Potent mimicry of fibronectin-induced intracellular signaling in glioma cells by the homodimeric snake venom disintegrin contortrostatin.
OBJECTIVE
The snake venom disintegrin contortrostatin (CN) is able to inhibit tumor progression and angiogenesis in vivo and therefore is of considerable interest as a potential antitumor drug. CN specifically binds to certain integrins on the tumor cell and angiogenic endothelial cell surface and inhibits their interaction with the extracellular matrix, resulting in blockage of cell motility and invasiveness. To understand the molecular consequences of CN binding to integrins, we set out to investigate and compare the effects of CN and fibronectin (FN) on integrin-induced signaling and the resulting alteration in cellular cytoskeletal morphology.


METHODS
Two different malignant glioma cell lines were exposed to soluble or immobilized CN, FN, or both, and the consequences for intracellular signaling and cellular adhesion to matrix were investigated.


RESULTS
CN binding to integrins can mimic the intracellular signaling cascade evoked by FN, because the phosphorylation of the key signaling proteins focal adhesion kinase, paxillin, and p130 Crk-associated substrate and the association of Src with focal adhesion kinase are similar. However, CN is at least one order of magnitude more potent than FN. When soluble CN is added to cells that are already attached to an FN-coated matrix, it effectively disrupts the binding of integrin to FN, leading to a decrease in integrin signaling, which, in turn, results in the disruption of the cytoskeleton and cellular detachment.


CONCLUSIONS
Our results provide a mechanistic explanation of how soluble CN might block cellular migration and invasion, namely, by disrupting and preventing the binding of integrins to the extracellular matrix. We envision that this property of CN could be used in the treatment of gliomas, namely, by intratumoral infusion of CN to prevent glioma and endothelial cell interactions with the extracellular matrix, leading to inhibition of cell invasion.
Schmitmeier
Stephanie
S
Kenneth Norris Jr. Comprehensive Cancer Center, Department of Biochemistry and Molecular Biology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
Markland
Francis S
FS
Schönthal
Axel H
AH
Chen
Thomas C
TC
D000199:Actins / Q000378:metabolism; D015153:Blotting, Western / Q000379:methods; D002452:Cell Count / Q000379:methods; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D019483:Disintegrins / Q000494:pharmacology*; D004347:Drug Interactions; D005353:Fibronectins / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique / Q000379:methods; D051417:Focal Adhesion Kinase 1 / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology; D005910:Glioma / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D016023:Integrins / Q000502:physiology; D051419:Paxillin / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism
D000199:Actins; D016895:Culture Media, Serum-Free; D019483:Disintegrins; D005353:Fibronectins; D016023:Integrins; D051419:Paxillin; C403494:contortrostatin; D014443:Tyrosine; D051417:Focal Adhesion Kinase 1; C496050:PTK2 protein, human