The p44/42 mitogen-activated protein kinase cascade is involved in the induction and maintenance of astrocyte stellation mediated by protein kinase C.
The mitogen-activated protein kinase (MAPK) is known to be involved in the differentiation of various types of cells. To understand the role of p44/42 MAPK (ERK1/2) in astrocyte differentiation, we investigated the effects of U0126 and PD98059, specific inhibitors of the MAPK-activating enzyme MEK, on astrocyte morphology in culture. Cultured rat cortical astrocytes exhibited flattened, polygonal morphology in the absence of stimulation, but differentiated into process-bearing stellate cells in response to the membrane-permeable cyclic AMP analog dibutyryl cyclic AMP (dBcAMP) or the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA). dBcAMP-induced astrocyte stellation was not affected by MEK inhibitors, while PMA-induced astrocyte stellation was significantly blocked by U0126 (0.1-10 microM) and PD98059 (10-30 microM). Western blot analysis with an antibody specific for phosphorylated ERK1/2 revealed that PMA, but not dBcAMP, induced phosphorylation of ERK1/2 in a time- and concentration-dependent manner. The PMA-induced astrocyte stellation and ERK1/2 phosphorylation were blocked by specific PKC inhibitors, GF-109203X (0.01-1 microM) and calphostin C (1 microM). In addition, when U0126 or PD98059 was added after treatment with PMA, stellate astrocytes returned to polygonal. These results suggest that the MEK/ERK cascade is involved in the induction and maintenance of astrocyte stellation mediated by PKC, but not by cyclic AMP signaling.
Abe
K
K
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan. kazuhoab@mol.f.u-tokyo.ac.jp
Saito
H
H
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D003994:Bucladesine / Q000494:pharmacology; D002070:Butadienes / Q000494:pharmacology; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002070:Butadienes; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009570:Nitriles; C113580:U 0126; D003994:Bucladesine; D011493:Protein Kinase C; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one