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Identification of mitogen‐activated protein kinase‐activated protein kinase‐2 as a vimentin kinase activated by okadaic acid in 9L rat brain tumor cells
Author(s) -
Cheng TingJen,
Lai YiuKay
Publication year - 1998
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/(sici)1097-4644(19981101)71:2<169::aid-jcb3>3.0.co;2-t
Subject(s) - protein kinase a , cyclin dependent kinase 2 , ask1 , vimentin , mitogen activated protein kinase kinase , microbiology and biotechnology , map2k7 , cyclin dependent kinase 9 , kinase , map kinase kinase kinase , c raf , biology , protein kinase r , dephosphorylation , phosphatase , intermediate filament protein , cyclin dependent kinase 1 , phosphorylation , biochemistry , intermediate filament , cytoskeleton , cell , cell cycle , immunology , immunohistochemistry
Organization of intermediate filament, a major component of cytoskeleton, is regulated by protein phosphorylation/dephosphorylation, which is a dynamic process governed by a balance between the activities of involved protein kinases and phosphatases. Blocking dephosphorylation by protein phosphatase inhibitors such as okadaic acid (OA) leads to an apparent activation of protein kinase(s) and to genuine activation of phosphatase‐regulated protein kinase(s). Treatment of 9L rat brain tumor cells with OA results in a drastically increased phosphorylation of vimentin, an intermediate filament protein. In‐gel renaturing assays and in vitro kinase assays using vimentin as the exogenous substrate indicate that certain protein kinase(s) is activated in OA‐treated cells. With specific protein kinase inhibitors, we show the possible involvement of the cdc2 kinase‐ and p38 mitogen‐activated protein kinase (p38 MAPK )‐mediated pathways in this process. Subsequent in vitro assays demonstrate that vimentin may serve as an excellent substrate for MAPK‐activated protein kinase‐2 (MAPKAPK‐2), the downstream effector of p38 MAPK , and that MAPKAPK‐2 is activated with OA treatment. Comparative analysis of tryptic phosphopeptide maps also indicates that corresponding phosphopeptides emerged in vimentin from OA‐treated cells and were phosphorylated by MAPKAPK‐2. Taken together, the results clearly demonstrate that MAPKAPK‐2 may function as a vimentin kinase in vitro and in vivo. These findings shed new light on the possible involvement of the p38 MAPK signaling cascade, via MAPKAPK‐2, in the maintenance of integrity and possible physiological regulation of intermediate filaments. J. Cell. Biochem. 71:169–181, 1998. © 1998 Wiley‐Liss, Inc.