title: Tyrosine phosphorylation on spleen tyrosine kinase (Syk) is differentially regulated in human and murine platelets by protein kinase C isoforms.
abstract: Protein kinase C (PKC) isoforms differentially regulate platelet functional responses downstream of glycoprotein VI (GPVI) signaling, but the role of PKCs regulating upstream effectors such as Syk is not known. We investigated the role of PKC on Syk tyrosine phosphorylation using the pan-PKC inhibitor GF109203X (GFX). GPVI-mediated phosphorylation on Syk Tyr-323, Tyr-352, and Tyr-525/526 was rapidly dephosphorylated, but GFX treatment inhibited this dephosphorylation on Tyr-525/526 in human platelets but not in wild type murine platelets. GFX treatment did not affect tyrosine phosphorylation on FcRγ chain or Src family kinases. Phosphorylation of Lat Tyr-191 and PLCγ2 Tyr-759 was also increased upon treatment with GFX. We evaluated whether secreted ADP is required for such dephosphorylation. Exogenous addition of ADP to GFX-treated platelets did not affect tyrosine phosphorylation on Syk. FcγRIIA- or CLEC-2-mediated Syk tyrosine phosphorylation was also potentiated with GFX in human platelets. Because potentiation of Syk phosphorylation is not observed in murine platelets, PKC-deficient mice cannot be used to identify the PKC isoform regulating Syk phosphorylation. We therefore used selective inhibitors of PKC isoforms. Only PKCβ inhibition resulted in Syk hyperphosphorylation similar to that in platelets treated with GFX. This result indicates that PKCβ is the isoform responsible for Syk negative regulation in human platelets. In conclusion, we have elucidated a novel pathway of Syk regulation by PKCβ in human platelets.
authors: From the Department of Physiology.
authors: Lorena
authors: L
authors: Buitrago
authors: Dheeraj
authors: D
authors: Bhavanasi
authors: Carol
authors: C
authors: Dangelmaier
authors: Bhanu Kanth
authors: BK
authors: Manne
authors: Rachit
authors: R
authors: Badolia
authors: Alessandra
authors: A
authors: Borgognone
authors: Alexander Y
authors: AY
authors: Tsygankov
authors: Steven E
authors: SE
authors: McKenzie
authors: Satya P
authors: SP
authors: Kunapuli
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D025461:Feedback, Physiological / Q000187:drug effects; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D037181:Lectins, C-Type / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D051966:Phospholipase C gamma / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine / Q000378:metabolism*; D010974:Platelet Aggregation / Q000187:drug effects; D064546:Protein Kinase C beta / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011961:Receptors, Fc / Q000378:metabolism; D000072377:Syk Kinase
chemical_list: C104778:CLEC2B protein, human; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D037181:Lectins, C-Type; D008562:Membrane Glycoproteins; D047428:Protein Kinase Inhibitors; D011961:Receptors, Fc; D019000:Phosphotyrosine; D000244:Adenosine Diphosphate; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D064546:Protein Kinase C beta; D051966:Phospholipase C gamma
keywords: GPVI; Phosphotyrosine Signaling; Platelets; Protein Kinase C (PKC); Protein Phosphorylation; Protein-tyrosine Kinase (Tyrosine Kinase); Syk
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