Glucocorticoid Regulation of Mouse and Human Dual Specificity Phosphatase 1 (DUSP1) Genes: UNUSUAL CIS-ACTING ELEMENTS AND UNEXPECTED EVOLUTIONARY DIVERGENCE*

Anti-inflammatory effects of glucocorticoids (GCs) are partly mediated by up-regulation of DUSP1 (dual specificity phosphatase 1), which dephosphorylates and inactivates mitogen-activated protein kinases. We identified putative GC-responsive regions containing GC receptor (GR) binding site consensus sequences that are well conserved between human and mouse DUSP1 loci in position, orientation, and sequence (at least 11 of 15 positions identical) and lie within regions of extended sequence conservation (minimum 65% identity over at least 100 bp). These were located ∼29, 28, 24, 4.6, and 1.3 kb upstream of the DUSP1 transcription start site. The homology-based approach successfully identified four cis-acting regions that mediated transcriptional responses to dexamethasone. However, there was surprising interspecies divergence in site usage. This could not be explained by variations of the GR binding sites themselves. Instead, variations in flanking sequences appear to have driven the evolutionary divergence in mechanisms of regulation of mouse and human DUSP1 genes. There was a good correlation between the ability of cis-acting elements to respond to GC in transiently transfected reporter constructs and their ability to recruit GR in the context of intact chromatin. We propose that divergence of gene regulation has involved the loss or gain of binding sites for accessory transcription factors that assist in GR recruitment. Finally, a novel GC-responsive region of the human DUSP1 gene contains a highly unusual element, in which three closely spaced GR half-sites are required for potent transcriptional activation by GC

Posttranslational Regulation of Tristetraprolin Subcellular Localization and Protein Stability by p38 Mitogen-Activated Protein Kinase and Extracellular Signal-Regulated Kinase Pathways

The p38 mitogen-activated protein kinase (MAPK) signaling pathway, acting through the downstream kinase MK2, regulates the stability of many proinflammatory mRNAs that contain adenosine/uridine-rich elements (AREs). It is thought to do this by modulating the expression or activity of ARE-binding proteins that regulate mRNA turnover. MK2 phosphorylates the ARE-binding and mRNA-destabilizing protein tristetraprolin (TTP) at serines 52 and 178. Here we show that the p38 MAPK pathway regulates the subcellular localization and stability of TTP protein. A p38 MAPK inhibitor causes rapid dephosphorylation of TTP, relocalization from the cytoplasm to the nucleus, and degradation by the 20S/26S proteasome. Hence, continuous activity of the p38 MAPK pathway is required to maintain the phosphorylation status, cytoplasmic localization, and stability of TTP protein. The regulation of both subcellular localization and protein stability is dependent on MK2 and on the integrity of serines 52 and 178. Furthermore, the extracellular signal-regulated kinase (ERK) pathway synergizes with the p38 MAPK pathway to regulate both stability and localization of TTP. This effect is independent of kinases that are known to be synergistically activated by ERK and p38 MAPK. We present a model for the actions of TTP and the p38 MAPK pathway during distinct phases of the inflammatory response