RESUMEN
Glucocorticoids are stress hormones that maintain homeostasis through gene regulation mediated by nuclear receptors. We have discovered that other cellular stressors are integrated with glucocorticoid signaling through a new hormone-independent phosphorylation site, Ser134, on the human glucocorticoid receptor (GR). Ser134 phosphorylation is induced by a variety of stress-activating stimuli in a p38 mitogen-activated protein kinase (MAPK)-dependent manner. Cells expressing a mutant glucocorticoid receptor incapable of phosphorylation at Ser134 (S134A-GR) had significantly altered hormone-dependent genome-wide transcriptional responses and associated hormone-mediated cellular functions. The phosphorylation of Ser134 significantly increased the association of the GR with the zeta isoform of the 14-3-3 class of signaling proteins (14-3-3zeta) on chromatin promoter regions, resulting in a blunted hormone-dependent transcriptional response of select genes. These data argue that the phosphorylation of Ser134 acts as a molecular sensor on the GR, monitoring the level of cellular stress to redirect glucocorticoid-regulated signaling through altered 14-3-3zeta cofactor binding and promoter recruitment. This posttranslational modification allows prior cellular stress signals to dictate the transcriptional response to glucocorticoids.
Asunto(s)
Receptores Citoplasmáticos y Nucleares/metabolismo , Receptores de Glucocorticoides/metabolismo , Transducción de Señal , Estrés Fisiológico , Proteínas Quinasas p38 Activadas por Mitógenos/metabolismo , Proteínas 14-3-3/metabolismo , Secuencia de Aminoácidos , Línea Celular Tumoral , Dexametasona/farmacología , Perfilación de la Expresión Génica , Regulación de la Expresión Génica , Glucocorticoides/farmacología , Glucocorticoides/fisiología , Humanos , Imidazoles/farmacología , Inmunoprecipitación , Ligandos , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Mutación Missense , Fosforilación , Unión Proteica , Piridinas/farmacología , Receptores de Glucocorticoides/genética , Serina/metabolismo , Transcripción Genética , Proteínas Quinasas p38 Activadas por Mitógenos/antagonistas & inhibidoresRESUMEN
Aberrant glycogen synthase kinase 3beta (GSK-3beta) activity is associated with the progression of several pathological conditions such as diabetes, Alzheimer's, and cancer. GSK-3beta regulates cellular processes by directly phosphorylating metabolic enzymes and transcription factors. Here, we discovered a new target for GSK-3beta phosphorylation: the human glucocorticoid receptor (GR). Glucocorticoid signaling is essential for life and regulates diverse biological functions from cell growth to metabolism to apoptosis. Specifically, we found hormone-dependent GR phosphorylation on serine 404 by GSK-3beta. Cells expressing a GR that is incapable of GSK-3beta phosphorylation had a redirection of the global transcriptional response to hormone, including the activation of additional signaling pathways, in part due to the altered ability of unphosphorylatable GR to recruit transcriptional cofactors CBP/p300 and the p65 (RelA) subunit of NF-kappaB. Furthermore, GSK-3beta-mediated GR phosphorylation inhibited glucocorticoid-dependent NF-kappaB transrepression and attenuated the glucocorticoid-dependent cell death of osteoblasts. Collectively, our results describe a novel convergence point of the GSK-3beta and the GR pathways, resulting in altered hormone-regulated signaling. Our results also provide a mechanism by which GSK-3beta activity can dictate how cells will ultimately respond to glucocorticoids.