Cloning and characterization of salmon hsp90 cDNA: Upregulation by thermaland hyperosmotic stress

Accumulating evidence suggests that glucocorticoids are essential for devel opment of hypoosmoregulatory capacity in salmon during adaptation to seawat er. Heat shock protein (hsp)90 has been reported to function in signal tran sduction and the maturation and affinity of glucocorticoid receptors. We so ught to determine whether this hsp might be upregulated by thermal and hype rosmotic stress in salmon, a species that migrates between the freshwater a nd marine environments. A 2625-bp cDNA cloned from a salmon cDNA library wa s found to code for a protein of 722 amino acids exhibiting a high degree o f identity with zebra fish (92%) and human (89%) hsp90 beta. Accumulation o f hsp90 mRNA was observed in isolated branchial lamellae incubated under hy perosmotic conditions and in branchial lamellae of salmon exposed to hypero smotic stress in vivo. In contrast, exposure of kidney to hyperosmotic stre ss in vitro and in vivo failed to elicit an increase in the quantity of hsp 90 mRNA. By way of comparison, accumulation of hsp90 mRNA was observed in b oth branchial lamellae and kidney tissue subjected to thermal stress in vit ro and in vivo. Western blot analyses of proteins isolated from tissues und er identical conditions in vitro revealed that the pool of hsp90 increased with thermal stress but not with osmotic stress. The results suggest that a ccumulation of hsp90 mRNA in response to osmotic stress is unrelated to cel lular protein denaturation and that synthesis of hsp90 may be regulated at both the level of transcription and translation. J. Exp. Zool. 287:199-212, 2000. (C) 2000 Wiley-Liss, Inc.