The BH3-only Bim protein is a major determinant for initiating the intrinsic apoptotic pathway under both physiological and pathophysiological conditions. Tight regulation of its expression and activity at the transcriptional, translational and post-translational levels together with the induction of alternatively spliced isoforms with different pro-apoptotic potential, ensure timely activation of Bim. Under physiological conditions, Bim is essential for shaping immune responses where its absence promotes autoimmunity, while too early Bim induction eliminates cytotoxic T cells prematurely, resulting in chronic inflammation and tumor progression. Enhanced Bim induction in neurons causes neurodegenerative disorders including Alzheimer’s, Parkinson’s and Huntington’s diseases. Moreover, type I diabetes is promoted by genetically predisposed elevation of Bim in β-cells. On the contrary, cancer cells have developed mechanisms that suppress Bim expression necessary for tumor progression and metastasis. This review focuses on the intricate network regulating Bim activity and its involvement in physiological and pathophysiological processes.

A large percentage of redox-responsive gene promoters contain evolutionarily conserved guanine-rich clusters; guanines are the bases most susceptible to oxidative modification(s). Consequently, 7,8-dihydro-8-oxoguanine (8-oxoG) is one of the most abundant base lesions in promoters and is primarily repaired via the 8-oxoguanine DNA glycosylase-1 (OOG1)-initiated base excision repair pathway. In view of a prompt cellular response to oxidative challenge, we hypothesized that the 8-oxoG lesion and the cognate repair protein OGG1 are utilized in transcriptional gene activation. Here, we document TNFα-induced enrichment of both 8-oxoG and OGG1 in promoters of pro-inflammatory genes, which precedes interaction of NF-κB with its DNA-binding motif. OGG1 bound to 8-oxoG upstream from the NF-κB motif increased its DNA occupancy by promoting an on-rate of both homodimeric and heterodimeric forms of NF-κB. OGG1 depletion decreased both NF-κB binding and gene expression, whereas Nei-like glycosylase-1 and -2 had a marginal effect. These results are the first to document a novel paradigm wherein the DNA repair protein OGG1 bound to its substrate is coupled to DNA occupancy of NF-κB and functions in epigenetic regulation of gene expression.

Tumor necrosis factor  (TNF) is a pluripotent activator of inflammation by inducing a proinflammatory cytokine cascade. This phenomenon is mediated, in part, through inducible expression of the CXC chemokine, interleukin-8 (IL-8). In this study, we investigate the role of TNF-inducible reactive oxygen species (ROS) in IL-8 expression by “monocyte-like” U937 histiocytic lymphoma cells. TNF is a rapid activator of IL-8 gene expression by U937, producing a 50-fold induction of mRNA within 1 hour of treatment. In gene transfection assays, the effect of TNF requires the presence of an inducible nuclear factor-κB (NF-κB) (Rel A) binding site in the IL-8 promoter. TNF treatment induces a rapid translocation of the 65 kD transcriptional activator NF-κB subunit, Rel A, whose binding in the nucleus occurs before changes in intracellular ROS. Pretreatment (or up to 15 minutes posttreatment) relative to TNF with the antioxidant dimethyl sulfoxide (DMSO) (2% [vol/vol]) blocks 80% of NF-κB–dependent transcription. Surprisingly, however, DMSO has no effect on inducible Rel A binding. Similar selective effects on NF-κB transcription are seen with the unrelated antioxidants, N-acetylcysteine (NAC) and vitamin C. These data indicate that TNF induces a delayed ROS-dependent signalling pathway that is required for NF-κB transcriptional activation and is separable from that required for its nuclear translocation. Further definition of this pathway will yield new insights into inflammation initiated by TNF signalling.

Herein, the restricted expression of serum response factors (SRF) closely overlapped withNkx2-5 and GATA4 transcripts in early chick embryos coinciding with the earliest appearance of cardiac α-actin (αCA) transcripts and nascent myocardial cells. The combinatorial expression of SRF, a MADS box factor Nkx2-5 (a NK4 homeodomain), and/or GATA4, a dual C4 zinc finger protein, in heterologous CV1 fibroblasts and Schneider 2 insect cells demonstrated synergistic induction of αCA promoter activity. These three factors induced endogenous αCA mRNA over a 100-fold in murine embryonic stem cells. In addition, the DNA-binding defective mutant Nkx2-5pm efficiently coactivated the αCA promoter in the presence of SRF and GATA4 in the presence of all four SREs and was substantially weakened when individual SREs were mutated and or serially deleted. In contrast, the introduction of SRFpm, a SRF DNA-binding mutant, blocked the activation with all of the αCA promoter constructions. These assays indicated a dependence upon cooperative SRF binding for facilitating the recruitment of Nkx2-5 and GATA4 to the αCA promoter. Furthermore, the recruitment of Nkx2-5 and GATA4 by SRF was observed to strongly enhance SRF DNA binding affinity. This mechanism allowed for the formation of higher ordered αCA promoter DNA binding complexes, led to a model of SRF physical association with Nkx2-5 and GATA4.

Respiratory syncytial virus (RSV) produces intense pulmonary inflammation, in part, through its ability to induce chemokine synthesis in infected airway epithelial cells. In this study, we compare mechanisms for induction of the CXC chemokine IL-8, in human type II alveolar (A549) cells by RSV infection and by stimulation with the cytokine TNF. Promoter deletion and mutagenesis experiments indicate that although the region from −99 to −54 nt is sufficient for TNF-induced IL-8 transcription, this region alone is not sufficient for RSV-induced IL-8 transcription. Instead, RSV requires participation of a previously unrecognized element, spanning from −162 to −132 nt, that we term the RSV response element (RSVRE), and a previously characterized element at −132 to −99 nt, containing an AP-1 binding site. RSV infection of A549 cells induces increased RSVRE- and AP-1-binding activities and increased synthesis of IFN regulatory factor-1 protein, which is present in the RSVRE-binding complex. These data confirm that the IL-8 gene enhancers are controlled in a stimulus-specific fashion and participation of distinct promoter elements is required to activate gene transcription. These observations are important for rational design of inhibitors of RSV-induced lung inflammation.