Activation of ERK1 and ERK2 is required for manganese-induced neurite outgrowth in rat pheochromocytoma (PC12) cells

Mn²⁺ treatment has been shown to promote neurite outgrowth in rat pheochromocytoma (PC12) cells in a time- and dose-dependent manner. This process is mediated through the interactions of extracellular matrix (ECM) proteins and integrin receptors. Studies were performed to determine whether the phosphorylation of the MAP kinases, ERK1 and 2, is required for Mn²⁺- induced neurite outgrowth. A time- and dose-dependent increase in phosphorylation of both ERK1 and 2 was observed upon treatment of PC12 cells with Mn²⁺. Phosphorylation of the ERKs occurred as early as 2 hr after initiating treatment, with a maximum increase occurring at approximately 24 hr. Inhibition of MEK with the specific inhibitor, PD98059, blocked the phosphorylation of ERK1 and 2 and increased Mn²⁺ toxicity. When cells were grown in serum-free defined medium, Mn²⁺-induced phosphorylation of ERK1 and ERK2 occurred in cells grown on surfaces treated with growth serum or fibronectin but not on surfaces treated with poly-L-lysine. In addition, the pentapeptide GRGDS, which blocks RGD-mediated interactions, inhibited Mn²⁺induced phosphorylation of ERK1 and 2. The Mn²⁺induced increase in phosphorylated ERK1 and 2 was not seen in a PC12 cell line that does not respond to Mn²⁺. These data support the hypothesis that integrin-mediated activation of the MAPK signal transduction pathway leading to the activation of ERK1 and 2 is required for Mn²⁺-induced PC12 differentiation and neurite outgrowth.