The stress response is initiated in energy deprived renal epithelia coordinate with disruption of cell architecture including loss of Na/K-ATPase attachment to the cytoskeleton; HSP-72 elaboration coincides with cellular restitution. Assessing putative cytoprotective effects of the heat shock proteins (HSPs) in injured kidney has been confounded by the cellular stress used to pre-induce the HSPs. We examined whether HSPs could be pharmacologically induced in renal epithelia and whether prior HSP induction would protect against cellular injury from ATP depletion.

Confluent LLC-PK1cells were treated with Herbimycin A(H), geldanamycin (G) or vehicle for a 2 hour interval (treatment) followed by replacement with normal media for 6 hours (elaboration period). At the end of the elaboration period, the cells were energy deprived for 4 hours by replacement of the growth media with substrate free media and Antimycin A. Gel retardation assays indicated that both H and G caused marked activation of heat shock transcription factor (HSF) by the end of the treatment interval. At the end of the 6 hour elaboration period, Western analysis showed that both H and G induced the cytosolic 70 kD HSPs (HSP-72 and HSC-73). Neither compound altered cellular ATP levels nor disrupted membrane protein-cytoskeleton interactions, as assayed by detergent solubility of Na/K-ATPase, when HSF was activated or when the 70 kD HSPs (HSP-70) were induced. Both H and G, then, initiated the stress response without causing evident cellular injury.

Pre-treated cells were then subjected to metabolic inhibition to determine whether HSP-70 induction by H or G was associated with cytoprotection as manifested by prevention of the cellular ATP depletion or Na/K-ATPase solubilization typical of energy deprived cells. Neither compound altered the rapidity nor depth or ATP depletion from metabolic inhibition. However, prior treatment with H and G prevented solubilization of Na/K-ATPase in cells subjected to 4 hours ATP depletion. Therefore, HSP-70 levels can be pharmacologically enhanced in renal epithelia and prior HSP-70 induction is associated with cytoprotection that is not attributable to preservation of cellular energy. One action of HSP-70, then, may be to stabilize membrane and cytoskeletal protein interactions in metabolically deprived renal epithelia.