Differential Regulation of Nuclear and Cytosolic Ca2+ in HeLa Cells

doi:10.1074/jbc.271.49.31210

Differential Regulation of Nuclear and Cytosolic Ca²⁺ in HeLa Cells*

From the Department of Medical Biochemistry, University of Wales College of Medicine, Heath Park, Cardiff, CF4 4XN, United Kingdom and the
^§ Cardiovascular Division, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908

^‡ To whom correspondence should be addressed. Tel.: 44 (0)1222 742802; Fax: 44 (0)1222 766276.

Abstract

The results reported in this study address the controversial issue that nuclear free Ca²⁺ ([Ca²⁺]_n) may be regulated independently of cytosolic free Ca²⁺ ([Ca²⁺]_c). We have measured [Ca²⁺]_n and [Ca²⁺]_c with recombinant aequorin targeted to the nucleus and cytosol in HeLa cells. We found that histamine, ATP, and ionomycin increased [Ca²⁺]_c quantitatively more than [Ca²⁺]_n, although the time course of these changes was similar. The difference between [Ca²⁺]_c and [Ca²⁺]_n depended on the stimulus, and the relative difference between [Ca²⁺]_n and [Ca²⁺]_c was less with ionomycin than with histamine or ATP. After depletion of the internal Ca²⁺ store, restoration of extracellular Ca²⁺ resulted in only increased [Ca²⁺]_c without a significant increase in [Ca²⁺]_n. Treatment with cyclopiazonic acid resulted in a delayed increases in [Ca²⁺]_n compared to [Ca²⁺]_c. These differences in both timing and magnitude of nuclear Ca²⁺ signals confirm that the cell can limit or delay increases in nuclear free Ca²⁺. Taken with the fact that an inositol phosphate signaling system resides in the nucleus and its envelope, our data support the hypothesis that [Ca²⁺]_n may be independently regulated.

Footnotes

↵* This research was supported in part by grants from the Wellcome Trust and the Arthritis and Rheumatism Council, and by National Institutes of Health Grant HL38918. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

InsP₃

inositol 1,4,5-trisphosphate

[Ca²⁺]_n

nuclear free Ca²⁺

[Ca²⁺]_c

cytosolic free Ca²⁺

RAd

replication-deficient adenovirus

CPA

cyclopiazonic acid, RAdLA, RAd luciferase-aequorin

RAdNPA

RAd nucleoplasmin-aequorin

I_CRAC

calcium release-activated current

MOPS

4-morpholinepropanesulfonic acid.
- Received June 17, 1996.