Activation of human platelets by cross-linking of the low-affinity receptor for immunoglobulin G (FcgammaRIIA) is initiated by Src kinase-mediated phosphorylation of the immunoreceptor tyrosine-based activation motif (ITAM) within the receptor, but the identity of the enzyme responsible for its dephosphorylation and inactivation is unknown. Here we report that the 18-kDa low-molecular-weight phosphotyrosine phosphatase (LMW-PTP) is expressed in human platelets and undergoes subcellular redistribution upon FcgammaRIIA cross-linking. In vitro, LMW-PTP was found to efficiently dephosphorylate activated FcgammaRIIA and LAT, but not Syk or phospholipase Cgamma2. In the megakaryocytic cell line DAMI, antibody-induced phosphorylation of FcgammaRIIA was rapid and transient. The late dephosphorylation of FcgammaRIIA was dramatically delayed upon reduction of LMW-PTP expression by siRNA. Strikingly, overexpression of LMW-PTP resulted in the inhibition of antibody-induced phosphorylation of FcgammaRIIA, and caused a more rapid dephosphorylation. In addition, overexpression of LMW-PTP inhibited activation of Syk downstream of FcgammaRIIA and reduced intracellular Ca(2+) mobilization. These results demonstrate that LMW-PTP is responsible for FcgammaRIIA dephosphorylation, and is implicated in the down-regulation of cell activation mediated by this ITAM-bearing immunoreceptor.
The low-molecular-weight phosphotyrosine phosphatase is a negative regulator of FcgammaRIIA-mediated cell activation / F. Mancini; S.Rigacci; A.Berti; C. Balduini; M. Torti. - In: BLOOD. - ISSN 0006-4971. - STAMPA. - 110(6):(2007), pp. 1871-1878.
The low-molecular-weight phosphotyrosine phosphatase is a negative regulator of FcgammaRIIA-mediated cell activation.
RIGACCI, STEFANIA;BERTI, ANDREA;
2007
Abstract
Activation of human platelets by cross-linking of the low-affinity receptor for immunoglobulin G (FcgammaRIIA) is initiated by Src kinase-mediated phosphorylation of the immunoreceptor tyrosine-based activation motif (ITAM) within the receptor, but the identity of the enzyme responsible for its dephosphorylation and inactivation is unknown. Here we report that the 18-kDa low-molecular-weight phosphotyrosine phosphatase (LMW-PTP) is expressed in human platelets and undergoes subcellular redistribution upon FcgammaRIIA cross-linking. In vitro, LMW-PTP was found to efficiently dephosphorylate activated FcgammaRIIA and LAT, but not Syk or phospholipase Cgamma2. In the megakaryocytic cell line DAMI, antibody-induced phosphorylation of FcgammaRIIA was rapid and transient. The late dephosphorylation of FcgammaRIIA was dramatically delayed upon reduction of LMW-PTP expression by siRNA. Strikingly, overexpression of LMW-PTP resulted in the inhibition of antibody-induced phosphorylation of FcgammaRIIA, and caused a more rapid dephosphorylation. In addition, overexpression of LMW-PTP inhibited activation of Syk downstream of FcgammaRIIA and reduced intracellular Ca(2+) mobilization. These results demonstrate that LMW-PTP is responsible for FcgammaRIIA dephosphorylation, and is implicated in the down-regulation of cell activation mediated by this ITAM-bearing immunoreceptor.File | Dimensione | Formato | |
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