Abstract
Glucocorticoids (GCs) are rapidly released in response to stress and play an important role in the physiological adjustments to re-establish homeostasis. The mode of action of GCs for stress coping is mediated largely by the steroid binding to the glucocorticoid receptor (GR), a ligand-bound transcription factor, and modulating the expression of target genes. However, GCs also exert rapid actions that are independent of transcriptional regulation by modulating second messenger signaling. However, a membrane-specific protein that transduces rapid GCs signal is yet to be characterized. Here, using freshly isolated hepatocytes from rainbow trout (Oncorhynchus mykiss) and fura2 fluorescence microscopy, we report that stressed levels of cortisol rapidly stimulate the rise in cytosolic free calcium ([Ca2+]i). Pharmacological manipulations using specific extra- and intra-cellular calcium chelators, plasma membrane and endoplasmic reticulum channel blockers and receptors, indicated extracellular Ca2+ entry is required for the cortisol-mediated rise in ([Ca2+]i). Particularly, the calcium release-activated calcium (CRAC) channel gating appears to be a key target for the rapid action of cortisol in the ([Ca2+]i) rise in trout hepatocytes. To test this further, we carried out in silico molecular docking studies using the Drosophila CRAC channel modulator 1 (ORAI1) protein, the pore forming subunit of CRAC channel that is highly conserved. The result predicts a putative binding site on CRAC for cortisol to modulate channel gating, suggesting a direct, as well as an indirect regulation (by other membrane receptors) of CRAC channel gating by cortisol. Altogether, CRAC channel may be a novel cortisol-gated Ca2+ channel transducing rapid nongenomic signalling in hepatocytes during acute stress.
Highlights
Glucocorticoids (GCs) are rapidly released in response to stress and play an important role in the physiological adjustments to re-establish homeostasis
Our results point to a rapid effect of cortisol on calcium release-activated calcium (CRAC) channel gating as a mechanism for the nongenomic cortisol action on hepatocyte stress response[11,24]
We propose two modes of action of cortisol in regulating CRAC channel gating (Fig. 5). (1) An indirect effect of cortisol by activating a yet unknown membrane receptor to deplete endoplasmic reticulum (ER) stores, resulting in the interaction of stromal interaction molecule (STIM) with ORAI1 to open CRAC channels and causing an increases in ([Ca2+]i)
Summary
Glucocorticoids (GCs) are rapidly released in response to stress and play an important role in the physiological adjustments to re-establish homeostasis. The calcium release-activated calcium (CRAC) channel gating appears to be a key target for the rapid action of cortisol in the ([Ca2+]i) rise in trout hepatocytes. GCs promote energy substrate redistribution and is essential for the metabolic adjustments to regain homeostasis in the face of stressor exposure[1] This steroid action is mediated by binding to an intracellular receptor, the glucocorticoid receptor (GR), which acts as a transcription factor upon ligand-binding to regulate GC-responsive transcriptional machinery[1]. Cortisol rapidly increased the phosphorylation of protein kinase A (PKA), Akt /protein kinase B (PKB) and protein kinase C (PKC) in rainbow trout (Oncorhynchus mykiss) hepatocytes[24], suggesting possible activation of second messenger signaling via putative membrane receptor(s)[4,24,25]. Our results indicate that cortisol rapidly increases ( [Ca2+]i) in hepatocytes, and, for the first time, suggests a possible direct role for this steroid in CRAC channel gating
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
