Differential regulation of tyrosine phosphorylation in tumor cells by contortrostatin, a homodimeric disintegrin, and monomeric disintegrins echistatin and flavoridin

The homodimeric disintegrin contortrostatin was compared directly to the mo nomeric disintegrins echistatin and flavoridin for the ability to affect pr otein tyrosine phosphorylation in tumor cells. It was observed that contort rostatin had a, dramatic effect on the tyrosine phosphorylation status of s everal proteins in T24 human bladder cancer cells, including robust inducti on of phosphorylation of proteins in the range of 120-140 kDa. Echistatin a lone had no effect on tyrosine phosphorylation in T24 cells, but dose-depen dently inhibits the effects of contortrostatin when both are added simultan eously. Among the proteins that undergo tyrosine phosphorylation in respons e to contortrostatin treatment is GAS, a 130 kDa adapter protein involved i n integrin signaling. Flavoridin alone was found to have no effect on GAS, but can completely block contortrostatin-induced phosphorylation of this pr otein in MDA-MB-435 cells. These observations strongly suggest that the hom odimeric structure of contortrostatin functionally distinguishes it from ot her monomeric members of the disintegrin family. (C) 2000 Elsevier Science Ltd. All rights reserved.