A comparison of 60, 70, and 90 kDa stress protein expression in normal rat NRK-52 and human HK-2 kidney cell lines following in vitro exposure to arsenite and cadmium alone or in combination

Arsenite and cadmium are two potent nephrotoxicants and common Superfund site elements. These elements are included among the stress protein inducers, but information regarding relationships between toxicity produced by combinations of these agents to the stress protein response is lacking. In this study, the immortalized cell lines normal rat kidney NRK-52E and human kidney HK-2 were exposed in vitro to arsenite (As(3+)), cadmium (Cd(2+)), or to equimolar As(3+) plus Cd(2+) mixture combinations for 3 and 5 h over a concentration range of 0.1-100 microM. After a 12-h recovery period, cultured cells were then evaluated for expression of the 60, 70, and 90 kDa major stress protein families. Results indicated that expression of stress proteins varied depending on the species of kidney cells exposed, the exposure concentrations, and the length of exposure to each element on an individual basis and for combined mixtures. For the HK-2 kidney cell line, increased levels of the 70 kDa stress protein was observed for single and combined element exposures whereas there was no change or a decrease of stress proteins 60 and 90 kDa. Increased 70 kDa expression was observed for 10-microM doses of single elements and for a lower dose of 1 microM of the As plus Cd mixture at 3- and 5-h exposures. NRK-52 kidney cells exposed to equivalent doses of As(3+) and Cd(2+) alone or in combination showed increased levels of all stress proteins 60, 70, and 90 kDa. This increase was seen for 10 microM of the As plus Cd mixture at 3 h whereas for single element exposures, increased stress protein levels were generally observed for the 100-microM doses. At 5 h- exposure, 60 and 90 kDa levels increased for 10 microM of Cd(2+) and 60 kDa levels increased for 1 microM of As(3+). However, exposures to 10 microM of the As plus Cd mixture decreased 60 kDa protein expression to control levels at 5 h. For both kidney cell lines, there was a decrease in the stress protein expression levels for all three stress protein families for 100-microM doses of the mixture combination for 3- and 5-h exposures. These data indicate a dose- and combination-related correlation between depression of the stress protein response and the onset of overt cellular toxicity and/or cell death. The threshold for these changes was cell line specific.