The human glucocorticoid receptor: One gene, multiple proteins and diverse responses

Glucocorticoids are a vital class of endogenous steroid hormones that regulate essential biological processes including growth, development, metabolism, behavior and apoptosis. Most, if not all, of these actions are thought to be mediated through the glucocorticoid receptor. The exact mechanisms of how one hormone, via one receptor, modulates such diverse biological functions are largely unknown. However, recent studies from our lab and others have suggested that a contribution for the diversity results from multiple isoforms of the glucocorticoid receptor that result from alternative RNA splicing and translation initiation of the glucocorticoid receptor mRNA. Additionally, each isoform is subject to several post-translational modifications, including phosphorylation, ubiquitination and sumoylation, which have been shown to modulate the receptor protein stability and/or function. Together these data provide potentially diverse mechanisms to establish cell type specific regulation of gene expression by a single transcription factor. Here, we summarize the recent advances and processes that generate these receptor isoforms and these post-translational modifications. We speculate that the composition and proportion of individual isoforms expressed in particular cellular contexts account for the diverse effects of glucocorticoid hormones.