The heat shock proteins are a large super-family of proteins with molecular weights ranging from 8 to 170 kDa, with the members referred to as hsp 27, hsp 60, hsc 70 (constitutive form), hsp 70 (inducible form), and hsp 90 being the proteins classically identified to be induced as a result of heat treatment of mammalian cells (Macario 1995).
When the UROtsa cells were exposed acutely to either heat or NaAs[O.sub.2], there was no induction in the levels of hsp 27 mRNA or protein, or any alteration in the steady-state phosphorylation status of the protein.
In the previous studies comparing mortal and immortalized proximal tubule cells, the decreased induction of hsp 27 in the immortalized HK-2 cells was potentially explained by the fact that the HK-2 cells had very high levels of basal hsp 27 compared with the mortal cell line (Kim et al.
Compared with hsp 27, the basal level of hsp 60 expression in the in situ human bladder was low in all the cell types comprising the bladder (Somji et al.
Assuming that the findings in cell culture predict the response of human bladder urothelium in vivo, these observations suggest that the hsp 27 gene in the human bladder urothelium is not induced by acute exposure to arsenite, whereas, the hsp 60, hsc 70, and hsp 70 genes respond in the classical manner defined by the literature.
Only a few studies have examined the expression of hsp 27, hsp 60, hsc 70, and hsp 70 when cells are continually exposed to stressful stimuli over an extended period.
The expression of hsp 27, hsp 60, and hsc 70 in the UROtsa cells exposed to lethal and sublethal levels of NaAs[O.sub.2] for 16 days was similar to that of the HPT cells.
It was demonstrated that hsp 27 has a high level of basal expression in the urothelium of both the in situ human bladder and the UROtsa-derived cell line.
Biological and clinical implications of heat shock protein 27000 (Hsp 27): a review.