Cortisol Rapidly Facilitates Glucocorticoid Receptor Translocation to the Plasma Membrane in Primary Trout Hepatocytes

Simple Summary Glucocorticoids elicit rapid cell signalling that is independent of the activation of the glucocorticoid receptor (GR) as a transcription factor. However, the mechanisms for this rapid nongenomic signalling by glucocorticoids are unclear. Here, we show that cortisol rapidly causes the translocation of intracellular GR to the plasma membrane in hepatocytes within minutes, and this response is mediated by the entry of extracellular calcium. We propose that this rapid cortisol action may sensitize the cells to nongenomic signalling via membrane-anchored GR. Glucocorticoids (GCs) stimulate rapid cell signalling by activating the membrane-anchored intracellular glucocorticoid receptor (GR). However, the recruitment of the GR to the plasma membrane to facilitate nongenomic signalling is far from clear. As cytosolic free calcium ([Ca2+]i) is involved in intracellular protein dynamics, we tested the hypothesis that acute elevation in cortisol levels rapidly stimulates GR translocation to the plasma membrane via a calcium-dependent process in rainbow trout (Oncorhynchus mykiss) hepatocytes. To test this, we monitored temporal changes in intracellular GR distribution in response to cortisol exposure. Immunofluorescence labelling showed that the GR was present in cytosolic and nuclear compartments in trout hepatocytes. However, upon cortisol exposure, the GR rapidly (within 5 min) formed punctate and colocalized with caveolin-1, suggesting plasma membrane localization of the receptor. This redistribution of the GR to the plasma membrane was transient and lasted for 30 min and was evident even upon exposure to cortisol-BSA, a membrane-impermeable analogue of the steroid. The rapid cortisol-mediated GR translocation to the plasma membrane involved F-actin polymerization and was completely abolished in the presence of either EGTA or Cpd5J-4, a calcium release-activated calcium (CRAC) channel blocker. Additionally, the modulation of the biophysical properties of the plasma membrane by cholesterol or methyl beta-cyclodextrin, which led to changes in ([Ca2+]i) levels, modified GR translocation to the plasma membrane. Altogether, acute cortisol-mediated rise in ([Ca2+]i) levels rapidly stimulated the translocation of intracellular GR to the plasma membrane, and we propose this as a mechanism promoting the nongenomic action of the GR for hepatocyte stress resistance.

Automated summary

Glucocorticoids can rapidly elicit cell signaling independent of the activation of glucocorticoid receptor (GR) as a transcription factor. The mechanism for this rapid nongenomic signaling involves the translocation of intracellular GR to the plasma membrane, which is mediated by the entry of extracellular calcium. This rapid action of cortisol may enhance cellular sensitivity to nongenomic signaling through membrane-anchored GR.