The mechanism of mimecan transcription induced by glucocorticoid in pituitary corticotroph cells.

Mimecan, a secretary protein that is expressed in mouse and human pituitary corticotroph cells, is up-regulated by glucocorticoids (GC) in the corticotroph cells via classical glucocorticoid receptor (GR) pathways. In this study, we further explore the GC mechanism for mimecan expression in these cells. Five putative GR response elements (GREs) were identified in ~2 kb of the mimecan promoter by programme analysis. An EMSA assay further indicated that these putative GREs were bound by the GR. Moreover, three proximal GREs are conserved between species. Although luciferase assays showed that the -1474/+43 region of the mimecan promoter achieved the highest expression of mimecan, the -803/+43 mimecan promoter region was sufficient for the GC-mediated expression of mimecan. The mutations of three conserved GREs located in the -1474/+43 mimecan promoter region did not affect mimecan transcription, which suggests that the effects of GC on mimecan are independent of the GREs in the promoter. In addition, cycloheximide, a protein synthesis inhibitor, blocked GC-induced mimecan expression in AtT-20 cells. Taken together, these results suggest that, although there are 3-5 GREs in the mimecan promoter, GC may regulate mimecan transcription indirectly through the synthesis of intermediate proteins and not through the GREs in pituitary corticotroph cells.