Zn2+-induced NF-κB-dependent transcriptional activity involves site-specific p65/RelA phosphorylation

Zinc is an essential micronutrient, but is proinflammatory when inhaled into the lung. While it is recognized that zinc exposure of airway epithelial cells activates the transcription factor NF-κB and increases the expression of inflammatory cytokines to mediate this response, the underlying mechanism of NF-κB activation remains to be characterized. In this study, we investigated these Zn2+-induced signaling mechanisms in the BEAS-2B human airway epithelial cell line. Fifty micromolars Zn2+ induced NF-κB-dependent transcriptional activity. However, this occurred independently of IκBα degradation, an essential event in activation of the canonical NF-κB pathway, which is induced by physiological stimuli such as TNFα and IL-1β. We also observed that 50 μM Zn2+ exposure caused p65/RelA phosphorylation on Ser 276, Ser 529, and Ser 536 in both cytoplasmic and nuclear cell fractions. Mutational analysis pointed to Ser 536 of p65/RelA as the determinant of Zn2+-induced NF-κB transactivation in BEAS-2B cells. Pharmacological inhibition of IKKα/β activity reduced both Zn2+-induced p65/RelA phosphorylation at Ser 536 and NF-κB-dependent transcriptional activity, suggesting that IKKα/β is necessary for these Zn2+-induced effects. Taken together, these data show that exposure to supraphysiological concentrations of Zn2+ induces NF-κB-dependent transcription through an alternate mechanism, suggesting a novel pathway for cellular responses to environmental stress.