Anthrax lethal toxin inhibits growth of and vascular endothelial growth factor release from endothelial cells expressing the human herpes virus 8 viral G protein coupled receptor.
OBJECTIVE
In this study, we tested the hypothesis that inhibition of mitogen-activated protein kinase kinases (MKK) inhibits tumor growth by acting on angiogenic signaling and by extension may form the basis of an effective strategy for treatment of Kaposi's sarcoma.


METHODS
Murine endothelial cells expressing the human herpes virus 8 G protein-coupled receptor (vGPCR-SVEC) were treated with anthrax lethal toxin (LeTx). LeTx is a binary toxin ordinarily secreted by Bacillus anthracis and is composed of two proteins: protective antigen (the binding moiety) and lethal factor (the active moiety). Lethal factor is a protease that cleaves and inactivates MKKs.


RESULTS
In vitro, treatment of vGPCR-SVEC with LeTx inhibited MKK signaling, moderately inhibited cell proliferation, and blocked the ability of these cells to form colonies in soft agar. Treatment with LeTx also blocked the ability of these cells to release several angioproliferative cytokines, notably vascular endothelial growth factor (VEGF). In contrast, inhibition of mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 with U0126 caused a substantial inhibition of proliferation but only modestly inhibited VEGF release. In xenograft models, i.v. injection of LeTx caused reduced tumor growth characterized immunohistochemically by inhibition of MKK signaling, decreased rates of proliferation, and reduced levels of VEGF and VEGF receptor 2, with a corresponding decrease in vascular density.


CONCLUSIONS
These data support a role for MKK signaling in tumor growth and vascularization and are consistent with the hypothesis that inhibition of MKK signaling by LeTx or a similar agent may be an effective strategy for the treatment of Kaposi's sarcoma as well as other vascular tumors.
Depeille
Philippe
P
Laboratory of Cancer and Developmental Cell Biology, Van Andel Research Institute, Grand Rapids, Michigan , USA.
Young
John J
JJ
Boguslawski
Elissa A
EA
Berghuis
Bree D
BD
Kort
Eric J
EJ
Resau
James H
JH
Frankel
Arthur E
AE
Duesbery
Nicholas S
NS
D000818:Animals; D000942:Antigens, Bacterial / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D042783:Endothelial Cells / Q000378:metabolism*; D051379:Mice; D008833:Microcirculation; D041681:NIH 3T3 Cells; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000096:biosynthesis; D019707:Receptors, Chemokine / Q000378:metabolism*; D012514:Sarcoma, Kaposi / Q000378:metabolism / Q000628:therapy; D015398:Signal Transduction; D013997:Time Factors; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
D000942:Antigens, Bacterial; D001427:Bacterial Toxins; C115448:G protein-coupled receptor, Human herpesvirus 8; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D019707:Receptors, Chemokine; D042461:Vascular Endothelial Growth Factor A; C030325:anthrax toxin