Stress-activated protein kinases are negatively regulated by cell density.
Stimulation by UV irradiation, TNFalpha, as well as PDGF or EGF activates the JNK/SAPK signalling pathway in mouse fibroblasts. This results in the phosphorylation of the N-terminal domain of c-Jun, increasing its transactivation potency. Using an antibody that specifically recognizes c-Jun phosphorylated at Ser63, we show that culture confluency drastically inhibited c-Jun N-terminal phosphorylation due to the inhibition of the JNK/SAPK pathway. Transfection experiments demonstrate that the inhibition occurs at the same level as, or upstream of, the small G-proteins cdc42 and Rac1. In contrast, the classical MAPK pathway was insensitive to confluency. The inhibition of JNK/SAPK activation depended on the integrity of the actin microfilament network. These results were confirmed and extended in monolayer wounding experiments. After PDGF, EGF or UV stimulation, c-Jun was predominantly phosphorylated in cells bordering the wound, which are the cells that move to occupy the wounded area. Thus, modulation of the stress-dependent signal cascade by confluency will restrict c-Jun N-terminal phosphorylation in response to mitogenic or chemotactic agents to cells that border a wounded area.
Lallemand
D
D
Unité des Virus Oncogènes, Unité associée 1644 du Centre National de la Recherche Scientifique, Paris Cedex 15 France.
Ham
J
J
Garbay
S
S
Bakiri
L
L
Traincard
F
F
Jeannequin
O
O
Pfarr
C M
CM
Yaniv
M
M
D000199:Actins / Q000378:metabolism; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002452:Cell Count; D018797:Cell Cycle Proteins / Q000378:metabolism; D002465:Cell Movement; D003599:Cytoskeleton / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology* / Q000187:drug effects / Q000528:radiation effects; D019204:GTP-Binding Proteins / Q000378:metabolism; D006133:Growth Substances / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D051379:Mice; D020928:Mitogen-Activated Protein Kinases; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D015398:Signal Transduction; D014466:Ultraviolet Rays; D020764:cdc42 GTP-Binding Protein; D048051:p38 Mitogen-Activated Protein Kinases; D020744:rac GTP-Binding Proteins
D000199:Actins; D018797:Cell Cycle Proteins; D006133:Growth Substances; D016755:Proto-Oncogene Proteins c-jun; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins