Interleukin 1 induces beta-endorphin secretion via Fos and Jun in AtT-20 pituitary cells

Protein-tyrosine phosphatase-alpha and Src functionally link focal adhesions to the endoplasmic reticulum to mediate interleukin-1-induced Ca2+ signaling

Calcium (Ca2+) signaling by the pro-inflammatory cytokine interleukin-1 (IL-1) is dependent on focal adhesions, which contain diverse structural and signaling proteins including protein phosphatases. We examined here the role of protein-tyrosine phosphatase (PTP) alpha in regulating IL-1-induced Ca2+ signaling in fibroblasts. IL-1 promoted recruitment of PTPalpha to focal adhesions and endoplasmic reticulum (ER) fractions, as well as tyrosine phosphorylation of the ER Ca2+ release channel IP3R. In response to IL-1, catalytically active PTPalpha was required for Ca2+ release from the ER, Src-dependent phosphorylation of IP3R1 and accumulation of IP3R1 in focal adhesions. In pulldown assays and immunoprecipitations PTPalpha was required for the association of PTPalpha with IP3R1 and c-Src, and this association was increased by IL-1. Collectively, these data indicate that PTPalpha acts as an adaptor to mediate functional links between focal adhesions and the ER that enable IL-1-induced Ca2+ signaling.

Moderate hypercapnia-induced anesthetic effects and endogenous opioids

The purpose of this report is to explore the mechanisms of hypercapnia-induced antinociception. We carried out three experiments, the first to confirm whether moderate hypercapnia induces anesthetic effects, the second to determine whether naloxone reverses the anesthetic effects, and the third to evaluate whether beta-endorphin is related to the anesthetic effects. In a pre-test, we determined the optimal CO(2) concentration in a chamber which would cause moderate hypercapnia in rats. Eighteen rats were divided into control, hypercapnia, and hypercapnia plus naloxone groups in experiment 1. The naloxone group rats were injected with naloxone (10 mg/kg) intraperitoneally before gas inhalation. After 60 min gas inhalation, 10% formalin was injected into the left rear paw of all rats, and nociceptive behaviors were observed for 1 h. In experiment 2, 11 rats were divided into control and hypercapnia groups. The brain was removed and fixed under pentobarbital anesthesia. Sections were immunostained for c-Fos and beta-endorphin (ACTH) with the ABC method. All neurons double-labeled for c-Fos and beta-endorphin (ACTH) in the arcuate nucleus were counted by blinded investigators. Moderate hypercapnia (PaCO(2) 83+/-7 mmHg) reduced nociceptive behavior in the formalin test and naloxone pre-treatment attenuated this phenomenon. However, beta-endorphin-producing neurons were not activated by CO(2) inhalation. Endogenous opioids are related to moderate, hypercapnia-induced anesthetic effects, but, beta-endorphin-producing neurons in the hypothalamus were not activated by the CO(2) inhalation stress.

SHP-2 promoting migration and metastasis of MCF-7 with loss of E-cadherin, dephosphorylation of FAK and secretion of MMP-9 induced by IL-1beta in vivo and in vitro

Shp-2, an src homology (SH) two-containing phosphotyrosine phosphatase, appears to be involved in cytoplasmic signaling downstream of a variety of cell surface receptors. It also plays an important role in the control of cell spreading, migration, and cytoskeletal architecture. In our study, abrogation of SHP-2 catalytic activity with a'dominant-negative mutant (SHP-2C > S) displayed an increased number of focal adhesion, high expression of E-cadhenrin and phosphorylation of the focal adhesion kinase (FAK). Interestingly, the cells expressing SHP-2C > S showed reduced IL-1beta-stimulated chemotaxis compared with either mock- or SHP-2 wild type-transfected cells. We also found that SHP-2-GFP-transfected cell lines did not express E-cadherin nearly and produced high level of the matrix metalloproteinase MMP-9 in the supernatants. The loss of E-cadherin-mediated adhesion and the increase of MMP-9-induced migration had been shown to play an important role in the transition of epithelial tumors from a benign to an invasive state. These findings have raised the possibility that SHP-2 can promote the cancer cell to invasion the distant tissues. To determine whether SHP-2 promotes invasion and metastasis, we transfected MCF-7 breast cancer cell lines with SHP-2-GFP, SHP-2C > S-GFP and analyzed the effects of the SHP-2 on cell migration, invasion, and metastasis. In vitro, SHP-2-GFP-transfected cells migrated more efficiently, showed an increased invasion of Matrigel, and adhered less efficiently to monolayers of fibroblast cells. When injected into the abdominal cavity of nude mice, SHP-2-GFP-transfected cells metastasized widely to the lung, kidney, but MCF-7 with SHP-2C > S-GFP was not observed in the these organs. These results demonstrate that SHP-2 promotes invasion and metastasis of MCF-7 with the loss of E-cadherin, the dephosphorylation of FAK and the secretion of MMP-9 induced by IL-1beta.

The immune system as the sixth sense

One of the truly remarkable discoveries in modern biology is the finding that the nervous system and immune system use a common chemical language for intra- and inter-system communication. This review will discuss some of the pivotal results that deciphered this chemical language. Specifically the nervous and immune systems produce a common set of peptide and nonpeptide neurotransmitters and cytokines that act on a common repertoire of receptors in the two systems. The paper will also review more recent studies that have delineated hardwired and humoral pathways for such bidirectional communication. This is discussed in the context of the idea that the sharing of ligands and receptors allows the immune system to serve as the sixth sense that notifies the nervous system of the presence of entities, such as viruses and bacteria, that are imperceptible to the classic senses. Lastly, this review will suggest ways to apply the newfound knowledge of the sixth sense to understand a placebo effect and to treat human disease.

IL‐1 induced release of Ca2+from internal stores is dependent on cell‐matrix interactions and regulates ERK activation

The cellular mechanisms that modulate interleukin-1 (IL-1) signaling are not defined. In fibroblasts, IL-1 signaling is affected by the nature of cell-matrix adhesions including focal adhesions, adhesive domains that sequester IL-1 receptors. We conducted studies to elucidate which steps of cellular Ca2+ handling are affected by focal adhesions and by which mechanisms focal adhesions modulate IL-1-induced Ca2+ signals and ERK activation in human gingival fibroblasts. Cells were plated on poly-l-lysine or fibronectin and treated with tenascin, Hep-I, or SPARC peptides to inhibit focal adhesion formation. These treatments blocked IL-1 and thapsigargin-induced Ca2+ release from the endoplasmic reticulum, indicating that the ER-release pathway is focal adhesion dependent. Focal adhesions were also required for Ca2+ entry through store-operated channels and for IL-1-induced ERK activation. Thus interactions with the extracellular matrix and focal adhesion formation regulate IL-1-induced generation of intracellular Ca2+ signals that in turn are required for ERK activation.

The protein tyrosine phosphatase SHP-2 regulates interleukin-1-induced ERK activation in fibroblasts

Focal adhesion complexes are actin-rich, cytoskeletal structures that mediate cell adhesion to the substratum and also selectively regulate signal transduction pathways required for interleukin (IL)-1beta signaling to the MAP kinase, ERK. IL-1-induced ERK activation is markedly diminished in fibroblasts deprived of focal adhesions whereas activation of p38 and JNK is unaffected. While IL-1 signaling is known to involve the activity of protein and lipid kinases including MAP kinases, FAK, and PI3K, little is known about the role of phosphatases in the regulation of IL-1 signal generation and attenuation. Here we demonstrate that SHP-2, a protein tyrosine phosphatase present in focal adhesions, modulates IL-1-induced ERK activation and the transient actin stress fiber disorganization that occurs following IL-1 treatment in human gingival fibroblasts. Using a combination of immunoblotting, immunoprecipitation, and immunostaining we show that SHP-2 is present in nascent focal adhesions and undergoes phosphorylation on tyrosine 542 in response to IL-1 stimulation. Blocking anti-SHP-2 antibodies, electoporated into the cytosol of fibroblasts, inhibited IL-1-induced ERK activation, actin filament assembly, and cell contraction, indicating a role for SHP-2 in these processes. In summary, our data indicate that SHP-2, a focal adhesion-associated protein, participates in IL-1-induced ERK activation likely via an adaptor function.

Native somatostatin sst2 and sst5 receptors functionally coupled to Gi/o-protein, but not to the serum response element in AtT-20 mouse tumour corticotrophs

Of the five cloned somatostatin (SRIF: somatotropin release inhibitory factor) receptors (sst1-5), only sst2 and sst5 receptors appear to be endogenously expressed and functionally active in AtT-20 mouse anterior pituitary tumour cells. In this study, the presence and the functional coupling of SRIF receptors to G-protein in AtT-20 cells was evaluated by receptor autoradiography and guanosine-5'-Omicron-(3-[35S]thio)-triphosphate ([35S]GTPgammaS) binding, respectively. In addition, transcriptional effects via the serum response element (SRE) were assessed in AtT-20-SRE-luci cells, engineered to express constitutively SRE upstream of the luciferase reporter gene. [125I]LTT-SRIF-28, [125I]CGP 23996 and [125I]Tyr3-octreotide binding illustrates the high level of sst2/5 receptor in AtT-20 cell membranes. SRIF-14 and SRIF-28 produced a concentration-dependent increase in [35S]GTPgammaS binding (pEC50=6.72 and 7.45; Emax=79 and 74.9, respectively) which was completely abolished by pertussis toxin. sst2/5 receptor-selective ligands caused a concentration-dependent increase in [35S]GTPgammaS binding (pEC50=7.74-5.84; Emax=76.6-20.2) while sst1/3/4 receptor-selective ligands were devoid of activity. The binding profiles of [125I]LTT-SRIF-28 and the inhibition of cAMP accumulation correlated highly significantly with their corresponding [35S]GTPgammaS binding profiles (r=0.862 and 0.874, respectively). The effects of the sst2 receptor-preferring agonists Tyr3-octreotide and BIM 23027 on [35S]GTPgammaS binding, but not those of SRIF-14 and the sst5/1 receptor selective-agonist L-817,818, were competitively antagonised by the sst2 receptor antagonist d-Tyr8-CYN 154806 (pKB=7.36 and 7.72, respectively; slope factors not significantly different from unity). In AtT-20-SRE-luci cells, which carry a SRE-luciferase construct functioning in a very efficient manner, SRIF and its analogues did not affect luciferase activity. Taken together, these results demonstrate that in AtT-20 cells the expression of sst2 and sst5 receptors fit with their functional coupling to G(i/o)-proteins. The pharmacological implications of the existence of different ligand/receptor complexes are discussed. However, the intracellular pathways coupled to the activation of sst2 and sst5 receptors appear not to modulate the SRE-mediated transcriptional activity, suggesting that SRIF effects on gene expression coupled to mechanisms that have promoters other than SRE.

c-Fos associates with the endoplasmic reticulum and activates phospholipid metabolism

c-Fos, a transcription factor that constitutes DNA-binding AP-1 complexes, regulates gene expression that promotes long-lasting cellular changes. We show that, in addition to its transcription factor activity, c-Fos regulates the metabolism of phospholipids cytoplasmically by an AP-1-independent activity. Two waves of c-Fos expression that promote subsequent waves of stimulation of 32P-orthophosphate incorporation into phospholipids are evidenced in quiescent cultured fibroblasts induced to re-enter the cell cycle. The first wave of c-Fos expression peaks at 7.5 min and returns to control levels by 15 min. The second wave starts by 30 min and remains elevated at 120 min. In the first wave, the lipids that incorporate 32P are predominantly second-messenger polyphosphoinositides (PIP, PIP2, PIP3); whereas in the second wave, membrane-biogenesis-related lipids (PI, PE, PA), become radioactive. Both waves of phospholipid activation depend on c-Fos expression. It is interesting that a peptide that blocks AP-1 nuclear import does not affect phospholipid activation. Immunocytochemical examination showed c-Fos immunoreactivity associated to the endoplasmic reticulum. We conclude that c-Fos, rapidly induced upon cell stimulation, associates to the endoplasmic reticulum where it first regulates the synthesis/ replenishment of phospholipids required for signal transduction pathways and subsequently regulates enzymes involved in the genesis of new membrane necessary for cell growth.

Blockade of lipopolysaccharide-induced fever by a mu-opioid receptor-selective antagonist in rats

The endogenous opioid system has been found to be involved in fever caused by pyrogens. In the present study, we have investigated the role of the mu-opioid receptor in the brain in fever induced by lipopolysaccharide. Rats were microinjected with 1 microg of the mu-opioid receptor-selective antagonist, cyclic D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP), into the preoptic anterior hypothalamus. Thirty minutes later, lipopolysaccharide (50 microg/kg) was injected intraperitoneally (i.p.). CTAP reduced by 1 degrees C the fever induced by lipopolysaccharide. However, it did not affect lipopolysaccharide fever when it was given 3 h after lipopolysaccharide injection. These data indicate that mu-opioid receptors within the preoptic anterior hypothalamus mediate the initiation of lipopolysaccharide fever and suggest that the opioid system is involved in the pathogenesis of fever in rats.

Pathophysiological role of the cytokine network in the anterior pituitary gland

Recent evidence has demonstrated that cytokines and other growth factors act in the anterior pituitary gland. Using the traditional criteria employed to determine autocrine or paracrine functions our review shows that, in addition to their role as lymphocyte messengers, certain cytokines are autocrine or paracrine regulators of anterior pituitary function and growth. The cytokines known to regulate and/or be expressed in the anterior pituitary include the inflammatory cytokine family (IL-1 and its endogenous antagonist, IL-1ra; TNF-alpha, and IL-6), the Th1-cytokines (IL-2 and IFN-gamma), and other cytokines such as LIF, MIF, and TGF-beta. This review examines at the cellular, molecular, and physiological levels whether: (1) each cytokine alters some aspect of pituitary physiology; (2) receptors for the cytokine are expressed in the gland; and (3) the cytokine is produced in the anterior pituitary. Should physiological stimuli regulate pituitary cytokine production, this would constitute additional proof of their autocrine/paracrine role. In this context, we analyze in this review the current literature on the actions of cytokines known to regulate anterior pituitary hormone secretion, selecting the in vivo studies that support the direct action of the cytokine in the anterior pituitary. Further support for direct regulatory action is provided by in vitro studies, in explant cultures or pituitary cell lines. The cytokine receptors that have been demonstrated in the pituitary of several species are also discussed. The endogenous production of the homologous cytokines and the regulation of this expression are analyzed. The evidence indicating that cytokines also regulate the growth and proliferation of pituitary cells is reviewed. This action is particularly important since it suggests that intrinsically produced cytokines may play a role in the pathogenesis of pituitary adenomas. The complex cell to cell communication involved in the action of these factors is discussed.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Medial prefrontal cortical injections of c-fos antisense oligonucleotides transiently lower c-Fos protein and mimic amphetamine withdrawal behaviours

Prefrontal cerebral cortical areas display decreased expression of several transcription factor/immediate-early genes, including c-fos, during amphetamine withdrawal. Antisense strategies can help to test possible roles for this prefrontal c-fos down-regulation in the behavioural correlates of amphetamine withdrawal. Medial prefrontal cortical injections delivering 1.7 nmoles of anti c-fos oligonucleotides revealed an approximately 3 h half-life for phosphothioate and a 15 min half-life for phosphodiester oligonucleotides. Antisense phosphothioates complementary to the c-fos translational start site reduced levels of c-Fos protein, while exerting modest and variable effects on c-fos messenger RNA levels. Neither missense phosphorothioate nor antisense phosphodiester oligonucleotides significantly reduced levels of either c-fos messenger RNA or protein. Animals injected with anti c-fos phosphothioate oligonucleotides into the medial prefrontal cortex displayed marked reductions in linear locomotor activity and repetitive movements measured in a novel environment, effects not seen when missense oligonucleotides were used or when animals were accustomed to the activity monitor prior to antisense oligonucleotide injection. Behavioural changes produced by prefrontal cortical injections of c-fos antisense oligonucleotides closely mimic alterations recorded during amphetamine withdrawal. Prefrontal c-fos could thus conceivably play roles in the neurobiological underpinnings of psychostimulant withdrawal and of responses to stressors such as exposure to novel environments.

Brain substrates activated by electroacupuncture (EA) of different frequencies (II): Role of Fos/Jun proteins in EA-induced transcription of preproenkephalin and preprodynorphin genes

Antisense oligodeoxynucleotides (ODNs) of c-fos and/or c-jun were used in this study to investigate the role of Fos and Jun proteins in electroacupuncture (EA)-induced transcription of the opioid genes, preproenkephalin (PPE), preprodynorphin (PPD) and proopiomelanocortin (POMC). As the results showed, EA-induced Fos and fun expression was blocked efficiently and specifically by e-fos and c-jun antisense ODNs, respectively. This treatment significantly prevented EA-induced PPD, but not PPE, mRNA expression. These results suggest that Fos and Jun proteins are involved in PPD rather than PPE gene transcription activated by EA stimulation.

Regulation of nerve growth factor mRNA by interleukin-1 in rat hippocampal astrocytes is mediated by NFkappaB

Cytokines such as interleukin-1beta (Il-1) are produced in the brain during development and during inflammatory processes that result from lesions or disease. One function of Il-1 in the brain appears to be the stimulation of astrocytes to proliferate and produce a variety of cytokines and trophic factors, including nerve growth factor. The mechanisms by which Il-1 exerts its actions on astrocytes remain poorly defined. We present evidence that this cytokine elicits activation of the NFkappaB transcription factor and that this transcription factor mediates effects of Il-1 on nerve growth factor mRNA expression. Elucidation of the processes by which cytokines activate astrocytes and influence trophic factor expression may provide insight into mechanisms governing inflammatory processes within the central nervous system.

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.

Immediate early genes in blood pressure regulation

The immediate early genes c-fos and c-jun are transcription regulating factors. c-fos expression is widely used as a marker of neuronal activation and has been used in this study to identify those neurons, presumably vasomotor neurons, that are activated after interventions that alter blood pressure. c-fos and c-jun are expressed in the rostral ventral medulla (RVM) when the tonically active inhibitory inputs to the RVM are removed, either acutely or chronically, as in the SHR model of gentic hypertension. The injection of antisense oligonucleotide complementary to c-fos mRNA in the RVM attenuates the expression of c-fos, lowers resting blood pressure and attenuates blood pressure responses that are evoked via RVM mechanisms. These studies suggest a link between immediate early gene expression in neurons in the RVM and the regulation of blood pressure. c-fos could have an important role in regulating the activity of these central cardiovascular neurons. The role of the immediate early gene c-jun in cardiovascular control remains to be elucidated.

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.

Does endotoxin stimulate cells by mimicking ceramide?

Recent studies indicate that tumor necrosis factor (TNF) and interleukin 1 (IL-1) stimulate cells via the intracellular messenger ceramide. Bacterial endotoxin (lipopolysaccharide; LPS) shows strong structural and functional resemblance to ceramide. Here, Samuel Wright and Richard Kolesnick review data suggesting that LPS may provoke cellular responses by mimicking the action of ceramide.

Interleukin-1 beta and tumour necrosis factor-alpha stimulate the mRNA expression of interleukin-1 receptors in mouse anterior pituitary AtT-20 cells

The RT-PCR technique was used to study IL-1 receptor mRNA levels in AtT-20 cells. IL-1 beta increased type I IL-1 receptor mRNA levels within 1 h, with elevated levels remaining after 24 h, whereas it induced a bell-shaped alteration of type II IL-1 receptor mRNA levels, with a peak after 6 h. Tumour necrosis factor-alpha (TNF alpha) similarly up-regulated type II IL-1 receptor mRNA levels, and type I IL-1 receptor mRNAs albeit to a lesser extent than IL-1 beta. Furthermore, IL-1 beta also induced increases in TNF alpha and c-fos mRNAs. The IL-1 receptor antagonist can fully block all the above effects of IL-1 beta. Up-regulation of type II IL-1R mRNA levels in AtT-20 cells could constitute an important way to modulate IL-1 actions, since type II IL-1R is believed to antagonize IL-1 effects.

c-fos expression in central cardiovascular pathways

Injection of muscimol in the caudal ventrolateral medulla increases blood pressure and stimulates neuronal c-fos expression in the rostral ventral medulla (RVM). The blockade of c-fos expression in the RVM by antisense oligonucleotides attenuates the blood pressure response to this muscimol-induced disinhibition of the RVM and also reduces resting blood pressure. The results suggest that cardiovascular neurons in the RVM express c-fos and that the basal and stimulated expression of the c-fos gene is important in the central regulation of blood pressure.

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.

ANTISENSE oligonucleotides: a new tool in neuroscience

1. Recent studies have shown that gene expression can be selectively attenuated by administration of short sequences of nucleotides (oligonucleotides) that are complementary to a portion of messenger RNA coding for a particular gene product. 2. This technique is known as ANTISENSE, because the oligonucleotides are complementary to the mRNA which has the same sequence as the SENSE strand of DNA. 3. In the present review we focus, after a brief discussion of gene expression and mechanisms of action of ANTISENSE, on the methodological aspects of ANTISENSE experiments in neuroscience. In particular, we address the advantages, disadvantages and controls for the ANTISENSE technique, as well as the choice, design, mode of delivery, dose and storage of ANTISENSE oligonucleotides.

Interleukin 1 induction of the c-jun promoter

Interleukin 1 (IL-1) induces pleiotropic effects in many cell types during inflammation and immunity. We have recently shown how the IL-1 signal is transmitted to the nucleus: In T cells and in pituitary cells, IL-1 induced genes via activation of the nuclear factor AP-1. We now demonstrate how IL-1 activates the AP-1 factor in liver cells, which are a major target for IL-1 during the acute phase response in vivo. IL-1 induced gene transcription of both AP-1 components, c-jun and c-fos. IL-1 also increased the stability of c-jun mRNA. We define two enhancer sites in the jun promoter that are required for induction by IL-1. Although the binding sites share some similarity with the AP-1 binding site, the nuclear factors binding the jun motifs are not composed of Jun or Fos proteins. Thus these data identify two binding proteins that serve as one of the first nuclear targets for IL-1 signal transduction.

Molecular identification of two types of interleukin-1 receptors in the murine pituitary gland

The present study was carried out to characterize interleukin-1 (IL-1) receptors on murine pituitary cells. Receptor autoradiography confirmed the existence of binding sites for IL-1 alpha in the murine adenohypophysis, but not in the neural or intermediate lobes. Specific binding of IL-1 to isolated pituitary membranes revealed a Kd of 0.9 nM with a Bmax of 37 fmol/mg protein. To examine the possibility that the adenohypophysis synthesizes a receptor for IL-1, immunocytochemistry experiments with a specific monoclonal antibody against the type I receptor revealed the existence of this protein in only the adenohypophysis. Identity of the type I IL-1 receptor was similar to that found on T cells as determined by: 1) amplification of the predicted 619 bp fragment spanning the cytoplasmic, transmembrane and extracellular domains from RNA of pituitary and T cell origin, as well as clonal AtT-20 pituitary cells, and 2) restriction fragment analysis and sequencing of the amplified cDNAs. The pituitary gland and AtT-20 cells also expressed transcripts for the newly identified type II receptor for IL-1 as assessed by amplification of a specific 325 bp fragment, restriction fragment analysis and nucleotide sequencing, and these transcripts were similar to those found on B lymphocytes. These data identify two different forms of the IL-1 receptor in both normal and transformed pituitary cells and establish that these receptors are similar at the molecular level to those first identified on T and B lymphocytes.

Molecular biology of vertebrate learning: is c-fos a new beginning?

An elevated expression of c-fos nuclear protooncogene (immediate early gene) has been shown repeatedly to correlate with long-term neuronal responses. This paper reviews recent data suggesting that neuronal plasticity, including learning and memory formation, may involve c-fos expression as well. On the basis of biological functions of the Fos protein, well known to be a component of a transcription factor, AP-1, (activator protein 1) a hypothesis suggesting a role of transcription factors in the integration of information during learning processes is proposed.

Mechanisms of nerve growth factor mRNA regulation by interleukin-1 beta in hippocampal cultures: role of second messengers

Cytokines such as interleukin-1, which are found in the brain after trauma, regulate expression of nerve growth factor (NGF) mRNA and protein in hippocampal cultures. We have investigated possible mechanisms by which Il-1 beta regulates NGF in hippocampal cells. The induction of NGF mRNA by Il-1 beta was blocked by a receptor antagonist indicating that this effect is receptor mediated. Il-1 beta elicited a dramatic induction of c-fos mRNA and a slight elevation of c-jun mRNA in a time dependent manner which may allow for a role in the induction of NGF mRNA expression. We examined whether specific second messenger pathways were involved in mediating the action of Il-1 beta in the hippocampus. Activation of cAMP with forskolin or treatment with 8-Br-cAMP had no effect on NGF mRNA levels. Moreover, exposure of hippocampal cultures to Il-1 beta evoked no change in cAMP levels, indicating that this second messenger system played little or no role in the regulation of NGF expression by Il-1 beta in these cells. Further, interleukin-1 elicited no change in membrane inositol phosphate turnover, nor did it affect intracellular calcium levels. Treatment of cell cultures with the phorbol ester PMA elicited an increase in NGF mRNA, suggesting that activation of protein kinase C (PKC) may mediate NGF mRNA expression. However, prolonged treatment of cultures with PMA to desensitize PKC did not eliminate the Il-1 beta induction of NGF mRNA. Il-1 beta, therefore, did not appear to activate NGF expression via cAMP, Ca2+, or a PKC isoform that is downregulated by prolonged PMA treatment. However, a phosphorylation event may be involved in the signal transduction mechanism, as treatment with okadaic acid to inhibit protein phosphatase 2a potentiated the induction of NGF mRNA by Il-1 beta. The results presented indicate that Il-1 beta acts via its receptor to induce a rise in NGF expression. Identification of the specific second messenger pathway has remained elusive; however, a phosphorylation event appears to be intermediary. Moreover, the induction of c-fos and c-jun may represent a final common path in activation of NGF gene expression by different signals such as Il-1 beta and PMA.