Purkinje cell protein-2 (Pcp2) stimulates differentiation in PC12 cells by Gβγ -mediated activation of Ras and p38 MAPK

Purkinje cell protein-2 (Pcp2 or L7) is highly expressed in cerebellar Purkinje cells and retinal bipolar neurons and interacts with the Gαi/o family of G-proteins. Although the expression pattern of Pcp2 in the developing central nervous system suggests a role in differentiation, its function remains unknown. We established Tet-off inducible expression of Pcp2 in PC12 cells (rat pheochromocytoma cells) to determine whether Pcp2 regulates neuronal differentiation. Utilizing a polyclonal antibody, Pcp2 was localized in the cell body and throughout neurites of differentiated PC12 cells, similar to its localization in cerebellar Purkinje cells. Pcp2 expression in PC12 cells stimulated process formation (5-fold) and NGF (nerve growth factor)-stimulated neurite length (2-fold). Under basal conditions, Pcp2-PC12 cells demonstrated a 5-fold increase in Ras activation relative to noninduced PC12 cells and there was no change in extracellularsignal-regulated kinase 1/2 activity with Pcp2 expression. However, Pcp2 induction led to a >3-fold increase in basal p38 MAPK (mitogen-activated protein kinase) activity and the addition of NGF significantly stimulated both Ras and p38 MAPK in Pcp2PC12 cells relative to the controls. Pretreatment of Pcp2-PC12 cells with the p38-specific inhibitor SB203580 blocked both the increased neurite formation and NGF-stimulated neurite growth. Pertussis toxin treatment had no effect on neurite growth in control cells, but completely blocked Pcp2-mediated increased neurite growth. Transient transfection of the β-adrenergic receptor kinase C-terminus to prevent signalling through Gβγ in Pcp2-PC12 cells also inhibited the Pcp2-induced phenotype and reduced the Pcp2-stimulated Ras activation. Taken together, these findings demonstrate that Pcp2 induces differentiation in PC12 cells, in part through Gβγ -mediated Ras and p38 MAPK activation and suggest the potential for similar signalling mechanisms in Purkinje cells.