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IκB kinase (IKK) phosphorylation of SNAP-23 controls platelet secretion

Zubair A. Karim, Jinchao Zhang, Meenakshi Banerjee, Michael C. Chicka, Rania Al Hawas, Tara R. Hamilton, Paul A. Roche, Sidney W. Whiteheart

Key points

  • Nongenomic role for IkappaB kinase (IKK) in platelet secretion: IKK phosphorylates SNAP-23, which affects granule-plasma membrane fusion.

  • Pharmacologic inhibition or deletion of platelet IKK affects bleeding times suggesting the utility of IKK inhibitors as anti-thrombotics.

Abstract

Platelet secretion plays a key role in thrombosis, thus the platelet secretory machinery offers a unique target to modulate hemostasis. We report the regulation of platelet secretion via phosphorylation of SNAP-23 at Ser95. Phosphorylation of this t-SNARE occurs upon activation of known elements of the platelet signaling cascades (i.e. Phospholipase C, [Ca2+]i, Protein Kinase C) and requires IκB Kinase β (IKKβ. Other elements of the NFκB/IκB cascade (i.e. IKKα, β, γ/NEMO and CARMA/MALT1/Bcl10 complex) are present in anucleate platelets and IκB is phosphorylated upon activation suggesting that this pathway is active in platelets and implying a nongenomic role for IKK. Inhibition of IKKβ either pharmacologically (with BMS-345541, BAY11-7082, or TPCA-1) or by genetic manipulation (Platelet Factor 4 Cre::IKKβflox/flox), blocked SNAP-23 phosphorylation, platelet secretion, and SNARE complex formation; but, had no effect on platelet morphology or other metrics of platelet activation. Consistently, SNAP-23 phosphorylation enhanced membrane fusion of SNARE-containing proteoliposomes. In vivo studies with IKK inhibitors or platelet-specific IKKβ knockout mice showed that blocking IKKβ activity significantly prolonged tail-bleeding times suggesting that currently available IKK inhibitors may affect hemostasis.

  • Submitted November 30, 2012.
  • Accepted April 12, 2013.