NF‐κB is responsible for upregulating gene products that control cell survival. In this study, we demonstrate that SIRT1, a nicotinamide adenosine dinucleotide‐dependent histone deacetylase, regulates the transcriptional activity of NF‐κB. SIRT1, the mammalian ortholog of the yeast SIR2 (Silencing Information Regulator) and a member of the Sirtuin family, has been implicated in modulating transcriptional silencing and cell survival. SIRT1 physically interacts with the RelA/p65 subunit of NF‐κB and inhibits transcription by deacetylating RelA/p65 at lysine 310. Treatment of cells with resveratrol, a small‐molecule agonist of Sirtuin activity, potentiates chromatin‐associated SIRT1 protein on the cIAP‐2 promoter region, an effect that correlates with a loss of NF‐κB‐regulated gene expression and sensitization of cells to TNFα‐induced apoptosis. While SIRT1 is capable of protecting cells from p53‐induced apoptosis, our work provides evidence that SIRT1 activity augments apoptosis in response to TNFα by the ability of the deacetylase to inhibit the transactivation potential of the RelA/p65 protein.

MURR1 is a multifunctional protein that inhibits nuclear factor B (NF-B), a transcription factor with pleiotropic functions affecting innate and adaptive immunity, apoptosis, cell cycle regulation, and oncogenesis. Here we report the discovery of a new family of proteins with homology to MURR1. These proteins form multimeric complexes and were identified in a biochemical screen for MURR1-associated factors. The family is defined by the presence of a conserved and unique motif termed the COMM (copper metabolism gene MURR1) domain, which functions as an interface for proteinprotein interactions. Like MURR1, several of these factors also associate with and inhibit NF-B. The proteins designated as COMMD or COMM domain containing 1-10 are extensively conserved in multicellular eukaryotic organisms and define a novel family of structural and functional homologs of MURR1. The prototype of this family, MURR1/COMMD1, suppresses NF-B not by affecting nuclear translocation or binding of NF-B to cognate motifs; rather, it functions in the nucleus by affecting the association of NF-B with chromatin.NF-B is a dimeric complex formed by members of a highly conserved family of proteins that share a defining motif designated the Rel homology domain (RHD).1 Through transcriptional regulation of many gene products, NF-B participates in a number of biological processes including innate and adaptive immune responses, programmed cell death, cell cycle progression, and oncogenesis (1-6). Additionally, by its ability to regulate transcription of various viral genomes including human immunodeficiency virus-1 (HIV-1) (7-10), NF-B also participates in viral cycle progression.Studies into the regulation of NF-B activation have largely focused on the role of cytoplasmic sequestration of the NF-B complex as a mainstay level of control. In most cells NF-B is localized in the cytoplasm through the interaction of the complex with members of the IB family (11). These proteins contain ankyrin repeats that allow their interaction with NF-B and mask the nuclear localization signal present in the RHD. Phosphorylation of IB by a multimeric kinase known as the IB kinase complex targets these proteins for ubiquitination and proteasomal degradation (3,12). This allows the translocation of NF-B to the nucleus where it binds to cognate DNA sequences present in an array of gene promoters.MURR1 is a recently identified factor that has been shown to participate in two apparently distinct activities, regulation of the transcription factor NF-B and control of copper metabolism (13). Mutations in MURR1 are responsible for copper toxicosis in an inbred canine strain (Bedlington terriers) (14), and an interaction between MURR1 and the copper transporter ATP7B (15) has been recently reported.In addition to its role in copper metabolism in mammals, more recent studies implicate MURR1 in the regulation of the transcription factor NF-B (13, 16). MURR1 was found to be a broad inhibitor of NF-B, affecting B-responsive transcription from endogenous and viral promoters in...

Over the last several years, significant progress has been made in identifying chromatin-regulated events that govern NF-B transcription. Using either laminin attachment or tumor necrosis factor alpha as a physiological stimulus of NF-B activation, we demonstrate that IB kinase ␣ (IKK␣) is recruited to chromatin in distinct phases. In the initial phase, IKK␣ is responsible for derepressing the silencing mediator for retinoic acid and thyroid hormone receptor (

Understanding how signaling cascades stimulate chromatin-remodeling events through derepression is one of the foremost questions in the transcription field. Here, we demonstrate that NF-kappaB transcription requires IKKalpha to phosphorylate SMRT on chromatin, stimulating the exchange of corepressor for coactivator complexes. IKKalpha-induced phosphorylation coincides with a loss of chromatin-associated SMRT and HDAC3 and with nuclear export of the SMRT corepressor, events required for expression of the NF-kappaB-regulated cIAP-2 and IL-8 genes. Although SMRT derepression corresponds with the recruitment of TBL1/TBLR1, this complex alone is insufficient to relieve repression. Using a nonphosphorylatable SMRT protein, we demonstrate that IKKalpha-induced phosphorylation is required to recruit 14-3-3epsilon and Ubc5 for SMRT derepression. Failure of IKKalpha to stimulate the removal of SMRT from chromatin inhibits the recruitment of NF-kappaB to promoters, blocking transcription and sensitizing cells to apoptosis. Our work provides evidence that IKKalpha orchestrates SMRT derepression, a prerequisite for NF-kappaB transcription and survival.

Hepatocellular carcinoma is a common malignancy causing significant morbidity and mortality worldwide. In this study we use expression microarray technology to identify novel genes that consistently displayed altered expression levels in the earliest identifiable precursors to hepatocellular carcinoma, dysplastic and macroregenerative nodules. The gene expression profiles from nine patients with end-stage hepatitis C cirrhosis that contained a combined 11 dysplastic or macroregenerative nodules were compared to the patient's matched cirrhotic liver tissue. A total of 53 genes were consistently dysregulated in the patient liver specimens. Six of seven genes were validated by quantitative real-time reverse transcriptase-polymerase chain reaction, or by immunohistochemical studies performed on an independent set of lesions. The novel genes, including caveolin-1, semaphorin E, and FMS-like tyrosine kinase 3 ligand, have putative roles in carcinogenesis but have not been reported in hepatocellular carcinogenesis. Microarray expression analysis of dysplastic and macroregenerative liver nodules provide insight into the earliest changes in hepatocellular carcinogenesis.