Neuronal depolarization enhances the transcription of the neuronal serine protease inhibitor neuroserpin

Neuroserpin is an axonally secreted neuronal serine protease inhibitor. Based on its inhibitory activity towards tissue plasminogen activator (tPA) and its predominant expression in the cerebral cortex, the hippocampus, and the amygdala, a role for neuroserpin in the regulation of neural plasticity has been suggested. We recently found that neuroserpin mRNA is increased in cultured hippocampal neurons upon depolarization with elevated extracellular KCl. Using luciferase reporter constructs containing segments of the promoter region of the neuroserpin gene, we identified a 200-bp segment near the transcription initiation site that is responsible for both the neuron- specific expression of the neuroserpin gene and the enhanced transcription resulting from depolarization. Nerve growth factor, which alone had no effect on the expression of neuroserpin mRNA in hippocampal neurons, had a marked potentiating effect when supplied in combination with elevated extracellular KCl. In contrast, the transcription factor zif/268 blocked neuroserpin transcription. These results implicate neuroserpin as an activity-regulated modulator of tPA activity at the synapse and provide further support for the occurrence of activity-regulated proteolytic processes at the synapse.