Effect of manganese on tyrosylprotein sulfotransferase activity in PC12 cells

Recent studies in our laboratory have revealed that Mn²⁺ is capable of promoting cell spreading and neurite outgrowth in PC12 cells, a process which is dependent on Mn²⁺ stimulation of the interaction between extracellular matrix (ECM) components and their corresponding integrin receptors. Since the major ECM proteins implicated in the Mn²⁺-induced morphogenesis, fibronectin and vitronectin, are both tyrosine sulfated, it was of interest to determine whether Mn²⁺ can regulate the activity of the enzyme responsible for tyrosine sulfation, tyrosylprotein sulfotransferase (TPST). Results of the present studies demonstrated that Mn²⁺ can suppress TPST activity in PC12 cells in both a time and concentration-dependent manner at concentrations of Mn²⁺ (0.1 to 1 mM) that promote morphological changes in PC12 cells. Since uptake of Mn²⁺ may occur via the Ca²⁺ channel, LaCl₃, an inhibitor of Ca²⁺ transport, was examined and found not to prevent the suppression of TPST activity induced by Mn²⁺, suggesting that Mn²⁺ may function at an extracellular site. Suppression of TPST activity occurred with cells plated in serum-free medium on a substrata consisting of either serum or polylysine, suggesting that attachment to extracellular matrix was not an absolute requirement for regulation of activity. Consistent with this is the fact that an RGD-containing pentapeptide did not prevent suppression of TPST activity. Results from the present study demonstrated that Mn²⁺ is capable of promoting the suppression of TPST activity in PC12 cells at concentrations that have been shown to induce cell spreading and neurite outgrowth. However, unlike the Mn²⁺-induced morphological changes, the presence of ECM proteins is not an absolute requirement for suppression of TPST activity.