Divalent lead cations induce cyclooxygenase-2 gene expression by epidermal growth factor receptor/nuclear factor-kappa B signaling in A431carcinoma cells

Divalent lead cations (Pb ²⁺) are toxic metal pollutants that may contribute to inflammatory diseases in people and animals. Human vascular smooth muscle cells in culture respond to low concentrations of Pb ²⁺ ions by activating mediators of inflammation via the plasma membrane epidermal growth factor receptor (EGFR). These include cyclooxygenase-2 (COX-2) and cytosolic phospholipase A ₂ as well as the hormone-like lipid compound prostaglandin E ₂. To further clarify the mechanism by which Pb ²⁺ induces such mediators of inflammation, we tested human epidermoid carcinoma cell line A431 that expresses high levels of EGFR. Reverse transcription PCR and western blots confirmed A431 cells treated with a low concentration (1μM) of Pb ²⁺ in the form of lead (II) nitrate increased expression of COX-2 mRNA and its encoded protein in a time-dependent manner. Promoter deletion analysis revealed the transcription factor known as nuclear factor-kappa B (NF-κB) was a necessary component of the COX-2 gene response. NF-κB inhibitor BAY 11-7082 suppressed Pb ²⁺-induced COX-2 mRNA expression, and EGFR inhibitors AG1478 and PD153035 as well as EGFR small interfering RNA reduced the coincident nuclear translocation of NF-κB. Our findings support the hypothesis that low concentrations of Pb2 ⁺ ions incite inflammation by inducing COX-2 gene expression via the EGFR/NF-κB signal transduction pathway.