NMDA receptor stimulation induces temporary α-tubulin degradation signaled by nitric oxide-mediated tyrosine nitration in the nervous system of Sepia officinalis

Abstract

Biochemical and immunohistochemical evidence is reported, showing basal protein nitration in specific regions of the optic lobes of Sepia officinalis, mainly in the fiber layers of the plexiform zone. SDS–PAGE analysis of optic lobe extracts revealed an intense 3-nitrotyrosine immunoreactive band identified as α-tubulin by immunoprecipitation and partial purification. Stimulation of NMDA receptors resulted in a selective decrease in α-tubulin levels within 30 min with partial recovery after 4 h. The effect was suppressed by the NO synthase (NOS) inhibitor l-nitroarginine. Incubation of optic lobes with free 3-nitrotyrosine resulted likewise in a selective loss of α-tubulin, due apparently to incorporation of the amino acid into the C-terminus of detyrosinated α-tubulin to give the nitrated protein purportedly more susceptible to degradation. Overall, these results point to a novel potential physiologic role of NO and free 3-nitrotyrosine in the control of the α-tubulin tyrosination/detyrosination cycle and turnover in Sepia nervous tissue.