Protein kinase Cδ-mediated proteasomal degradation of MAP kinase phosphatase-1 contributes to glutamate-induced neuronal cell death

Abstract

Mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) is a dual-specificity phosphatase that is involved in the regulation of cell survival, differentiation and apoptosis through inactivating MAPKs by dephosphorylation. Here, we provide evidence for a role of MKP-1 in the glutamate-induced cell death of HT22 hippocampal cells and primary mouse cortical neurons. We suggest that, during glutamate-induced oxidative stress, protein kinase C (PKC) δ becomes activated and induces sustained activation of extracellular signal-regulated kinase 1/2 (ERK1/2) through a mechanism that involves degradation of MKP-1. Glutamate-induced activation of ERK1/2 was blocked by inhibition of PKCδ, confirming that ERK1/2 is regulated by PKCδ. Prolonged exposure to glutamate caused reduction in the protein level of MKP-1, which correlated with the sustained activation of ERK1/2. Furthermore, knockdown of endogenous MKP-1 by small interfering (si)RNA resulted in pronounced enhancement of ERK1/2 phosphorylation accompanied by increased cytotoxicity under glutamate exposure. In glutamate-treated cells, MKP-1 was polyubiquitylated and proteasome inhibitors markedly blocked the degradation of MKP-1. Moreover, inhibition of glutamate-induced PKCδ activation suppressed the downregulation and ubiquitylation of MKP-1. Taken together, these results demonstrate that activation of PKCδ triggers degradation of MKP-1 through the ubiquitin-proteasome pathway, thereby contributing to persistent activation of ERK1/2 under glutamate-induced oxidative toxicity.

Preconditioning Mediated by Sublethal Oxygen—Glucose Deprivation-Induced Cyclooxygenase-2 Expression via the Signal Transducers and Activators of Transcription 3 Phosphorylation

“…In our previous study, we showed that ePKC mediated ischemic PC neuroprotection in vitro (Bright et al, 2004;Choi et al, 2006;Kim et al, 2007;Lange-Asschenfeldt et al, 2004;Perez-Pinzon et al, 2005;Raval et al, 2003Raval et al, , 2005. We also showed that ePKC activation induced phosphorylation of ERK1/2, which indicated activation of ERK1/2 and which was downstream of ePKC activation (Kim et al, 2007).…”

MKP-1 antagonizes C/EBP β activity and lowers the apoptotic threshold after ischemic injury

“…Likewise, in neural tissue, BDNF-TrkB receptor signaling stimulates MKP-1 activity and facilitates ischemic tolerance, whereas loss of MKP-1 function sensitizes neuronal cells to glutamate-mediated toxicity. 34,35 However, it is possible that like other preconditioning paradigms, low-grade injury induced by MKP-1 produces protection through compensatory induction of endogenous protective genes. It is also possible that MKP-1-C/EBPb effects may vary depending on the cellular context.…”

Neuroprotective Effect of Protein Kinase Cδ Inhibitor Rottlerin in Cell Culture and Animal Models of Parkinson's Disease

“…Overexpression of the dominant-negative mutants, PKC␦ D327A (caspase-cleavage resistant), PKC␦ K376R (kinase inactive), and PKC␦ Y311F (phosphorylation defective) loss-of-function mutants, as well as suppression of PKC␦ by siRNA provided protection against apoptotic cell death induced by various dopaminergic toxins, including MPP ϩ , in dopaminergic neuronal cells (Kaul et al, 2003(Kaul et al, , 2005Yang et al, 2004). Recently, another study showed that glutamate-induced cell death was significantly attenuated in cells transfected with PKC␦ siRNA, suggesting that PKC␦ may play an important role in excitotoxicity (Choi et al, 2006). An excitotoxic mechanism has been proposed in degenerative processes of PD (Greenamyre and Hastings, 2004).…”