Expression of hsp 27, hsp 60, hsc 70, and hsp 70 stress response genes in cultured human urothelial cells (UROtsa) exposed to lethal and sublethal concentrations of sodium arsenite

The stress response is one mechanism that the bladder urothelium could potentially employ to protect itself from cellular damage after exposure to arsenic and, in so doing, influence the shape of the dose-response curve at low concentrations of exposure to this environmental pollutant. In the present study, we used the cultured human urothelial cell line UROtsa, a model of human urothelium, to determine the expression of heat shock proteins hsp 27, hsp 60, hsc 70, and hsp 70 after acute and extended exposure of the cells to lethal and sublethal levels of sodium arsenite (NaAsO₂). Acute exposure was modeled by exposing confluent cultures of UROtsa cells to 100 μM NaAsO₂ for 4 hr followed by a 48-hr recovery period. Extended exposure was modeled by exposing confluent UROtsa cells to 1,4, and 8 μM NaAsO₂ for 16 days, with the highest concentration producing cell death by 4 days of exposure. The expression of hsp 27, hsp 60, hsc 70 mRNA and protein was determined by reverse-transcription polymerase chain reaction and Western analysis. Cell viability was determined by the MTT [(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. The results demostrated that the expression of hsp 27, hsp 60, and hsc 70 mRNA and protein were not consistently increased by either acute or extended exposure to NaAsO₂. In contrast, hsp 70 expression was induced by NaAsO₂ after both acute and extended exposure. The degree and duration of the induction of the hsp 70 protein in the extended time course of exposure to NaAsO₂ correlated directly with UROtsa cell cytotoxicity. The substantial level of basal expression of hsp 27, hsp 60, and hsc 70, shown previously in human bladder urothelium, coupled with the inducible expression of hsp 70, could provide the human urothelium with a mechanism to withstand and recover from a low level of arsenite exposure.