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 Vögtle, 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

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13 Citations (Scopus)
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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 the ITIM and immunoreceptor tyrosine-based switch motif (ITSM) within the cytoplasmic tail of G6b-B provides a docking site for SH2 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 (Y) residues 212 and 238 within the ITIM and ITSM were mutated to phenylalanine (F), respectively. Mice homozygous for the mutation (G6b-B diY/F) were macrothrombocytopenic, due to a reduction in platelet production, had large clusters of megakaryocytes and myelofibrosis at sites of hematopoiesis, similar to that observed in G6b knockout (G6b KO) mice. Platelets from G6b-B diY/F mice were hypo-responsive to collagen, due to a significant reduction in expression of the immunoreceptor tyrosine-based activation motif (ITAM)-containing collagen receptor complex GPVI-FcR γ-chain, and thrombin, that could be partially rescued by co-stimulating the platelets with ADP. In contrast, platelets from G6b-B diY/F, G6b KO and megakaryocyte-specific Shp2 KO mice were hyper-responsive 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 in order to mediate its regulatory effects on platelet homeostasis.

Original languageEnglish
Pages (from-to)1413–1425
Number of pages13
JournalBlood
Volume133
Issue number13
Early online date11 Jun 2018
DOIs
Publication statusPublished - 27 Sep 2018

Keywords

  • C6orf25
  • MPIG6B
  • G6b-B
  • Megakaryocytes
  • Platelets
  • Thrombocytopenia
  • Hemostasis
  • Transgenic mouse

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