HEME OXYGENASE IS NOT EXPRESSED AS A STRESS PROTEIN AFTER RENAL ISCHEMIA

Stressful stimuli such as heat, oxidative stress, heavy metals, and ti ssue trauma induce the expression of a family of proteins commonly ref erred to as stress proteins or heat shock proteins. The functions of t hese proteins are varied but include glycolysis, antioxidant defense, and several postulated ''chaperone'' functions involving the folding, unfolding, and translocation of other proteins. Heme oxygenase, the en zyme that catalyzes the degradation of heme to biliverdin, is also hea t inducible and is, therefore, a heat shock protein. In the kidney, is chemia has been observed by several investigators to induce expression of the more commonly studied heat shock proteins HSP 70 and HSP 72. I n addition, exposure of the kidney to myoglobin after glycerol injecti on induced heme oxygenase. The purpose of this study was to determine whether heme oxygenase is expressed as a stress protein after renal is chemia. Renal ischemia was induced in rats after right nephrectomy by clamping the renal artery for 40 minutes. Gene expression was evaluate d after 60 minutes to 96 hours of postischemic reperfusion. There was essentially no expression of heme oxygenase at any of the time points evaluated. The absence of heme oxygenase expression was in striking co ntrast to the prompt and dramatic expression of HSP 70. This finding i s consistent with the concept that all ''stress proteins'' are not equ ivalent and that, although there is considerable overlap between heat- sensitive gene promoters and oxidant stress-sensitive gene promoters, there is specificity for the type of stimulus that is able to activate any given stress protein gene.