Plexin-B1 activates NF-κB and IL-8 to promote a pro-angiogenic response in endothelial cells.
BACKGROUND
The semaphorins and their receptors, the plexins, are proteins related to c-Met and the scatter factors that have been implicated in an expanding signal transduction network involving co-receptors, RhoA and Ras activation and deactivation, and phosphorylation events. Our previous work has demonstrated that Semaphorin 4D (Sema4D) acts through its receptor, Plexin-B1, on endothelial cells to promote angiogenesis in a RhoA and Akt-dependent manner. Since NF-κB has been linked to promotion of angiogenesis and can be activated by Akt in some contexts, we wanted to examine NF-κB in Sema4D treated cells to determine if there was biological significance for the pro-angiogenic phenotype observed in endothelium.


RESULTS
Using RNA interference techniques, gel shifts and NF-κB reporter assays, we demonstrated NF-κB translocation to the nucleus in Sema4D treated endothelial cells occurring downstream of Plexin-B1. This response was necessary for endothelial cell migration and capillary tube formation and protected endothelial cells against apoptosis as well, but had no effect on cell proliferation. We dissected Plexin-B1 signaling with chimeric receptor constructs and discovered that the ability to activate NF-κB was dependent upon Plexin-B1 acting through Rho and Akt, but did not involve its role as a Ras inhibitor. Indeed, inhibition of Rho by C3 toxin and Akt by LY294002 blocked Sema4D-mediated endothelial cell migration and tubulogenesis. We also observed that Sema4D treatment of endothelial cells induced production of the NF-κB downstream target IL-8, a response necessary for angiogenesis. Finally, we could show through co-immunofluorescence for p65 and CD31 that Sema4D produced by tumor xenografts in nude mice activated NF-κB in vessels of the tumor stroma.


CONCLUSIONS
These findings provide evidence that Sema4D/Plexin-B1-mediated NF-κB activation and IL-8 production is critical in the generation a pro-angiogenic phenotype in endothelial cells and suggests a new therapeutic target for the anti-angiogenic treatment of some cancers.
Department of Oncology and Diagnostic Sciences, University of Maryland Dental School, Baltimore, Maryland, United States of America.
Ying-Hua
YH
Yang
Hua
H
Zhou
Nada O
NO
Binmadi
Patrizia
P
Proia
John R
JR
Basile
D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002196:Capillaries / Q000187:drug effects / Q000378:metabolism; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D002471:Cell Transformation, Neoplastic; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D061307:Human Umbilical Vein Endothelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism*; D051379:Mice; D009389:Neovascularization, Pathologic / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D039961:Semaphorins / Q000235:genetics / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D051996:Transcription Factor RelA / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
D015703:Antigens, CD; C093224:CD100 antigen; D016209:Interleukin-8; D009419:Nerve Tissue Proteins; C492119:PLXNB1 protein, human; D011956:Receptors, Cell Surface; D039961:Semaphorins; D051996:Transcription Factor RelA; D051057:Proto-Oncogene Proteins c-akt; D020742:rhoA GTP-Binding Protein