Positive and Negative Regulation of Nuclear Factor-κB-mediated Transcription by IκB-ζ, an Inducible Nuclear Protein

Abstract

IB-is an inducible nuclear protein that interacts with nuclear factor-B (NF-B) via its carboxyl-terminal ankyrin-repeats. Previous studies using an NF-B reporter have shown that IB-inhibits the activity of NF-B. In the present study, we dissected the aminoterminal region of IB-, which shows no homology to any other proteins. Indirect immunofluorescence studies demonstrated the presence of a bipartite nuclear localization signal spanning amino acids 163-178. Using GAL4 fusion proteins, we found that internal fragments containing amino acids 329 -402 possessed intrinsic transcriptional activation activity. Interestingly, the activity was not detected in GAL4 fusion proteins of the full-length IB-. On the other hand, the GAL4-dependent transcriptional activity was generated by co-expression of the GAL4-NF-B p50 subunit fusion protein and the full-length IB-, neither of which exhibited the activity on their own. A new splicing variant, IB-(D), with a deletion of amino acids 236 -429, was found to lack transactivation activity. Forced expression of IB-, but not IB-(D), augmented interleukin-6 production, indicating the functional significance of the transactivation activity. In contrast, tumor necrosis factor-␣ production was inhibited by expression of IB-, highlighting the dual functions of this molecule. These results indicate that IB-harbors latent transcriptional activation activity, and that the activity is expressed upon interaction with the NF-B p50 subunit. In addition to the inhibitory activity on NF-B-mediated transcription, the transcriptional activation activity of IBshould be crucial for the regulation of inflammation.

The myxoid liposarcoma FUS-DDIT3 fusion oncoprotein deregulates NF-κB target genes by interaction with NFKBIZ

“…NFKBIZ promotes transcription (Kitamura et al, 2000;Motoyama et al, 2005) but may also act as an inhibitor of p50 containing NF-kB complexes (Yamazaki et al, 2001;Totzke et al, 2006). In this study, we report that the MMP1 and LCN2 genes encoding matrix metalloproteinase 1 and lipocalin 2 (a cofactor for MMP9), both involved in extracellular matrix remodeling, are strongly expressed in FUS-DDIT3 carrying cell lines.…”

“…IL8, IL6 and LCN2 are transcriptional targets of NFKBIZ In addition to IL8, MMP1 has also been shown to be regulated by the NF-kB system, and both IL6 and LCN2 have been reported to be downstream targets of NFKBIZ (Vincenti et al, 1998;Motoyama et al, 2005;Oikawa et al, 2006). To test whether these genes were transcriptionally controlled by NFKBIZ in our system, we used a tamoxifen-regulated vector system (Littlewood et al, 1995).…”

Molecular modeling‐based evaluation of dual function of IκBζ ankyrin repeat domain in toll‐like receptor signaling

“…In mice, there is no expression of IkBz in the resting state and it is induced by lipopolysaccharide (LPS), interleukin-1 beta (IL-b), peptidoglycan, bacterial lipoprotein, flagellin, and C P G DNA, but not by tumor necrosis factor alpha (TNFa) (Yamazaki et al, 2001;Yamamoto et al, 2004;Motoyama et al, 2005). Conversely, human IkBz expression is strongly induced by TNFa (Totzke et al, 2006).…”

“…Although IkBz (D) mRNA has been detected in macrophages, the corresponding protein has not been found. Following induction, IkBz associates with the NF-kB subunit in the nucleus, where it positively or negatively regulates its transcriptional activity (Motoyama et al, 2005). Previous biochemical studies suggest that following the endogenous expression of mouse IkBz in response to LPS, IkBz is translocated into the nucleus, where it preferentially associates with the p50/ p50 homodimer of NF-kB, which is already bound to DNA.…”

“…Wet lab experiments have shown that human IkBz binds to the p50/p65 heterodimer, while mouse IkBz shows a preference for p50/p50 homodimer. Because it is evident that only C-terminal ARD (452-718) is capable of binding with its partners (Yamazaki et al, 2001;Motoyama et al, 2005;Totzke et al, 2006), we have concentrated solely on the C-terminal ARD in the present study.…”