Dual specificity phosphatase 1 (DUSP1) limits the expression of pro-inflammatory gene
products by dephosphorylating and inactivating mitogen-activated protein kinases
(MAPKs), in particular p38 MAPK and cJun N-terminal kinase. In many mouse and
human cell types, glucocorticoids (GCs) increase the expression of DUSP1. The
resulting inhibition of intracellular signalling pathways is thought to contribute to the
powerful anti-inflammatory effects of GCs. The purpose of this project was to define
mechanisms by which GCs control expression of mouse and human DUSP1 genes.
Orthologous genes of distantly related species often respond to GCs via regulatory
elements that are evolutionarily conserved in sequence and position. Therefore interspecies
sequence comparison was used as one tool to identify GC-responsive regions
(GRRs) of mouse and human DUSP1 genes. Functional assays of GRRs were carried
out by transient and stable transfection of mouse and human cells. Interactions of these
cis-acting elements with transcription factors (including the GC receptor itself, GR)
were assessed by in vitro DNA-binding assays and chromatin immunoprecipitation.
A number of conserved, putative GRRs were identified up to 29 kb upstream of the
DUSP1 transcription start site (TSS). Surprisingly, some of these were found to be
differently utilised by mouse and human DUSP1 genes, in spite of their sequence
similarity. Strongly GC-responsive elements were found 4.6 and 1.3 kb upstream of the
human DUSP1 TSS. The corresponding regions of the mouse DUSP1 gene were
unresponsive or very weakly responsive to GC. Instead the mouse gene appeared to be
regulated via an element 29 kb upstream of the TSS, the corresponding human element
being unresponsive. GC responsiveness correlated with the ability to recruit GR in vivo,
but could not be explained on the basis of differences in the sequences of GR binding
sites. These observations suggest that recruitment of GR to DUSP1 loci and
transcriptional activation in response to GC are critically dependent on “accessory”
transcription factors. GC responses of mammalian DUSP1 genes appear to have
evolved via gain and/or loss of binding sites for accessory factors, whilst maintaining
overall output. GC regulation of DUSP1 genes involves atypical GR binding sites and,
unusually, does not appear to require dimerisation of GR.