Glucocorticoids (GCs) act through the glucocorticoid receptor (GR, also known as 
NR3C1) to regulate immunity, energy metabolism and tissue repair. Upon ligand 
binding, activated GR mediates cellular effects by regulating gene expression, 
but some GR effects can occur rapidly without new transcription. Here, we show 
that GCs rapidly inhibit cell migration, in response to both GR agonist and 
antagonist ligand binding. The inhibitory effect on migration is prevented by GR 
knockdown with siRNA, confirming GR specificity, but not by actinomycin D 
treatment, suggesting a non-transcriptional mechanism. We identified a rapid 
onset increase in microtubule polymerisation following GC treatment, identifying 
cytoskeletal stabilisation as the likely mechanism of action. HDAC6 
overexpression, but not knockdown of αTAT1, rescued the GC effect, implicating 
HDAC6 as the GR effector. Consistent with this hypothesis, ligand-dependent 
cytoplasmic interaction between GR and HDAC6 was demonstrated by quantitative 
imaging. Taken together, we propose that activated GR inhibits HDAC6 function, 
and thereby increases the stability of the microtubule network to reduce cell 
motility. We therefore report a novel, non-transcriptional mechanism whereby GCs 
impair cell motility through inhibition of HDAC6 and rapid reorganization of the 
cell architecture.This article has an associated First Person interview with the 
first author of the paper.