Mechanisms of manganese-induced rat pheochromocytoma (PC12) cell death and cell differentiation

Mn is a neurotoxin that leads to a syndrome resembling Parkinson's disease after prolonged exposure to high concentrations. Our laboratory has been investigating the mechanism by which Mn induces neuronal cell death. To accomplish this, ire have utilized rat pheochromocytoma (PC12) cells as a model since they possess much of the biochemical machinery associated with dopaminergic neurons. Mn, like nerve growth factor (NGF), can induce neuronal differentiation of PC12 cells but Mn-induced cell differentiation is dependent on its interaction with the cell surface integrin receptors and basement membrane proteins, vitronectin or fibronectin. Similar to NGF Mn-induced neurtite outgrowth is dependent on the phosphorylation and activation of the MAP kinases, ERKI and 2 (p44/42). Unlike NGF, Mn is also cytotoxic having an IC50 value of similar to600 muM. Although many apoptotic signals are turned on by Mn, cell death is caused ultimately by disruption of mitochondrial function leading to loss of ATP. RT-PCR and immunoblotting studies suggest that some uptake of Mn into PC12 cells depends on the divalent metal transporter 1 (DMTI). DMTI exists in trio isoforms resulting from alternate splicing of a single gene product with one of the two mRNA species containing an iron response clement (IRE) motif downstream from the stop codon. The presence of the IRE provides a binding site for the iron response proteins (IRPI and 2); binding of either of these proteins could stabilize DMTI mRNA and would increase expression of the +IRE form of the transporter. Iron and Mn compete for transport into PC12 cells via DMTl, so removal of iron from the culture media enhances Mn toxicity. The two isoforms of DMTI ( IRE) are distributed in different subcellular compartments with the (+/-IRE) species selectively present in the nucleus of neuronal and neuronal-like cells. (C) 2002 Elsevier Science Inc. All rights reserved.