Introduction Stress proteins are ubiquitously expressed among living organisms ranging from bacteria to humans. Therefore, it is thought that they have essential functions for the survival of cells and in develop- mental processes. Some recent reports have demonstrated the cytoprotective functions of heat shock proteins (HSPs) against environmental stresses, and these functions are considered important in enabling living cells to tolerate envi- ronmental changes (1–3). There are several fami- lies of HSPs, defined on the basis of molecular weight (4), the structures of which are conserved from prokaryotic cells to eukaryotic cells (3). The high level of expression of some classes of HSPs has been identified as a conserved reaction of cells to physical, chemical and biological stimuli (5–7). HSPs are believed to assist cells to adapt or sur- vive by a rapid but transient reprogramming of cellular metabolic activity, to protect them from further oxidative and thermal stresses in respon- sive tissues (8, 9). Owing to its responsiveness to diverse forms of stress, the heat shock response has undergone widespread application in biomoni- toring and environmental toxicology (10). Potential mechanisms for protection by HSPs include the prevention of protein degradation, the maintenance of ATP levels, and the induction of classical scavengers such as glutathione, which itself plays a role in the induction of HSPs (11). Some groups of HSPs have chaperone activity. Chaperones represent a group of highly conserved protein species, which are localised in various cell compartments and assist newly synthesised pro- teins to fold or translocate through membranes, stabilise certain protein conformations, and help to eliminate denatured proteins by way of degradation (12, 13). The HSP70 family, whose members are found in the cytosol and in other cell compart- ments, play a major role in protein chaperone and cytoprotection activities. Under normal conditions, these proteins are involved in protein folding and assembly (14), and under adverse conditions they act as a cellular defence mechanism. The analysis of these proteins provides a possible biomarker of chemical-mediated toxicity. Under stress condi- tions, the synthesis of HSPs can be increased many fold (7), and so has the potential to provide a sensi- tive, highly-amplified toxicity signal. Increased Heat Shock Protein 70 Expression Following Toxicant-mediated Cytotoxicity: A Ubiquitous Marker of Toxicant Exposure? Parivash Farzaneh, 1,2 Abdolamir Allameh, 2 Steven Pratt, 1 Nicholas Moore, 1 Lucy Travis, 1 Elke Gottschalg, 1 Clive Kind 3 and Jeffrey Fry 1 1 School of Biomedical Sciences, University of Nottingham Medical School, Nottingham, UK; 2 Department of Biochemistry, Faculty of Medical Sciences, Tarbiat Modarres University, Tehran, Islamic Republic of Iran; 3 AstraZeneca, Loughborough, UK Summary — The up-regulation of heat shock protein (HSP) expression has been proposed as a general biomarker of cellular protection against various environmental stresses and chemicals. The present study investigated the possibility of using HSP70 up-regulation as a biomarker of toxicant exposure in vitro. Cells of a rat hepatoma cell line (FGC4) were exposed to concentrations of 1,3-dichloroacetone, duro- quinone, diquat dibromide, menadione, hydrogen peroxide, cadmium chloride (CdCl 2 ) and sodium (meta)arsenite (NaAsO 2 ) that elicited 20–50% cytotoxicity over a 24-hour period, and HSP70 levels were measured by ELISA. Up-regulation of HSP70 expression was demonstrated following treatment with menadione, CdCl 2 and NaAsO 2 , but not with the other chemicals tested. A shorter exposure time (6 hours) and/or the use of non-toxic concentrations reduced the level of HSP70 up-regulation with mena- dione, CdCl 2 and NaAsO 2 , but did not uncover any up-regulation with the other chemicals. Although the toxicity of the majority of the chemicals tested is believed to involve an oxidative stress component, the results of this study clearly demonstrate that up-regulation of HSP70 expression cannot be used as a gen- eral biomarker of toxicant exposure in vitro. Key words: arsenite, cadmium, cytotoxicity, dichloroacetone, diquat, duroquinone, heat shock protein, HSP70, hydrogen peroxide, menadione. Address for correspondence: J. Fry, School of Biomedical Sciences, University of Nottingham Medical School, Queen’s Medical Centre, Nottingham NG7 2UH, UK E-mail: jeff.fry@nottingham.ac.uk. ATLA 33, 105–110, 2005 105