Nuclear factor-kappaB (NF-kappaB) plays a role in the transcriptional regulation of genes involved in inflammation and cell survival. In this report we demonstrate that NF-kappaB recruits a coactivator complex that has striking similarities to that recruited by nuclear receptors. Inactivation of either cyclic AMP response element binding protein (CREB)-binding protein (CBP), members of the p160 family of coactivators, or the CBP-associated factor (p/CAF) by nuclear antibody microinjection prevents NF-kappaB-dependent transactivation. Like nuclear receptor-dependent gene expression, NF-kappaB-dependent gene expression requires specific LXXLL motifs in one of the p160 family members, and enhancement of NF-kappaB activity requires the histone acetyltransferase (HAT) activity of p/CAF but not that of CBP. This coactivator complex is differentially recruited by members of the Rel family. The p50 homodimer fails to recruit coactivators, although the p50-p65 heterodimeric form of the transcription factor assembles the integrator complex. These findings provide new mechanistic insights into how this family of dimeric transcription factors has a differential effect on gene expression.

In certain cancers, constitutive Wnt signaling results from mutation in one or more pathway components. The result is the accumulation and nuclear localization of b-catenin, which interacts with the lymphoid enhancer factor-1 (LEF)/T-cell factor (TCF) family of HMG-box transcription factors, which activate important growth regulatory genes, including cyclin D1 and c-myc. As exempli®ed by APC and axin, the negative regulation of b-catenin is important for tumor suppression. Another potential mode of negative regulation is transcriptional repression of cyclin D1 and other Wnt target genes. In mammals, the transcriptional repressors in the Wnt pathway are not well de®ned. We have previously identi®ed HBP1 as an HMG-box repressor and a cell cycle inhibitor. Here, we show that HBP1 is a repressor of the cyclin D1 gene and inhibits the Wnt signaling pathway. The inhibition of Wnt signaling and growth requires a common domain of HBP1. The apparent mechanism is an inhibition of TCF/LEF DNA binding through a physical interaction with HBP1. These data suggest that the suppression of Wnt signaling by HBP1 may be a mechanism to prevent inappropriate proliferation.

Regulatory T cells (Tregs) play a pivotal role in suppressing immune responses regulating behavior and gene expression in effector T cells, macrophages, and dendritic cells. Tregs infiltrate the infarcted myocardium; however, their role the inflammatory and reparative response after myocardial infarction remains poorly understood. We used FoxP3(EGFP) reporter mice to study Treg trafficking in the infarcted heart and examined the effects of Treg depletion on postinfarction remodeling using an anti-CD25 antibody. Moreover, we investigated the in vitro effects of Tregs on cardiac fibroblast phenotype and function. Low numbers of Tregs infiltrated the infarcted myocardium after 24-72 h of reperfusion. Treg depletion had no significant effects on cardiac dysfunction and scar size after reperfused myocardial infarction but accelerated ventricular dilation and accentuated apical remodeling. Enhanced myocardial dilation in Treg-depleted animals was associated with increased expression of chemokine (C-C motif) ligand 2 and accentuated macrophage infiltration. In vitro, Tregs modulated the cardiac fibroblast phenotype, reducing expression of α-smooth muscle actin, decreasing expression of matrix metalloproteinase-3, and attenuating contraction of fibroblast-populated collagen pads. Our findings suggest that endogenous Tregs have modest effects on the inflammatory and reparative response after myocardial infarction. However, the anti-inflammatory and matrix-preserving properties of Tregs may suggest a role for Treg-based cell therapy in the attenuation of adverse postinfarction remodeling.

Transcriptional coactivators may function as nuclear integrators by coordinating diverse signaling events. Here we show that the p65 (RelA) component of nuclear factor-B (NF-B) and p53 mutually repress each other's ability to activate transcription. Additionally, tumor necrosis factor-activated NF-B is inhibited by UV lightinduced p53. Both p65 and p53 depend upon the coactivator CREB-binding protein (CBP) for maximal activity. Increased levels of the coactivator relieve p53-mediated repression of NF-B activity and p65-mediated repression of p53-dependent gene expression. Nuclear competition for limiting amounts of CBP provides a novel mechanism for altering the balance between the expression of NF-B-dependent proliferation or survival genes and p53-dependent genes involved in cell cycle arrest and apoptosis. Nuclear factor-B (NF-B)1 is an inducible transcription factor that plays an essential role in the regulation of gene expression in response to inflammatory stimuli (1). It is composed of members of the Rel family (p50, p52, p65 (RelA), c-Rel, and RelB), which share a region of homology known as the Rel homology domain capable of directing DNA binding and mediating dimerization. In most cells, NF-B is found in an inactive form in the cytoplasm bound to an inhibitory protein, IB. In response to multiple activating signals, the inhibitor is degraded by the ubiquitin-proteasome complex, and NF-B translocates to the nucleus and induces gene expression. NF-B components can interact with other DNA binding proteins, as well as with a series of non-DNA-binding coactivator proteins. Among these interactions, the p65 component of NF-B, like a variety of signal-dependent transcriptional activators, can associate with CREB-binding protein (CBP) or its structural homolog p300 (2, 3).Activation of NF-B is associated with resistance to programmed cell death (4 -10). Mice with a targeted mutation in the p65 component of NF-B die before birth with extensive liver cell apoptosis (11). Fibroblasts derived from these mice show increased apoptosis following TNF␣ stimulation, an effect that can be reversed by overexpression of p65 (4). Inhibition of NF-B activation increases cell death in response to multiple stimuli (7). Moreover, inhibition of constitutively active NF-B in lymphoid cell lines causes apoptosis (8). One mechanism by which NF-B inhibits cell death is to induce the expression of genes that promote resistance to apoptosis. These anti-apoptotic gene include A20 (12), the immediate early response gene IEX-1L (13), as well as TRAF1 (TNFR-associated factor 1), TRAF2, and the inhibitor-of-apoptosis (IAP) proteins c-IAP and c-IAP2 (14). Thus NF-B can activate a set of genes that function cooperatively to suppress apoptosis.In contrast to NF-BЈs role in promoting cell survival, the p53 tumor suppressor gene plays an important role in cell cycle arrest or apoptosis in response to various types of stress (15,16). p53 functions as a transcriptional activator by binding to specific DNA sequence elements (17) and interacting wi...