CBP (CREB Binding Protein) Integrates NF-κB (Nuclear Factor-κB) and Glucocorticoid Receptor Physical Interactions and Antagonism

Abstract

Nuclear factor-kappaB (NF-kappaB) and the glucocorticoid receptor (GR) are transcription factors with opposing actions in the modulation of immune/inflammatory responses. NF-kappaB induces the expression of proinflammatory genes, while GR suppresses immune function in part by suppressing expression of the same genes. Previously, we demonstrated that physiological antagonism between NF-kappaB and GR is due to a mutual transcriptional antagonism that requires the p65 subunit of NF-kappaB and multiple domains of GR (1). To elucidate the mechanism(s) of NF-kappaB p65 and GR transcriptional antagonism, we analyzed the interactions of wild-type p65 and p65 RHD (rel homology domain, a dominant negative mutant of p65 which lacks a transactivation domain) with GR. We show that p65RHD blocks p65-mediated transactivation, yet does not block the repression of GR transactivation by p65, indicating that transcriptional activity by p65 is not required to repress GR function. Both p65 and p65 RHD physically interact with GR, but only intact p65 represses GR-mediated signaling, implicating the p65 transactivation domain in the transcriptional repression of GR. To further characterize p65-GR interactions, we examined the role of the transcriptional co-integrator CREB binding protein (CBP) in their mutual antagonism. GR-mediated repression of p65 transactivation and p65-mediated repression of GR transactivation, as well as the physical interaction between NF-kappaB and GR, are enhanced by CBP. GR bound to the antagonist RU 486, although transcriptionally inactive, retains the ability to repress p65 transactivation. However, CBP does not physically interact with antagonist-bound GR and does not enhance its repressive effect on p65. These data suggest that CBP functions as an integrator of p65/GR physical interaction, rather than as a limiting cofactor for which p65 and GR compete.

Cross-talk between nuclear receptors and nuclear factor κB

“…Experimentally, however, it has been demonstrated that activation of GR does not affect the interaction between RelA and CBP and that a nuclear GAL4-RelA point mutant, defective in CBP recruitment, could still be functionally repressed by GR (De Bosscher et al, 2000b), arguing against a general CBPcompetition model for inhibition or RelA by GR. Instead, CBP may act as an integrator, facilitating the physical interaction between GRa and NF-kB (McKay and Cidlowski, 2000). Although GR interactions with specific coactivators are critical for direct GR target gene transactivation, they appear to be dispensable for at least certain aspects of GR-mediated transrepression of NF-kB (Wu et al, 2004).…”

Steroid Responsiveness of Renal Epithelial Cells

“…Interaction between GR and NF-B has been shown to result in functional antagonism (13,33). The mechanism underlying this antagonism might be competition for cofactors, including CBP, as has been proposed in some studies (15,33). Based on this model of functional antagonism, we would like to propose that a high level of constitutive NF-B activation contributes to the low level of GR reporter gene activity we observed in HK-2 cells or vice versa.…”

“…In parallel, we observed a high level of constitutive NF-B activation in non-stimulated HK-2 cells compared with A549 cells. Interaction between GR and NF-B has been shown to result in functional antagonism (13,33). The mechanism underlying this antagonism might be competition for cofactors, including CBP, as has been proposed in some studies (15,33).…”

Signal Transduction Pathways in use of Dexamethasone Implant in the Eye

“…A few mechanisms have been suggested for inhibition. One of these, the direct protein-protein interaction between NF-kB and GRs, is important for the mutual transcriptional antagonism between NF-kB and GRs or the cross-repression of the cAMP response element binding protein (CREBP) [67] and the catalytic protein kinase A subunit [68]. Glucocorticoids inhibit transcriptional up-regulation of T cell-derived cytokines, such as IL1-2, IL-4, IL-10, and g-interferon (1-3), and proinflammatory cytokines, such as IL-1, granulocyte-macrophage colonystimulating factor, and tumor necrosis factor-α [69,70].…”