All JNKs can kill, but nuclear localization is critical for neuronal death.
JNKs are implicated in a range of brain pathologies and receive considerable attention as potential therapeutic targets. However, JNKs also regulate physiological and homeostatic processes. An attractive hypothesis from the drug development perspective is that distinct JNK isoforms mediate "physiological" and "pathological" responses. However, this lacks experimental evaluation. Here we investigate the isoforms, subcellular pools, and c-Jun/ATF2 targets of JNK in death of central nervous system neurons following withdrawal of trophic support. We use gene knockouts, gene silencing, subcellularly targeted dominant negative constructs, and pharmacological inhibitors. Combined small interfering RNA knockdown of all JNKs 1, 2, and 3, provides substantial neuroprotection. In contrast, knockdown or knock-out of individual JNKs or two JNKs together does not protect. This explains why the evidence for JNK in neuronal death has to date been largely pharmacological. Complete knockdown of c-Jun and ATF2 using small interfering RNA also fails to protect, casting doubt on c-Jun as a critical effector of JNK in neuronal death. Nonetheless, the death requires nuclear but not cytosolic JNK activity as nuclear dominant negative inhibitors of JNK protect, whereas cytosolic inhibitors only block physiological JNK function. Thus any one of the three JNKs is capable of mediating apoptosis and inhibition of nuclear JNK is protective.
Björkblom
Benny
B
Turku Centre for Biotechnology, University of Turku and Abo Akademi University, Turku, FIN 20521 Finland.
Vainio
Jenni C
JC
Hongisto
Vesa
V
Herdegen
Thomas
T
Courtney
Michael J
MJ
Coffey
Eleanor T
ET
D051698:Activating Transcription Factor 2 / Q000378:metabolism; D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001927:Brain Diseases / Q000188:drug therapy / Q000201:enzymology; D002467:Cell Nucleus / Q000201:enzymology*; D003593:Cytoplasm / Q000201:enzymology; D020868:Gene Silencing; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D048057:Mitogen-Activated Protein Kinase 10 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048055:Mitogen-Activated Protein Kinase 8 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048056:Mitogen-Activated Protein Kinase 9 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009474:Neurons / Q000201:enzymology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology
D051698:Activating Transcription Factor 2; C497106:Atf2 protein, mouse; D007527:Isoenzymes; D047428:Protein Kinase Inhibitors; D016755:Proto-Oncogene Proteins c-jun; D034741:RNA, Small Interfering; D048057:Mitogen-Activated Protein Kinase 10; D048056:Mitogen-Activated Protein Kinase 9; D048055:Mitogen-Activated Protein Kinase 8