Overexpression of HSP-70 attenuates increases in [Ca2+]i and protects human epidermoid A-431 cells after chemical hypoxia.

Abstract

This laboratory previously reported that thermotolerance diminishes the NaCN-induced increase in intracellular free calcium concentrations ([Ca2+]i) in human epidermoid A-431 cells and that blocking this increase protects the cells from NaCN toxicity. In this study, we report that cell viability after exposure to NaCN (10 mM, 1 h) is enhanced by the overexpression of HSP-70 resulting from heat shock (45 degrees C, 10 min), treatment with a protein kinase C activator phorbol 12 myristate 13-acetate (PMA; 1 microM, 4 h), or HSP-70 cDNA transfection. Because the toxicity of NaCN is mediated by increases in [Ca2+]i, we sought to determine whether the overexpression of HSP-70 might protect the cells by altering the [Ca2+]i response induced by NaCN. Basal [Ca2+]i in vector-, HSF1 cDNA-, and HSP-70 cDNA-transfected cells was 114 +/- 11 (n = 11), 95 +/- 5 (n = 6), and 151 +/- 11 (n = 15) nM, respectively, suggesting that HSP-70 metabolism is associated with maintenance of resting [Ca2+]i. Removal of external Ca2+ reduced the resting [Ca2+]i in all of these cells. With external Ca2+ reduced the resting [Ca2+]i by 97 +/- 21% in vector-transfected cells and 111 +/- 5% in HSF1 vector-transfected cells but by only 27 +/- 8% in HSP-70 cDNA-transfected cells. Heat shock or PMA treatment of vector- or HSF1 cDNA-transfected cells to induce HSP-70 also attenuated the NaCN-induced increase in [Ca2+]i, perhaps because of a decrease in Vmax for the uptake of external Ca2+. Removal of external Ca2+ or treatment with inhibitors of Na+/Ca2+ exchangers eliminated the NaCN-induced increase in [Ca2+]i in HSP-70 cDNA-transfected cells, but ryanodine treatment did not. HSP-70 cDNA transfection also reduced Ca2+ mobilization stimulated by various Ca(2+)-mobilizing agents. The results suggest that HSP-70 overexpression protects cells from NaCN cytotoxicity, perhaps by attenuating the [Ca2+]i response.

• Authors: J G Kiang, X Z Ding, D E McClain
• Journal: Toxicology and applied pharmacology (Toxicol Appl Pharmacol) Vol. 149 Issue 2 Pg. 185-94 (Apr 1998) ISSN: 0041-008X [Print] United States
• PMID: 9571987 (Publication Type: Journal Article, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• DNA, Complementary
• Enzyme Inhibitors
• HSP70 Heat-Shock Proteins
• Sodium-Calcium Exchanger
• Protein Kinase C
• Tetradecanoylphorbol Acetate
• Sodium Cyanide
• Calcium

Topics

• Calcium (metabolism)
• Cell Hypoxia
• DNA, Complementary (genetics)
• Enzyme Inhibitors (toxicity)
• HSP70 Heat-Shock Proteins (biosynthesis, genetics)
• Hot Temperature
• Humans
• Protein Kinase C (metabolism)
• Sodium Cyanide (toxicity)
• Sodium-Calcium Exchanger (drug effects)
• Tetradecanoylphorbol Acetate
• Transfection
• Tumor Cells, Cultured (drug effects)