Megakaryocyte-specific deletion of the protein-tyrosine phosphatases Shp1 and Shp2 causes abnormal megakaryocyte development, platelet production, and function

Abstract

Key Points• The protein-tyrosine phosphatases Shp1 and Shp2 are critical regulators of megakaryocyte development, platelet production, and function.• Shp1 and Shp2 perform mainly distinct functions in megakaryocytes and platelets, with little functional overlap.The SH2 domain-containing protein-tyrosine phosphatases Shp1 and Shp2 have been implicated in regulating signaling from a variety of platelet and megakaryocyte receptors.In this study, we investigate the functions of Shp1 and Shp2 in megakaryocytes and platelets. Megakaryocyte/platelet (MP)-specific deletion of Shp1 in mice resulted in platelets being less responsive to collagen-related peptide due to reduced GPVI expression and signaling via the Src family kinase (SFK)-Syk-PLCg2 pathway, and fibrinogen due to reduced SFK activity. By contrast, deletion of Shp2 in the MP lineage resulted in macrothrombocytopenia and platelets being hyper-responsive to anti-CLEC-2 antibody and fibrinogen. Shp1-and Shp2-deficient megakaryocytes had partial blocks at 2N/4N ploidy; however, only the latter exhibited reduced proplatelet formation, thrombopoietin, and integrin signaling. Mice deficient in both Shp1 and Shp2 were severely macrothrombocytopenic and had reduced platelet surface glycoprotein expression, including GPVI, aIIbb3, and GPIba. Megakaryocytes from these mice were blocked at 2N/4N ploidy and did not survive ex vivo. Deletion of the immunoreceptor tyrosine-based inhibition motif-containing receptor G6b-B in the MP lineage phenocopied multiple features of Shp1/2-deficient mice, suggesting G6b-B is a critical regulator of Shp1 and Shp2. This study establishes Shp1 and Shp2 as major regulators of megakaryocyte development, platelet production, and function. (Blood. 2013;121(20):4205-4220)

Prolonged thrombocytopenia in a child with severe neonatal alloimmune reaction and Noonan syndrome

“…Mutations in PTPN11 occur in 50% of patients, SOS1 in 13%, RAF in 3-17%, and KRAS in less than 5% [7]. PTPN11 encodes SH2 domain, which contains protein-tyrosine phosphatases Shp1 and Shp2; Shp1 is expressed in hematopoietic and epithelial cells, while Shp2 is expressed widely and they are both key regulators in megakaryocyte development, platelet formation, and function (including interaction with collagen and fibrinogen); these two phosphatases seem to have opposite roles in platelet function (Shp1 reduces platelet response to collagen and fibrinogen by positively regulating immune receptor tyrosine-based activation motif-containing receptors and integrin signaling, whilst Shp2 behaves in the opposite way) [8].…”

Paired immunoglobulin-like receptor B regulates platelet activation

“…Alexandra et al recently showed that deletion of Shp1 in mice resulted in platelets being less responsive to CRP by reducing both GPVI expression and signaling via the Src-Syk-PLCg2 pathway. 37 On the contrary, deletion of Shp2 resulted in platelets being hyper-responsive to agonists. 37 Although the phosphorylation of Shp1 Y564 and Shp2 Y580 was suppressed in PIRB-TM platelets in response to CRP, the distinct roles of Shp1 and Shp2 in platelet activation suggest that PIRB negatively regulates platelet activation, probably by enhancing the phosphatase activities of Shp2 instead of Shp1.…”

“…37 On the contrary, deletion of Shp2 resulted in platelets being hyper-responsive to agonists. 37 Although the phosphorylation of Shp1 Y564 and Shp2 Y580 was suppressed in PIRB-TM platelets in response to CRP, the distinct roles of Shp1 and Shp2 in platelet activation suggest that PIRB negatively regulates platelet activation, probably by enhancing the phosphatase activities of Shp2 instead of Shp1. However, further investigation will be needed to clarify this.…”

Cyclic nucleotide‐dependent inhibitory signaling interweaves with activating pathways to determine platelet responses

“…Absence of spinophilin also results in reduced cAMP synthesis in response to PGI 2 , highlighting multiple functions of this scaffold protein in platelets. Studies on SHP‐1‐deficient mice have identified a main role of SHP‐1 in regulating GPVI and integrin αIIbß3 signaling but did not reveal any defect in GPCR signaling 39. Because SHP‐1 is ablated during megakaryocyte differentiation in these mice, it is possible that the role of SHP‐1 in regulating GPCR signaling is not apparent because of compensatory mechanisms and/or redundancy with the closely related SHP‐2 phosphatase.…”

“…Because SHP‐1 is ablated during megakaryocyte differentiation in these mice, it is possible that the role of SHP‐1 in regulating GPCR signaling is not apparent because of compensatory mechanisms and/or redundancy with the closely related SHP‐2 phosphatase. Indeed, platelets deficient in both SHP‐1 and SHP‐2, display marked defects in PAR4 receptor signaling, suggesting a level of redundancy 39. Whether a spinophilin/RGS18 complex exists in SHP‐1 deficient platelets remains to be determined.…”