Divergent effects of the MEKK-1/JNK pathway on NB2a/d1 differentiation: some activity is required for outgrowth and stabilization of neurites but overactivation inhibits both phenomena.
c-Jun N-terminal kinase (JNK), along with its upstream activator MEKK-1, is typically thought of as a stress-activated kinase that mediates apoptosis. However, additional studies indicate that the MEKK-1/JNK pathway mediates critical aspects of neuronal survival and differentiation. Herein, we demonstrate that transfection of differentiated NB2a/d1 cells with a construct expression constitutively activated (ca) MEKK-1 increases levels of phospho-dependent neurofilament (NF) immunoreactivity within perikarya, while expression of a dominant-negative (dn) form of MEKK-1 decreases it. Steady-state levels of perikaryal phospho-NF immunoreactivity are reduced and the increase resulting from expression of caMEKK-1 is prevented, by the JNK inhibitor SP600125, suggesting that JNK is a major downstream effector of MEKK-1 on NF phosphorylation. Unexpectedly, both caMEKK-1 and dnMEKK-1 inhibited neuritogenesis as well as translocation of NFs into newly elaborated neurites. The JNK inhibitor SP600125 also inhibited NF transport in a dose-dependent manner. caMEKK-1 also prevented the increase in NF transport otherwise mediated by MAP kinase. Finally, both caMEKK-1 and dnMEKK-1 prevented initial neuritogenesis. These findings indicate that the MEKK-1/JNK pathway regulates critical aspects of initial outgrowth, and subsequent stabilization of axonal neurites.
DeFuria
Jason
J
Departments of Biological Sciences and Biochemistry, Center Cell Neurobiology and Neurodegeneration Research, University of Massachusetts, Lowell, Lowell, MA 01854, USA.
Chen
Po
P
Shea
Thomas B
TB
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D045744:Cell Line, Tumor; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D048728:MAP Kinase Kinase Kinase 1 / Q000378:metabolism*; D051379:Mice; D016501:Neurites / Q000201:enzymology*; D009447:Neuroblastoma; D009454:Neurofibrils / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D021381:Protein Transport / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology
D048031:JNK Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1