The 90-kDa heat shock protein (HSP90) acts as a specific molecular chaperone in the folding and regulates a wide range of associated proteins such as steroid hormone receptors. It is known that HSP90 possesses two different chaperone sites, both in the N-and C-domains, and that the chaperone activity of HSP90 is blocked by binding of geldanamycin (GA) to the Ndomain, the same as the ATP-binding site. Here we show that Cisplatin [cis-diamminedichloroplatinum (II), CDDP], an antineoplastic agent, associates with HSP90 and reduces its chaperone activity. In order to analyse the binding proteins, bovine brain cytosols were applied to a CDDP-affinity column and binding proteins were eluted by CDDP. In the elutants, only 90-kDa protein bands were detected on SDS\PAGE, and the protein was cross-reacted with the anti-HSP90 antibody on immunoblotting. No protein bands were detected in the elutants
Mammalian chaperonin homolog (HSP60) was purified from porcine livers cytosol using a tandem ATP-Sepharose column and Mono Q column chromatography. A partial amino acid sequence (96 amino acid residues) of this protein was determined and coincided with those of human HSP60 with 96.9% homology, which was deduced from the nucleotide sequence of the cDNA. The sequence of the NH2 termini of the purified protein (5 amino acid residues) coincided with the signal sequence of HSP60. These facts led to the identification of the 60-kDa liver protein with the chaperonin homolog. Dihydrofolate reductase was able to form a stable complex with the liver chaperonin homolog. The liver chaperonin homolog was detected by at least five spots around pI = 5.6 on two-dimensional gel electrophoresis. Immunoblotting studies using an antibody against chaperonin homolog showed that the chaperonin homolog was localized in the cytosol, mitochondrial, and nuclear fractions of porcine liver. The chaperonin homolog was localized both in the mitochondria and cytoplasm of rat kidneys at the electron microscopic level. The chaperonin homolog in the cytosol, but not in the other subcellular fractions, was cross-reacted with an antibody against the synthetic peptide corresponding to the signal peptide of HSP60 as well as the purified chaperonin homolog on immunoblotting. These results suggested that the functional chaperonin homolog in the cytosol may be transported into the mitochondria and the protein may be processed to mitochondrial HSP60 in the organella.
We investigated the expression and changes in the intracellular localization of a 72-kDa heat shock protein (HSP72) in rat gastric pyloric and fundic mucosa before and after water-immersion stress. Severe mucosal damage was found in the fundic mucosal area of the stomach after this stress. However, no mucosal lesion developed in the pyloric mucosal area. HSP72 in both the soluble and insoluble fractions of the pyloric and the fundic mucosal areas was significantly increased after water-immersion stress, peaking 6h after the initiation of the stress. The increase in HSP72 was more significant in the pyloric mucosal area than in the fundic mucosal area under both normal and stress conditions. The increase of HSP72 in the pyloric mucosal cells occurred prior to the formation of the mucosal lesions, whereas the increase of HSP72 in the fundic mucosal cells was observed after ulcer formation. An immunohistochemical study showed that HSP72 was constitutively expressed in the cytoplasm of the gastric mucosal cells, and that the intranuclear induction of HSP72 was remarkably intense in the pyloric mucosal cells, especially in the proliferative zone, compared with the fundic mucosal cells. Our results may suggest that HSP72 has an important cytoprotective function in gastric mucosal cells and that there is a "biophysical" difference between pyloric and the fundic mucosal cells.
We purified the constitutive 73-kDa heat-shock protein (HSP73) from the bovine brain, and produced a specific antibody against the protein in a rabbit. On immunoblotting, the antibody cross reacted only with a protein band with a molecular mass of 73 kDa in a crude extract from normal rat kidneys, which was regarded as rat renal HSP73. The intrarenal immunohistochemical distribution of HSP73 was examined by using this antibody, on both normal rat kidneys and kidneys with puromycin aminonucleoside nephrosis. HSP73 was predominantly present in epithelial cells of the glomeruli and the tubules. In normal kidneys, HSP73 was generally localized in both the cytoplasm and the nucleus of these epithelial cells, except for proximal tubular epithelial cells. On the other hand, in kidneys with puromycin aminonucleoside nephrosis, HSP73 accumulated in the cytoplasm at a level higher than in the nucleus in association with the severity of renal dysfunction and proteinuria. These findings indicate that HSP73 is mainly expressed in glomerular and tubular epithelial cells in the kidney under a physiological condition, and that its expression changes from the nucleus to the cytoplasm under pathological conditions such as a protein overload to these epithelial cells.
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