Depletion of intracellular calcium stores by calcium ionophore A23187 induces the genes for glucose-regulated proteins in hamster fibroblasts.

Animal cells respond to calcium ionophore (A23187) treatment with the coordinate induction of a set of genes encoding proteins identical to the glucose-regulated proteins (GRPs). By monitoring the intracellular free calcium with the fluorescent indicator fura-2 while employing both intracellular and extracellular calcium buffers, we demonstrated that A23187 can induce the GRP94 and GRP78 genes without an increase in cytoplasmic calcium ([Ca2+]i). Induction of GRP mRNA during glucose starvation was also independent of [Ca2+]i. Instead, gene induction by A23187 was closely correlated with the depletion of intracellular calcium stores. We conclude that perturbations of sequestered calcium ions by A23187 can serve as a stimulus for gene expression.