Abstract
Protein seryl/threonyl phosphatase inhibitors such as calyculin A block inside-out and outside-in platelet signaling. Our studies demonstrate that the addition of calyculin A blocks platelet adhesion and spreading on fibrinogen, responses that depend on integrin alphaIIb beta3 signaling. We hypothesized that this reflects a change in alphaIIb beta3 structure caused by a specific state of phosphorylation. We show that addition of calyculin A leads to increased phosphorylation of the beta3 subunit, and phosphoamino acid analysis reveals that only threonine residues become phosphorylated; sequence analysis by Edman degradation established that threonine 753 became stoichiometrically phosphorylated during inhibition of platelet phosphatases by calyculin A. This region of beta3 is linked to outside-in signaling such as platelet spreading responses. The effect of calyculin A on platelet adhesion and spreading and on the phosphorylation of T-753 in beta3 is reversed by the calcium ionophore A23187, demonstrating that these effects of calyculin A are not generally toxic ones. We propose that phosphorylation of beta3 on threonine 753, a region of beta3 linked to outside-in signaling, may be a mechanism by which integrin alphaIIb beta3 function is regulated.
Highlights
Effective hemostasis depends on three basic platelet responses [1]
Previous studies have shown that calyculin A, a serine/threonine phosphatase inhibitor, inhibits platelet aggregation, which is dependent on ␣IIb3 function
3 Phosphorylation Correlates with Decreased Outside-in Signaling—Previous studies have shown that calyculin A, an inhibitor of protein seryl/threonyl phosphatase types 1 and 2A, markedly reduces platelet aggregation induced by collagen [18] and low doses of thrombin [17]
Summary
Effective hemostasis depends on three basic platelet responses [1]. First, adhesion, which includes attachment and spreading reactions, initiates events that lead to formation of a hemostatic plug. Suggesting that a phosphorylation event controls ␣IIb3 activation is in accordance with protein phosphorylation events regulating numerous platelet responses, including adhesion and aggregation [13]. Previous studies have shown that calyculin A, a serine/threonine phosphatase inhibitor, inhibits platelet aggregation, which is dependent on ␣IIb3 function.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.