The low-molecular-weight phosphotyrosine phosphatase is a negative regulator of FcgammaRIIA-mediated cell activation.
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.
Mancini
Francesca
F
Department of Biochemistry, University of Pavia, Pavia, Italy.
Rigacci
Stefania
S
Berti
Andrea
A
Balduini
Cesare
C
Torti
Mauro
M
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008533:Megakaryocytes / Q000166:cytology / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008970:Molecular Weight; D051966:Phospholipase C gamma / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D015539:Platelet Activation; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D017452:Receptors, IgG / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase
D048868:Adaptor Proteins, Signal Transducing; D015703:Antigens, CD; C080568:Fc gamma receptor IIA; D047908:Intracellular Signaling Peptides and Proteins; C110810:LAT protein, human; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D017452:Receptors, IgG; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C490429:ACP1 protein, human; D017027:Protein Tyrosine Phosphatases; D051966:Phospholipase C gamma; D002118:Calcium