Regulation of c-Jun N-terminal kinase,p38 kinase and AP-1 DNA binding in cultured brain neurons: roles in glutamate excitotoxicity and lithium neuroprotection

In rat cerebellar granule cells, glutamate induced rapid activation of c-Jun N-terminal kinase (JNK) and p38 kinase to phosphorylate c-Jun (at Ser63) and p53 (at Ser15), respectively, and a subsequent marked increase in activator protein-1 (AP-1) binding that preceded apoptotic death. These glutamate-induced effects and apoptosis could largely be prevented by long-term (7 days) pretreatment with 0.5-2 mm lithium, an antibipolar drug. Glutamate's actions could also be prevented by known blockers of this pathway, MK-801 (an NMDA receptor blocker), SB 203580 (a p38 kinase inhibitor) and curcumin (an AP-1 binding inhibitor). The concentration- and time-dependent suppression of glutamate's effects by lithium and curcumin correlated well with their neuroprotective effects. These results suggest a prominent role of JNK and p38, as well as their downstream AP-1 binding activation and p53 phosphorylation in mediating glutamate excitotoxicity. Moreover, the neuroprotective effects of lithium are mediated, at least in part, by suppressing NMDA receptor-mediated activation of the mitogen-activated protein kinase pathway.     

c-Jun N-terminal protein kinase signalling pathway mediates lovastatin-induced rat brain neuroblast apoptosis

We have previously shown that lovastatin, an HMG-CoA reductase inhibitor, induces apoptosis in rat brain neuroblasts. c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) are implicated in regulation of neuronal apoptosis. In this work, we investigated the role of JNK and p38 MAPK in neuroblast apoptosis induced by lovastatin. We found that lovastatin induced the activation of JNK, but not p38 MAPK. It also induced c-Jun phosphorylation with a subsequent increase in activator protein-1 (AP-1) binding, AP-1-mediated gene expression and BimEL protein levels. The effects of lovastatin were prevented by mevalonate. Pre-treatment with iJNK-I (a selective JNK inhibitor) prevented the effect of lovastatin on both neuroblast apoptosis and the activation of the JNK cascade. Furthermore, we found that the activation of the JNK signalling pathway triggered by lovastatin is accompanied by caspase-3 activation which is also inhibited by iJNK-I pre-treatment. Finally, a specific inhibitor of p38 MAPK, SB203580, had no effect on lovastatin-induced neuroblast apoptosis. Taken together, our data suggest that the activation of the JNK/c-Jun/BimEL signalling pathway plays a crucial role in lovastatin-induced neuroblast apoptosis. Our findings may also contribute to elucidate the intracellular mechanisms involved in the central nervous system side effects associated with statin therapy.     

JNK1 differentially regulates osteopontin-induced nuclear factor-inducing kinase/MEKK1-dependent activating protein-1-mediated promatrix metalloproteinase-9 activation

We have recently demonstrated that nuclear factor-inducing kinase (NIK) plays a crucial role in osteopontin (OPN)-induced mitogen-activated protein kinase/I kappa B alpha kinase-dependent nuclear factor kappa B (NF kappa B)-mediated promatrix metalloproteinase-9 activation (Rangaswami, H., Bulbule, A., and Kundu, G. C. (2004) J. Biol. Chem. 279, 38921-38935). However, the molecular mechanism(s) by which OPN regulates NIK/MEKK1-dependent activating protein-1 (AP-1)-mediated promatrix metalloproteinase-9 activation and whether JNK1 plays any role in regulating both these pathways that control the cell motility are not well defined. Here we report that OPN induces alpha v beta3 integrin-mediated MEKK1 phosphorylation and MEKK1-dependent JNK1 phosphorylation and activation. Overexpression of NIK enhances OPN-induced c-Jun expression, whereas overexpressed NIK had no role in OPN-induced JNK1 phosphorylation and activation. Sustained activation of JNK1 by overexpression of wild type but not kinase negative MEKK1 resulted in suppression of ERK1/2 activation. But this did not affect the OPN-induced NIK-dependent ERK1/2 activation. OPN stimulated both NIK and MEKK1-dependent c-Jun expression, leading to AP-1 activation, whereas NIK-dependent AP-1 activation is independent of JNK1. OPN also enhanced JNK1-dependent/independent AP-1-mediated urokinase type plasminogen activator (uPA) secretion, uPA-dependent promatrix metalloproteinase-9 (MMP-9) activation, cell motility, and invasion. OPN stimulates tumor growth, and the levels of c-Jun, AP-1, urokinase type plasminogen activator, and MMP-9 were higher in OPN-induced tumor compared with control. To our knowledge this is first report that OPN induces NIK/MEKK1-mediated JNK1-dependent/independent AP-1-mediated pro-MMP-9 activation and regulates the negative crosstalk between NIK/ERK1/2 and MEKK1/JNK1 pathways that ultimately controls the cell motility, invasiveness, and tumor growth.