Mr. Ritter et al., Contortrostatin, a snake venom disintegrin, induces alpha nu beta 3-mediated tyrosine phosphorylation of CAS and FAK in tumor cells, J CELL BIOC, 79(1), 2000, pp. 28-37
Contortrostatin is a homodimeric disintegrin that inhibits platelet aggrega
tion and cell adhesion to extracellular matrix proteins by blocking integri
ns. The effect of contortrostatin on integrin-mediated signaling in tumor c
ells was investigated by studying tyrosine phosphorylation events and activ
ation of specific signaling molecules. We found that at concentrations as l
ow as 1 nM, soluble contortrostatin activates integrin signals leading to i
ncreased tyrosine phosphorylation of FAK and GAS, and that these signals ar
e abolished by inhibiting Src family kinases. Using transfected 293 cells e
xpressing specific integrins, it was determined that contortrostatin-genera
ted signals are mediated exclusively by the alpha nu beta 3 integrin. This
observation was extended by showing that cells lacking alpha nu beta 3, but
expressing alpha nu beta 5 and alpha 5 beta 1, do not respond in this way
to contortrostatin treatment. In cells expressing alpha nu beta 3, blocking
contortrostatin binding with antibodies against alpha nu beta 3 completely
abrogates contortrostatin signals. Monovalent disintegrins echistatin and
favoridin were incapable of affecting tyrosine phosphorylation alone, but w
hen added simultaneously with contortrostatin, completely inhibited contort
rostatin-initiated signals. We propose that the homodimeric nature of conto
rtrostatin imparts the ability to crosslink alpha nu beta 3 integrins, caus
ing Src activation and hyperphosphorylation of FAK and GAS. This activity m
ay represent a novel mechanism by which tumor cell motility can be inhibite
d, (C) 2000 Wiley-Liss, Inc.