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Selective dephosphorylation of the threonine 183 residue of ERK2 upon αllbβ3 engagement in platelets
Author(s) -
Pawlowski Marc,
Ragab Ashraf,
Rosa Jean-Philippe,
Bryckaert Marijke
Publication year - 2002
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(02)02862-4
Subject(s) - dephosphorylation , phosphatase , okadaic acid , threonine , phosphorylation , serine , kinase , biochemistry , chemistry , protein phosphatase 2 , thrombin , cytosol , microbiology and biotechnology , platelet , biology , enzyme , immunology
Thrombin‐induced extracellular signal‐regulated kinase 2 (ERK2) activation is negatively regulated in conditions of αllbβ3 integrin engagement and platelet aggregation. Here we show by Western blotting with antibodies against mono‐ and biphosphorylated forms of ERK2 that the dephosphorylation of ERK2 by αllbβ3 engagement affects threonine 183 and not tyrosine 185 . Addition of a potent serine/threonine phosphatase inhibitor, okadaic acid (OA), restored thrombin‐induced threonine phosphorylation of ERK2 in conditions of platelet aggregation, whereas OA had no effect in the absence of αllbβ3 engagement. These observations are consistent with αllbβ3 engagement acting via at least one serine/threonine phosphatase, which dephosphorylates the phosphothreonine 183 residue of ERK2. Moreover, a small amount (14%) of ERK2 was translocated to the αllbβ3‐dependent cytoskeleton, mostly in a monophosphorylated (i.e. inactive) form, suggesting that cytoskeleton‐associated ERK2 plays only a minor role, if any. Finally, we show that negative regulation (i.e. dephosphorylation) occurs primarily or totally in the cytosol and that the αllbβ3‐dependent ERK2 Thr 183 ‐specific phosphatase is different from phosphatase 1 (PP1) or PP2A. We conclude that αllbβ3 engagement down‐regulates ERK2 through selective dephosphorylation of the phosphothreonine 183 residue by a cytosolic serine/threonine phosphatase different from known platelet phosphatases.