GR acetylation

Project leader: Thorsten Heinzel
Doctoral candidate: Dima Ward

Background and previous work
Reduced availability of energy is a key stressor in most living species. In particular, metabolic enzymes respond to impaired energy availability and are regulated by both sensing and employing metabolic co-factors such as ATP/ADP, NADH/NAD+, and acetyl-CoA. AMPactivated kinase (AMPK) and SIRT1 are key players in sensing an energy deficit and the regulation of SIRT1 activity and expression depends on the metabolic state. SIRT1 in turn affects the acetylation of key transcription factors. Recent reports suggest that acetylation modulates the properties of the glucocorticoid receptor (GR) which is involved in the regulation of metabolism, inflammation, development and reproduction. Specific inhibitors as well as siRNA experiments suggest that SIRT1 is the primary GR deacetylase. We identified novel acetylation sites in the N-terminal region of GR. The reduced activity of GR in reporter gene assays suggests that the acetylation status is indeed relevant for GR function. Moreover, glucose deprivation as well as AMPK signalling reduces GR acetylation by modulating SIRT1 activity, indicating that energy metabolism regulates GR in an acetylationdependent manner.

Specific aims and working programme
Our data indicate that GR acetylation is under the control of the AMPK-NAD+-SIRT1 axis. We will investigate the molecular mechanisms underlying the regulatory properties of GR acetylation including the role of downstream targets and upstream signalling proteins. We will investigate whether GR acetylation represents an important node within the network of metabolic regulators. As this network relies on multiple feed-back and feed-forward circuits to create an adaptive stress response, non-linear effects play an important role. We will analyse GR acetylation levels as well as interactions with SIRT1 and p300 under differential metabolic conditions where AMPK is active or inactive. GR acetylation site mutants will be employed to clarify the role of GR acetylation. Using ChIP we will investigate GR-promoter interactions and associated epigenetic status. We are planning to analyse functional interactions between SIRT and GR in conditional SIRT1 knockout mice. Furthermore, metabolic stress and/or glucocorticoids have been shown to affect long-term settings of the hypothalamic-pituitary axis as well as of inflammatory responses. We will therefore investigate the effects of GR acetylation on epigenetic reprogramming events which may affect resilience to stressors.