Uncoupling ITIM receptor G6b-B from tyrosine phosphatases Shp1 and Shp2 disrupts murine platelet homeostasis

Mitchell J. Geer, Johanna P. van Geffen, Piraveen Gopalasingam, Timo Vogtle, Christopher W. Smith, Silke Heising, Marijke J. E. Kuijpers, Bibian M. E. Tullemans, Gavin E. Jarvis, Johannes A. Eble, Mark Jeeves, Michael Overduin, Johan W. M. Heemskerk, Alexandra Mazharian, Yotis A. Senis*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptor G6b-B has emerged as a key regulator of platelet homeostasis. However, it remains unclear how it mediates its effects. Tyrosine phosphorylation of ITIM and immunoreceptor tyrosine-based switch motif (ITSM) within the cytoplasmic tail of G6b-B provides a docking site for Src homology 2 domain-containing protein-tyrosine phosphatases Shp1 and Shp2, which are also critical regulators of platelet production and function. In this study, we investigate the physiological consequences of uncoupling G6b-B from Shp1 and Shp2. To address this, we generated a transgenic mouse model expressing a mutant form of G6b-B in which tyrosine residues 212 and 238 within ITIM and ITSM were mutated to phenylalanine. Mice homozygous for the mutation (G6b-B diY/F) were macrothrombocytopenic, as a result of the reduction in platelet production, and had large clusters of megakaryocytes and myelofibrosis at sites of hematopoiesis, similar to those observed in G6b-deficient mice and patients. Platelets from G6b-B diY/F mice were hyporesponsive to collagen, as a result of the significant reduction in the expression of the immunoreceptor tyrosine-based activation motif (ITAM)-containing collagen receptor complex GPVI-FcR gamma-chain, as well as thrombin, which could be partially rescued by costimulating the platelets with adenosine diphosphate. In contrast, platelets from G6b-B diY/F, G6b KO, and megakaryocyte-specific Shp2 KO mice were hyperresponsive to antibody-mediated cross-linking of the hemi-ITAM-containing podoplanin receptor CLEC-2, suggesting that G6b-B inhibits CLEC-2-mediated platelet activation through Shp2. Findings from this study demonstrate that G6b-B must engage with Shp1 and Shp2 to mediate its regulatory effects on platelet homeostasis.
Original languageEnglish
Pages (from-to)1413-1425
Number of pages13
JournalBlood
Volume132
Issue number13
DOIs
Publication statusPublished - 27 Sept 2018

Keywords

  • ACTIVATION
  • PROTEIN
  • THROMBOCYTOPENIA
  • PHOSPHORYLATION
  • MICE

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