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IL-17 Enhances Chemokine Gene Expression through mRNA Stabilization¹

Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH 44195

	Abstract

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IL-17 plays an important role in host defense and autoimmunity via the induction of proinflammatory gene expression, particularly in combination with TNF-. The molecular mechanisms by which IL-17 regulates such expression are not well understood. Using the mouse chemokine CXCL1 (KC) gene as a model, we have examined the effects of IL-17 alone or in combination with TNF- on transcriptional and posttranscriptional events. Although treatment of mouse embryonic fibroblasts with IL-17 alone only modestly increased KC expression, the combination of IL-17 with TNF- induced a synergistic response. IL-17 treatment exerted a strong posttranscriptional effect by extending the t_1/2 of the highly unstable, TNF--induced KC mRNA. Using a tetracycline-regulated transgene in HeLa cells, we determined that IL-17 treatment alone promoted stabilization of KC mRNA in the absence of TNF-. IL-17 treatment exerted little effect on KC transcription or NF-B activation, suggesting that it primarily acts posttranscriptionally. We identified a number of other mRNAs whose t_1/2 are prolonged in response to IL-17, suggesting that this is a common mechanism by which IL-17 promotes enhanced gene expression. Finally, activator of NF-B1 protein (Act1), an adaptor protein recently implicated in IL-17 signaling, was necessary for IL-17-induced stabilization, and overexpression of Act1 resulted in stabilization of KC mRNA, indicating that events downstream of Act1 are sufficient to initiate this process. Thus, the synergy between TNF- and IL-17 reflects their independent actions on KC gene expression; TNF- serves as a stimulus to initiate transcription through activation of NF-B, whereas IL-17 drives mRNA stabilization through an Act1-dependent pathway.

	Introduction

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Interleukin-17 is a proinflammatory cytokine produced predominately by a distinct class of Th lymphocytes now termed Th17 cells (1, 2). The response to IL-17 depends upon a widely expressed receptor present on multiple cell populations resident within many normal tissues and results in elevated expression of a variety of proinflammatory genes, including CXC chemokines (3, 4). Although IL-17 is important for host protection against challenge by bacterial infection, it has also been demonstrated to play a significant role in tissue destructive inflammation in the setting of autoimmunity (4, 5).

Although IL-17 is recognized to participate in host defense and autoimmunity through the induction of proinflammatory gene expression, the molecular mechanisms by which this is achieved remain poorly defined. It has been repeatedly observed that IL-17 treatment alone is a relatively poor stimulus for gene expression. However, IL-17 can cooperate with other cytokines, particularly TNF-, to induce a synergistic response (3, 6). A number of studies have linked response to IL-17 with the activation of NF-B, although the magnitude of activation appears to be relatively modest (7, 8). Several reports have also shown that IL-17 can operate at a posttranscriptional level to stabilize otherwise unstable cytokine mRNAs (9, 10, 11).

The modulation of mRNA t_1/2 has emerged as an important means of regulation for a number of proinflammatory cytokine and chemokine genes. Many of these mRNAs exhibit very short t_1/2 based upon the content of adenine uridine-rich sequence elements (2) located within their 3' untranslated regions (UTRs)³ (12, 13, 14, 15, 16). Studies focusing on TNF- have demonstrated that mRNA instability is an essential mechanism for silencing inflammatory gene expression in the absence of overt inflammation (17, 18, 19). During the initiation of an inflammatory reaction, there is a need to rapidly elevate the level of cytokine and chemokine expression, and in the context of unstable mRNA, this necessitates substantial extension of mRNA t_1/2. Stimulation through Toll-IL-1 family receptors (TIRs) has been reported to promote enhanced stability of several mRNAs (16, 20, 21, 22, 23).

In the present study, we have examined the mechanisms through which IL-17 promotes enhanced gene expression using mouse chemokine CXCL1 (KC), a neutrophil-directed chemokine, as a model. Transcription of the KC gene depends upon activation of NF-B in response to TIR ligands such as LPS and IL-1 as well as TNF- (21, 24). KC mRNA, however, is highly unstable, and expression is markedly enhanced by stimuli that can promote stabilization (21, 22). Interestingly, whereas many TIR ligands can stabilize KC mRNA, stimulation by TNF- does not promote this activity, and hence, TNF- alone is a relatively weak KC inducer in many cell types (21, 25).

We have found that whereas IL-17 alone was a relatively poor stimulus for KC expression in mouse embryo fibroblasts (MEFs), the combination of TNF- and IL-17 together produced a potent response. The data demonstrate that IL-17 and TNF- contribute to elevated KC expression through mechanistically distinct routes. The primary mechanistic target for IL-17 appears to be the stabilization of KC mRNA. Furthermore, we have identified a number of other mRNAs whose t_1/2 is prolonged in response to IL-17 treatment, suggesting that this is a major mechanism by which IL-17 induces gene expression. Finally, the IL-17-induced stabilization of KC mRNA is dependent upon IL-17R signaling through a pathway that requires the adaptor protein, activator of NF-B1 protein (Act1).

	Materials and Methods

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Reagents

DMEM, Dulbecco’s PBS, and antibiotics were obtained from Central Cell Services of the Lerner Research Institute. FBS was purchased from BioWhittaker. G418, formamide, MOPS, salmon sperm DNA, and diethyl-pyrocarbonate were purchased from Sigma-Aldrich. Doxycycline (Dox) and the vector pTRE2 were obtained from BD Clontech. PolyFect tranfection reagent was obtained from Qiagen, Tri-Reagent was purchased from Molecular Research Center, and nylon transfer membrane was purchased from Micron Separation. Recombinant human and mouse IL-1, IL-17, and TNF-, and the KC ELISA kit were purchased from R&D Systems. Luciferase assay buffer and passive lysis buffer were purchased from Promega. PerkinElmer Life Sciences was the source of [-³²P]dCTP. Protein assay reagents were purchased from Bio-Rad.

Cell culture

MEF 3T3 tet-off and HeLa tet-off cell lines were purchased from BD Clontech. Each cell line stably expresses the tet repressor protein fused with the VP16 trans activation domain. The cells were maintained in DMEM supplemented with 10% FBS, penicillin, and streptomycin, and were kept under antibiotic selection with G418 (400 µg/ml). MEFs from either heterozygous or homozygous Act1-deficient mice were prepared, as previously described, and were cultured in DMEM supplemented with 10% FBS, penicillin, and streptomycin (26).

Plasmids

Plasmids encoding KC, MIP-2, MCP-1, GAPDH, and the 5x B firefly luciferase reporter have been described previously (27, 28, 29, 30). To measure KC mRNA transcription, we used a plasmid (290gKC-RBG) containing 290 nt of the promoter, the first three exons (and introns) of the KC gene, and a fourth exon in which the KC 3'UTR is substituted with the 3'UTR from the rabbit globin gene. The details of the construction of this plasmid and its behavior have been described earlier (31). To measure the effects of IL-17 on KC mRNA expressed from a tetracycline-sensitive promoter, a plasmid containing the 5'UTR and coding region of KC mRNA linked with the last 322 nt of the KC mRNA 3'UTR was used (pTRE2 KC3) (27). Expression plasmids encoding human MyD88, dominant-negative version of IB or IB superrepressor (IB SR), and Act1 were described previously (28, 32, 33).

Transfection

HeLa cells were transiently transfected using PolyFect tranfection reagent (Qiagen), following the manufacturer’s protocol for HeLa cells. The cells were plated in 100-mm dishes and grown to 70% confluence before transfection. Following transfection, cultures were divided into smaller treatment groups and incubated for 18 h before treatment.

KC ELISA, luciferase analysis, Northern blot hybridization, and microarray

KC ELISA was performed using a kit from R&D Systems, according to the manufacturer’s protocol. Luciferase activity of cell lysates was determined using a kit from Promega, according to the manufacturer’s protocol. Total RNA was isolated using Tri-Reagent, according to the manufacturer’s protocol, and mRNA levels were determined by Northern blot hybridization, as previously described (27). Oligonucleotide-based microarrays were done by the Gene Expression and Genotyping Core in the Comprehensive Cancer Center at Case Western Reserve University School of Medicine using the Affymetrix Mouse Genome 430 2.0 array.

	Results

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TNF- and IL-17 cooperatively induce KC expression

To characterize the effect of IL-17 treatment on KC expression, MEFs were stimulated with TNF- or IL-17 alone or in combination, and KC protein production was measured by ELISA (Fig. 1A). When used alone, both IL-17 and TNF- were relatively weak inducers of KC expression, but the combination of TNF- plus IL-17 was a potent stimulus for the production of KC protein, which was comparable to the level produced in response to IL-1. In comparison, the effect induced by the combination of IL-1 and IL-17 was only slightly larger than that induced by IL-1 alone. This cooperative effect of TNF- and IL-17 on KC protein secretion was also demonstrable at the level of KC mRNA accumulation (Fig. 1B). KC mRNA was barely detectable at any time point following treatment with IL-17 alone. In response to TNF- alone, message was detectable at the earliest time point (1 h), but the levels declined dramatically over the next 2 h. The level of KC mRNA following 1 h of treatment with the combination of TNF- and IL-17 was similar to that seen in cells stimulated with TNF- alone, but KC mRNA levels remained elevated for a prolonged period.

View larger version (43K): [in this window] [in a new window]   FIGURE 1. IL-17 and TNF- cooperatively induce KC expression. A, MEFs were stimulated with 10 ng/ml each of the indicated cytokines for 8 h. Supernatants were collected, and KC protein production was determined by ELISA. Each treatment was performed in duplicate, and values represent the average of the two samples. B, Total RNA was isolated from MEFs that had been stimulated with 10 ng/ml each cytokine for the indicated times. KC and GAPDH mRNA levels were determined by Northern hybridization. Similar results were obtained in three separate experiments.

IL-17 increases the t_1/2 of TNF--induced KC mRNA

As mentioned earlier, the expression of KC is known to be regulated both by the induction of gene transcription and by stabilization of rapidly decaying mRNA (21, 22, 25). Indeed, whereas TNF- and IL-1 are both potent stimuli for inducing KC gene transcription, only IL-1 is capable of promoting mRNA stability (21, 25). The finding that treatment with IL-17 alone resulted in little accumulation of message at the early time point, but can prolong the expression of KC mRNA when used in combination with TNF-, suggests that it is a poor stimulus of transcription and instead promotes stabilization of the message. Hence, we hypothesized that the cooperation between TNF- and IL-17 results from distinct mechanistic contributions of each stimulus to KC mRNA accumulation.

We first tested the ability of IL-17 treatment to modulate the t_1/2 of KC mRNA. Cultures of MEFs were stimulated with IL-1, TNF-, or TNF- plus IL-17 for 1 h, and actinomycin D (ActD) was added to block further transcription. Following further incubation for the indicated times, total RNA was prepared and used to determine KC and GAPDH mRNA levels by Northern hybridization. The KC mRNA induced by treatment with TNF- rapidly decayed following addition of ActD with a t_1/2 of 20 min (Fig. 2A). In cells stimulated with TNF- plus IL-17, however, the t_1/2 was prolonged to nearly 60 min. The rate of decay in cells treated with TNF-/IL-17 was comparable to that in cells treated with IL-1, which is known to serve as a stimulus for KC mRNA stabilization (21, 25).

View larger version (36K): [in this window] [in a new window]   FIGURE 2. IL-17 prolongs the t1/2 of TNF--induced KC mRNA. A, MEFs were stimulated with 10 ng/ml of the indicated cytokines for 1 h, followed by the addition of ActD (5 µg/ml). Total RNA was isolated at the indicated times and used to determine KC and GAPDH mRNA levels by Northern hybridization. The autoradiographs were quantified using the NIH Image software, and KC mRNA levels were normalized to GAPDH mRNA levels and plotted as percentage of mRNA remaining vs time. The t1/2 were derived from the equations that defined each line in the graph. B, MEFs were stimulated with TNF- for 1 h, and the medium was replaced with fresh medium containing ActD (5 µg/ml) alone or with IL-1 (10 ng/ml) or IL-17 (10 ng/ml). Following incubation for the indicated times, total RNA was prepared and used to determine KC and GAPDH mRNA levels by Northern hybridization. The autoradiographs were quantified and plotted as in A. Similar results were obtained in three separate experiments.

IL-17 independently induces KC mRNA stability

The preceding findings establish that IL-17 can stabilize TNF--induced KC mRNA, although whether this capacity is codependent on TNF- or whether TNF- is required solely to provide the transcriptional stimulus remains unknown. To distinguish between these possibilities, we evaluated the effect of IL-17 on the stability of KC mRNA transcribed under control of a tetracycline-regulated promoter. HeLa cells stably expressing the tetR-VP-16 fusion protein were transfected with a plasmid containing the KC 5'UTR, coding region, and a segment of the 3'UTR under control of a tet-regulated promoter (pTRE2 KC3). After transfection, the cultures were subdivided into different treatment groups and rested overnight. Dox was added alone or with the indicated treatments, and total RNA was isolated at various times and used to determine levels of KC and GAPDH mRNA by Northern hybridization (Fig. 3). In the absence of treatment, KC message decayed rapidly following the addition of Dox, whereas treatment with IL-1, but not TNF-, increased the t_1/2 of the mRNA. Treatment with IL-17 alone was sufficient to increase the stability of the KC mRNA. Thus, IL-17, like IL-1, can independently drive stabilization of KC mRNA.

View larger version (42K): [in this window] [in a new window]   FIGURE 3. IL-17 can independently promote KC mRNA stabilization. Pools of HeLa tet-off cells were transfected with 2 µg of pTRE2 KC3, divided into different treatment groups, and allowed to rest for 18 h. Cultures were treated with Dox (100 ng/ml) either alone or in the presence of IL-1 (10 ng/ml), TNF- (10 ng/ml), or IL-17 (25 ng/ml). At the indicated times, total RNA was prepared and used to determine levels of KC and GAPDH mRNA by Northern hybridization. Similar results were obtained in three separate experiments.

IL-17 is a poor stimulus for KC transcription and NF-B activation

Because KC expression is also regulated at the level of transcription initiation, we used two experimental approaches to determine whether IL-17 also exerted an effect on this process. First, we examined the effect of IL-17 on expression of a KC gene under control of a 290-nt fragment from the KC promoter (290gKC-RBG) (31). This construct is regulated solely by transcription from the promoter because the KC 3'UTR, which determines posttranscriptional control, has been replaced by the 3'UTR from the rabbit globin mRNA. Although IL-17 induced modest KC protein production, it was a much weaker stimulus for this response than either IL-1 or TNF- (Fig. 4A). In addition, the response induced by a combination of TNF- and IL-17 was only slightly larger than the response to TNF- alone. This small effect of IL-17 at the level of transcription cannot account for the large responses seen when measuring the accumulation of endogenous KC mRNA or protein.

View larger version (27K): [in this window] [in a new window]   FIGURE 4. NF-B activation is not required for IL-17-induced mRNA stabilization. A, HeLa tet-off cells were transfected with 2 µg of 290gKC-RBG, and the cells were divided into the indicated treatment groups and allowed to rest for 18 h. Cultures were stimulated with IL-1 (10 ng/ml), TNF- (10 ng/ml), IL-17 (25 ng/ml), or the combination of TNF- and IL-17 for 8 h. Supernatants were then collected, and KC protein production was determined by ELISA. Each treatment was performed in duplicate, and values represent the mean of the two samples. B, HeLa tet-off cells were transfected with 2 µg of 5x B luciferase reporter, and following overnight culture, were stimulated with the indicated cytokines for 8 h. Cell lysates were prepared, and luciferase activity was determined. Values represent the mean of duplicate samples. C, Pools of HeLa tet-off cells were transfected with 2 µg of pTRE2 KC3, 2 µg of 5x B luciferase, and 2 µg of either pcDNA3 or an expression plasmid encoding the IB SR, and separated into two treatment groups. The first group was either untreated or stimulated for 8 h with IL-1 or IL-17 before preparation of cell lysates for determination of luciferase activity. The second group was treated with Dox alone or with IL-1 or IL-17 for the indicated times before isolation of total RNA and analysis of KC and GAPDH mRNA levels by Northern hybridization. Similar results were obtained in two separate experiments.

Our data indicate that IL-17 prolongs the t_1/2 of KC mRNA, but has little effect on activation of NF-B and KC gene transcription. However, multiple reports indicate that inhibitors of NF-B block IL-17-induced gene expression (7, 35, 36, 37, 38), and thus, we wanted to determine whether KC mRNA stabilization induced by IL-17 also required NF-B activation. To assess this possibility, HeLa tet-off cells were cotransfected with the pTRE2 KC3 plasmid and either empty vector or a vector encoding the IB SR, known to provide potent inhibition of the activation of NF-B. Although the IB SR effectively blocked the activation of NF-B in response to IL-1, it did not inhibit the ability of either IL-17 or IL-1 to promote stabilization of KC mRNA (Fig. 4C). Thus, it appears that NF-B activity is not necessary for stabilization of the mRNA. Surprisingly, the KC mRNA consistently had a prolonged t_1/2 under all treatment conditions in the presence of the IB SR.

IL-17 stabilizes other rapidly decaying mRNAs

To determine whether mRNA stabilization was a general mechanism by which IL-17 regulated expression of a variety of genes, we tested the effect of IL-17 treatment on the decay of other mRNAs. As a first step, we examined the stability of several additional chemokine mRNAs in MEFs stimulated with either TNF- or the combination of TNF- plus IL-17. The t_1/2 of MIP-2 mRNA in cells treated with TNF- plus IL-17 was markedly prolonged compared with that observed in cells stimulated by TNF- alone (Fig. 5A). MCP-1 mRNA was also more stable in cells treated with IL-17, although the effect is less dramatic due to the relatively longer t_1/2 of this message in cells treated with TNF- alone.

View larger version (33K): [in this window] [in a new window]   FIGURE 5. IL-17 stabilizes other short-lived TNF--induced mRNAs. A, MEFs were stimulated with TNF- (10 ng/ml) or TNF- + IL-17 (10 ng/ml) for 1 h, followed by the addition of ActD (5 µg/ml). Total RNA was isolated at the indicated times and used to determine MIP-2, MCP-1, and GAPDH mRNA levels by Northern hybridization. B, Total RNA was isolated from untreated MEFs or MEFs treated with TNF- for 1 h, TNF- for 1 h, followed by ActD for 2 h, or TNF- for 1 h, followed by ActD + IL-17 for 2 h, and used in Affymetrix oligonucleotide-based microarray analysis, as described in Materials and Methods. Genes meeting the criteria described in the text are listed, and the percentage of mRNA remaining following 2 h of ActD+/– IL-17 is provided.

Act1 is required for IL-17-induced mRNA stabilization

The cytoplasmic adaptor protein Act1 has recently been shown to interact with the IL-17R and to be required for IL-17-induced proinflammatory gene expression (26, 39). We thus wanted to determine whether Act1 was necessary for IL-17-induced mRNA stabilization. In MEFs from Act1^+/– mice, KC mRNA induced by treatment with TNF- and IL-17 together had a t_1/2 of 60 min (Act^+/+ and Act1^+/– MEFs behave equivalently), whereas that induced in Act1-deficient MEFs was markedly less stable (t_1/2 < 20 min) (Fig. 6A). Hence, Act1 is required for the modulation of mRNA stability in response to IL-17. Act1 was not required for IL-1-induced stabilization, and the adaptor MyD88, although required for IL-1-induced stabilization, did not play a role in IL-17-induced stabilization (data not shown) (39).

View larger version (65K): [in this window] [in a new window]   FIGURE 6. Act1 is necessary for IL-1-induced KC mRNA stabilization. A, MEFs from Act1+/– and Act1–/– mice were treated with TNF- (10 ng/ml) and IL-17 (50 ng/ml) for 1 h before the addition of ActD. Cultures were incubated for the indicated times before preparation of total RNA and analysis of KC and GAPDH mRNA levels by Northern hybridization. B, Pools of HeLa tet-off cells were transfected with 2 µg of pTRE2 KC3 and 4 µg of pcDNA3 or pcDNA3 containing MyD88 or Act1. Cells were divided into the specified experimental groups and cultured overnight. Cell cultures were treated with Dox and incubated for the indicated times before the preparation of total RNA and determination of KC and GAPDH mRNA levels by Northern hybridization. Similar results were obtained in two separate experiments.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion Disclosures References

 
Although IL-17 is known to participate in both host defense and autoimmunity via the induction of proinflammatory gene expression, the molecular mechanisms by which this occurs have not been well characterized. In the present study, the chemokine KC has been used as a model to evaluate the effects of IL-17 on transcriptional and posttranscriptional regulation. As has been reported for other targets of IL-17, KC expression is only modestly increased in response to IL-17 alone, but the combination of IL-17 and TNF- induces strong expression of KC at both the mRNA and protein level. TNF-, although a potent transcriptional activator, does not alter KC mRNA decay and is thus a relatively weak stimulus for KC expression (21, 22, 25). In contrast, the data presented demonstrate that IL-17 is able to markedly prolong the t_1/2 of KC mRNA, but has little effect on KC transcription or NF-B activation. The ability of IL-17 in combination with other stimuli such as TNF- to promote enhanced mRNA stability for a number of cytokines and chemokines, including human IL-8, has been previously reported (9, 10, 11). These reports, taken with our finding that IL-17 extends the t_1/2 of multiple short-lived mRNAs, indicate that a major way in which IL-17 induces gene expression is through mRNA stabilization. Thus, the cooperative effects of TNF- and IL-17 on KC gene expression reflect their independent, but synergistic mechanisms; TNF- induces transcription and IL-17 stabilizes the mRNA. In contrast, TIR ligands such as IL-1 and LPS induce transcription and prolong the t_1/2 of the constitutively unstable mRNA, and thus independently strongly drive KC expression (21, 22, 25).

Although inhibitors of NF-B activity have been reported to block IL-17-induced gene expression, we have shown that this activity is not required for the generation of mRNA stability. Given this finding and the relatively modest effect of IL-17 treatment on the activation of NF-B, we believe that this transcription factor is, at best, only modestly involved in IL-17-induced gene expression. However, NF-B activity is necessary for expression of KC and other IL-17-stimulated genes due to its requirement in controlling their transcription. Collectively, the data indicate that although NF-B is required for expression of many IL-17-sensitive genes, IL-17 acts downstream of this factor to alter gene expression at a distinct mechanistic level.

The cytoplasmic adaptor Act1 has recently been shown to interact with the IL-17R via SEFIR domains present in both proteins (26, 39). This interaction is required both for the modest activation of NF-B induced by IL-17 treatment and for the induction of gene expression. The data presented in this study indicate that Act1 is necessary for the ability of IL-17 to promote enhanced KC mRNA stability. Moreover, overexpression of Act1 is capable of initiating the stabilization mechanism independently of IL-17, suggesting that other IL-17-linked signaling events are not necessary and that signals downstream of Act1 are sufficient. Act1 does not play a role in IL-1-induced KC mRNA stabilization, and whereas the adaptor MyD88 is essential for IL-1-induced KC mRNA stabilization, it does not play a role in mediating the response to IL-17 (39) (data not shown). The signaling events downstream of Act1 that couple the IL-17R with KC mRNA stabilization are presently unknown. TIR ligand-induced mRNA stabilization is believed to involve activation of the p38 MAPK pathway (23, 40, 41, 42). Because IL-17 has been reported to promote enhanced stability of COX2 mRNA via p38 MAPK activation (9) and because IL-1 and IL-17 have similar effects on the stability of mRNA containing the KC 3'UTR, they may share a common downstream signaling cascade.

Regulation of mRNA stability is an important means of controlling expression of a number of proinflammatory genes. These mRNAs are inherently unstable, providing an essential check to ensure that the gene is not inappropriately expressed (17, 18, 19). Moreover, it is a potential mechanism by which the duration of the inflammatory response is limited. However, the ability to prolong the t_1/2 of the message is necessary to reach a high level of expression in the setting of inflammation. Thus, regulation of mRNA decay rates provides additional control over proinflammatory gene expression. IL-17 is the first stimulus we are aware of that acts primarily at a posttranscriptional level without also initiating transcription. This finding further emphasizes the importance of the role of regulated mRNA stability in the control of proinflammatory gene expression.

	Disclosures

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The authors have no financial conflict of interest.

	Footnotes

 
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by U.S. Public Health Service Grants CA39621, AI50739, and T32 GM07250.

² Address correspondence and reprint requests to: Thomas Hamilton, Department of Immunology, NE40 Cleveland Clinic, 9500 Euclid, Cleveland, OH 44195. E-mail address: hamiltt{at}ccf.org

³ Abbreviations used in this paper: UTR, untranslated region; Act1, activator of NF-B1 protein; ActD, actinomycin D; Dox, doxycycline; IB SR, dominant-negative version of IB or IB superrepressor; KC, mouse chemokine CXCL1; MEF, mouse embryo fibroblast; TIR, Toll-IL-1 family receptor.

Received for publication March 29, 2007. Accepted for publication June 29, 2007.

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Top Abstract Introduction Materials and Methods Results Discussion Disclosures References

 

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