Lead (Pb²⁺) is a cytotoxic metal ion whose mechanism of action is not established. However, Pb²⁺ is known to interact with a wide variety of molecules involved in signal transduction. In this study the effect of Pb²⁺ on protein phosphorylation in bovine adrenal chromaffin cells and human SH SY5Y cells was examined. Cells were incubated with 32Pi for 1 h in the presence of Pb²⁺ (1–10 μM) and the proteins were separated by two-dimensional PAGE. An increase in the phosphorylation of a number of proteins was observed in response to Pb²⁺, including three spots, MW 25 kDa, and pI's in the range 4.0–4.5. These proteins were immunoidentified as three isoforms of the heat-shock protein 27 kDa (Hsp27), and the identity of the most basic spot was confirmed by amino acid sequencing. Phosphorylation of p38MAPK was increased by Pb²⁺ and the effect of Pb²⁺ on Hsp27 phosphorylation was blocked by the p38MAPK inhibitor SB203580 (1 μM). The results were similar for bovine chromaffin cells and human SH SY5Y cells. This is the first report showing that Pb²⁺ can modulate the phosphorylation state of Hsp27 via activation of the p38MAPK pathway.
Toxicology and Applied Pharmacology Vol. 178, Issue 1, p. 44-51