Reduced expression of nuclear cyclic adenosine 5′-monophospate response element-binding proteins and IFN-γ promoter function in disease due to an intracellular pathogen

Mycobacterium tuberculosis-induced IFN-γ protein and mRNA expression have been shown to be reduced in tuberculosis patients, compared with healthy tuberculin reactors. To determine whether this decrease was associated with reduced activity of the IFN-γ promoter, we first studied binding of nuclear proteins to the radiolabeled proximal IFN-γ promoter (-71 to -40 bp), using EMSAs with nuclear extracts of freshly isolated peripheral blood T cells. Nuclear extracts of T cells from most tuberculosis patients showed markedly reduced expression of proteins that bind to the proximal IFN-γ promoter, compared with findings in nuclear extracts of T cells from healthy tuberculin reactors. These DNA-binding complexes contained CREB proteins, based on competitive EMSAs, supershift assays, and Western blotting with an anti-CREB Ab. Transient transfection of PBLs with a luciferase reporter construct under the control of the IFN-γ promoter revealed reduced IFN-γ promoter activity in tuberculosis patients. Transient transfection of Jurkat cells with a dominant-negative CREB repressor plasmid reduced IFN-γ promoter activity. These data suggest that reduced expression of CREB nuclear proteins in tuberculosis patients results in decreased IFN-γ promoter activity and reduced IFN-γ production.