|Ph.D Student||Varshavsky Asya|
|Subject||The Role of Semaphorin 3B in Angiogenesis and Tumor|
|Department||Department of Medicine||Supervisor||Professor Emeritus Gera Neufeld|
|Full Thesis text|
Semaphorin 3B (sema3B) was originally identified along with semaphoring 3F (sema3F) as a tumor suppressor of lung cancer. Sema3F functions as an anti-angiogenic factor that repels endothelial cells and inhibits their proliferation. However, tumor cells expressing either endogenous or recombinant sema3B failed to repel endothelial cells efficiently. Sema3B found in the conditioned medium of such cells was almost completely cleaved by furin like pro-protein convertases, a family of endoproteases which are often over-expressed in malignant cells, to inactive 61 and 22 kDa fragments. We have generated a sema3B variant named sema3B-m, which was point mutated at the pro-protein convertases cleavage site, thereby conferring partial resistance to the 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-m expressing cells rapidly caused disassembly of focal adhesions and a collapse of the actin cytoskeleton of endothelial cells, inhibited VEGF induced phosphorylation of ERK1/2, induced apoptosis of endothelial cells, inhibited their proliferation/survival and inhibited the formation of tubes from endothelial cells in an in-vitro angiogenesis assay much more potently than conditioned medium from cells expressing sema3B. Furthermore, HEK293 cells expressing sema3B-m inhibited bFGF induces angiogenesis in-vivo more potently than cells expressing sema3B. Repulsion of endothelial cells by sema3B-m was mediated primarily by the neuropilin-1 receptor but sema3B-m was also able to transduce signals via neuropilin-2. These results suggest that up-regulation of furin like pro-protein convertases in malignant cells may enable tumors to evade the anti-angiogenic effects of sema3B.