Differential Inhibition of HSP72 and HSP25 Produces Profound Impairment of Cellular Integrity

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Abstract
To test a putative cause and effect relationship between heat-shock protein (HSP) expression and response to renal cell injury, HSP72 and HSP25 were differentially inhibited in LLC-PK1 cells by means of transcription factor decoy and short interference RNA (siRNA). Cellular injury was assessed by solubilization of NaK ATPase (S-NaK). An exonuclease-resistant, ethylene glycol–bridged, circular oligonucleotide decoy for heat-shock transcription factor (HSF)-1, based on the sequence of the porcine heat-shock element, was constructed and validated. It was found that under all experimental conditions, cells had comparable ATP levels; that decoy of unligated or scrambled sequence was ineffective; that HSP72 mRNA and HSP72/HSP25 proteins were significantly reduced in decoy-treated cells; and that the dampened response to HSF activation in decoy-treated, injured cells was accompanied by a substantially amplified loss of cellular integrity (S-NaK was 85% compared with baseline levels). Specific inhibition of HSP72 that used siRNA directed against an inducible porcine HSP72 gene resulted in complete ablation of injury-induced HSP72. Isolated inhibition of HSP72 was also associated with marked NaK ATPase detachment from the cytoskeleton (S-NaK was 135% compared with baseline levels). These studies suggest that an HSF-1 decoy effectively dampens the HSP72/HSP25 response to injury in renal cells; that HSP72 siRNA ablates injury-induced induction of HSP72; and that dampening of the HSP72/HSP25 response and ablation of the HSP72 response are both associated with impaired restitution of cellular polarity.