Heat shock proteins (Hsp 70) response is not systematic to cell stress - Case of the mycotoxin ochratoxin A

Ochratoxin A (OTA) is a mycotoxin routinely detected in improperly stored animal and human food supplies as well as in human sera worldwide. OTA has multiple toxic effects; however, the most prominent is nephrotoxicity. Thus, OTA is involved in the pathogenesis of human nephropathy in Balkan areas. In this study, we address the question of the appropriate functioning of the basal cellular defense mechanisms, after exposure to OTA, which, up to now, has not been investigated satisfactorily. In this context, we have monitored the effect of OTA on (i) the inhibition of cell viability, (ii) the oxidative damage using the GSH depletion, (iii) the inhibition of protein synthesis through the incorporation of [H-3] Leucine and (iv) the induction of Hsp 70 gene expression as a parameter of cytotoxicity, oxidative damage and particularly as a protective and adaptative response. This study was conducted using the Human Hep G2 hepatocytes and monkey kidney Vero cells under exposure conditions ranging from non-cytotoxic to sub-lethal. Our results clearly showed that OTA inhibits cell proliferation, strongly reduces protein synthesis and induces the decrease of GSH in concentration-dependent manner in both Hep G2 and Vero cells. However, although cytotoxicity and oxidative damage (main inducers of Hsp expression) occur, no change was observed in Hsp 70 level under the multiple tested conditions. Inhibition of protein synthesis could not explain the absence of Hsp 70 response since concentrations, which did not influence protein synthesis, also failed to display the expected Hsp 70 response. Our data are consistent with recently published reports where considerable differences were noticed in the ability of relevant toxicants to induce Hsp. These results raised doubt about the universal character of Hsp induction which seems to be more complex than originally envisioned. It could be concluded that Hsp 70 induction is not systematic to cell stress. (C) 2007 Elsevier Ireland Ltd. All rights reserved.