Platelets are small cells in the blood that are that play an important role in stopping a bleeding but when inappropriately activated also contribute to thrombosis and cardiovascular disease. One of the complications with studying how platelets maintain normal haemostatic control and/or promote thrombosis is that they lack a nucleus thereby prohibiting genetic approaches to reduce protein levels. Most of our present knowledge therefore derives from genetic animal models and pharmacological targeting of signaling pathways, each having its own drawbacks associated with species differences and pharmacological non-specificity. In this project aim to optimise a protein degradation approach in human platelets using rationally designed small molecule degraders called PROTACs (PROteolysis TArgeting Chimeras) to investigate signaling pathways involved in their haemostatic and thrombotic function. PROTACs are small heterobifunctional molecules that target proteins for ubiquitination leading to proteasomal degradation. We recently made the discovery by proteomic analysis that a generic tyrosine kinase PROTAC leads to potent and specific degradation of six protein tyrosine kinases (BTK/TEC, FAK/PYK2 and FER/FES) within hours, demonstrating that human platelets have the complete proteosome required for degradation.
These are exciting findings as it is the first time that a human platelet ‘knockout’ has been generated. In this proposal, we will expand these observations by using newly developed PROTAC molecules that target the tyrosine kinases FAK and PYK2, two tyrosine kinases implicated in platelet function, and develop a highly efficient technology to study platelet signaling pathways and function. We anticipate that the use of PROTACs will be transformative to the platelet research community and be the first step in developing alternative ways to modulate platelet function and thrombosis.
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