Role of Ca2+ in the regulation of nickel-inducible Cap43 gene expression

We have recently cloned a gene, Cap43, that was significantly induced by exposure to nontoxic levels of both water-soluble and -insoluble Ni2+ compounds. In this paper, we utilized the expression levels of this gene as a tool to identify second messengers involved in nickel-inducible transcription. We report here that the Ca2+ ionophore A23187 substantially stimulated Cap43 gene expression. In addition, we found that BAPTA-AM, a specific chelator of free intracellular Ca2+, consistently attenuated the induction of Cap43, indicating that elevation of intracellular Ca2+ was essential for this response. TPEN, a chelator of heavy metals, such as Ni2+ With a very low affinity for Ca2+, did not attenuate Cap43 induced by Ni or calcium ionophore, suggesting that elevations of Ca2+ but probably not elevations of other metal ions were involved in the induction of Cap43, A direct measurement of Ca2+ levels using the fluorescent probe Fluo-3 AM showed elevations of free intracellular Ca2+ in Ni-treated cells. A strong induction of Cap43 by okadaic acid suggested the involvement of a serine/threonine phosphorylation in a signaling pathway that was presumably activated by Ni and that led to enhanced Cap43 gene expression. However, calcium-dependent protein kinase(s) involved in the nickel-activated signaling pathway remains to be identified. (C) 1999 Academic Press.