Modulation of cell migration by neuritin (Cpg15)

Neuritin (Nrn or cpg15) is a GPI-anchored protein identified among a pool of candidate plasticity-related genes induced by kainate in rat hippocampus. It is involved in neurite elongation, and promotes synaptic maturation. Its expression is regulated by neurotrophines, NGF, calcium levels and androgens. Neuronal migration involves molecular mechanisms which are often similar to those involved in neurite outgrowth: cytoskeletal dynamic, cell adhesion, and chemoattraction/repulsion. A preliminary microarray analysis performed on Gn11 cells (a model widely utilized to study cell migration) showed Nrn as one of the more abundant genes expressed in this cell line. Therefore, our goal was to investigate whether Nrn regulates neuronal migration. To this aim, we used two similar cell lines, characterized by a different migratory behavior: Gn11 cells (migrating) and GT1-7 cells (non migrating), and analyzed Nrn mRNA and protein expression levels. Interestingly, Nrn1 expression was much higher in migrating Gn11 cells than in non-migrating GT1-7 cells. In Boyden microchemotaxis and wound-healing assays, the migratory ability of Gn11 cells was reduced by Nrn silencing, and increased by Nrn over-expression. This effect was confirmed utilizing cultures derived from rat ganglionic eminence and by electroporating living brain slices with a Nrn-encoding plasmid into the ganglionic eminences. ICC and Western blot analyses of post-translational modifications of alpha-tubulin known to be associated with different microtubule dynamics showed an enrichment of stable microtubules in Nrn silenced cells that likely reflects the diminished migratory capability of the cells. These results demonstrate that the migratory properties of neuronal cells may be altered by modulating Nrn levels and strongly suggest, for the first time, that Nrn is a regulator of cell migration. (Grants: Telethon-GGP06063, and GGP07063; Italian Ministry of Labour, Health and Social Affairs; Fondazione Cariplo, University of Milan).