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J. Biol. Chem., Vol. 277, Issue 42, 39713-39721, October 18, 2002

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Spontaneous Calcium Oscillations Control c-fos Transcription via the Serum Response Element in Neuroendocrine Cells^*

Andrés Maturana^§, Goedele Van Haasteren, Isabelle Piuz, Cyril Castelbou^§, Nicolas Demaurex^§¶, and Werner Schlegel

From the  Fondation pour Recherches Médicales, University of Geneva, 1211 Geneva 4, Switzerland and the ^§ Department of Physiology, University of Geneva Medical Center, 1211 Geneva 4, Switzerland

In excitable cells the localization of Ca²⁺ signals plays a central role in the cellular response, especially in the control of gene transcription. To study the effect of localized Ca²⁺ signals on the transcriptional activation of the c-fos oncogene, we stably expressed various c-fos -lactamase reporter constructs in pituitary AtT20 cells. A significant, but heterogenous expression of c-fos -lactamase was observed in unstimulated cells, and a further increase was observed using KCl depolarization, epidermal growth factor (EGF), pituitary adenylate cyclase-activating polypeptide (PACAP), and serum. The KCl response was almost abolished by a nuclear Ca²⁺ clamp, indicating that a rise in nuclear Ca²⁺ is required. In contrast, the basal expression was not affected by the nuclear Ca²⁺ clamp, but it was strongly reduced by nifedipine, a specific antagonist of L-type Ca²⁺ channels. Spontaneous Ca²⁺ oscillations, blocked by nifedipine, were observed in the cytosol but did not propagate to the nucleus, suggesting that a rise in cytosolic Ca²⁺ is sufficient for basal c-fos expression. Inactivation of the c-fos promoter cAMP/Ca²⁺ response element (CRE) had no effect on basal or stimulated expression, whereas inactivation of the serum response element (SRE) had the same marked inhibitory effect as nifedipine. These experiments suggest that in AtT20 cells spontaneous Ca²⁺ oscillations maintain a basal c-fos transcription through the serum response element. Further induction of c-fos expression by depolarization requires a nuclear Ca²⁺ increase.

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