Cortisol modulates HSP90 mRNA expression in primary cultures of trout hepatocytes

The objective of the present study was to understand the role of cortisol in the cellular stress response process in fish. Specifically, our studies addressed whether cortisol exposure modified heat shock protein 90 (HSP90) mRNA expression in rainbow trout (Oncorhynchus mykiss) hepatocytes maintained in primary culture. We also subjected these hepatocytes to heat shock (HS) in order to examine the role of cortisol on HS-induced HSP90 mRNA expression. A cDNA fragment of 500 bp was cloned from trout liver by reverse transcriptase- polymerase chain reaction (RT-PCR) with primers designed from the conserved regions of chinook salmon and zebrafish HSP90 cDNAs. The PCR product showed very high homology to chinook salmon (98%), zebrafish (84%) and human (77%) HSP90. Heat shock (+6 degrees C) induced transient elevation in HSP90 mRNA in trout hepatocytes, peaking within 10-h post-HS, and remained elevated over a 24-h period. Cortisol did not modify the unstimulated expression of HSP90 mRNA, whereas the HS-induced HSP90 mRNA expression was attenuated in trout hepatocytes. Our results suggest that elevated plasma cortisol levels modulate the cellular stress response by affecting the transcription of HSP90 in fish.