We have recently cloned a gene, Cap43, that was significantly induced by ex
posure to nontoxic levels of both water-soluble and -insoluble Ni2+ compoun
ds. 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 Cap4
3 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 re
sponse. TPEN, a chelator of heavy metals, such as Ni2+ With a very low affi
nity for Ca2+, did not attenuate Cap43 induced by Ni or calcium ionophore,
suggesting that elevations of Ca2+ but probably not elevations of other met
al ions were involved in the induction of Cap43, A direct measurement of Ca
2+ levels using the fluorescent probe Fluo-3 AM showed elevations of free i
ntracellular Ca2+ in Ni-treated cells. A strong induction of Cap43 by okada
ic acid suggested the involvement of a serine/threonine phosphorylation in
a signaling pathway that was presumably activated by Ni and that led to enh
anced Cap43 gene expression. However, calcium-dependent protein kinase(s) i
nvolved in the nickel-activated signaling pathway remains to be identified.
(C) 1999 Academic Press.