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The BEACH-domain containing protein, Nbeal2, interacts with Dock7, Sec16a and Vac14

Louisa Mayer, Maria Jasztal, Mercedes Pardo, Salvadora Aguera de Haro, Janine Collins, Tadbir K. Bariana, Peter A. Smethurst, Luigi Grassi, Romina Petersen, Paquita Nurden, Rémi Favier, Lu Yu, Stuart Meacham, William J. Astle, Jyoti Choudhary, Wyatt W. Yue, Willem H. Ouwehand and Jose A. Guerrero

Key points

  • Nbeal2 interacts with Dock7, Sec16a and Vac14 and missense variants causing Gray Platelet Syndrome disrupt the binding of Dock7 and Vac14.

  • The level of the α-granule protein Dock7 in platelets from Nbeal2-/- mice and GPS cases is reduced and its signaling pathway is dysregulated.

Abstract

Mutations in NBEAL2, the gene encoding the scaffolding protein Nbeal2 are causal of Gray Platelet Syndrome (GPS), a rare recessive bleeding disorder characterized by platelets lacking α-granules and progressive marrow fibrosis. We present here the interactome of Nbeal2 with additional validation by reverse immunoprecipitation of Dock7, Sec16a and Vac14 as interactors of Nbeal2. We show that GPS-causing mutations in its BEACH domain have profound and possible effects on the interaction with Dock7 and Vac14, respectively. Proximity ligation assays show that these two proteins are physically proximal to Nbeal2 in human megakaryocytes. In addition, we demonstrate that Nbeal2 is primarily localized in the cytoplasm and Dock7 on the membrane of or in α-granules. Interestingly, platelets from GPS cases and Nbeal2-/- mice are almost devoid of Dock7 resulting in a profound dysregulation of its signaling pathway, leading to defective actin polymerization, platelet activation and shape change. This study shows for the first time proteins interacting with Nbeal2 and points to the dysregulation of the canonical signaling pathway of Dock7 as a possible cause of the aberrant formation of platelets in GPS cases and Nbeal2 deficient mice.

  • Submitted August 4, 2017.
  • Accepted November 21, 2017.