PREFERENTIAL ACTIVATION OF HSF-BINDING ACTIVITY AND HSP70 GENE-EXPRESSION IN XENOPUS HEART AFTER MILD HYPERTHERMIA

We have examined the effect of mild hyperthermia on the pattern of hea t shock transcription factor (HSF) binding activity, heat shock protei n 70 (hsp70) and hsp30 gene expression and protein denaturation in sel ected tissues of adult Xenopus namely, heart, hind limb muscle, eye, l iver and spleen. In these studies it was found that heart tissue was t he most thermally sensitive of all of the tissues examined since maint enance of adult frogs at 26 degrees C resulted in a preferential activ ation of HSF binding. Thus, heart has a lowered set point temperature for HSF activation compared to the other tissues examined. At 30 degre es C HSF activation was observed in all of the tissues examined. Heart HSF activation at 26 degrees C was correlated with an increase in hsp 70 mRNA and Hsp70 protein accumulation. At 28 degrees C the largest am ount of hsp70 and hsp30 mRNA accumulation was detected in heart and sk eletal muscle compared to other tissues while hsp70 mRNA accumulation was relatively low in spleen and hsp30 mRNA accumulation was not detec table in eyes, liver and spleen. Incubation of adult frogs at 30 degre es C resulted in enhanced hsp70 and hsp30 mRNA accumulation in all of the tissues. Finally, we have used differential scanning calorimetry ( DSC) to compare the temperatures at which protein denaturation occurs in heart and liver tissue. The onset of protein denaturation (T-0) occ urred approximately 8.5 degrees C lower in heart compared to liver. Al so the midpoint of the DSC profile (T-1/2) was approximately 10.4 degr ees C lower in heart than in liver. Thus, heart proteins are generally more thermolabile than proteins in liver tissue. Taken together these data suggest that heart is more sensitive than the other tissues exam ined with respect to moderate increases in environmental temperature.