Role of p38 MAPK in GR biological activities.

LORENA FRANCO , MÓNICA COSTAS AND OMAR COSO.

Valle Nevado, Chile

Congreso; 1 st International Meeting Latin American Society of Developmental Biology; 2003

The glucocorticoid receptor (GR) is a steroid hormone receptor known to regulate, either directly or indirectly, target genes involved in cell differentiation, thymocyte selection, lung maturation, bone turnover, glucose homeostasis and inflammation. Although steroid hormones, such as cortisol, act as a primary signal in activating the receptor´s transcriptional regulatory functions, GR-medated trasncriptional activation is also modulated both postively and negatively by phosphorylation. GR is phosphorylated in its N-terminal transcriptional regulatory region, by cyclin-dependent kinases (Cdks) and Mitogen-Activated Protein Kinases (MAPKs). Representative members of the MAPK family are Extracellular-signal Regulated Kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK) and p38 MAPK. Important roles for p38 have recently been described for oogenesis and wing morphogenesis in flies, adipocyte differentiation in vertebrates, and cell proliferation or survival in miscelaneous tissues.  The aim of the present study is to investigate the role of p38 in the regulation of GR biological activities. Results: We have observed, physical interactions between GR and p38, ERK2 and JNK by coimmunoprecipitation assays. GR was shown to be the subject of phosphorylation by p38, ERK2 and JNK by means of an in vitro kinase assay. L929 cells stimulated with TNF-a and Dexamethasone (Dex) showed a colocalization of p38 and GR in the nucleus by diverse techniques as confocal microscopy and western blots of subcellular fractions. GR transcriptional activation has been observed when L929 cells were transfected with MKK6, a positive regulator of p38, and this activation was abrogated in the presence of a p38 specific inhibitor (SB 203580). Transcriptional activation mediated by ligand induced GR was increased under condicions in which p38 is activated. In the murine fibroblast L929 cell line subcellular localization of p38 and GR was shown to be coincident under resting or stimulated conditions for both molecules. In order to determine if this interactions had an influence on cell fate, we examined the survival of cells treated with TNF-a, an apoptotic stimulus. We observed that Dex. protects cells from TNF-induced death and that this protection is dependent on p38 activity.