Regulation of transcription of the intracellular interleukin-1 receptor antagonist gene by AP-1 in mouse carcinoma cells.

Interleukin-1 receptor antagonist (IL-1Ra) is involved in many processes, including epidermal inflammation and hyperplasia after irritation or injury. However, the mechanism by which intracellular IL-1Ra (icIL-1Ra) expression is regulated in mouse keratinocytes has not been reported. We found that the CH72 mouse carcinoma cell line constitutively expresses the icIL-1Ra mRNA. To study the transcriptional factors responsible for the constitutive expression of icIL-1Ra, we functionally characterized 4.5 kb of the 5' flanking region of the human icIL-1Ra gene in these cells. We first demonstrated that icIL-1Ra expression in these cells was regulated at the level of transcription. Deletion analysis of the promoter showed that regulatory elements for constitutive expression were located -158 to -49 bp upstream of the transcription start site for icIL-1Ra. We investigated the cis- and trans-acting factors required for icIL-1Ra expression. An activating protein-1 (AP-1) site was identified as the positive regulatory element necessary for the constitutive expression of the icIL-1Ra promoter in CH72 cells. Moreover, electrophoretic mobility shift assay and cotransfection experiments showed that c-jun and c-fos proteins bound to the AP-1 site and functionally transactivated the icIL-1Ra promoter in mouse carcinoma CH72 cells. Copyright 2002 Wiley-Liss, Inc.