Semaphorin-3B Is an Angiogenesis Inhibitor That Is Inactivated by Furin-Like Pro-Protein Convertases

Abstract

Semaphorin-3B (sema3B) and semaphorin-3F (sema3F) are secreted tumor suppressors of lung cancer. Sema3F functions as an antiangiogenic factor that repels endothelial cells and compromises their proliferation/survival. However, tumor cells expressing either endogenous or recombinant sema3B fail to repel endothelial cells efficiently. Sema3B found in the conditioned medium of such cells is almost completely cleaved by furin-like pro-protein convertases, generating inactive 61-and 22-kDa fragments. We have generated a sema3B variant that was point mutated at the cleavage site (sema3B-m), thereby conferring partial resistance to cleavage. Conditioned medium from HEK293 cells expressing sema3b-m and conditioned medium of HEK293 cells expressing sema3B contained similar concentrations of semaphorin but sema3B-m was cleaved much less than sema3B. In contrast to HEK293 cells expressing native sema3B, cells expressing sema3b-m strongly repel endothelial cells. Conditioned medium from sema3B-mexpressing cells rapidly caused disassembly of focal adhesions and a collapse of the actin cytoskeleton of endothelial cells, inhibited vascular endothelial growth factor-induced phosphorylation of extracellular signal-regulated kinase 1/2, induced apoptosis of endothelial cells, and inhibited the formation of tubes from endothelial cells in an in vitro angiogenesis assay more potently than conditioned medium from cells expressing sema3B. Furthermore, HEK293 cells expressing sema3B-m inhibited basic fibroblast growth factorinduced angiogenesis in vivo much more potently than cells expressing sema3B. Repulsion of human umbilical vascular endothelial cells by sema3B-m was mediated primarily by the neuropilin-1 (np1) receptor but sema3B-m was also able to transduce signals via neuropilin-2 (np2). These results suggest that up-regulation of furin-like pro-protein convertases in malignant cells may enable tumors to evade the antiangiogenic effects of sema3B. [Cancer Res 2008;68(17):6922-31]

A Systematic Study of Site-specific GalNAc-type O-Glycosylation Modulating Proprotein Convertase Processing

“…5A). Sema3B was first identified together with semaphorin 3F as a tumor suppressor of small-cell lung carcinoma (33,34), and later Sema3B was found to function as an endothelial cell repellent (35). Sema3B is inactivated by furin cleavage at multiple processing sites.…”

“…Sema3B is inactivated by furin cleavage at multiple processing sites. The major furin site generates 20-and 80-kDa fragments, and Varshavsky and colleagues (35) show that processing at the most C-terminal site that generates ϳ2-and 78-kDa fragments is sufficient to disrupt its function as an inhibitor of angiogenesis. A role of O-glycosylation in this process is intriguing.…”

The role of the plexin-A2 receptor in semaphorin-3A and semaphorin-3B signal transduction

“…Class 3 semaphorin cDNAs were subcloned into the NSPI-CMV-myc-his lentiviral expression vector as described previously Varshavsky et al, 2008). An expression plasmid containing the extracellular domain of the Sema6A cDNA was kindly provided by Oded Behar (Hebrew University, Jerusalem, Israel).…”

Semaphorin signaling in cancer cells and in cells of the tumor microenvironment – two sides of a coin

“…For example, plexin-A expression has been observed in ovarian (Syed et al, 2005) and gastric (Zhao et al, 2007) carcinoma, as well as in tumor-derived cells of glioma (Rieger et al, 2003), melanoma, and breast (Castro-Rivera et al, 2008; Castro-Rivera et al, 2004;Kigel et al, 2008) and colon (Nguyen et al, 2006) cancer. The expression of plexin-B1 has been reported in ovarian and prostate cancers (Syed et al, 2005;Wong et al, 2007).…”