Overexpression of HSP-70 Attenuates Increases in [Ca2+]i and Protects Human Epidermoid A-431 Cells after Chemical Hypoxia

Authors: Kiang J.G.¹; Ding X.Z.¹; McClain D.E.²

Source: Toxicology and Applied Pharmacology, Volume 149, Number 2, April 1998 , pp. 185-194(10)

Publisher: Academic Press

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?C, 10 min), treatment with a protein kinase C activator phorbol 12 myristate 13-acetate (PMA; 1 muM, 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+ present, NaCN increased [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 Ca2+-mobilizing agents. The results suggest that HSP-70 overexpression protects cells from NaCN cytotoxicity, perhaps by attenuating the [Ca2+]i response.

Language: English

Document Type: Research article

Affiliations: 1: Division of Medicine, Walter Reed Army Institute of Research, Washington, DC, 20307-5100 2: Radiation Biochemistry Department, Armed Forces Radiobiology Research Institute, Bethesda, Maryland, 20889-5154

Publication date: 1998-04-01

• In this: publication
• By this: publisher
• In this Subject: Biology ,  Ecology ,  Therapeutics & Alternative Medicine ,  Toxicology ,  Biochemistry
• By this author: Kiang J.G. ;  Ding X.Z. ;  McClain D.E.

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