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Antiphospholipid antibodies induce thrombosis by PP2A activation via apoER2-Dab2-SHC1 complex formation in endothelium

Anastasia Sacharidou, Ken L. Chambliss, Victoria Ulrich, Jane E. Salmon, Yu-Min Shen, Joachim Herz, David Y. Hui, Lance S. Terada, Philip W. Shaul and Chieko Mineo

Key Points

  • The activation of PP2A in endothelium underlies thrombus formation induced by aPL in mice.

  • Endothelial apoER2 serves as a scaffold for aPL-induced assembly of a Dab2 and SHC1- containing complex that assembles and activates PP2A.

Publisher's Note: There is a Blood Commentary on this article in this issue.

Abstract

In the antiphospholipid syndrome (APS), antiphospholipid antibody (aPL) recognition of β2 glycoprotein I promotes thrombosis, and preclinical studies indicate that this is due to endothelial nitric oxide synthase (eNOS) antagonism via apolipoprotein E receptor 2 (apoER2)-dependent processes. How apoER2 molecularly links these events is unknown. Here, we show that, in endothelial cells, the apoER2 cytoplasmic tail serves as a scaffold for aPL-induced assembly and activation of the heterotrimeric protein phosphatase 2A (PP2A). Disabled-2 (Dab2) recruitment to the apoER2 NPXY motif promotes the activating L309 methylation of the PP2A catalytic subunit by leucine methyl transferase-1. Concurrently, Src homology domain-containing transforming protein 1 (SHC1) recruits the PP2A scaffolding subunit to the proline-rich apoER2 C terminus along with 2 distinct regulatory PP2A subunits that mediate inhibitory dephosphorylation of Akt and eNOS. In mice, the coupling of these processes in endothelium is demonstrated to underlie aPL-invoked thrombosis. By elucidating these intricacies in the pathogenesis of APS-related thrombosis, numerous potential new therapeutic targets have been identified.

  • Submitted November 3, 2017.
  • Accepted February 23, 2018.
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