Degradation of PEP-19, a Calmodulin-Binding Protein, by Calpain Is Implicated in Neuronal Cell Death Induced by Intracellular Ca2+ Overload

Neuroscience. 2008 Jun 23;154(2):473-81. doi: 10.1016/j.neuroscience.2008.03.044. Epub 2008 Mar 26.

Abstract

Excessive elevation of intracellular Ca2+ levels and, subsequently, hyperactivation of Ca2+/calmodulin-dependent processes might play an important role in the pathologic events following cerebral ischemia. PEP-19 is a neuronally expressed polypeptide that acts as an endogenous negative regulator of calmodulin by inhibiting the association of calmodulin with enzymes and other proteins. The aims of the present study were to investigate the effect of PEP-19 overexpression on cell death triggered by Ca2+ overload and how the polypeptide levels are affected by glutamate-induced excitotoxicity and cerebral ischemia. Expression of PEP-19 in HEK293T cells suppressed calmodulin-dependent signaling and protected against cell death elicited by Ca2+ ionophore. Likewise, primary cortical neurons overexpressing PEP-19 became resistant to glutamate-induced cell death. In immunoprecipitation assay, wild type PEP-19 associated with calmodulin, whereas mutated PEP-19, which contains mutations within the calmodulin binding site of PEP-19, failed to associate with calmodulin. We found that the mutation abrogates both the ability to suppress calmodulin-dependent signaling and to protect cells from death. Additionally, the endogenous PEP-19 levels in neurons were significantly reduced following glutamate exposure, this reduction precedes neuronal cell death and can be blocked by treatment with calpain inhibitors. These data suggest that PEP-19 is a substrate for calpain, and that the decreased PEP-19 levels result from its degradation by calpain. A similar reduction of PEP-19 also occurred in the hippocampus of gerbils subjected to transient global ischemia. In contrast to the reduction in PEP-19, no changes in calmodulin occurred following excitotoxicity, suggesting the loss of negative regulation of calmodulin by PEP-19. Taken together, these results provide evidence that PEP-19 overexpression enhances resistance to Ca2+-mediated cytotoxicity, which might be mediated through calmodulin inhibition, and also raises the possibility that PEP-19 degradation by calpain might produce an aberrant activation of calmodulin functions, which in turn causes neuronal cell death.

MeSH terms

  • Animals
  • Blotting, Western
  • Calcium / toxicity*
  • Calmodulin / antagonists & inhibitors
  • Calmodulin-Binding Proteins / metabolism*
  • Calpain / metabolism*
  • Cell Death / drug effects
  • Cell Death / physiology
  • Cell Line
  • Cerebral Cortex / cytology
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / physiology
  • Cysteine Endopeptidases / metabolism
  • Excitatory Amino Acid Agonists / toxicity
  • Female
  • Gerbillinae
  • Glutamic Acid / toxicity
  • Humans
  • Neurons / drug effects
  • Neurons / physiology*
  • Neuroprotective Agents / pharmacology
  • Peptides / genetics
  • Peptides / metabolism*
  • Plasmids / genetics
  • Pregnancy
  • Rats
  • Reverse Transcriptase Polymerase Chain Reaction
  • Transfection

Substances

  • Calmodulin
  • Calmodulin-Binding Proteins
  • Excitatory Amino Acid Agonists
  • Neuroprotective Agents
  • Peptides
  • peptide 19, rat
  • Glutamic Acid
  • Calpain
  • Cysteine Endopeptidases
  • Calcium