Overexpression of a neuropeptide nociceptin/orphanin FQ precursor gene, N23K/N27K, induces neurite outgrowth in mouse NS20Y cells.

We recently discovered N23K and its splicing variant N27K as transcripts upregulated in mouse NS20Y cells after differentiation induced by dibutylyl cyclic AMP (dbcAMP) treatment. N23K and N27K encode precursor proteins for an opioid neuropeptide, nociceptin/orphanin FQ, but the transient expression of N23K and N27K suggests that it may be involved in neuronal differentiation. In the present study, we report that NS20Y cells transfected with N23K and/or N27K but not with vector alone formed neurites, with the expressed protein distributed in the perinuclear region and distal parts of the neurites. The granular staining of the N23K and N27K proteins was also colocalized with secretogranin I, indicating incorporation into large dense core vesicles. This cellular targeting of the N23K and/or N27K protein is similar to that of dbcAMP-induced processes in nontransfected NS20Y cells. In addition, the neurites of transfectants that expressed both N23K and N27K were longer than those of the transfectants that expressed N23K or N27K alone. Our results demonstrate that N23K and N27K participate in the regulation of neurite outgrowth.