NAP, a neuroprotective drug candidate in clinical trials, stimulates microtubule assembly in the living cell.

NAP (NAPVSIPQ), derived from activity-dependent neuroprotective protein (ADNP) provides neuroprotection in vitro and in vivo against a wide variety of neurotoxic substances. To further understand the mechanism by which NAP provides broad neuroprotection it was essential to find NAP's binding partners. Previous results, using affinity chromatography coupled with mass spectrometry, identified tubulin, the subunit protein of microtubules, as the major NAP binding protein in neurons and glial cells. Here, following microtubule depolymerization in the presence of nocodazole, NAP treatment enhanced rapid microtubule assembly and stimulated neurite outgrowth. Nocodazole is an established inhibitor of axoplasmic transport and cell division that exerts its effect by depolymerizing microtubules. NAP shows selectivity in interacting with brain tubulin and does not affect dividing cells. This data demonstrates that NAP functions as a neuroprotectant, at least in part, through its interaction with tubulin with a resulting increase in microtubule assembly.