Glucocorticoid receptor (GR) signaling

Category: receptor_pharmacology

Overview

GR (NR3C1) is a ligand-activated nuclear transcription factor. Cortisol + synthetic glucocorticoids bind cytoplasmic GR → HSP90 release → nuclear translocation → GRE binding. Two modes: transactivation (positive regulation — metabolic + anti-inflammatory cytokine reduction) + transrepression (NF-κB + AP-1 tethering — anti-inflammatory). Therapeutic glucocorticoids: hydrocortisone (cortisol replacement), methylprednisolone (IV bolus for MS exacerbation, transplant rejection), prednisolone (active metabolite of prednisone — chronic immunosuppression), dexamethasone (long-acting, no mineralocorticoid activity, intracranial edema + COVID ARDS), inhaled (fluticasone, budesonide, beclomethasone, ciclesonide — high topical:systemic ratio for asthma/COPD), topical (clobetasol, betamethasone — DERM cluster). Fludrocortisone is mineralocorticoid-dominant.

Organ Systems

• endocrine
• immune-hematologic

Pathway Steps

1. cortisol-or-synthetic-glucocorticoid → gr-activation-translocation — via HSP90 release + nuclear import → GRE binding. Cortisol and synthetic glucocorticoids (prednisone, dexamethasone) are lipophilic and diffuse into cells to bind the cytoplasmic glucocorticoid receptor, which sheds chaperones (HSP90) and translocates to the nucleus. This ligand-activated nuclear receptor is the single target behind glucocorticoids’ broad effects.
2. gr-activation-translocation → antiinflammatory-gene-transcription — via transrepression of NF-κB + AP-1 + transactivation of MKP-1, GILZ. In the nucleus, GR induces anti-inflammatory genes (transactivation) and, by tethering to NF-κB/AP-1, represses pro-inflammatory genes (transrepression). This dual action gives glucocorticoids their immunosuppression — and the metabolic transactivation effects (hyperglycemia, osteoporosis) behind their side effects.

Known Modulators

• methylprednisolone (activator) — GR (intermediate-acting). IV bolus for MS exacerbation + asthma exacerbation + transplant rejection; mild mineralocorticoid activity
• prednisolone (activator) — GR (intermediate-acting). active metabolite of prednisone; chronic immunosuppression workhorse; bone density loss + cataract + glucose dysregulation tail
• fludrocortisone (activator) — mineralocorticoid receptor (dominant). classic mineralocorticoid; primary adrenal insufficiency + orthostatic hypotension off-label
• budesonide (activator) — GR (inhaled + oral controlled-release). inhaled asthma + COPD (Pulmicort); PO controlled-release for ileal Crohn (high hepatic first-pass minimizes systemic exposure)
• fluticasone (activator) — GR (inhaled/intranasal). inhaled steroid (Flovent) + nasal (Flonase); high topical:systemic ratio; CYP3A4 substrate (ritonavir DDI → Cushing's)
• beclomethasone (activator) — GR (inhaled). first inhaled steroid (QVAR); active metabolite beclomethasone-17-monopropionate
• ciclesonide (activator) — GR (inhaled prodrug → des-ciclesonide). inhaled steroid prodrug activated by lung esterases; minimal systemic exposure → low HPA suppression
• fluticasone furoate (activator) — GR (inhaled, once-daily). long-acting inhaled steroid; component of Trelegy (ICS/LAMA/LABA triple)
• triamcinolone (activator) — GR (intermediate-acting). IM/intra-articular depot + intranasal + topical; long local duration
• betamethasone (activator) — GR (long-acting). antenatal lung-maturation (preterm labor); topical + injectable forms
• mometasone (activator) — GR (inhaled/topical). inhaled asthma + topical dermatology; minimal systemic absorption

References

• PMID 21149445