Heat shock protein 27 expression in human proximal tubule cells exposed tolethal and sublethal concentrations of CdCl2

The expression of hsp 27 mRNA and protein was determined in cultured human proximal tubule (HPT) cells exposed to lethal and sublethal concentrations of Cd2+ under both acute and extended conditions. Initial procedures demons trated that HPT cells display the classic stress response following physica l and chemical stress. Heat stress (42.5 degrees C for 1 hr) caused an incr ease in both hsp 27 mRNA and protein as well as a shift in the protein to a more phosphorylated state. Results were similar when the cells were subjec ted to chemical stress (exposure to 100 mu M sodium arsenite for 4 hr). Acu te exposure to 53 mu M CdCl2 for 4 hr also resulted in an increase in hsp 2 7 mRNA and protein and a shift to the more phosphorylated protein isoform. Extended Cd2+ exposure involved continuous treatment with Cd2+ at both leth al and sublethal levels over a 16-day time course. The results of this trea tment showed that chronic exposure to Cd2+ failed to increase either hsp 27 mRNA or protein expression in HPT cells, even at lethal Cd2+ concentration s. In fact, hsp 27 protein levels decreased as compared to controls at both lethal and sublethal exposure to Cd2+. These findings imply that hsp 27 ex pression in human proximal tubule cells may have two distinct modes dependi ng on the nature (acute vs. chronic) of the stress.