Abstract
In previous study, we demonstrated that habutobin, thrombin-like enzyme, bound to β3subunit of integrin αIIbβ3on rabbit washed platelet, and then habutobin inhibited the collagen-induced aggregation. FAK tyrosine-phosphorylation (pTyr) was inhibited at an early stage of collagen-induced aggregation in the presence of habutobin. FAK contains six tyrosine (Tyr)-residues, which are phosphorylated in response to diverse stimuli. However, it was not cleared that habutobin was concerned in which tyrosine residues. In order to investigate the signal transduction pathway being concerned with habutobin-induced inhibition of platelet aggregation, the pTyr397and pTyr861of FAK were studied from Western blotting using the antibodies against pTyr397and pTyr861of FAK. From results of Western blot, pTyr397and pTyr861of FAK were prominently observed on collagen-induced aggregation in the absence of habutobin. The pTyr397of FAK, however, was decreased in a concentration dependent manner by habutobin, and it was not detectable in the presence of high concentration of habutobin (final 5 μg/ml) on an early stage of collagen-induced aggregation. While, the pTyr861of FAK was detectable in the presence of high concentration of habutobin. From these results, it was clarified that habutobin inhibited the phosphorylation of Tyr397of FAK. pTyr397of FAK included the activation of adaptor protein Shc and the p85 subunit of PI3K. It was suggested that habutobin inhibited the phosphorylation of PI3K. [J Physiol Sci. 2007;57 Suppl:S217]
