Characteristic expression of 105-kDa heat shock protein (HSP105) in various tissues of nonstressed and heat-stressed rats.

Although the induction of heat shock proteins (HSP) has been studied extensively in cultured cells, comparatively few studies have examined their expression in vivo. In this report, we investigated the expression and the state of 105-kDa heat shock protein (HSP105) in various tissues of rats, and found that two isoforms of HSP105 (HSP105-a and HSP105-b) were both moderately expressed in adrenal, spleen, liver and heart, and both increased markedly after heat shock. However, in brain HSP105-a was characteristically highly expressed over HSP105-b, but neither increased after heat shock. In addition, a 100-kDa protein (p100), a possible testis-specific HSP105 homologue was found in testis. When the effects of adrenaline and its antagonists on the heat-inducibility of HSP105 were examined, the induction of HSP105 in adrenal gland seemed to be negatively regulated through the alpha-adrenergic receptor. Furthermore, HSP105 was found to be associated with HSC70/HSP70, and to exist as high molecular mass complexes of 300-800-kDa and of 300-500-kDa in various tissues of nonstressed and heat-stressed rats, respectively. The molecular interaction between HSP105 and HSC70 suggests the possibility that HSP105 functions with HSC70 cooperatively in various tissues of rats.