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The nuclear function of the heterodimeric NF-kB transcription factor is regulated in part through reversible acetylation of its RelA subunit. We now demonstrate that the p300 and CBP acetyltransferases play a major role in the in vivo acetylation of RelA, principally targeting lysines 218, 221 and 310 for modi®cation. Analysis of the functional properties of hypoacetylated RelA mutants containing lysine-toarginine substitutions at these sites and of wild-type RelA co-expressed in the presence of a dominantly interfering mutant of p300 reveals that acetylation at lysine 221 in RelA enhances DNA binding and impairs assembly with IkBa. Conversely, acetylation of lysine 310 is required for full transcriptional activity of RelA in the absence of effects on DNA binding and IkBa assembly. Together, these ®nd-ings highlight how site-speci®c acetylation of RelA differentially regulates distinct biological activities of the NF-kB transcription factor complex.

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Accumulating evidence suggests that neurodegeneration induced by pathogenic proteins depends on contributions from surrounding glia. Here we demonstrate that NF-B signaling in microglia is critically involved in neuronal death induced by amyloid-␤ (A␤) peptides, which are widely presumed to cause Alzheimer disease. Constitutive inhibition of NF-B signaling in microglia by expression of the nondegradable IB␣ superrepressor blocked neurotoxicity, indicating a pivotal role for microglial NF-B signaling in mediating A␤ toxicity. Stimulation of microglia with A␤ increased acetylation of RelA/p65 at lysine 310, which regulates the NF-B pathway. Overexpression of SIRT1 deacetylase and the addition of the SIRT1 agonist resveratrol markedly reduced NF-B signaling stimulated by A␤ and had strong neuroprotective effects. Our results support a glial loop hypothesis by demonstrating a critical role for microglial NF-B signaling in A␤-dependent neurodegeneration. They also implicate SIRT1 in this pathway and highlight the therapeutic potential of resveratrol and other sirtuin-activating compounds in Alzheimer disease.Neurodegenerative diseases appear to be caused by pathogenic proteins that affect neurons directly or contribute to neuronal death by engaging neurotoxic pathways in surrounding glia (1-3). In Alzheimer disease (AD), 3 neurodegeneration may be exacerbated by chronic inflammatory reactions of cells surrounding neuritic plaques, including microglia and astrocytes (4, 5). High concentrations of fibrillar A␤ can activate microglia, resulting in tumor necrosis factor-␣-dependent expression of inducible nitric-oxide synthase (iNOS) and neuronal apoptosis (6). Nonfibrillar A␤, which may be the major pathogenic form of A␤ in the early stages of AD, also stimulates microglia to induce neurodegeneration. Dimeric and trimeric assemblies of A␤-(1-42) isolated from amyloid deposits elicited profound neurotoxicity in hippocampal neurons but only in the presence of microglia (7). Stimulation with soluble A␤ caused microglia to secrete toxic factors, including cathepsin B, and mediated neurodegeneration (8). Inhibiting the induction of long term potentiation with soluble A␤ involves activation of microglia and stimulation of iNOS and superoxide (9).We hypothesized that the pathogenic engagement of microglia by A␤ involves activation of NF-B, a transcription factor that mediates immune and inflammatory responses (10) and controls the expression of both iNOS and cathepsin B (11, 12). In AD brains, RelA/p65 immunoreactivity is greater in neurons and astrocytes surrounding amyloid plaques, raising the possibility of a role for NF-B in AD pathogenesis (13). In cultured neurons and glia, A␤ stimulation led to NF-B activation (12-15). However, it remains unclear whether NF-B signaling actually contributes to AD-related neurodegeneration.To test our hypothesis, we took advantage of the fact that NF-B activation is tightly regulated by inhibitory proteins, such as IB␣ (16). In response to stimuli, IB␣ is degraded to release the NF-B p50/...

Cells latently infected with HIV represent a currently insurmountable barrier to viral eradication in infected patients. Using the J‐Lat human T‐cell model of HIV latency, we have investigated the role of host factor binding to the κB enhancer elements of the HIV long terminal repeat (LTR) in the maintenance of viral latency. We show that NF‐κB p50–HDAC1 complexes constitutively bind the latent HIV LTR and induce histone deacetylation and repressive changes in chromatin structure of the HIV LTR, changes that impair recruitment of RNA polymerase II and transcriptional initiation. Knockdown of p50 expression with specific small hairpin RNAs reduces HDAC1 binding to the latent HIV LTR and induces RNA polymerase II recruitment. Similarly, inhibition of histone deacetylase (HDAC) activity with trichostatin A promotes binding of RNA polymerase II to the latent HIV LTR. This bound polymerase complex, however, remains non‐processive, generating only short viral transcripts. Synthesis of full‐length viral transcripts can be rescued under these conditions by expression of Tat. The combination of HDAC inhibitors and Tat merits consideration as a new strategy for purging latent HIV proviruses from their cellular reservoirs.

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The NF-B/Rel family of transcription factors plays a key role in regulating inflammatory and immune responses and other programs of cell growth and survival. The five known mammalian Rel genes encode seven Rel-related proteins: RelA/p65; p105 and its processing product, p50; p100 and its processing product, p52; c-Rel; and RelB. Each contains an N-terminal Rel homology domain (ϳ300 amino acids) that mediates DNA binding, dimerization, and interaction with the IB family of NF-B/Rel inhibitors. RelA, c-RelA, and RelB contain C-terminal transactivation domains, but p50 and p52 do not. Each NF-B/Rel protein forms different homo-or heterodimers with other members of the family, which may contribute to the activation of specific target genes (1, 5).The prototypical NF-B complex is a p50/RelA heterodimer. NF-B is largely sequestered in the cytoplasm through its association with an IB inhibitor. Nuclear NF-B expression is induced by various stimuli, including proinflammatory cytokines, growth factors, DNA-damaging agents, and viral proteins (13). The activation of NF-B can be divided into two phases. The first phase involves cytoplasmic events culminating in the activation of the IB kinases (IKK1 and IKK2). These kinases promote N-terminal phosphorylation of serines 32 and 36 in IB␣, leading to its polyubiquitylation and proteasome-mediated degradation. The liberated NF-B complex rapidly translocates to the nucleus, ending the first phase (13). The second phase occurs primarily in the nucleus and involves posttranslational modification of the NF-B transcription factor complex or relevant histones surrounding NF-B target genes (5). These modifications determine both the strength and duration of the NF-B-mediated transcriptional response (5).One of the nuclear events is the reversible acetylation of RelA (4). Endogenous RelA is acetylated in a stimulus-coupled manner after activation of cells with tumor necrosis factor alpha (TNF-␣), phorbol myristate acetate, or other stimuli at multiple sites, including lysines 122, 123, 218, 221, and 310 (4, 17). The acetyltransferases p300 and CBP appear to play a major role in the in vivo acetylation of RelA (6,17). Sitespecific acetylation of RelA regulates discrete biological actions of the NF-B complex (5, 6). For example, acetylation of lysine 221 by p300/CBP increases the DNA binding affinity of RelA for the B enhancer and, together with acetylation of lysine 218, impairs assembly of RelA with newly synthesized IB␣, which shuttles in and out of the nucleus. Acetylation of lysine 310 does not modulate DNA binding or IB␣ assembly but markedly enhances the transcriptional activity of NF-B. Deacetylation of lysine 310 by histone deacetylase 3 (HDAC3) or SIRT1 inhibits the transcriptional activity of RelA and augments cellular apoptosis in response to 32). While it is clear that signal-coupled acetylation of RelA participates in the nuclear regulation of NF-B action (4, 17), many unanswered questions remain. Chief among these is how the acetylation of RelA is regulated.

The eukaryotic transcription factor NF-κB regulates a wide range of host genes that control the inflammatory and immune responses, programmed cell death, cell proliferation and differentiation. The activation of NF-κB is tightly controlled both in the cytoplasm and in the nucleus. While the upstream cytoplasmic regulatory events for the activation of NF-κB are well studied, much less is known about the nuclear regulation of NF-κB. Emerging evidence suggests that NF-κB undergoes a variety of posttranslational modifications, and that these modifications play a key role in determining the duration and strength of NF-κB nuclear activity as well as its transcriptional output. Here we summarize the recent advances in our understanding of the posttranslational modifications of NF-κB, the interplay between the various modifications, and the physiological relevance of these modifications.