Inhibition of HSP70 Expression by Calcium Ionophore A23187 in Human Cells

doi:10.1074/jbc.271.27.16111

Inhibition of HSP70 Expression by Calcium Ionophore A23187 in Human Cells

AN EFFECT INDEPENDENT OF THE ACQUISITION OF DNA-BINDING ACTIVITY BY THE HEAT SHOCK TRANSCRIPTION FACTOR*

From the ^‡ Institute of Experimental Medicine, Consiglio Nazionale delle Ricerche, Viale K. Marx, 15/43, 00137 Rome, Italy and the
^§ Department of Experimental Medicine, University of L'Aquila, 67100 L'Aquila, Italy

^¶ To whom correspondence should be addressed:
Inst. of Experimental Medicine, CNR, Viale K. Marx, 15/43, 00137 Roma RM, Italy.
Tel.: 39-6-86090325; Fax: 39-6-86090332.

Abstract

Heat shock proteins (HSPs) are induced in mammalian cells in a variety of pathophysiological states and have an important role in cytoprotection in vitro and in vivo. In this study, we report that the calcium ionophore A23187, a glucose-regulated protein (GRP) inducer, dramatically inhibits HSP70 synthesis and HSP70 mRNA transcription after induction by heat shock, sodium arsenite, or prostaglandin A₁ treatment in human K562 cells. A23187 does not suppress, and it actually prolongs, the DNA-binding activity of the human heat shock transcription factor (HSF), while it alters HSF1 phosphorylation in heat shock-treated cells. To inhibit HSP70 expression, A23187 needs to be present during heat shock, while treatment before or after heat shock does not affect HSP70 mRNA transcription. The GRP inducer thapsigargin, which specifically inhibits the endoplasmic reticulum Ca²⁺-ATPase, has no effect on heat-induced HSP70 synthesis, indicating that A23187 inhibitory activity is not due to depletion of intracellular calcium stores and is independent of the concomitant induction of GRP genes. Inhibition of HSP70 expression is correlated with alterations in HSF1 phosphorylation in heat-shocked cells, but not in sodium arsenite-treated cells, indicating that different mechanisms may be involved in mediating A23187 inhibitory activity.

Footnotes

↵* This work was supported by grants from the Italian Ministry of Public Health (IX AIDS Research Project) and from the Italian National Research Council (Progetto Finalizzato “ACRO”). 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:

HSPs

heat shock proteins

HSF

heat shock transcription factor

HSE

heat shock element

GRP

glucose-regulated protein

PAGE

polyacrylamide gel electrophoresis

GAPDH

glyceraldehyde-phosphate dehydrogenase

EMSA

electrophoretic mobility shift assay

PGA₁

prostaglandin A₁.
↵² A. De Marco and M. G. Santoro, unpublished observation.
↵³ G. Elia and M. G. Santoro, unpublished observation.
- Received November 27, 1995.
- Revision received April 10, 1996.