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.

Proper regulation of NF‐κB activity is critical to maintain and balance the inflammatory response. Inactivation of the NF‐κB complex relies in part on the proteasome‐mediated degradation of promoter‐bound NF‐κB, but the detailed molecular mechanism initiating this process remains elusive. Here, we show that the methylation of the RelA subunit of NF‐κB has an important function in this process. Lysine methyltransferase Set9 physically associates with RelA in vitro and in vivo in response to TNF‐α stimulation. Mutational and mass spectrometric analyses reveal that RelA is monomethylated by Set9 at lysine residues 314 and 315 in vitro and in vivo. Methylation of RelA inhibits NF‐κB action by inducing the proteasome‐mediated degradation of promoter‐associated RelA. Depletion of Set9 by siRNA or mutation of the RelA methylation sites prolongs DNA binding of NF‐κB and enhances TNF‐α‐induced expression of NF‐κB target genes. Together, these findings unveil a novel mechanism by which methylation of RelA dictates the turnover of NF‐κB and controls the NF‐κB‐mediated inflammatory response.

Helicobacter pylori-initiated chronic gastritis is characterized by the cag pathogenicity island-dependent upregulation of proinflammatory cytokines, which is largely mediated by the transcription factor nuclear factor (NF)-jB. However, the cag pathogenicity island-encoded proteins and cellular signalling molecules that are involved in H. pylori-induced NF-jB activation and inflammatory response remain unclear. Here, we show that H. pylori virulence factor CagA and host protein transforming growth factor-b-activated kinase 1 (TAK1) are essential for H. pylori-induced activation of NF-jB. CagA physically associates with TAK1 and enhances its activity and TAK1-induced NF-jB activation through the tumour necrosis factor receptorassociated factor 6-mediated, Lys 63-linked ubiquitination of TAK1. These findings show that polyubiquitination of TAK1 regulates the activation of NF-jB, which in turn is used by H. pylori CagA for the H. pylori-induced inflammatory response.

Recent studies have emphasized the importance of cellular microenvironment in modulating cell growth and signaling. In vitro, collagen matrices, Matrigel, and other synthetic support systems have been used to simulate in vivo microenvironments, and epithelial cells grown in these matrices manifest significant differences in proliferation, differentiation, response to drugs, and other parameters. However, these substrates do not closely resemble the mesenchymal microenvironment that is typically associated with advanced carcinomas in vivo, which is produced to a large extent by fibroblasts. In this study, we have evaluated the ability of a fibroblast-derived three-dimensional matrix to regulate the growth of a panel of 11 human tumor epithelial cell lines. Although proliferative and morphological responses to three-dimensional cues segregated independently, general responsiveness to the matrix correlated with the ability of matrix to influence drug responses. Fibroblast-derived three-dimensional matrix increased β1-integrin-dependent survival of a subset of human cancer cell lines during taxol treatment, while it sensitized or minimally influenced survival of other cells. β1-integrin-dependent changes in cell resistance to taxol did not correlate with degree of modulation of FAK and Akt, implying additional signaling factors are involved. Based on these results, we propose these matrices potentially have value as in vitro drug screening platforms.

H. pylori infection causes chronic gastritis and peptic ulceration and is the strongest risk factor for the development of gastric cancer. The pathogenesis of H. pylori is believed to be associated with infection-initiated chronic gastritis, which is characterized by enhanced expression of many inflammatory genes. H. pylori utilizes various virulence factors, targeting different cellular proteins, to modulate the host inflammatory response. In this review, we explore the many different ways by which H. pylori initiates inflammation, leveling many “hits” on the gastric mucosa which can lead to the development of cancer. We also discuss some recent findings in understanding the pathogen-host interactions and the role of transcription factor NF-κB in H. pylori-induced inflammation.

Chronic infection with cagA-positive Helicobacter pylori is the strongest risk factor for the development of gastric adenocarcinoma. The cagA gene product CagA is injected into gastric epithelial cells and disturbs cellular functions by physically interacting with and deregulating a variety of cellular signaling molecules. RUNX3 is a tumor suppressor in many tissues, and it is frequently inactivated in gastric cancer. In this study, we show that H. pylori infection inactivates the gastric tumor suppressor RUNX3 in a CagA-dependent manner. CagA directly associates with RUNX3 through a specific recognition of the PY motif of RUNX3 by a WW domain of CagA. Deletion of the WW domains of CagA or mutation of the PY motif in RUNX3 abolishes the ability of CagA to induce the ubiquitination and degradation of RUNX3, thereby extinguishing its ability to inhibit the transcriptional activation of RUNX3. Our studies identify RUNX3 as a novel cellular target of H. pylori CagA and also reveal a mechanism by which CagA functions as an oncoprotein by blocking the activity of gastric tumor suppressor RUNX3.

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Recent studies on the lysine methylation of histones have moved rapidly thanks to the discoveries of a variety of histone lysine methyltransferases. Histone lysine methylation is known to either activate or repress gene expression depending upon the position and status of the methylated lysine residue. Recently, an increasing number of lysine methyltransferases have been identified to modify non-histone proteins. Among those enzymes, the most extensively studied is Set9, a SET domain-containing lysine methyltransferase. Set9 was initially found to target histone H3 lysine 4 for monomethylation and was subsequently shown to target a variety of non-histone proteins, especially transcription-related factors. Functional studies revealed that Set9-mediated methylation of different non-histone proteins leads to distinct biological consequences, most of which point to protein stability. Here we summarize the latest findings on the effects of Set9-mediated lysine methylation on the stability of non-histone proteins.