New protein kinase A and G-dependent signaling pathways and networks in the regulation of platelet activation

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Platelet function is tightly regulated by activatory and inhibitory signaling pathways. Cyclic nucleotide-dependent protein kinases A (PKA) and G (PKG) represent major key players in inhibition of important platelet activation steps, including adhesion, shape change, integrin activation, granule release, aggregation and pro-coagulant activity. However, our understanding of the complex network of PKA/PKG-dependent inhibitory signaling that modulates distinct platelet functions is incomplete. Based on our recently published data with phospho-CalDAG-GEFI and integrin regulation [A9, A4] we hypothesize that the identification and functional characterization of novel cAMP/PKA and cGMP/PKG substrates will identify important mechanisms of platelet inhibition. Furthermore, these studies may indicate attractive candidates for novel diagnostic and /or therapeutic targets for selective platelet activation or inhibition.Based on preliminary phosphoproteome data we intend to investigate the role of newly identified PKA/PKG-specific and PKA/PKG-common substrate proteins in inhibitory platelet function by using established biochemical and functional in vitro methods that enable analysis of phospho-deficient/-mimetic megakaryocytic mutants and knockdowns as well as phosphoprotein ligands in platelets. Functional characterization of the novel PKA/PKG-common substrate endosulfine-alpha (ENSA) will be additionally addressed by generation of a megakaryocyte- and platelet-specific ENSA-deficient mouse model. Quantitative LC-MS-based phosphoproteomic and advanced platelet function analysis will be used to comprehensively elucidate the signaling crosstalk between PKA- or PKG-mediated inhibiting, and thrombin- or collagen-mediated activating pathways and its consequences for platelet function. Based on bioinformatics analysis of quantitative phosphoproteomic data we aim to identify relevant inhibitory downstream signatures and to develop a dynamic platelet inhibitory model.