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

Blood. 2018 Sep 27;132(13):1413-1425. doi: 10.1182/blood-2017-10-802975. Epub 2018 Jun 11.


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 γ-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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites
  • Blood Platelets / metabolism
  • Blood Platelets / pathology*
  • Homeostasis
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Models, Molecular
  • Phosphorylation
  • Point Mutation
  • Protein Interaction Maps
  • Protein Tyrosine Phosphatase, Non-Receptor Type 11 / chemistry
  • Protein Tyrosine Phosphatase, Non-Receptor Type 11 / metabolism*
  • Protein Tyrosine Phosphatase, Non-Receptor Type 6 / chemistry
  • Protein Tyrosine Phosphatase, Non-Receptor Type 6 / metabolism*
  • Receptors, Immunologic / chemistry
  • Receptors, Immunologic / genetics
  • Receptors, Immunologic / metabolism*
  • Signal Transduction
  • Thrombocytopenia / genetics
  • Thrombocytopenia / metabolism*
  • Thrombocytopenia / pathology
  • src Homology Domains


  • G6b-B receptor, mouse
  • Receptors, Immunologic
  • Protein Tyrosine Phosphatase, Non-Receptor Type 11
  • Protein Tyrosine Phosphatase, Non-Receptor Type 6
  • Ptpn11 protein, mouse