Thrombin and Collagen Induce a Feedback Inhibitory Signaling Pathway in Platelets Involving Dissociation of the Catalytic Subunit of Protein Kinase A from an NFκB-IκB Complex

• Published in: The Journal of biological chemistry 2010-06, Vol.285 (24), p.18352-18363
• Main Authors: Gambaryan, Stepan, Kobsar, Anna, Rukoyatkina, Natalia, Herterich, Sabine, Geiger, Joerg, Smolenski, Albert, Lohmann, Suzanne M., Walter, Ulrich
• Format: Article
• Language: English
• Subjects: cAMP; Cell Biology; Cyclic AMP (cAMP); NFκB; PKA; Platelet; Protein Kinase A (PKA); Protein Phosphorylation; Signal Transduction; VASP
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M109.077602

Protein kinase A (PKA) activation by cAMP phosphorylates multiple target proteins in numerous platelet inhibitory pathways that have a very important role in maintaining circulating platelets in a resting state. Here we show that in thrombin- and collagen-stimulated platelets, PKA is activated by cAMP-independent mechanisms involving dissociation of the catalytic subunit of PKA (PKAc) from an NFκB-IκBα-PKAc complex. We demonstrate mRNA and protein expression for most of the NFκB family members in platelets. From resting platelets, PKAc was co-immunoprecipitated with IκBα, and conversely, IκBα was also co-immunoprecipitated with PKAc. This interaction was significantly reduced in thrombin- and collagen-stimulated platelets. Stimulation of platelets with thrombin- or collagen-activated IKK, at least partly by PI3 kinase-dependent pathways, leading to phosphorylation of IκBα, disruption of an IκBα-PKAc complex, and release of free, active PKAc, which phosphorylated VASP and other PKA substrates. IKK inhibitor inhibited thrombin-stimulated IkBα phosphorylation, PKA-IkBα dissociation, and VASP phosphorylation, and potentiated integrin αIIbβ3 activation and the early phase of platelet aggregation. We conclude that thrombin and collagen not only cause platelet activation but also appear to fine-tune this response by initiating downstream NFκB-dependent PKAc activation, as a novel feedback inhibitory signaling mechanism for preventing undesired platelet activation.