Interleukin 1 induction of the c-jun promoter

Phosphorylation of ATF2 and interaction with NFY induces c-Jun in the gonadotrope

Induction of c-Jun and c-Fos, partners that comprise the AP1 transcription factor, is critical for GnRH regulation of FSHβ gene expression. The signaling pathways that are necessary for regulation of AP1 in the gonadotrope cell are not known. Here, we investigate the mechanism of c-Jun induction by GnRH, the sole regulator of c-Jun in the gonadotrope. We identify that GnRH phosphorylates ATF2 via p38 and JNK, the same pathways responsible for GnRH induction of c-Jun. Upon phosphorylation, ATF2 binds the CRE element within the c-Jun proximal promoter and interacts with NFY. Functional ATF2 is necessary for both GnRH induction of c-Jun and FSHβ. Taken together, these studies elucidate the specificity of c-Jun induction by GnRH in the gonadotrope by demonstrating GnRH activation of the p38 and JNK signaling pathways that lead to phosphorylation of ATF2, providing critical insight into GnRH regulation of its target gene, the gonadotropin subunit FSHβ.

Interleukin-1 (IL-1) family of cytokines: role in type 2 diabetes

Cytokines are small cell signaling protein molecules which encompass a large and diverse family. They consist of immunomodulating agents such as interleukins and inteferons. Virtually all nucleated cells, especially endo/epithelial cells and macrophages are potent producers of IL-1, IL-6 and TNF-α. IL-1 family is a group of cytokines which play a central role in the regulation of immune and inflammatory responses. Type 2 diabetes (T2D) has been recognized as an immune mediated disease leading to impaired insulin signaling and selective destruction of insulin producing β-cells in which cytokines play an important role. Disturbance of anti-inflammatory response could be a critical component of the chronic inflammation resulting in T2D. IL-1 family of cytokines has important roles in endocrinology and in the regulation of responses associated with inflammatory stress. The IL-1 family consists of two pro-inflammatory cytokines, IL-1α and IL-1β, and a naturally occurring anti-inflammatory agent, the IL-1 receptor antagonist (IL-1Ra or IL-1RN). This review is an insight into the different types of cytokines belonging to IL-1 family, their modes of action and association with Type 2 diabetes.

Exploring pathway interactions in insulin resistant mouse liver

BACKGROUND

Complex phenotypes such as insulin resistance involve different biological pathways that may interact and influence each other. Interpretation of related experimental data would be facilitated by identifying relevant pathway interactions in the context of the dataset.

RESULTS

We developed an analysis approach to study interactions between pathways by integrating gene and protein interaction networks, biological pathway information and high-throughput data. This approach was applied to a transcriptomics dataset to investigate pathway interactions in insulin resistant mouse liver in response to a glucose challenge. We identified regulated pathway interactions at different time points following the glucose challenge and also studied the underlying protein interactions to find possible mechanisms and key proteins involved in pathway cross-talk. A large number of pathway interactions were found for the comparison between the two diet groups at t = 0. The initial response to the glucose challenge (t = 0.6) was typed by an acute stress response and pathway interactions showed large overlap between the two diet groups, while the pathway interaction networks for the late response were more dissimilar.

CONCLUSIONS

Studying pathway interactions provides a new perspective on the data that complements established pathway analysis methods such as enrichment analysis. This study provided new insights in how interactions between pathways may be affected by insulin resistance. In addition, the analysis approach described here can be generally applied to different types of high-throughput data and will therefore be useful for analysis of other complex datasets as well.

Functional aspects of redox control during neuroinflammation

Neuroinflammation is a CNS reaction to injury in which some severe pathologies, regardless of their origin, converge. The phenomenon emphasizes crosstalk between neurons and glia and reveals a complex interaction with oxidizing agents through redox sensors localized in enzymes, receptors, and transcription factors. When oxidizing pressures cause reversible molecular changes, such as minimal or transitory proinflammatory cytokine overproduction, redox couples provide a means of translating the presence of reactive oxygen or nitrogen species into useful signals in the cell. Additionally, thiol-based redox sensors convey information about localized changes in redox potential induced by physiologic or pathologic situations. They are susceptible to oxidative changes and become key events during neuroinflammation, altering the course of a signaling response or the behavior of specific transcription factors. When oxidative stress augments the pressure on the intracellular environment, the effective reduction potential of redox pairs diminishes, and cell signaling shifts toward proinflammatory and proapoptotic signals, creating a vicious cycle between oxidative stress and neuroinflammation. In addition, electrophilic compounds derived from the oxidative cascade react with key protein thiols and interfere with redox signaling. This article reviews the relevant functional aspects of redox control during the neuroinflammatory process.

Expression profile of human gingival fibroblasts induced by interleukin-1beta reveals central role of nuclear factor-kappa B in stabilizing human gingival fibroblasts during inflammation

BACKGROUND

Interleukin (IL)-1beta is a key cytokine in the pathogenesis of periodontitis, and it induces inflammatory mediators in periodontal diseases. We developed immortalized human gingival fibroblasts (HGFs), investigated the effects of IL-1beta on the gene expression using expression arrays containing approximately 40,000 genes, and tested the role of nuclear factor-kappa B (NF-kappaB) in maintaining an activated HGF population.

METHODS

Total RNA was isolated from IL-1beta-induced and mock-induced control cells. Gene expression analyses were performed using expression arrays and confirmed by quantitative real-time polymerase chain reaction. Western blot analysis to show inhibitor of kappa B-alpha (IkappaBalpha) phosphorylation and immunostaining of cells for NF-kappaB nuclear translocation were performed. Apoptosis was confirmed by assay of poly ADP-ribose polymerase (PARP) cleavage.

RESULTS

A total of 382 probe sets corresponding to 254 genes were differentially expressed in IL-1beta-induced cells (P <0.001). A total of 215 genes were upregulated, and 39 genes were downregulated. Most notable NF-kappaB pathway members (NFkappaB1, NFkappaB2, IkappaBalpha, IkappaBepsilon, IkappaBzeta, REL, RELB, and TA-NFKBH) were upregulated. IkappaBalpha was phosphorylated, and NF-kappaB accumulated in the nucleus. An IL-1beta-induced set of 27 genes was downregulated by an NF-kappaB inhibitor, leading to a decreased number of viable cells and suggesting an antiapoptotic role for NF-kappaB.

CONCLUSIONS

IL-1beta leads to a large number of significant expression changes consistent with a pathologic role in periodontitis, including enhancement of inflammatory cytokines, chemokines, transcription factors, matrix metalloproteinases, adhesion molecules, and especially NF-kappaB-dependent antiapoptotic genes. NF-kappaB activation blocks apoptosis, thereby stabilizing the HGF population in inflammation.

IL-1beta-driven ST2L expression promotes maturation resistance in rapamycin-conditioned dendritic cells

Maturation resistance and tolerogenic properties can be conferred on human and murine dendritic cells (DC), crucial regulators of T cell responses, by exposure to rapamycin (RAPA), a "tolerance-sparing" immunosuppressive agent. Mechanisms underlying this acquired unresponsiveness, typified by diminished functional responses to TLR or CD40 ligation, have not been identified. We report that in vitro and in vivo conditioning of murine myeloid DC with RAPA elicits the de novo production of IL-1beta by otherwise phenotypically immature DC. Interestingly, IL-1beta production promotes overexpression of the transmembrane form of the IL-1R family member, IL-1R-like 1, also know as ST2 on RAPA-conditioned DC (RAPA-DC). ST2 is the recently identified receptor for IL-33, a cytokine favoring Th2 responses. In addition, transmembrane ST2, or ST2L, has been implicated as a potent negative regulator of TLR signaling. RAPA-DC generated from ST2-/- mice exhibited higher levels of costimulatory molecules (CD86) than wild-type RAPA-DC. Consistent with its regulatory function, IL-1beta-induced ST2L expression suppressed the responsiveness of RAPA-DC to TLR or CD40 ligation. Thus, as a result of their de novo production of IL-1beta, RAPA-DC up-regulate ST2L and become refractory to proinflammatory, maturation-inducing stimuli. This work identifies a novel mechanism through which a clinically important immunosuppressant impedes the capacity of DC to mature and consequently stimulate effector/adaptive T cell responses.

Adhesive and proteolytic phenotype of migrating endothelial cells induced by thymosin beta-4

The early stages of angiogenesis are usually accompanied by the occurrence of vascular leakage, and the deposition of fibrin in extravascular spaces. Initially, the fibrin network acts as a sealing matrix, but later on also as a scaffolding for invading endothelial cells. This process is induced by angiogenic growth factors, particularly by vascular endothelial growth factor (VEGF). Angiogenesis involves proteolytic activities, in particular cell-bound urokinase/plasmin and matrix metalloproteinase (MMPs) activities that modulate the fibrin structure and affect adhesion and migration of endothelial cells. Recent data show that formation of new vessels may be stimulated by thymosin beta-4 (Tbeta-4), but it is still not clear whether Tbeta-4 alone is angiogenic or the angiogenic potential of Tbeta-4 is mediated by VEGF. In this report to further characterize Tbeta-4 angiogenic activity, we produced its mutants that were deprived of the N-terminal tetrapeptide AcSDKP (Tbeta-4((AcSDKPT/4A))), the actin-binding sequence KLKKTET (Tbeta-4((KLKKTET/7A))) and with the nuclear localization sequence damaged by a point mutation Lys16Ala (Tbeta-4((K16A))). Then we tested their activity to induce expression and release of MMPs as well as plasminogen activators inhibitor type-1 (PAI-1). We also analyzed their effect on migration and proliferation of endothelial cells in three-dimensional (3D) fibrin matrix as well as on their ability to stimulate the outgrowth of human endothelial cells in capillary-like tubular structures. Our data demonstrate that increased intracellular expression of Tbeta-4 and its mutants is necessary and sufficient to induce PAI-1 gene expression in endothelial cells. Similarly, they stimulate expression and release of MMP-1, -2, and -3. As evaluated by using specific inhibitors to these MMPs, they modified specifically the structure of fibrin and thus facilitated migration of endothelial cells. To sum up, our data show that the mechanism by which Tbeta-4 induced transition of endothelial cells from quiescent to proangiogenic phenotype is characterized by increased expression of PAI-1 and MMPs did not require the presence of the N-terminal sequence AcSDKP, and depended only partially on its ability to bind G-actin or to enter the nucleus.

Expression of IL-1beta, IL-1 receptor type I and IL-1 receptor antagonist in human aortic smooth muscle cells: effects of all-trans-retinoic acid

The proinflammatory cytokine interleukin (IL)-1beta and the IL-1 receptor antagonist are expressed by atherosclerotic plaques and may be linked to the development of atherosclerosis. Existing evidence shows that retinoids and their receptors are involved in inflammatory response and that they are found in atherosclerotic plaques. In all-trans-retinoic acid (atRA)-treated human aortic smooth muscle cells (AOSMC), significant increases in IL-1beta levels were observed, compared with untreated cells. Examination of IL-1 receptor antagonist and IL-1 receptor type I levels did not show any difference between atRA-treated and -untreated AOSMC. The results show that atRA-treated AOSMC express both the precursor (33 kDa) and the active form (17 kDa) of the IL-1beta protein. atRA-treated carotid lesions showed significantly elevated IL-1beta mRNA levels (2.9 +/- 2.33) compared with untreated lesions (2.0 +/- 1.77; p < 0.05). These results support the role of atRA as a regulator of inflammation such as in atherosclerosis.

Leptomycin B Reduces Matrix Metalloproteinase-9 Expression and Suppresses Cutaneous Inflammation

Matrix metalloproteinase-9 (MMP-9), a type of gelatinase, plays many roles in tissue metabolism, especially in inflammation, and many regulatory elements have been reported in the promoter region of its encoding gene. Leptomycin B, which regulates the nucleo-cytoplasmic trafficking of proteins, including transcription-factor-related ones, has the potential to exert important biological effects. The addition of leptomycin B to keratinocytes in culture had no effect on matrix metalloproteinase-2 (another gelatinase) but caused the selective down-regulation of MMP-9 during the stimulation of differentiation with high Ca(2+) or transforming growth factor-beta, as well as during the stimulation of inflammation by tumor necrosis factor-alpha or interleukin-1alpha. This down-regulation depended on multiple regulatory elements in the promoter of MMP-9 including KRE-M9 (which we have recently identified), and a classical 12-o-tetradecanoyl-phorbol-13-acetate-responsive element. The topical application of leptomycin B to murine skin also effectively suppressed inflammation, including MMP-9 expression, after ultraviolet B irradiation. These results suggest that the application of leptomycin B and/or its derivatives could be useful for treating many inflammatory conditions.

Thymosin β4 induces the synthesis of plasminogen activator inhibitor 1 in cultured endothelial cells and increases its extracellular expression

Thymosin β4(Tβ4), a 4.9-kDa polypeptide primarily known as a main G-actin–sequestering peptide, is present in high concentrations in various cells and in the circulation. We have found that Tβ4 upregulates the expression of plasminogen activator inhibitor 1 (PAI-1) in endothelial cells measured both at the level of mRNA and protein synthesis. This effect seems to be cell specific and was not observed when other cells such as human fibroblasts, PC3, and U937 were tested. Tβ4 significantly activated the PAI-1 promoter in EA.hy 926 cells transiently transfected either with plasmid p800LUC containing PAI-1 promoter fragment (–800 to +71) or the PAI-1 promoter linked with green fluorescent protein. Tβ4 mediated up-regulation of PAI-1 involved activation of the mitogen-activated protein kinase cascade. Furthermore, Tβ4 enhanced c-Fos/c-Jun DNA-binding activity to the activator protein 1 (AP-1)–like element (–59 to –52). The specificity of this binding activity was demonstrated by competition electrophoretic mobility shift assay and after transfection of EA.hy 926 cells with the mutated PAI-1 promoter. Taken together, these data indicate that, in response to Tβ4 stimulation, AP-1 activity increases to enhance PAI-1 transcription through its unique AP-1–like element at –59 to –52 in the PAI-1 promoter.

Induction of c-jun and TGF-beta 1 in Fischer 344 rats during amiodarone-induced pulmonary fibrosis

Amiodarone (AM) is an antidysrhythmic agent with a propensity to cause pulmonary toxicity, including potentially fatal fibrosis. In the present study, the potential roles of c-Jun and transforming growth factor (TGF)-beta 1 in AM-induced inflammation and fibrogenesis were examined after intratracheal administration of AM (1.83 micromol/day on days 0 and 2) or an equivalent volume (0.4 ml) of distilled water to male Fischer 344 rats. Northern and immunoblot analyses demonstrated that lung TGF-beta 1 (mRNA and protein) expression was increased 1.5- to 1.8-fold relative to control during the early inflammation period and 1 day, 1 wk, and 2 wk post-AM treatment. Lung c-Jun protein expression was increased concomitantly with evidence of AM-induced fibrosis; at 5 wk post-AM treatment, c-Jun protein was increased 3.3-fold relative to control. The results indicate a role for induction of c-jun and TGF-beta 1 expression in the development of AM-induced pulmonary fibrosis in the Fischer 344 rat and provide potential targets for therapeutic intervention.

A MEK inhibitor, PD98059 enhances IL-1-induced NF-kappaB activation by the enhanced and sustained degradation of IkappaBalpha

Interleukin-1 (IL-1) mediates numerous host responses through rapid activation of nuclear factor-kappaB (NF-kappaB), but signal pathways leading to the NF-kappaB activation appear to be complicated and multiplex. We propose a novel regulatory system for NF-kappaB activation by the extracellular signal-related kinase (ERK) pathway. In a human glioblastoma cell line, T98G, IL-1-induced NF-kappaB activation was significantly augmented by the pretreatment of a specific MEK inhibitor, PD98059. In contrast, ectopic expression of a constitutive activated form of Raf (v-Raf) reduced IL-1-induced NF-kappaB activation, and this inhibition was completely reversed by PD98059. Interestingly, PD98059 sustained IL-1-induced NF-kappaB DNA binding activity by an electrophoretic mobility shift assay and also IkappaBalpha degradation, presumably by augmenting and sustaining the proteasome activation. Concomitantly, two NF-kappaB dependent genes, A20 and IkappaBalpha expression were prolonged with PD98059. These data suggested that MEK-ERK pathway exerts a regulatory effect on NF-kappaB activation, providing a novel insight on the role of MEK-ERK pathway.

Interleukin-1beta costimulates interferon-gamma production by human natural killer cells

Natural killer (NK) cells are an early source of immunoregulatory cytokines during the innate immune response to viruses, bacteria, and parasites. NK cells provide requisite IFN-gamma to monocytes for the elimination of obligate intracellular pathogens. IL-1beta is a pro-inflammatory cytokine produced by monocytes (i.e. a monokine) during the early immune response to infection, but its role in promoting human NK cell IFN-gamma production is unknown. The current study examines the ability of the monokine IL-1beta, plus IL-12, to costimulate IFN-gamma production by resting CD56(bright) and CD56(dim) human NK cell subsets. CD56(bright) NK cells stimulated with IL-1beta plus IL-12 produced abundant IFN-gamma protein, while little IFN-gamma was produced in identical cultures of CD56(dim) cells. In addition, upon activation with IL-1beta, CD56(bright) NK cells exhibited considerably greater phosphorylation of extracellular signal-regulated kinases p42/44 as compared to CD56(dim) NK cells. Quantitative PCR analysis showed brisk induction of IFN-gamma gene expression following costimulation with IL-1beta plus IL-12 in CD56(bright) NK cells, but intracellular flow cytometry revealed that only a fraction (42+/-2.3%) of CD56(bright) NK cells account for this high IFN-gamma production. These data suggest that the monokine IL-1beta is a potent costimulus of IFN-gamma production by a subset of NK cells following infectious insult.

The role of interleukin-1 in the failing heart

The prevalence of congestive heart failure and its continued poor prognosis despite presently available therapeutic options emphasize the importance of pursuing the observations suggesting an important role for an immunomodulatory approach to decompensated cardiac failure. Furthermore, there are several pieces of background information that suggest that cytokines like IL-1 may play a significant role in the pathogenesis of several forms of myocardial dysfunction. Although it seems clear that IL-1 is not acting alone under circumstances of myocardial injury, but in concert with other pro-inflammatory molecules and their effectors, we believe that continued investigations into the cytokine hypothesis will ultimately increase the understanding of how pro-inflammatory molecules influence myocardial function and how the modulation of such factors may improve the myocardial response to injury. The specific observations that emphasize the importance of pursuing a substantive role for IL-1 in this process are: (1) IL-1 is elevated in several cardiac disease states, (2) IL-1 is produced by myocardial cells themselves in response to injury, (3)The alterations in gene expression seen in response IL-1 resembles in many ways the phenotype of the failing heart, and (4) The co-localization of the IL-1 response with that of several previously described negative transcriptional regulators (making them potential targets for therapeutic manipulation).

Regulation of IL-1-induced gingival collagenase gene expression by activator protein-1 (c-Fos/c-Jun)

Matrix metalloproteinase-1 is probably involved in the progression of periodontal disease. The aim of this study was to investigate whether IL-1beta stimulates the expression of the activator protein 1 (AP-1) transcription factor and, consequently, if the AP-1 transcription factor participates in the regulation of collagenase gene expression in human gingival fibroblast cells. In this study, we demonstrate that the concentration of the protein components of AP-1 transcription factor, c-Fos and c-Jun, is enhanced by IL-1beta both at mRNA and protein levels, utilizing Northern blot analysis, electrophoretic mobility gel shift assay and Western blot analysis. The IL-1beta stimulated the collagenase-CAT and AP-1-CAT activities in a dose dependent manner with respect to the amount of DNA used in transfections. Further, overexpression of c-Fos and c-Jun proteins revealed a dose-dependent transcriptional activation of the collagenase promoter. These findings, coupled with the existence of AP-1 consensus DNA binding sites on the collagenase gene promoter, show that regulation of collagenase gene expression by IL-1beta involves the transcription factor AP-1 in gingival fibroblasts.

Amino acids control mammalian gene transcription: activating transcription factor 2 is essential for the amino acid responsiveness of the CHOP promoter

In mammals, plasma concentration of amino acids is affected by nutritional or pathological conditions. It has been well established that nutrients, and particularly amino acids, are involved in the control of gene expression. Here we examined the molecular mechanisms involved in the regulation of CHOP (a CCAAT/enhancer-binding protein [C/EBP]-related gene) expression upon amino acid limitation. We have previously shown that regulation of CHOP mRNA expression by amino acid concentration has both transcriptional and posttranscriptional components. We report the analysis of cis- and trans-acting elements involved in the transcriptional activation of the human CHOP gene by leucine starvation. Using a transient expression assay, we show that a cis-positive element is essential for amino acid regulation of the CHOP promoter. This sequence is the first described that can regulate a basal promoter in response to starvation for several individual amino acids and therefore can be called an amino acid response element (AARE). In addition, we show that the CHOP AARE is related to C/EBP and ATF/CRE binding sites and binds in vitro the activating transcription factor 2 (ATF-2) in starved and unstarved conditions. Using ATF-2-deficient mouse embryonic fibroblasts and an ATF-2-dominant negative mutant, we demonstrate that expression of this transcription factor is essential for the transcriptional activation of CHOP by leucine starvation. Altogether, these results suggest that ATF-2 may be a member of a cascade of molecular events by which the cellular concentration of amino acids can regulate mammalian gene expression.

Proinflammatory cytokines

STUDY OBJECTIVES

To review the concept of proinflammatory cytokines.

DESIGN

Review of published literature.

SETTING

Academic (university hospital).

RESULTS

Cytokines are regulators of host responses to infection, immune responses, inflammation, and trauma. Some cytokines act to make disease worse (proinflammatory), whereas others serve to reduce inflammation and promote healing (anti-inflammatory). Attention also has focused on blocking cytokines, which are harmful to the host, particularly during overwhelming infection. Interleukin (IL)-1 and tumor necrosis factor (TNF) are proinflammatory cytokines, and when they are administered to humans, they produce fever, inflammation, tissue destruction, and, in some cases, shock and death. Reducing the biological activities of IL-1 and TNF is accomplished by several different, but highly specific, strategies, which involve neutralizing antibodies, soluble receptors, receptor antagonist, and inhibitors of proteases that convert inactive precursors to active, mature molecules. Blocking IL-1 or TNF has been highly successful in patients with rheumatoid arthritis, inflammatory bowel disease, or graft-vs-host disease but distinctly has not been successful in humans with sepsis. Agents such as TNF-neutralizing antibodies, soluble TNF receptors, and IL-1 receptor antagonist have been infused into > 10,000 patients in double-blind, placebo-controlled trials. Although there has been a highly consistent small increase (2 to 3%) in 28-day survival rates with anticytokine therapy, the effect has not been statistically significant.

CONCLUSIONS

Anticytokine therapy should be able to "rescue" the patient whose condition continues to deteriorate in the face of considerable support efforts. Unfortunately, it remains difficult to identify those patients who would benefit from anticytokine therapy for septic shock.

Influence of polyamines on DNA binding of heat shock and activator protein 1 transcription factors induced by heat shock

Polyamine depletion, obtained in FAO cells with specific inhibitors of biosynthetic enzymes, prevents or decreases the accumulation of hsp 70 mRNA following heat shock [Desiderio et al., Hepatology 24 (1996) 150-156]. The present study shows that under conditions of spermidine depletion caused by alpha-difluoromethylornithine, the DNA binding capacity of the transcription factor HSF induced by heat shock undergoes a severe and prompt deactivation. Replenishment of the spermidine pool before heat shock re-establishes the DNA binding activity of HSF and the inducibility of hsp 70 mRNA. Similar to HSF, but with a different time-course, the DNA binding of the transcription factor AP-1 activated by heat shock is also impaired in spermidine-depleted cells and reversed by exogenous spermidine. STAT3 provides an example of a transcription factor slightly activated by heat shock but insensitive to polyamine decrease.

Characterization of CD44 Induction by IL-1: A Critical Role for Egr-1

The adhesion molecule CD44 is a multifunctional, ubiquitously expressed glycoprotein that participates in the process of leukocyte recruitment to sites of inflammation and to their migration through lymphatic tissues. In this study, we have investigated the effect of the proinflammatory cytokine IL-1α on CD44 gene expression in the human immortalized endothelial cell line ECV304. Immunoblotting of cell extracts showed constitutive expression of a 85-kDa protein corresponding to the standard form of CD44, which was potently up-regulated following IL-1α treatment. Furthermore, IL-1α induced expression of v3- and v6-containing isoforms of CD44, which migrated at 110 and 140–180 kDa, respectively. The effect of IL-1α on CD44 standard, v3- and v6-containing isoforms was dose and time dependent and was inhibited in the presence of IL-1 receptor antagonist. To elucidate the molecular mechanisms regulating CD44 expression in response to IL-1α, we investigated the effect of IL-1α on CD44 mRNA expression. Reverse-transcriptase PCR and Northern analysis demonstrated an increase in CD44 mRNA expression indicating a transcriptional mechanism of control by IL-1α. Furthermore, IL-1α increased expression of a reporter gene under the control of the CD44 promoter (up to −1.75 kb). The effect of IL-1α was critically dependent on the site spanning −151 to −701 of the promoter. This effect required the presence of an Egr-1 motif at position −301 within the CD44 promoter since mutation of this site abolished responsiveness. IL-1α also induced Egr-1 expression in these cells. These studies therefore identify Egr-1 as a critical transcription factor involved in CD44 induction by IL-1α.

Smad3-Smad4 and AP-1 complexes synergize in transcriptional activation of the c-Jun promoter by transforming growth factor beta

Transcriptional regulation by transforming growth factor beta (TGF-beta) is a complex process which is likely to involve cross talk between different DNA responsive elements and transcription factors to achieve maximal promoter activation and specificity. Here, we describe a concurrent requirement for two discrete responsive elements in the regulation of the c-Jun promoter, one a binding site for a Smad3-Smad4 complex and the other an AP-1 binding site. The two elements are located 120 bp apart in the proximal c-Jun promoter, and each was able to independently bind its corresponding transcription factor complex. The effects of independently mutating each of these elements were nonadditive; disruption of either sequence resulted in complete or severe reductions in TGF-beta responsiveness. This simultaneous requirement for two distinct and independent DNA binding elements suggests that Smad and AP-1 complexes function synergistically to mediate TGF-beta-induced transcriptional activation of the c-Jun promoter.

On the role of c-Jun in the induction of PAI-1 gene expression by phorbol ester, serum, and IL-1alpha in HepG2 cells

We have characterized the regulation of plasminogen activator inhibitor-1 (PAI-1) gene expression by phorbol 12-myristate 13-acetate (PMA), serum, and interleukin-1alpha (IL-1alpha) in the human hepatoma cell line HepG2. PMA, serum, and IL-1alpha induced a rapid and transient 28-fold (PMA), 9-fold (serum), and 23-fold (IL-1alpha) increase in PAI-1 mRNA, peaking after approximately 4 hours. These inductions of PAI-1 mRNA accumulation were reduced by pretreatment of the HepG2 cells with the protein tyrosine kinase inhibitor genistein. Conversely, stimulation of tyrosine phosphorylation by sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, caused an increase in PAI-1 mRNA levels. The effects of PMA, serum, and IL-1alpha on PAI-1 mRNA expression have been compared with their ability to modulate the expression of a chloramphenicol acetyltransferase (CAT) reporter plasmid, which was under control of the -489 to +75 region of the PAI-1 promoter, and stably transfected into HepG2 cells. This region of the PAI-1 promoter was previously found to contain a tetradecanoyl phorbol acetate-response element (TRE; between -58 and -50) necessary for PMA responsiveness and with a high affinity for c-Jun homodimers. Whereas incubation of these transfected HepG2 cells with PMA and serum showed an induction profile of CAT mRNA similar to that of PAI-1 mRNA, hardly any induction of CAT mRNA was found with IL-1alpha. In line with these findings, IL-1alpha poorly induced c-Jun homodimer binding to the PAI-1 TRE in gel mobility-shift assays. Pretreatment of HepG2 cells with the protein kinase C inhibitor Ro 31-8220 or the mitogen-activated protein kinase kinase (MAPKK)1,2 activity blocker PD98059 selectively suppressed the induction of PAI-1 (and CAT) expression by PMA, but not that by IL-1alpha. In contrast, the protein tyrosine kinase inhibitor herbimycin A blocked PAI-1 mRNA induction by IL-1 alpha only. We propose 2 separate PAI-1 inductory pathways for PMA and IL-1alpha in HepG2, both involving protein tyrosine kinase activation; the serum-induced signaling pathway may (partially) overlap with the PMA-activated protein kinase C/mitogen-activated protein kinase kinase pathway, leading to c-Jun homodimer binding to the PAI-1 TRE.

Interleukin 7 receptor control of T cell receptor gamma gene rearrangement: role of receptor-associated chains and locus accessibility

VDJ recombination of T cell receptor and immunoglobulin loci occurs in immature lymphoid cells. Although the molecular mechanisms of DNA cleavage and ligation have become more clear, it is not understood what controls which target loci undergo rearrangement. In interleukin 7 receptor (IL-7R)alpha-/- murine thymocytes, it has been shown that rearrangement of the T cell receptor (TCR)-gamma locus is virtually abrogated, whereas other rearranging loci are less severely affected. By examining different strains of mice with targeted mutations, we now observe that the signaling pathway leading from IL-7Ralpha to rearrangement of the TCR-gamma locus requires the gammac receptor chain and the gammac-associated Janus kinase Jak3. Production of sterile transcripts from the TCR-gamma locus, a process that generally precedes rearrangement of a locus, was greatly repressed in IL-7Ralpha-/- thymocytes. The repressed transcription was not due to a lack in transcription factors since the three transcription factors known to regulate this locus were readily detected in IL-7Ralpha-/- thymocytes. Instead, the TCR-gamma locus was shown to be methylated in IL-7Ralpha-/- thymocytes. Treatment of IL-7Ralpha-/- precursor T cells with the specific histone deacetylase inhibitor trichostatin A released the block of TCR-gamma gene rearrangement. This data supports the model that IL-7R promotes TCR-gamma gene rearrangement by regulating accessibility of the locus via demethylation and histone acetylation of the locus.

Role of Nuclear Factor-κB and Mitogen-Activated Protein Kinase Signaling Pathways in IL-1β-Mediated Induction of α-PDGF Receptor Expression in Rat Pulmonary Myofibroblasts

Induction of the α-platelet-derived growth factor receptor (PDGF-Rα) by IL-1β in lung myofibroblasts enhances mitogenic and chemotactic responses to PDGF, and this could be a mechanism of myofibroblast hyperplasia during lung fibrogenesis. Since the regulation of many genes by IL-1β involves activation of NF-κB and mitogen-activated protein (MAP) kinases, we examined these signaling pathways in the control of PDGF-Rα expression by IL-1β in cultured rat lung myofibroblasts. Treatment of cells with pyrrolidine dithiocarbamate (PDTC), an antioxidant that inhibits NF-κB activation, completely blocked PDGF-Rα up-regulation by IL-1β as assayed by [125I]PDGF-AA binding and PDGF-Rα mRNA expression, suggesting a role for NF-κB. However, while IL-1β and TNF-α both induced nuclear binding of the Rel proteins p50 and p65 to an NF-κB consensus oligonucleotide in gel shift assays and caused transient degradation of inhibitor of NF-κB-α (IκB-α) in the cytoplasm of myofibroblasts, only IL-1β up-regulated PDGF-Rα. These results suggest that NF-κB activation alone is not sufficient for up-regulation of PDGF-Rα. An investigation of MAP kinase signaling pathways revealed that IL-1β or PDTC activated extracellular signal-regulated kinase-2 (ERK-2) and c-jun NH2 terminal kinase-1 (JNK-1) phosphorylation of PHAS-1 and c-Jun substrates, respectively. Pretreatment of cells with the MAP kinase kinase-1 (MEK1) inhibitor PD 98059 blocked IL-1β-induced activation of ERK-2 by more than 90% but enhanced IL-1β-stimulated induction of PDGF-Rα expression fourfold. Taken together, these data suggest that IL-1β activates both positive and negative signaling pathways that control the expression of PDGF-Rα. IL-1β appears to mediate its negative effects on PDGF-Rα expression via MAP kinase activation, while the factor(s) that mediate induction of PDGF-Rα remain to be elucidated.

The interleukin 1 receptor: ligand interactions and signal transduction

The interleukin 1 (IL-1) receptor is a critical component in mediating the inflammatory responses of IL-1, which affect nearly every cell type. Recently, major inroads have been made toward understanding the mechanism by which IL-1 interacts with its receptor and activates signal transduction. The receptor-ligand association has been visualized by X-ray crystal structure analysis, revealing intimate details that distinguish IL-1beta from the naturally-occuring receptor antagonist. Signaling studies have focused primarily on the ability of IL-1 to transduce the activation of the transcription factor, NF-kappaB, which is of central importance to inflammatory and immune responses. Virtually all of the effort has targeted the activation of a kinase which results in the phosphorylation of the inhibitory IkappaB molecule at two serines that precedes the proteolytic degradation of this inhibitor and the release of active NF-kappaB. The recent characterization of an IL-1 receptor associated kinase (IRAK) and a continuous molecular path between this kinase and that which directly phosphorylates IkappaB would seem to all but close the basic understanding of IL-1 receptor signal transduction. However, at least half of the IL-1-dependent NF-kappaB activation is independent of IRAK and uses a novel pathway involving the recruitment of phosphatidylinositol 3-kinase (PI3K) to a distinct site within the cytoplasmic domain of the IL-1 receptor. This novel pathway for NF-kappaB activation and the fact that other important transcription factors are also activated by an IL-1 receptor-dependent signal event, clearly defines additional mechanisms that influence inflammation.

Regulation of spermidine/spermine N1-acetyltransferase expression by cytokines and polyamines in human hepatocarcinoma cells (HepG2)

Spermidine/spermine N1-acetyltransferase (cSAT), a key enzyme in polyamine degradation, is induced by various hepatotoxins and liver tumor promoters. In this paper we demonstrate that physiological factors, such as cytokines, control cSAT expression in HepG2 human hepatocarcinoma cells. Hepatocyte growth factor (HGF) induced the cSAT mRNA precursor (3.5 kb) at 4 h. The mature form of mRNA (1.3 kb) increased 6-8-fold between 8 and 10 h, and remained elevated until 18 h. An increase in cSAT activity (2-fold) and high levels of N1-acetylspermidine were observed concomitantly. Interleukin-1 beta (IL-1 beta) enhanced cSAT expression (both mRNA and enzyme activity) similar to HGF, while tumor necrosis factor-alpha (TNF-alpha) was less effective. This system also provides a useful means for examining the involvement of negative and positive changes of polyamines in the induction of cSAT and c-jun, a gene that participates in the control of cSAT expression. alpha-Difluoromethylornithine (DFMO) pretreatment, by lowering putrescine and spermidine in HGF- or IL-1 beta-treated cells, prevented the induction of cSAT. This effect was reversed by exogenous putrescine or spermidine. IL-1 beta induced c-jun mRNA more than HGF. DFMO prevented almost completely the enhancement of c-jun mRNA expression by IL-1 beta, and this effect was reversed by exogenous putrescine or spermidine. Therefore, we suggest that cSAT and c-jun expression is specifically regulated by polyamine-mediated mechanisms in IL-1 beta treated HepG2 cells. Since cSAT is inducibile by cytokines that control tumor metabolism and growth as well as tumor-host interaction, we hypothesize an involvement of cSAT in hepatoma growth.

Nuclear and non-nuclear targets of genotoxic agents in the induction of gene expression. Shared principles in yeast, rodents, man and plants

The interplay between environmental cues and the genetic response is decisive for the development, health and well-being of an organism. For some environmental factors a narrow margin separates beneficial and toxic impacts. With the increasing exposure to UV-B this dichotomy has reached public attention. This review will be concerned with the mechanisms that mediate a cellular genetic response to noxious agents. The toxic stimuli find access to the regulatory network inside cells by interacting at several points with cellular molecules - a process that converts the 'outside information' into 'cellular language'. As a consequence of such interactions, many adverse agents cause massive signal transduction and changes of gene expression. There is an interesting conservation of the mechanisms from yeast to man. An understanding of the genetic programs and of their phenotypic consequences is lagging behind.

Oxidant-induced activation of nuclear factor-kappa B in cultured guinea pig gastric epithelial cells

The aim of this study was to reveal oxidant-sensitive components in gastric epithelial cells, which may regulate inflammatory processes in gastric mucosa. Gel mobility shift assay showed that treatment of cultured guinea pig gastric epithelial cells with hydrogen peroxide or diamide produced a KB oligonucleotide-protein complex within 5 min. The binding proteins consisted of a p50/p65 heterodimer, which was identified by immunosupershift, UV cross-linking, and immunoprecipitation analyses. Immunocytochemical study demonstrated that surface epithelial cells and parietal cells expressed p500 and p65 mainly in the cytosol, and the oxidants rapidly initiated the nuclear translocation of the components. The oxidants caused the up-regulation of p105 (a p50 precursor) synthesis and the expression of inducible nitric oxide synthase mRNA. These results suggest that the oxidant-sensitive p50/p65 heterodimer in gastric epithelial cells may play an important role in transcriptional activation of genes involved in inflammatory responses of the stomach.

Reactive oxygen species mediate cytokine activation of c-Jun NH2-terminal kinases

Interleukin 1 (IL-1) and tumor necrosis factor alpha (TNFalpha) are known to induce production of reactive oxygen species (ROS), which have been suggested to act as second messengers. Here we demonstrate that ROS production by bovine chondrocytes upon cytokine stimulation induces c-jun expression. Since c-jun expression is regulated by its own gene product via phosphorylation by c-Jun NH2-terminal kinases (JNKs), we investigated if cytokines and ROS could modulate JNK activity in chondrocyte monolayer cultures. Treatment of bovine chondrocytes with both IL-1 and TNFalpha leads to rapid induction of JNK activity, stimulating JNK activity 7- and 20-fold, respectively. Importantly, the observation that antioxidant treatment antagonizes IL-1 and TNFalpha activation of JNK provides strong evidence that ROS can act as mediators of JNK activity. Moreover, potent activation of JNK is also observed by direct addition of the ROS hydrogen peroxide (H2O2) to the chondrocyte cultures. Nitric oxide (NO), a multifunctional ROS, also appears to simulate JNK, albeit to a lesser extent. These findings identify JNK as another molecular target for the actions of NO and H2O2. In addition, the inhibitory effect of diphenyleneiodonium on JNK activation implicates the involvement of flavonoid-containing enzymes in the ROS-mediated signaling process. Overstimulation of JNK activity by excessive production of ROS may, therefore, underlie pathological conditions such as arthritis and cancer.

Inhibition of interleukin-1 responsiveness by type II receptor gene transfer: a surface "receptor" with anti-interleukin-1 function

The hypothesis that the type II receptor (RII) acts as a decoy for interleukin-1 (IL-1) was tested by gene transfer in cells expressing only the type I receptor (8387 fibroblasts). RII-transfected cells showed defective responsiveness to IL-1 in terms of NFkappaB activation, cytokine gene expression and production. Blocking monoclonal antibodies against RII restored the capacity of RII-transfected cells to respond to IL-1 beta. Hence defective IL-1 responsiveness of RII-transfected cells requires surface expression of the molecule. RII-transfected cells showed normal responsiveness to TNF, which shares functional properties and elements in the signal transduction pathway with IL-1. Cells transfected with a deletion mutant of RII missing 26 of 29 amino acids of the cytoplasmic portion of the molecule showed impaired responsiveness to IL-2. Cells transfected with full-length or the cytoplasmic deletion mutant of RII released copious amounts of RII in the supernatant. However, transfected cells showed defective responsiveness to brief exposure to IL-1, in the absence of measurable released RII. These results indicate that impairment of the responsiveness to IL-1 following RII gene transfer was dependent upon surface expression of the molecule, specific for IL-1 and unaffected by truncation of the cytoplasmic portion. Thus, the type II "receptor" is a decoy surface molecule, regulated by antiinflammatory signals, whose only known function is to capture and block IL-1.

Mechanisms of interleukin-1beta regulation of nitric oxide synthase in cardiac myocytes

Cytokines and endotoxin stimulate inducible NO synthase (iNOS) in different types of cells; however, little is known about regulatory mechanisms. Using the Griess reagent for nitric levels, Western blots for iNOS protein, Northern blots for iNOS mRNA, and transient transfection studies to monitor transcription, we determined potential mechanisms involved in interleukin-1beta stimulation of iNOS in cultured neonatal ventricular myocytes. When myocytes were treated with interleukin-1beta (5 ng/mL), nitrite levels increased, and this effect was inhibited 80% by the specific iNOS inhibitor aminoguanidine. Neither interferon gamma nor tumor necrosis factor-alpha alone stimulated nitrite production. Bacterial endotoxin alone stimulated nitrites and potentiated the effect of interleukin. To determine whether a tyrosine kinase-mediated signaling pathway was involved in interleukin action, we used the inhibitor genistein, which blocked interleukin-stimulated nitrites, iNOS protein, and iNOS mRNA. To determine the effect of activation of protein kinase C, we treated cells with the phorbol ester phorbol 12-myristate 13-acetate (PMA). PMA decreased both interleukin-stimulated nitrites and iNOS protein by 40%. To determine the involvement of cyclic nucleotides, cells were treated with either dibutyryl cAMP or cGMP. cAMP (1 mmol/L) stimulated iNOS mRNA, protein, and nitrite production, whereas cGMP had no effect. To test for a direct effect of interleukin on transcription of the iNOS gene, we transfected the full-length mouse iNOS 5' regulatory sequences (-1592 to +160) coupled to a luciferase reporter gene (-1592iNOSLuc). Interleukin stimulated luciferase activity 1.8 +/- 0.2-fold. To determine whether interleukin also affects iNOS mRNA stability, interleukin-stimulated iNOS mRNA was allowed to decay in the presence of the transcription inhibitor actinomycin D. iNOS mRNA t1/2 (approximately 1 hour) was not affected by interleukin. Thus, our data suggest that (1) interleukin-1beta is the primary cytokine in myocyte iNOS regulation and acts predominantly at the transcriptional level; (2) interleukin stimulation of iNOS mRNA and protein is coupled to a tyrosine kinase-mediated signaling pathway; and (3) protein kinase C and cAMP can modify interleukin signaling by decreasing and increasing iNOS, respectively.

Calcium signals and protein tyrosine kinases are required for the induction of c-jun in Jurkat cells stimulated by the T cell-receptor complex and oxidative signals

The regulation of c-jun plays an important role in T cell activation, proliferation, and expression of interleukin-2. In the present study, we determined whether Ca2+ signals and the activity of protein tyrosine kinases (PTKs) were required for the induction of c-jun in Jurkat cells stimulated with cross-linked anti-T cell receptor/CD3 antibodies or exposed to oxidative stress in the form of micromolar concentrations of H2O2. Jurkat cells exhibited rapid elevations in intracellular calcium [Ca2+]i levels in response to H2O2 and cross-linked anti-CD3 antibodies that mainly reflected the influx of extracellular Ca2+. The Ca2+ flux in response to oxidative signals was distinguished by an exquisite sensitivity to inhibition with Ni2+, suggesting the involvement of cation channels. PTK activity was needed for [Ca2+]i elevations in response to both oxidative and anti-CD3 signals, although H2O2 induction of [Ca2+]i increases was more resistant to inhibition by genistein than anti-CD3 [Ca2+]i responses. Both oxidative signals and anti-CD3 stimulation induced increased levels of c-jun and c-fos mRNA. The increased expression of c-jun with H2O2 was preceded by [Ca2+]i increases and accompanied by activation of c-Jun aminoterminal kinases (JNKs), as well as increased AP-1 binding activity. Induction of c-jun with oxidative signals and anti-CD3 was also shown to be crucially dependent on [Ca2+]i elevations because the chelation of [Ca2+]i with BAPTA resulted in a dose-dependent inhibition of c-jun expression. Furthermore, inhibition studies demonstrated that the optimal induction of c-jun mRNA in response to oxidative signals required PTK as well as protein kinase C (PKC). Thus, these findings suggest that both [Ca2+]i signals and the activity of PTKs are essential for the optimal expression of c-jun in response to TCR/CD3 signals and changes in redox potentials.

Osmotic regulation of cytokine synthesis in vitro

These studies were undertaken to investigate the therapeutic mechanism of saturated solutions of KI, used to treat infectious and inflammatory diseases. The addition of 12-50 mM KI to cultured human peripheral blood mononuclear cells resulted in 319-395 mosM final solute concentration and induced interleukin (IL)-8 synthesis. Maximal IL-8 production was seen when 40 mM salt was added (375 mosM) and was equal to IL-8 induced by endotoxin or IL-1 alpha. However, there was no induction of IL-1 alpha, IL-1 beta, or tumor necrosis factor to account for the synthesis of IL-8; the effect of KI was not due to contaminating endotoxins. Hyperosmolar NaCl also induced IL-8 and increased steady-state levels of IL-8 mRNA similar to those induced by IL-1 alpha. IL-8 gene expression was elevated for 96 hr in peripheral blood mononuclear cells incubated with hyperosmolar NaCl. In human THP-1 macrophagic cells, osmotic stimulation with KI, NaI, or NaCl also induced IL-8 production. IL-1 signal transduction includes the phosphorylation of the p38 mitogen-activated protein kinase that is observed following osmotic stress. Using specific blockade of this kinase, a dose-response inhibition of hyperosmolar NaCl-induced IL-8 synthesis was observed, similar to that in cells stimulated with IL-1. Thus, these studies suggest that IL-1 and osmotic shock utilize the same mitogen-activated protein kinase for signal transduction and IL-8 synthesis.

Schizosaccharomyces pombe atf1+ encodes a transcription factor required for sexual development and entry into stationary phase

We describe the identification and characterization of a transcription factor encoded by the atf1+ gene of the fission yeast Schizosaccharomyces pombe. The factor Atf1, contains a bZIP domain at its C-terminus with strong homology to members of the ATF/CREB family of mammalian factors and in vitro binds specifically to ATF/CRE recognition sites. Furthermore the ATF-like binding activity detected in extracts from fission yeast cells is entirely lost upon deletion of the atf1+ gene. Upon growth to saturation, fission yeast cells exit the mitotic cycle and enter a G0-like stationary phase. However, on rich medium, entry of atf1- cells into stationary phase is restricted and they rapidly lose viability; this does not occur on minimal medium unless cAMP levels are raised. Thus stationary phase entry appears to be regulated negatively by cAMP and positively by Atf1. atf1- cells are also sterile and this sterility appears to be due to a combination of two defects: first, upon nitrogen starvation the majority of atf1- cells fail to arrest in the G1 phase of the cell cycle and second, the induction of ste11+ expression is lost. Thus expression of ste11+ represents a second example of an event that is negatively regulated by the cAMP pathway and positively regulated by Atf1. Despite their close association however, these two regulatory pathways function independently and Atf1 activity is not directly modulated by cAMP levels or mutations that alter the activity of components of the cAMP signalling pathway. Thus Atf1 is a transcription factor that plays an important role in the response of cells to adverse environmental conditions, which is to exit the mitotic cell cycle and either sexually differentiate or enter a resting state.

Interleukin-1 signal transduction

Interleukin 1 (IL1) is a potent pro-inflammatory cytokine which has been implicated in the pathogenesis of chronic inflammatory disease. Despite much effect, the signal transduction pathway activated by IL1 has remained obscure. Recently, much attention has focussed on IL1 receptors and early events triggered by IL1 in cells, including activation of transcription factors and serine/threonine protein kinases. Two main types of IL1 receptors have been described, IL1RI and IL1RII. They appear to belong to a family of proteins which include most notably a Drosophila protein, Toll. Following receptor binding IL1 has been shown to increase protein phosphorylation in cells, and much effort has been made to identify the protein kinases responsible. Novel enzymes have been discovered, including a family of MAP kinase--like enzymes which are also activated by a range of stresses such as hypertonic stress and heat shock. Attention has also been focussed in the activation of the transcription factor NF kappa B, which is rapidly activated by IL1. This review will describe our current understanding of how IL1 activated cells and will particularly describe more recent work on IL1 receptors and early post-receptors events.

Expressions of c-jun and p53 proteins in human middle ear cholesteatoma: relationship to keratinocyte proliferation, differentiation, and programmed cell death

The c-jun protein functions as a transcription factor for many genes, and the p53 protein functions as a negative regulator of cellular proliferation, which is related to the apoptosis pathway that induces DNA damage. It has recently been shown that c-jun promotes keratinocyte proliferation and p53 induces apoptosis of various cells. In this study, the presence of c-jun and p53 in cholesteatoma was demonstrated by immunoblotting assays using polyclonal rabbit anti-c-jun antibody and monoclonal anti-p53 protein antibody, respectively. The cholesteatoma tissue incubated with anti-c-jun antibody showed the staining of keratinocytes on the basal and spinous layers of epithelium. The c-jun protein was localized in the basal layer of normal skin, and the p53 protein was present in the nucleus of keratinocytes in the granular layer of cholesteatoma epithelium. The keratinocytes of normal external ear canal skins and normal human skins were slightly stained in the granular layer of the epidermis. The present findings suggest that c-jun and p53 proteins have a role in keratinocyte differentiation, proliferation, and apoptosis in the cholesteatoma.

Lactoferrin down-modulates the activity of the granulocyte macrophage colony-stimulating factor promoter in interleukin-1 beta-stimulated cells

The human neutrophil lactoferrin (Lf), a cationic iron-binding glycoprotein, has an inhibitor role on granulocyte macrophage colony-stimulating factor (GM-CSF) production via interleukin-1 (IL-1). The nuclear localization of Lf suggests that it may be involved in the transcriptional regulation of GM-CSF gene expression. To explore this possibility, the effect of Lf on GM-CSF gene expression was investigated in various cell lines and in primary cultures of fibroblasts. Down-regulation of GM-CSF mRNA level was observed in Lf-transfected embryonic fibroblasts induced to produce GM-CSF by IL-1 beta. In 5637 cell-line and in embryonic fibroblasts, co-transfection experiments, in which an Lf expression vector was used together with a vector carrying a reporter gene linked to the GM-CSF promoter, revealed that Lf reduces the activity of the GM-CSF promoter. This effect is marked in IL-1 beta-stimulated cells. These findings suggest that Lf plays a negative role in GM-CSF expression at the transcriptional level, perhaps through the mediation of IL-1 beta.

ATF-2 contains a phosphorylation-dependent transcriptional activation domain

The ATF-2 transcription factor can mediate adenovirus E1A-inducible transcriptional activation. Deletion analysis has indicated that the N-terminal region of ATF-2 is essential for this response. Furthermore, the N-terminus can activate transcription in the absence of E1A when fused to a heterologous DNA binding domain. However, in the intact protein this activation domain is masked. In this report we show that residues in the N-terminus required for activation are also required for mediating E1A stimulation. In particular two threonine residues at positions 69 and 71 are essential. These residues are phosphorylated in vivo and can be efficiently phosphorylated in vitro by the JNK/SAPK subgroup of the MAPK family. ATF-2 can bind to a UV-inducible kinase through a region in the N-terminus that is distinct from the sites of phosphorylation; this binding region is both necessary for phosphorylation by JNK/SAPK in vitro and for transcriptional activation in vivo. The activity of the N-terminus is stimulated by UV irradiation which stimulates the signalling pathway leading to JNK/SAPK. Finally, although ATF-2 binds to the E1A protein, the N-terminal activation domain is not required for this interaction. The results show that ATF-2, like other members of the ATF/CREB family of DNA binding proteins is regulated by specific signalling pathways.

ATF-2 is preferentially activated by stress-activated protein kinases to mediate c-jun induction in response to genotoxic agents

The major regulators of the c-jun promoter are ATF-2 and c-Jun. They act as pre-bound heterodimers on two 'AP-1-like' sites, and are preferentially addressed by different types of extracellular signals. The transactivating potential of ATF-2 is stimulated to a higher extent than that of c-Jun by a broad group of agents causing DNA damage and other types of cellular stress, such as short-wavelength UV, or the alkylating compounds N-methyl-N'-nitro-N-nitroso-guanidine (MNNG) or methylmethanesulphonate (MMS). In contrast, treatment with the phorbol ester TPA preferentially enhances c-Jun-dependent transactivation but does not affect ATF-2. Accordingly, UV and MMS but not TPA induce c-jun transcription in F9 cells, which express ATF-2, but not c-Jun. Stimulation of ATF-2-dependent transactivation by genotoxic agents requires the presence of threonines 69 and 71 located in the N-terminal transactivation domain. These sites are the target of p54 and p46 stress-activated protein kinases (SAPKs) which bind to, and phosphorylate ATF-2 in vitro. However, p46 and p54 kinase activity is not increased by phorbol ester, which strongly suggests that the protein kinase phosphorylating c-Jun in response to TPA is distinct from SAPKs and does not act on ATF-2. Our data demonstrate that distinct signal transduction pathways converge at c-Jun/ATF-2, whereby each subunit is individually addressed by a specific class of protein kinases. This allows fine tuned modulation of c-jun expression by a large spectrum of extracellular signals.

Signal transduction by tumor necrosis factor mediated by JNK protein kinases

JNK protein kinases are distantly related to mitogen-activated protein kinases (ERKs) and are activated by dual phosphorylation on Tyr and Thr. The JNK protein kinase group includes the 46-kDa isoform JNK1. Here we describe the molecular cloning of a second member of the JNK group, the 55-kDa protein kinase JNK2. The activities of both JNK isoforms are markedly increased by exposure of cells to UV radiation. Furthermore, JNK protein kinase activation is observed in cells treated with tumor necrosis factor. Although both JNK isoforms phosphorylate the NH2-terminal activation domain of the transcription factor c-Jun, the activity of JNK2 was approximately 10-fold greater than that of JNK1. This difference in c-Jun phosphorylation correlates with increased binding of c-Jun to JNK2 compared with JNK1. The distinct in vitro biochemical properties of these JNK isoforms suggest that they may have different functions in vivo. Evidence in favor of this hypothesis was obtained from the observation that JNK1, but not JNK2, complements a defect in the expression of the mitogen-activated protein kinase HOG1 in the yeast Saccharomyces cerevisiae. Together, these data indicate a role for the JNK group of protein kinases in the signal transduction pathway initiated by proinflammatory cytokines and UV radiation.

Signal transduction by tumor necrosis factor mediated by JNK protein kinases

JNK protein kinases are distantly related to mitogen-activated protein kinases (ERKs) and are activated by dual phosphorylation on Tyr and Thr. The JNK protein kinase group includes the 46-kDa isoform JNK1. Here we describe the molecular cloning of a second member of the JNK group, the 55-kDa protein kinase JNK2. The activities of both JNK isoforms are markedly increased by exposure of cells to UV radiation. Furthermore, JNK protein kinase activation is observed in cells treated with tumor necrosis factor. Although both JNK isoforms phosphorylate the NH2-terminal activation domain of the transcription factor c-Jun, the activity of JNK2 was approximately 10-fold greater than that of JNK1. This difference in c-Jun phosphorylation correlates with increased binding of c-Jun to JNK2 compared with JNK1. The distinct in vitro biochemical properties of these JNK isoforms suggest that they may have different functions in vivo. Evidence in favor of this hypothesis was obtained from the observation that JNK1, but not JNK2, complements a defect in the expression of the mitogen-activated protein kinase HOG1 in the yeast Saccharomyces cerevisiae. Together, these data indicate a role for the JNK group of protein kinases in the signal transduction pathway initiated by proinflammatory cytokines and UV radiation.

Interleukin-1 alpha is released during transfection of keratinocytes

Keratinocytes are known to produce, store, and release IL-1 alpha and therefore we suspected that the DNA-mediated cell transfection procedure may release the stored IL-1 alpha from keratinocytes into the medium. Using enzyme-linked immunosorbent assay, we determined the IL-1 alpha concentration in culture supernatants during keratinocyte transfection. The following transfection methods were compared: lipofection with lipofectACE and lipofectAMINE (GIBCO), Ca3(PO4)2 co-precipitation, and polybrene-dimethylsulfoxide (DMSO). The supernatants were collected immediately prior to transfection, after 5-h incubation with lipofectin or Ca3(PO4)2, and 24 and 48 h after transfection. In the polybrene-DMSO method, the supernatant was also collected immediately before and after DMSO shock. LipofectAMINE caused the highest release of IL-1 alpha, whereas the lipofectACE and polybrene-DMSO mediated transfection with confluent cells released the least. The other two methods released intermediate levels of IL-1 alpha. Our data indicate that a substantial amount of IL-1 alpha is released during the keratinocyte transfection procedure, which can affect the results of transfection in studies of gene expression.