Epidermal growth factor-mediated activation of the ETS domain transcription factor Elk-1 requires nuclear calcium

Cytosolic and nuclear Ca2+ have been shown to differentially regulate transcription. However, the impact of spatially distinct Ca2+ signals on mitogen-activated protein kinase-mediated gene expression remains unknown. Here we investigated the role of nuclear and cytosolic Ca2+ signals in epidermal growth factor (EGF)-induced transactivation of the ternary complex factor Elk-1 using a GAL4-Elk-1 construct. EGF increased Ca2+ in both the nucleus and cytosol of HepG2 or 293 cells. Pretreatment with the intracellular Ca2+ chelator bis(2-aminophenyl)ethyleneglycol-N,N N',N'-tetraacetic acid significantly reduced EGF-induced transactivation of Elk-1, indicating that EGF-stimulated Elk-1 transcriptional activity is dependent on intracellular Ca2+. To determine the relative contribution of nuclear and cytosolic Ca2+ signals during EGF-mediated Elk-1 transactivation, Ca2+ signals in either compartment were selectively impaired by targeted expression of the Ca2+ binding protein parvalbumin to either the nucleus or cytosol. Suppression of nuclear but not cytosolic Ca2+ signals inhibited EGF-induced transactivation of Elk-1. However, suppression of nuclear Ca2+ signals did not affect the ability of ERK either to become phosphorylated or to undergo translocation to the nucleus in response to EGF. Elk-1 phosphorylation and nuclear localization following EGF stimulation were also unaffected by suppressing nuclear Ca2+ signals. These results suggest that nuclear Ca2+ is required for EGF-mediated transcriptional activation of Elk-1 and that phosphorylation of Elk-1 alone is not sufficient to induce its transcriptional activation in response to EGF. Thus, subcellular targeting of parvalbumin reveals a distinct role for nuclear Ca2+ signals in mitogen-activated protein kinase-mediated gene transcription.