Manganese induces neurite outgrowth in PC12 cells via upregulation of alpha(v) integrins

Previous studies have demonstrated that the divalent cation manganese (Mn) causes PC12 cells to form neurites in the absence of NGF. Since divalent cations modulate the binding affinity and specificity of integrins, and integrin function affects neurite outgrowth, we tested the hypothesis that Mn induces neurite outgrowth through an integrin-dependent signaling pathway. Our studies support this hypothesis. Function-blocking antisera specific for beta(1) integrins block the neurite-promoting activity of Mn by 90-95%. Bioassays and biochemical studies with antisera specific for the alpha(v), alpha(5), or alpha(8) integrin subunit suggest that the alpha(v)beta(1) heterodimer is one of the principal beta(1) integrins mediating the response of PC12 cells to Mn. This is corroborated by studies in which Mn failed to induce neurite outgrowth in a clone of PC12 cells that does not express alpha(v) at levels detectable by immunoprecipitation or immunocytochemistry. SDS-PAGE analysis of biotinylated surface proteins immunoprecipitated from Mn-responsive PC12 cells, as well as confocal laser microscopy of PC12 immunostained for surface alpha(v) indicate that Mn increases the surface expression of alpha(v) integrins. This increase appears to be due in part to synthesis of alpha(v) since specific inhibitors of RNA and protein synthesis block the neurite-promoting activity of Mn. These data indicate that Mn induces neurite outgrowth in PC12 cells by upregulating alpha(v) integrins, suggesting that Mn potentially represents an additional mechanism for regulating the rate and direction of neurite outgrowth during development and regeneration.