Down-regulation of human granzyme B expression by glucocorticoids - Dexamethasone inhibits binding to the Ikaros and AP-1 regulatory elements of the granzyme B promoter

The serine protease granzyme B is an essential component of the granule exo cytosis pathway, a major apoptotic mechanism used by cytotoxic T lymphocyte s and natural killer cells to induce target cell apoptosis, Granzyme B gene transcription is induced in activated lymphocytes upon antigenic stimulati on, and several regulatory regions including CBF, AP-1, and Ikaros binding sites have been shown to be essential in the control of granzyme B promoter activation. Dexamethasone, a glucocorticoid that is widely used as an immu nomodulatory and anti-inflammatory agent, inhibits granzyme B mRNA transcri pt in phytohemagglutinin-activated peripheral blood mononuclear cells. Tran sfection of a reporter construct containing the -148 to +60 region of the h uman granzyme B promoter demonstrated that this region was the target for d examethasone repression. Mutation of Ikaros or AP-1 binding sites in the co ntext of the granzyme B promoter demonstrated that both sites participate i n dexamethasone-mediated inhibition of the granzyme B promoter activity. El ectromobility shift assay revealed that dexamethasone abolished the binding of nuclear transcription factors to the Ikaros binding site and reduced AP -1 binding activity. These results indicate that dexamethasone is able to a brogate the transcriptional activity of the human granzyme B gene promoter by inhibiting the binding of nuclear factors at the AP-1 and Ikaros sites.