Objectives: 

The mineralocorticoid receptor (MR), a member of the nuclear receptor superfamily of transcription factors, is activated by aldosterone and mediates its natriferic action in tight epithelia. MR is also expressed in non-epithelial tissues. Importantly, it mediates the deleterious effects of inappropriately high aldosterone levels in the heart, where it induces the development of cardiac fibrosis. In the absence of ligand, MR forms part of large cytosolic oligomeric protein complexes that include molecular chaperones such as heat shock protein 90 (hsp90). Recent evidence suggests that hsp90 is essential in the process of ligand-induced MR nuclear translocation. In addition, we have recently demonstrated that hsp90 expression levels control MR cell type-specific subcellular localization in the absence of ligand. In this study we asked whether modulation of hsp90 activity through acetylation plays a role in the control of MR subcellular localization and ligand-induced nuclear translocation.

Materials: 

We examined MR subcellular localization and nuclear translocation dynamics in two different cell systems (COS7 cells and HL-1 cardiomyocytes) using our newly developed set of functional fluorescent MR constructs (Aguilar-Sanchez et al. Endocrinology, 2012). Acetylation and deacetylation of residue K295 were mimicked by introducing point mutations K295Q or K295R. Endogenous hsp90 de-acetylation was induced by overexpression of histone deacetylase 6 (HDAC6).

Results: 

Our results show that hsp90 acetylation shifts MR localization towards the nucleus in the absence of ligand. Aldosterone-induced nuclear localization kinetic is modulated by hsp90 acetylation. Wild-type or deacetylated hsp90 delay the onset of translocation but increase its rate.

Conclusions: 

Hsp90 acetylation at residue K295 modulates the interaction of the chaperone with MR and controls the subcellular localization and aldosterone-induced nuclear translocation of the receptor in the two cell models tested.