Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 279, Issue 11, Pages 10176-10184Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M310486200
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Funding
- NIDDK NIH HHS [T32-DK07320, DK60720] Funding Source: Medline
- NIGMS NIH HHS [GM37537, GM62890] Funding Source: Medline
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MAPKAP kinase 2 (MK2) is required for tumor necrosis factor synthesis. Tristetraprolin (TTP) binds to the 3'-untranslated region of tumor necrosis factor mRNA and regulates its fate. We identified in vitro and in vivo phosphorylation sites in TTP using nanoflow high pressure liquid chromatography microelectrospray ionization tandem mass spectrometry and novel methods for direct digestion of TTP bound to affinity matrices (GSH-beads or anti-Myc linked to magnetic beads). MK2Delta3B, activated in Escherichia coli by p38alpha, phosphorylates TTP in vitro at major sites Ser(52) and Ser(178) (> 10-fold in abundance) as well as at several minor sites that were detected after enriching for phosphopeptides with immobilized metal affinity chromatography. MK2 phosphorylation of TTP creates a functional 14-3-3 binding site. In cells, TTP was phosphorylated at Ser(52), Ser(178), Thr(250), and Ser(316) and at SP sites in a cluster (Ser(80)/ Ser(82)/Ser(85)). Anisomycin treatment of NIH 3T3 cells increased phosphorylation of Ser(52) and Ser(178). Overexpression of MK2 sufficed to increase phosphorylation of Ser(52) and Ser(178) but not Ser(80)/Ser(82)/ Ser(85) or Thr(250). Thus, Ser(52) and Ser(178) are putative MK2 sites in vivo. Identified phosphosite(s) may be biologic switches controlling mRNA stability and translation.
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