Inhibition of mitogen-activated protein kinase kinase induces apoptosis of human chondrocytes.
We previously have reported that the mitogen-activated protein kinase (MAPK) pathway is stimulated by adhesion of human chondrocytes to anti-beta(1)-integrin antibodies or collagen type II in vitro. These mechanisms most likely prevent chondrocyte dedifferentiation to fibroblast-like cells and chondrocyte death. To investigate whether this pathway plays an essential role for the differentiation, phenotype, and survival of chondrocytes, we blocked mitogen-activated protein kinase/extracellular signal-regulated kinase (Erk) (MEK), a kinase upstream of the kinase Erk by using U0126. Exposure of chondrocytes to U0126 caused activation of caspase-3 in a dose-dependent manner. Western blot analysis with an antibody specific for dually phosphorylated Erk shows that collagen type II induced phosphorylation of Erk1/2 was specifically blocked by U0126 in a dose-dependent manner. Immunohistochemical analysis showed that treated chondrocytes were caspase-3 positive. In treated chondrocytes, the cleavage of 116-kDa poly(ADP-ribose)polymerase resulted in the 85-kDa apoptosis-related cleavage fragment and was associated with caspase-3 activity. Analysis by electron microscopy showed typical morphological signs of apoptosis, such as crescent-shaped clumps of heterochromatin, and a degraded pericellular matrix. Thus, these results indicate that the MEK/Erk signal transduction pathway is involved in the maintenance of chondrocytes differentiation and survival. These data stimulate further investigations on the role of mitogen-activated protein kinase pathways in human chondrocytes.
Shakibaei
M
M
Institute of Anatomy, Freie Universität Berlin, Königin-Luise-Strasse 15, D-14195 Berlin, Germany. mehshaki@zedat.fu-berlin.de
Schulze-Tanzil
G
G
de Souza
P
P
John
T
T
Rahmanzadeh
M
M
Rahmanzadeh
R
R
Merker
H J
HJ
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002070:Butadienes / Q000494:pharmacology*; D002467:Cell Nucleus / Q000187:drug effects / Q000648:ultrastructure; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006570:Heterochromatin / Q000187:drug effects / Q000648:ultrastructure; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism
D002070:Butadienes; D004791:Enzyme Inhibitors; D006570:Heterochromatin; D009570:Nitriles; C113580:U 0126; D007334:Insulin-Like Growth Factor I; D011065:Poly(ADP-ribose) Polymerases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases