VEGFR activation (22,(80)(81)(82).…”

“…In endothelium, Nrp1 enhances VEGF-mediated phosphorylation and signaling via VEGFR2 (18)(19)(20) and enhances VEGF-induced endothelial permeability (18), chemotaxis (18,19), proliferation, and cell survival (19). Emerging data suggests that although semaphorins can modulate endothelial signaling by competitively inhibiting VEGF signaling (21), they may have independent effects on endothelial function (22,23).…”

Regulation of immune cell responses by semaphorins and their receptors

“…77,78 Similarly, Sema3F inhibits cell spreading and migration in breast carcinoma, melanoma and ECs, resulting in reduced metastatic dissemination. [78][79][80] Furthermore, since NP-1 is a receptor for both class III semaphorins and VEGF, class III semaphorins may function as antiangiogenic factors by competitively interfering with VEGF receptors. 68 …”