Antisense RNA of proto-oncogene c-fos blocks renewed growth of quiescent 3T3 cells

Towards Gene-Inhibition Therapy: A Review of Progress and Prospects in the Field of Antiviral Antisense Nucleic Acids and Ribozymes

Antisense RNA and its derivatives may provide the basis for highly selective gene inhibition therapies of virus infections. In this review, I concentrate on advances made in the study of antisense RNA and ribozymes during the last five years and their implications for the development of such therapies. It appears that antisense RNAs synthesized at realistic levels within the cell can be much more effective inhibitors than originally supposed. Looking at those experiments that enable comparisons to be made, it seems that inhibitory antisense RNAs are not those that are complementary to particular sites within mRNAs but those that are able to make stable duplexes with their targets, perhaps by virtue of their secondary structure and length. The inclusion of ribozyme sequences within antisense RNAs confers RNA-cleaving activity upon them in vitro and possibly in cells, thereby offering the possibility of markedly increasing their therapeutic potential. The varieties of natural ribozyme and their adaptation as artificial catalysts are reviewed. The implications of these developments for antiviral therapy are discussed.

The temporary and accumulated effects of transcranial direct current stimulation for the treatment of advanced Parkinson's disease monkeys

Transcranial direct current stimulation (tDCS) is a useful noninvasive technique of cortical brain stimulation for the treatment of neurological disorders. Clinical research has demonstrated tDCS with anodal stimulation of primary motor cortex (M1) in Parkinson’s disease (PD) patients significantly improved their motor function. However, few studies have been focused on the optimization of parameters which contributed significantly to the treatment effects of tDCS and exploration of the underline neuronal mechanisms. Here, we used different stimulation parameters of anodal tDCS on M1 for the treatment of aged advanced PD monkeys induced with 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) administration, and then analyzed the temporary and accumulated effects of tDCS treatment. The results indicated anodal tDCS on M1 very significantly improved motor ability temporarily; importantly, the treatment effects of anodal tDCS on M1 were quantitatively correlated to the accumulated stimulation instead of the stimuli intensity or duration respectively. In addition, c-fos staining showed tDCS treatment effects activated the neurons both in M1 and substantia nigra (SN). Therefore, we propose that long time and continue anodal tDCS on M1 is a better strategy to improve the motor symptoms of PD than individual manipulation of stimuli intensity or duration.

Signal transduction and molecular targets of selected flavonoids

SIGNIFICANCE

Diet exerts a major influence on the risk for developing cancer and heart disease. Food factors such as flavonoids are alleged to protect cells from premature aging and disease by shielding DNA, proteins, and lipids from oxidative damage.

RECENT ADVANCES

Our work has focused on clarifying the effects of dietary components on cancer cell proliferation and tumor growth, discovering mechanisms to explain the effects, and identifying the specific molecular targets of these compounds. Our strategy for identifying specific molecular targets of phytochemicals involves the use of supercomputer technology combined with protein crystallography, molecular biology, and experimental laboratory verification.

CRITICAL ISSUES

One of the greatest challenges for scientists is to reduce the accumulation of distortion and half truths reported in the popular media regarding the health benefits of certain foods or food supplements. The use of these is not new, but interest has increased dramatically because of perceived health benefits that are presumably acquired without unpleasant side effects. Flavonoids are touted to exert many beneficial effects in vitro. However, whether they can produce these effects in vivo is disputed.

FUTURE DIRECTIONS

The World Health Organization indicates that one third of all cancer deaths are preventable and that diet is closely linked to prevention. Based on this idea and epidemiological findings, attention has centered on dietary phytochemicals as an effective intervention in cancer development. However, an unequivocal link between diet and cancer has not been established. Thus, identifying cancer preventive dietary agents with specific molecular targets is essential to move forward toward successful cancer prevention.

Effects of methanolic extracts from broad beans on cellular growth and antioxidant enzyme activity

OBJECTIVE

There are several reports of cellular-aging-dependent alterations in the antioxidant capacity of human fibroblasts. Fibroblasts show slower the growth rate at late passages (referred to hereafter as old cells) than at early passages (referred to hereafter as young cells). Antioxidants may control cellular growth by modulating reactive oxygen species (ROS). Methanolic extracts from broad beans (MEBB) contain phenolic compounds and have ROS-scavenging activities. In this study, we investigated the effects of MEBB on cellular growth and antioxidant levels in normal human lung fibroblasts.

METHODS

To determine cytosolic superoxide dismutase (SOD) activities, cytosolic glutathione peroxidase (GSH-Px) activities, catalase activities, reduced glutathione (GSH) concentrations, and growth rate, MEBB treatments were performed on young and old cells.

RESULTS

In young and old cells treated with 120 μg/ml MEBB, the growth rates increased by 28.1 and 15.2%, respectively, compared with controls. The MEBB treatment of young cells caused a 62.5% increase in SOD activity, but the treatment of old cells caused a 39.5% decrease. The catalase activities of the young and old cells treated with MEBB were equal to those of control cells. Young and old cells treated with MEBB were equal to the control cells in terms of GSH-Px activity. The GSH concentrations in the young and old cells treated with 120 μg/ml MEBB increased by 22.1 and 45.9%, respectively.

CONCLUSION

These studies elucidated a new cellular growth mechanism whereby human lung fibroblasts modulate intracellular GSH levels via the action of MEBB.

Loss of Serum Response Factor Activity Is the Basis of Reduced C-FOS Expression in Aging Human Fibroblasts

Les fibroblastes diploïdes humains subissent un nombre limité de dédoublements de population in vitro et sont largement utilisés comme modèle de vieillissement cellulaire. Malgré l'évidence grandissante que le vieillissement cellulaire est dû à une modification de l'expression du gène, l'activité des facteurs de transcription des cellules âgées est encore mal connue. Ici, nous rapportons que la réduction dramatique de l'expression du facteur de transcription fos durant le vieillissement cellulaire semble due à l'incapacité d'un autre facteur de transcription, le facteur réponse de sérum (FRS), de se lier à son site de reconnaissance appelé élément de réponse du sérum (ERS). Ce site est situé en amont de plusieurs gènes comprenant le gène humain c-fos. À l'opposé, les activités des protéines liées à la boîte TATA de la polymérase ARN ainsi qu'à l'élément réponse AMPc sont conservées chez les fibroblastes humains vieillissants. Nous présentons l'évidence que l'hyperphosphorilation du FRS induit une baisse du pouvoir de liaison observée au cours des dernières divisions cellulaires comme ceci a été précédemment suggéré pour la protéine fos.

Expression of thioredoxin during progression of hamster and human cholangiocarcinoma

Thioredoxin (Trx) is a multifunctional redox protein that has growth-promoting and anti-apoptotic effects on cells and protects cells from endogenous and exogenous free radicals. Recently, altered expression of Trx has been reported in various cancers. In the present study, we investigated altered expression of Trx at the precancerous and carcinogenic phases during cholangiocarcinogenesis in a hamster cholangiocarcinoma (ChC) model, using semiquantitative immunohistochemical and Western blot analyses. Moreover, to determine if the results correlated well with those in human ChCs, we carried out a comparative immunohistochemical study for Trx in tissue-arrayed human ChCs with different grades of tumor cell differentiation. Trx was found highly expressed in the cytoplasm of dysplastic bile ducts with highly abnormal growth patterns and ChCs irrespective of tumor type or tumor cell differentiation. Overexpression of Trx at the precancerous and carcinogenic phases was further supported by significant elevation of Trx protein in Western blotting. The results from the hamster ChCs were in good agreement with those from human ChCs. Our results strongly suggested that the redox regulatory function of Trx plays an important role in bile duct cell transformation and tumor progression during cholangiocarcinogenesis.

Serum deprivation induces SV40 early promoter activity

Proliferation and the expression of proliferation-associated genes are modulated by changing the serum concentration in the media of cultured cells. To determine if activity of the SV40 early promoter is modulated by serum, we examined the expression of SV40 early promoter driven marker genes in murine BALB/c 3T3T cells following serum deprivation or serum stimulation. SV40-promoter-regulated beta-galactosidase and chloramphenicol acetyl transferase genes were studied following either transient or stable transfection. The results show that serum deprivation of growing cells induces SV40 promoter activity while serum stimulation of quiescent G0 cells suppresses it. Kinetic analyses show a significant induction of the SV40 promoter activity during the first 2 days of serum deprivation which is maintained at a high level for 15 days. The induction of reporter gene expression by serum deprivation was selective for the SV40 early promoter because such an effect was not observed using the Rous sarcoma viral promoter. Nuclear run-off assays further show that the transcription controlled by the SV40 early promoter is approximately twofold greater in cells rendered quiescent by serum deprivation for 72 h than in growing cells cultured in medium containing serum. These results suggest that one reason SV40 T transformed cells commonly fail to undergo quiescence following serum deprivation is that the SV40 promoter is induced.

Inducible cAMP early repressor splice variants ICER I and IIgamma both repress transcription of c-fos and chromogranin A

Inducible cAMP early repressor (ICER) splice variants are generated upon activation of an alternative, intronic promoter within the CREM gene. ICER is proposed to downregulate both its own expression, and the expression of other genes, containing cAMP-responsive promoter elements. To examine the biological function of the two ICER splice variants, I and IIgamma, in comparable cellular systems, we generated HEK 293 cell variants with controllable overexpression of either ICER I or IIgamma. These two splice variants contain two different variants of DNA binding domains. Overexpression of either ICER I or IIgamma strongly represses CRE-driven reportergene transcription but not AP1- or NFkappaB-driven transcription. Thus, high specificity is maintained even at ICER overexpression. We here show that both ICER I and IIgamma repress Pituitary adenylate cyclase-activating polypeptide (PACAP)-mediated c-fos mRNA induction with similar efficiency, indicating that both splice variants play an important role in modulating PACAP-mediated transcriptional activation of the c-fos gene. ICER I and IIgamma also repress cAMP-mediated activation of chromogranin A (CgA), indicating that these splice variants may function as negative feedback regulators in CgA synthesis. The proliferation rate was not altered in cells overexpressing ICER I or IIgamma. Thus, in the epithelial cells HEK 293, ICER I and IIgamma splice variants seem to exert similar biological function.

Cot, a novel kinase of histone H3, induces cellular transformation through up-regulation of c-fos transcriptional activity

Post-translational modification of histones is critical for gene expression, mitosis, cell growth, apoptosis, and cancer development. Thus, finding protein kinases that are responsible for the phosphorylation of histones at critical sites is considered an important step in understanding the process of histone modification. The serine/threonine kinase Cot is a member of the mitogen-activated protein kinase (MAPK) kinase kinase family. We show here that Cot can phosphorylate histone H3 at Ser-10 in vivo and in vitro, and that the phosphorylation of histone H3 at Ser-10 is required for Cot-induced cell transformation. We found that activated Cot is recruited to the c-fos promoter resulting in increased activator protein-1 (AP-1) transactivation. The formation of the Cot-c-fos promoter complex was also apparent when histone H3 was phosphorylated at Ser-10. Furthermore, the use of dominant negative mutants of histone H3 revealed that Cot was required for phosphorylation of histone H3 at Ser-10 to induce neoplastic cell transformation. These results revealed an important function of Cot as a newly discovered histone H3 kinase. Moreover, the transforming ability of Cot results from the coordinated activation of histone H3, which ultimately converges on the regulation of the transcriptional activity of the c-fos promoter, followed by AP-1 transactivation activity.

Depletion of the AP-1 repressor JDP2 induces cell death similar to apoptosis

JDP2 is a ubiquitously expressed nuclear protein that efficiently represses the activity of the transcription factor AP-1. Thus far, all studies of JDP2 function have relied on the ectopic expression of the protein. In this study, we use a different approach: depletion of JDP2 from cells. Specific depletion of JDP2 resulted in p53-independent cell death that resembles apoptosis and was evident at 72 h. The death mechanism was caspase dependent as the cells could be rescued by treatment with caspase inhibitor zVAD. Our studies suggest that JDP2 functions as a general survival protein, not only following UV-irradiation, as reported earlier, but also under normal culture conditions. Thus, our data support that JDP2 is a cellular survival protein whose presence is necessary for normal cellular function.

50-Hz magnetic field (0.1-mT) altersc-fos mRNA expression of early post implantation mouse embryos and serum estradiol levels of gravid mice

BACKGROUND

We exposed pregnant mice to magnetic or sham fields for 24 hr/day during Gestation Day (GD) 5.5-8.5 to study the effects of 50-Hz 0.1-mT sinusoidal magnetic fields on early pregnancy in mouse embryos and mice.

METHODS

Mice were sacrificed on GD 8.5. Embryos and blood samples were collected. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect the expression of embryo c-fos mRNA. The blood samples were tested through radioimmunoassay for serum estradiol levels and general examinations.

RESULTS

We found that the expression of c-fos mRNA of embryos under exposure was enhanced. We reported that 50-Hz 0.1-mT magnetic exposure induced the decline of serum estradiol levels of pregnancy mice on GD 8.5. General examinations of blood including white blood cell (WBC) count, red blood cell (RBC) count, and hemoglobin (HGB) did not show significant differences between the exposure group and the control group (sham exposure).

CONCLUSIONS

Under the experimental conditions, 50-Hz 0.1-mT sinusoidal magnetic fields affected the development of early pregnancy mouse embryos and the dams to some extent.

c-Fos activated phospholipid synthesis is required for neurite elongation in differentiating PC12 cells

We have previously shown that c-Fos activates phospholipid synthesis through a mechanism independent of its genomic AP-1 activity. Herein, using PC12 cells induced to differentiate by nerve growth factor, the genomic effect of c-Fos in initiating neurite outgrowth is shown as distinct from its nongenomic effect of activating phospholipid synthesis and sustaining neurite elongation. Blocking c-Fos expression inhibited differentiation, phospholipid synthesis activation, and neuritogenesis. In cells primed to grow, blocking c-Fos expression determined neurite retraction. However, transfected cells expressing c-Fos or c-Fos deletion mutants with capacity to activate phospholipid synthesis sustain neurite outgrowth and elongation in the absence of nerve growth factor. Results disclose a dual function of c-Fos: it first releases the genomic program for differentiation and then associates to the endoplasmic reticulum and activates phospholipid synthesis. Because phospholipids are key membrane components, we hypothesize this latter phenomenon as crucial to support membrane genesis demands required for cell growth and neurite elongation.

Experience facilitates vomeronasal and olfactory influence on Fos expression in medial preoptic area during pheromone exposure or mating in male hamsters

Chemosensory stimuli are essential for mating in male hamsters but either main olfactory or vomeronasal input is sufficient in sexually experienced males. Activation in central chemosensory pathways and medial preoptic area, after stimulation with female chemosignals or after mating, was estimated by counting neurons expressing Fos protein in experienced and naive males, with or without vomeronasal organ lesions. Regions counted included main and accessory olfactory bulbs, corticomedial amygdala, bed nucleus stria terminalis and medial preoptic area. Chemosensory stimulation was more effective in activating medial preoptic area in experienced than in naive males. In experienced males with vomeronasal organs removed, main olfactory input was as effective in activating medial preoptic area as was the combination of main and accessory input available to intact animals. As previously reported, the main olfactory input remaining after vomeronasal lesions in naive males was poorly effective in activating medial preoptic area, and these animals had impaired mating behavior. The change in access of chemosensory input to medial preoptic area after experience suggests that an experience-dependent synaptic modulation in this pathway, perhaps in the amygdala, may underlie some changes in mating behavior with experience.

Transcription factor activation in response to cutaneous injury: role of AP-1 in reepithelialization

Reepithelialization is the process responsible for restoring an intact epidermis following cutaneous injury. A change in the activity of keratinocytes is required for reepithelialization to occur, and this is likely to be regulated by the altered expression of effector genes, mediated by transcription factors. The injury itself provides a stimulus for transcription factor activation either directly due to mechanical stress, or via paracrine mechanisms such as the release of growth factors from damaged cells. Members of the activator protein-1 family, in particular c-fos and c-jun, have been the most widely studied wound-induced transcription factors. The signal transduction pathways linking cellular injury to activator protein-1 stimulation appear to involve an increase in intracellular Ca2+ and activation of mitogen-activated protein kinases. Given that a number of genes involved in the reepithelialization of wounds are regulated by activator protein-1, a distinct role for this transcription factor in reepithelialization is beginning to emerge. This article reviews the evidence for activator protein-1 involvement in reepithelialization, with particular focus on the activation of this transcription factor in response to wounding, the second messenger/kinase pathways involved, and the modulation of downstream genes that have the capacity to regulate keratinocyte function.

AP-1 in cell proliferation and survival

A plethora of physiological and pathological stimuli induce and activate a group of DNA binding proteins that form AP-1 dimers. These proteins include the Jun, Fos and ATF subgroups of transcription factors. Recent studies using cells and mice deficient in individual AP-1 proteins have begun to shed light on their physiological functions in the control of cell proliferation, neoplastic transformation and apoptosis. Above all such studies have identified some of the target genes that mediate the effects of AP-1 proteins on cell proliferation and death. There is evidence that AP-1 proteins, mostly those that belong to the Jun group, control cell life and death through their ability to regulate the expression and function of cell cycle regulators such as Cyclin D1, p53, p21(cip1/waf1), p19(ARF) and p16. Amongst the Jun proteins, c-Jun is unique in its ability to positively regulate cell proliferation through the repression of tumor suppressor gene expression and function, and induction of cyclin D1 transcription. These actions are antagonized by JunB, which upregulates tumor suppressor genes and represses cyclin D1. An especially important target for AP-1 effects on cell life and death is the tumor suppressor p53, whose expression as well as transcriptional activity, are modulated by AP-1 proteins.

Expression of immediate early genes, HSP70, and COX-2 mRNAs in rat stomach following ethanol ingestion

The aim of this study was to show the temporal and spatial molecular responses in the rat stomach that follow absolute ethanol-induced acute mucosal injury. Intense signals for immediate early genes (IEG)/transcriptional factors such as c-fos, c-jun, and nerve growth factor-induced gene-A (NGFI-A) mRNAs were observed in the superficial mucosa and in the blood vessels from 15 min to 6 hr after administration, peaking at 15-30 min. Signals for heat shock protein (HSP) 70 mRNA were also detected in the superficial mucosa, in the fibroblasts around gastric erosions, and in the blood vessels from 15 min to 6 hr (peak at 1-2 hr). The signals for cyclooxygenase-2 (COX-2) mRNA were up-regulated in the surface mucous cells that surround the erosions from 30 min to 6 hr (peak at 60-90 min). These findings suggest that IEG, HSP70, and COX-2 are involved in gastric mucosal restitution in different ways.

Chemotactic response of periodontal ligament cells decreases with donor age: association with reduced expression of c-fos

OBJECTIVE

To understand the effects of aging on cellular motility of human periodontal ligament (PDL) cells, and to determine the possible link between cell proliferation and migration in relation to cellular aging.

MATERIALS AND METHODS

The chemotactic response of PDL cells from three juvenile and four older donors were compared. Then, migrated or unmigrated cells were examined for their cell cycle by morphological and immunocytochemical procedures. Finally, migrated or unmigrated cells were examined for the expression of c-fos and c-myc by in situhybridization.

RESULTS

PDL cells from older donors showed lower chemotaxis compared with the cells from juvenile donors (P < 0.05). Cells undergoing migration were found not to be in the S- or M-phase of the cell cycle. However, all migrated cells were found to express c-fos, while many of the cells which did not migrate were found not to express c-fos.

CONCLUSIONS

Cellular motility of PDL cells decreases with donor age as well as cell proliferation. Since the cells reaching senescence fail to express c-fos, the mechanisms linked to cellular senescence may be a possible underlying mechanism for low migration seen in the older cells.

Growth state-dependent regulation of plasminogen activator inhibitor type-1 gene expression during epithelial cell stimulation by serum and transforming growth factor-beta1

Transcription of the plasminogen activator inhibitor type-1 (PAI-1) gene appears to be growth state regulated in several cell types (e.g. , Ryan and Higgins, 1993, J Cell Physiol 155:376-384; Mu et al., 1998, J Cell Physiol 174:90-98). Transit of serum-stimulated normal rat kidney (NRK) epthelial cells through the first division cycle after release from quiescence (G(0)) provided a model system to assess the kinetics and mechanisms underlying PAI-1 expression in a growth "activated" phenotype. PAI-1 mRNA transcripts increased by more than 20-fold during the G(0)-->G(1) transition; induced expression had immediate-early response characteristics and abruptly declined prior to the onset of DNA synthesis. Transcriptional activity of the PAI-1 gene paralleled the steady-state mRNA abundance profile during this first synchronized growth cycle after release from quiescence. Although PAI-1 mRNA levels were up-regulated (approximately threefold) upon exposure to several different growth factors, neutralizing antibodies to transforming growth factor-beta1 (TGF-beta1) effectively attenuated the more than ninefold serum-associated PAI-1 inductive response by more than 70% (at both the mRNA transcript and protein levels). Similar to the metabolic requirements for serum-mediated PAI-1 transcription, PAI-1 induction upon addition of TGF-beta1 to quiescent NRK cell cultures was actinomycin D sensitive and resistant to cyclohexamide and puromycin, suggesting a primary mode of transcript control. The response to protein synthesis inhibitors, however, was complex. While cyclohexamide appeared to stabilize, or at least maintain, fetal bovine serum (FBS)- or TGF-beta1-stimulated PAI-1 mRNA levels, puromycin had no such affect. The amplitude and duration of induced PAI-1 expression were the same in either the presence or absence of puromycin. Cyclohexamide when used alone (i.e., in non-FBS- or TGF-beta1-treated cultures), moreover, effectively stimulated PAI-1 induction whereas puromycin was ineffective. Although TGF-beta1 was not a complete mitogen in the NRK cell system, incubation of quiescent renal cell cultures with TGF-beta1, prior to serum stimulation, resulted in a 10- to 12-fold increase in PAI-1 expression coincident with exit out of G(0). These data support a model in which PAI-1 gene expression is closely associated with creation of the growth-activated state and that cell cycle controls appear to be superimposed on the time course of the serum-induced expression of the PAI-1 gene.

Suppression of post-ischemic-induced fos protein expression by an antisense oligonucleotide to c-fos mRNA leads to increased tissue damage

Activation of c-fos, an immediate early gene, and the subsequent upregulation of Fos protein expression occur following neural injury, including focal cerebral ischemia (fci). Fos and Jun form a heterodimer known as activator protein 1, which regulates the expression of many late effector genes. To study the downstream effects of c-fos expression following ischemia, we suppressed the translation of c-fos by administering an antisense oligonucleotide (AO) to c-fos mRNA. Eighteen hours prior to fci, male, Long Evans (LE) rats received intraventricular injections of AO, mismatched AO (MS) or artificial cerebrospinal fluid (aCSF). Fci was induced by permanent right middle cerebral artery occlusion. At 24-h post-occlusion, neurological function was assessed, and the animals were sacrificed. The brains were removed and stained with triphenyltetrazolium chloride for infarct volume determination. Fos immunohistochemistry was performed in separate animals to determine the effects of treatment on Fos expression number of Fos positive cells. AO administration reduced the number of cells with fci-induced Fos expression by approximately 75%. No differences in neurological scores existed between any of the groups. AO-treated LE developed larger infarcts (40.1+/-1.0%, mean+/-S.D., p<0.001) than MS- or aCSF-treated controls (34.3+/-1.0%, 34.6+/-1.0%, respectively). These results suggest that c-fos activation and subsequent Fos protein expression exerts a neuroprotective effect, which is likely via upregulation of neurotrophins, following focal cerebral ischemia. This response, among others, may contribute to brain adaptation to injury that underlies functional recovery after stroke.

The tissue-specific transcription factor Pit-1/GHF-1 binds to the c-fos serum response element and activates c-fos transcription

Pit-1, a POU domain-containing transcription factor, is involved in two functions in the pituitary: PRL and GH tissue-specific expression and somatolactotroph cells expansion. To analyze the molecular basis of the latter function, we tested whether Pit-1 can directly transactivate expression of an early marker of cell cycle initiation, the c-fos gene. We show that Pit-1 overexpression in PC12 cells, which do not express Pit-1, increases c-fos expression. Moreover, cAMP-induced c-fos promoter activity is decreased in the somatolactotroph cell line GH3 when Pit-1 expression is reduced by hybrid arrest with an antisense sequence complementary to Pit-1 cDNA. In contrast to hormonal genes regulation, where it has been shown that any Pit-1 phosphorylation site is involved, we show that the Pit-1 phosphorylation sites are required to allow increase of c-fos promoter activity by Pit-1. We further show, by gel shift analyses, that Pit-1 is able to specifically bind the serum response element sequence present within the c-fos promoter but with a lesser affinity than the Pit-1 response element. Taken together, these results demonstrate that the tissue-specific transcription factor Pit-1 is able to enhance expression of genes involved in cell cycle initiation, suggesting that this mechanism allows Pit-1 to increase somato-lactotroph cell proliferation.

Antisense of c-fos gene attenuates Fos expression in the spinal cord induced by unilateral constriction of the sciatic nerve in the rat

Sciatic nerve constriction induces expression of c-fos protein in dorsal horn neurons of the spinal cord. Intrathecal administration of c-fos antisense (30 nmol/20 microl) into the lumbar region (L1-L5) 18 h prior to nerve ligation attenuated 80% of Fos-immunoreactivity 90 min after ligation compared to rats infused with c-fos sense or saline. Thus, c-fos antisense may be a useful tool in assessing the role of the c-fos gene in an animal model of neuropathic pain.

Suppression of postischemic hippocampal nerve growth factor expression by a c-fos antisense oligodeoxynucleotide

We examined the uptake and distribution of an antisense phosphorothioated oligodeoxynucleotide (s-ODN) to c-fos, rncfosr115, infused into the left cerebral ventricle of male Long-Evans rats and the effect of this s-ODN on subsequent Fos, NGF, neurotrophin-3 (NT-3), and actin expression. To establish the uptake and turnover of s-ODN in the brain, we studied the copurification of the immunoreactivity of biotin with biotinylated s-ODN that was recovered from different regions of the brain. A time-dependent diffusion and the localization of s-ODN were further demonstrated by labeling the 3'-OH terminus of s-ODN in situ with digoxigenin-dUTP using terminal transferase and detection using anti-digoxigenin IgG-FITC. Cellular uptake of the s-ODN was evident in both the hippocampal and cortical regions, consistent with a gradient originating at the ventricular surface. Degradation of the s-ODN was observed beginning 48 hr after delivery. The effectiveness of c-fos antisense s-ODN was demonstrated by its suppression of postischemic Fos expression, which was accompanied by an inhibition of ischemia-induced NGF mRNA expression in the dentate gyrus. Infusion of saline, the sense s-ODN, or a mismatch antisense s-ODN did not suppress Fos expression. That this effect of c-fos antisense s-ODN was specific to NGF was demonstrated by its lack of effect on the postischemic expression of the NT-3 and beta-actin genes. Our results demonstrate that c-fos antisense s-ODN blocks selected downstream events and support the contention that postischemic Fos regulates the subsequent expression of the NGF gene and that Fos expression may have a functional component in neuroregeneration after focal cerebral ischemia-reperfusion.

Synthesis of proto-oncogene proteins and cyclins depends on intact microfilaments

It is well established that microfilament disintegration by cytochalasin D (CD) as well as latrunculin (LAT)-A and LAT-B causes an inhibition of S phase entry of various nontransformed cell lines. Our experiments extended these observations to human embryonal diploid fibroblasts (Wi-38). To investigate the question whether this stop of DNA synthesis is due to a decline of the synthesis of proteins that are necessary for G1 progression and S phase entry, we examined the expression of two proto-oncogenes (c-fos, c-jun) and three cyclins (D1, E, A) after altering the microfilament system. Disintegration of microfilaments by CD, LAT-A, or LAT-B of asynchronously growing fibroblasts caused a strong dose-dependent and time-dependent inhibition of total protein synthesis. Expression of c-jun, cyclins D1, E, and A decreased by about the same percentage as total protein synthesis. The strong induction of total protein synthesis after reactivating serum-starved fibroblasts by adding fetal calf serum was suppressed, when CD or LAT-A were added to the culture medium during this reactivation process. While expression of cyclin E as well as cyclin A decreased by about the same percentage as total protein synthesis, cyclin D1 was more suppressed after microfilament disintegration. After reactivating growth-arrested Wi-38 fibroblasts, cultured in suspension for 12 h, by transferring them to a rigid substratum they could adhere to, total protein synthesis was strongly induced. Again alteration of microfilaments by CD suppressed that increase. The expression of cyclin D1 was slightly more suppressed than total protein synthesis after addition of CD during that reactivation process. Our results suggest that alteration of microfilaments causes a strong decline of total protein synthesis accompanied by a decrease of the expression of proteins that are required for G1 progression and S phase entry. The diminished presence of proteins that are important for cell cycle progression could explain the inhibition of DNA synthesis after microfilament disintegration by various drugs.

Antioxidants stimulate transcriptional activation of the c-fos gene by multiple pathways in human fetal lung fibroblasts (WI-38)

We have examined the effects of three structurally distinct antioxidants (N-acetylcysteine [NAC], Trolox C [a water-soluble vitamin E derivative], and nordihydroguaiaretic acid [NGA]) on the expression of the c-fos gene over a 2-hour period. Determination of cellular glutathione concentration (the primary determinant of the cellular redox state) over the same time-course verifies that all the compounds studied cause an increase in cellular reduction potential. The level of c-fos messenger RNA increased rapidly in response to micromolar concentrations of these compounds, reaching a peak in 30-60 minutes. Induction of c-fos expression by these antioxidants is at least partly due to an increase in transcription, as determined by nuclear run-on assay. Down regulation of protein kinase C (PKC) by pretreatment for 24 hours with 500 nm PMA prevents induction by subsequent stimulation with either PMA or NGA. NAC induction of c-fos is unaffected by PMA pretreatment, while Trolox C superinduced c-fos following PMA pretreatment. None of these treatments stimulated translocation of PKC-alpha from the cytosol to the membrane. These results suggest that increasing the intracellular reducing potential induces c-fos expression through multiple pathways.

c-Fos protein is a mediator in mitogenic response to ACTH

Pulses (up to 2 h) of the adrenocorticotropic hormone (ACTH) rapidly activate p42 and p44 MAPK (5 min), induce the c-Fos protein (1 h, 80% of cells) and stimulate entry of mouse Y-1 adrenocortical cells into the S phase of the cell cycle. This set of sequential events is also triggered in Y-1 cells by bFGF, and reflects a mitogenic response to ACTH. We report here that 90% inhibition of c-fos mRNA translation with a c-fos antisense oligodeoxynucleotide completely blocks the entry of Y1 cells into S phase stimulated by pulses of ACTH. These results indicate that c-Fos protein is an intracellular mediator of the mitogenic response to ACTH.

Pituitary adenylate cyclase-activating polypeptide stimulates both c-fos gene expression and cell survival in rat cerebellar granule neurons through activation of the protein kinase A pathway

A high density of pituitary adenylate cyclase-activating polypeptide (PACAP) receptors coupled to both adenylyl cyclase and phospholipase C is found in the external granule cell layer of the rat cerebellum during postnatal development. It has recently been reported that synthetic PACAP promotes cell survival and neurite outgrowth in immature granule cells. In the present study, we have investigated the transduction pathways that mediate the neurotrophic activity of PACAP in cultured granule cells from eight-day-old rat cerebellum. The effect of PACAP on cell survival was mimicked by dibutyryladenosine 3',5'-cyclic-monophosphate but not phorbol 12-myristate 13-acetate suggesting that only the adenylyl cyclase pathway is involved in the neurotrophic activity of PACAP. PACAP also induced a transient increase in c-fos messenger RNA level. The ability of PACAP to stimulate c-fos gene expression was mimicked by dibutyryladenosine 3',5'-cyclic-monophosphate but not phorbol 12-myristate 13-acetate. Similar effects of PACAP on granule cell survival were observed whether the cells were continuously incubated with PACAP for 48 h or only exposed to PACAP during 1 h. The protein kinase A inhibitor H89 significantly reduced the effect of PACAP on c-fos messenger RNA level whereas the specific protein kinase C inhibitor chelerythrine did not modify c-fos gene expression. These data indicate that the action of PACAP on cerebellar granule cell survival and c-fos gene expression are both mediated through the adenylyl cyclase/protein kinase A pathway. The observation that a short-term stimulation by PACAP can be converted into a long-lasting response indicates that the effect of the peptide on cell survival must involve immediate-early gene activation. The fact that a brief exposure to PACAP causes both c-fos gene expression and promotes cell survival strongly suggests that c-fos is involved in the trophic effect of PACAP on immature cerebellar granule cells.

Growth-regulatory activity of the growth arrest-specific gene, GAS1, in NIH3T3 fibroblasts

The growth arrest-specific gene, Gas-1, is preferentially expressed in quiescent NIH3T3 cells and inhibits DNA synthesis, suggesting that Gas-1 may be a tumor suppressor gene. When GAS1 cDNA, under the control of the strong constitutive CMV promoter, was transfected into NIH3T3 cells, no stable transfectant cell lines were produced, confirming that high levels of expression of GAS1 mRNA inhibit proliferation. GAS1, under the control of a dexamethasone-inducible promoter, was also transfected into NIH3T3 cells, resulting in normal numbers of transfectant clones. When expression of GAS1 mRNA was induced with dexamethasone, the growth rate was greatly inhibited. Morphological changes characteristic of growth arrest were also observed. To determine if antisense inhibition of expression of Gas-1 will transform normal fibroblasts, GAS1 cDNA, cloned in the antisense orientation, was transfected into NIH3T3 cells and expression of endogenous Gas-1 mRNA was inhibited. The GAS1-antisense cells had altered morphology and grew to a much higher saturation density than control cell lines with a loss of contact inhibition. However, there was no change in requirements for serum or any development of anchorage-independence. Antisense inhibition of expression of GAS1 is therefore insufficient to transform the cells, suggesting that additional genetic events are required for a fully malignant phenotype.

Antisense oligomers of cfos and cjun block glucocorticoid stimulation of thyrotropin-releasing hormone (TRH) gene expression in cultured anterior pituitary cells

The proto-oncogenes, cfos/cjun, are co-localized with thyrotropin-releasing hormone (TRH) in cultured anterior pituitary cells and increase following exposure to dexamethasone (Dex). To assess the role of cfos and cjun in the Dex stimulation of TRH gene expression, we used antisense oligonucleotides to block cfos and cjun expression in order to reduce formation of activating protein-1 (AP-1). The results showed that the antisense oligonucleotides together effectively reduced cfos/cjun gene expression and consequently the glucocorticoid stimulation of TRH peptide and mRNA. The findings indicate that cfos/cjun are involved in the glucocorticoid activation of TRH gene expression.

Regulation of the glucocorticoid receptor gene by the AP-1 transcription factor

The glucocorticoid receptor (GR) is a ligand-activated nuclear transcription factor, and AP- 1 (Fos/Jun or Jun/Jun) is a transcription factor whose components are nuclear proteins encoded by c-fos and c-jun protooncogenes. Serum stimulation of serum-starved NIH 3T3 cells resulted in an approx 188-fold induction of c-fos mRNA at 30 min and an approximately ninefold induction of c-jun mRNA at 1 h, followed by an increase in GR mRNA levels at 3-12 hour (twofold). Sequential induction of cFos, cJun, and GR protein levels also occurred. Overexpression of the cFos protein in NIH 3T3 cells (NIH 3T3 [cFos 3] and NIH 3T3 [cFos 10]) caused an increase in the endogenous GR protein. Previous and present studies showed that a putative AP-1 site within the GR promoter binds AP-1 proteins (both Jun and Fos family members). To address the molecular mechanism involved in transcriptional activation of the GR gene, we investigated the relevance of AP-1 binding complexes in this activation and in overall regulation of GR gene transcription. Transient transfection with a full length GR promoter linked to a luciferase gene into both NIH 3T3 (cFos 3) and NIH 3T3 (cFos 10) cells gave rise to an induction of luciferase activity. This induction was abolished following mutation or deletion of the GR AP-1 site from the promoter. These findings suggest that cFos is responsible for the induction of GR expression in serum-stimulated NIH 3T3 cells, and serum growth factors may stimulate GR transcription by a cFos-dependent mechanism at the putative AP-1 site. These studies support a role for the AP-1 transcription factor in regulating GR gene expression.

Colocalization of antisense RNAs and ribozymes with their target mRNAs

The use of complementary RNA sequences such as antisense RNAs and ribozymes to regulate the expression of specific genes in eukaryotic cells has been well-documented, particularly with their application to both human gene therapy and plant biotechnology. Despite the simplicity of this approach, this technique usually results in only partial suppression of gene expression and, in some instances, even fails to regulate the gene of interest. The variation observed with antisense RNA and ribozyme-mediated regulation is further complicated by the many factors with the potential to impact on the effectiveness of these RNAs. Recent advances in the understanding of the global architecture of the nucleus, chromatin structure, and RNA metabolism provide useful and necessary information for designing novel approaches to improving antisense RNA and ribozyme regulation. These studies predict that the position of genes within the nucleus is not random and that transcripts produced from these genes follow specific tracks in migrating to the cell cytoplasm. These observations have the potential to impact significantly on the ways in which RNA-mediated forms of gene regulation are applied. The purpose of this review is to discuss the concept of colocalizing antisense RNAs and ribozymes with their target mRNAs and to introduce a variety of approaches aimed at achieving this goal.

Implications of immediate-early gene induction in the brain following sexual stimulation of female and male rodents

Induction of immediate-early genes (IEGs), such as c-fos, has been widely used to mark the activation of brain regions following different types of sexual stimulation and behavior. A relatively common set of hormone-concentrating basal forebrain and midbrain structures in female and male rodents is activated by copulatory stimulation, in particular, stimulation of sensory nerves that innervate the penis or vagina/cervix, olfactory or pheromonal stimuli, and conditioned sexual incentives. These regions include the preoptic area, lateral septum, bed nucleus of the stria terminalis, paraventricular hypothalamus, ventromedial hypothalamus, medial amygdala, ventral premammillary nuclei, ventral tegmentum, central tegmental field, mesencephalic central gray, and peripeduncular nuclei. Regions that do not contain classic intracellular steroid receptors, such as the ventral and dorsal striatum or cortex, are also activated. IEGs have also been colocalized with cytoplasmic proteins like GnRH and oxytocin, and have been used in conjunction with retrograde tracers to reveal functional pathways associated with different sexual behaviors. Steroid hormones can also alter the ability of sexual stimulation to induce IEGs. Despite the many similarities, some differences in IEG induction between sexes have also been found. We review these findings and raise the question of what IEG induction in the brain actually means for sexual behavior, that is, whether it indicates the perception of sexual stimulation, commands for motor output, or the stimulation of a future behavioral or neuroendocrine event related to the consequences of sexual stimulation. To understand the role of a particular activated region, the behavioral or neuroendocrine effects of lesions, electrical stimulation, drug or hormone infusions, must also be known.

Unmasking a growth-promoting effect of the adrenocorticotropic hormone in Y1 mouse adrenocortical tumor cells

The adrenocorticotropic hormone (ACTH) inhibits the growth of Y1 mouse adrenocortical tumor cells as well as normal adrenocortical cells in culture but stimulates adrenocortical cell growth in vivo. In this study, we investigated this paradoxical effect of ACTH on cell proliferation in Y1 adrenal cells and have unmasked a growth-promoting effect of the hormone. Y1 cells were arrested in the G1 phase of the cell cycle by serum starvation and monitored for progression through S phase by measuring [3H]thymidine incorporation into DNA and by measuring the number of nuclei labeled with bromodeoxyuridine. Y1 cells were stimulated to progress through S phase and to divide after a brief pulse of ACTH (up to 2 h). This effect of ACTH appeared to be cAMP independent, since ACTH also induced cell cycle progression in Kin-8, a Y1 mutant with defective cAMP-dependent protein kinase activity. The growth-promoting effect of ACTH in Y1 was preceded by the rapid activation of p44 and p42 mitogen-activated protein kinases and by the accumulation of c-FOS protein. In contrast, continuous treatment with ACTH (14 h) inhibited cell cycle progression in Y1 cells by a cAMP-dependent pathway. The inhibitory effect of ACTH mapped to the midpoint of G1. Together, the results demonstrate a dual effect of ACTH on cell cycle progress, a cAMP-independent growth-promoting effect early in G1 possibly mediated by mitogen-activated protein kinase and c-FOS, and a cAMP-dependent inhibitory effect at mid-G1. It is suggested that the growth-inhibitory effect of ACTH at mid-G1 represents an ACTH-regulated check point that limits cell cycle progression.

Serum- and polypeptide growth factor-inducible gene expression in mouse fibroblasts

Complex cellular processes such as proliferation, differentiation, and apoptosis are regulated in part by extracellular signaling molecules: for example, polypeptide growth factors, cytokines, and peptide hormones. Many polypeptide growth factors exert their mitogenic effects by binding to specific cell surface receptor protein tyrosine kinases. This interaction triggers numerous biochemical responses, including changes in phospholipid metabolism, the activation of a protein phosphorylation cascade, and the enhanced expression of specific immediate-early, delayed-early, or late response genes. In this review, I summarize the major findings obtained from studies investigating the effects of serum or individual polypeptide growth factors on gene expression in murine fibroblasts. Several experimental approaches, including differential hybridization screening of cDNA libraries and differential display, have been employed to identify mRNA species that are expressed at elevated levels in serum- or polypeptide growth factor-stimulated cells. These studies have demonstrated that serum- and growth factor-inducible genes encode a diverse family of proteins, including DNA-binding transcription factors, cytoskeletal and extracellular matrix proteins, metabolic enzymes, secreted chemokines, and serine-threonine kinases. Some of these gene products act as effectors of specific cell cycle functions (e.g., enzymes involved in nucleotide and DNA synthesis), others are required to successfully convert a metabolically inactive cell to a metabolically active cell that will eventually increase in size and then divide (e.g., glucose-metabolizing enzymes), and some actually function as positive or negative regulators of cell cycle progression. In conclusion, research conducted during the past 15 years on serum- and growth factor-regulated gene expression in murine fibroblasts has provided significant insight into mitogenic signal transduction and cell growth control.

Naturally occurring antisense RNA

Within the last few years a number of mammalian genes have been found for which there exist naturally occurring "antisense" RNA species with complementarity to mRNAs. Effects of antisense RNA on "sense" RNA have yet to be established. Nevertheless, it is apparent that mammalian cells have devoted genetic information and machinery to processing RNA:RNA hybrids, and it is becoming clear that there may be many more genes than previously suspected to which natural antisense RNAs exist. If naturally occurring antisense RNAs are mediators of alterations in gene expression, the question arises as to whether these pathways can be exploited pharmacologically.

Comparison of in vitro proliferative capacity of human periodontal ligament cells in juvenile and aged donors

OBJECTIVE

The aim of this study is to compare the in vitro proliferative capacity of periodontal ligament (PDL) cells from aged and juvenile donors.

MATERIALS AND METHODS

Flow-cytometric analysis of the cell cycle was used to compare the length of each cell cycle, and the ratio of the cells progressing through the cycles between four PDL cells from juvenile donors and four cells from aged donors. Then, replicative capacity of the PDL cells from three juvenile and three aged donors was compared by serial cultures. Finally, expression of c-fos was compared between cells proliferating and cells which had reached senescent.

RESULTS

Flow-cytometric analysis of the cell cycle had revealed that although there were no differences in the length of each phase of the cell cycle, significant differences were found in the ratio of the cells entering from Gap I to DNA synthesis phase of the cell cycle (P < 0.025). Replicative capacity was much longer in two cells from juvenile donors (about 20 population doublings), while all cells from aged donors showed short dividing abilities (less than eight population doublings), hence entered senescent phases shortly. Additionally, no c-fos was detected in cells which had reached senescence upon stimulation with serum.

CONCLUSIONS

It is generally believed that aged humans have an impaired wound healing ability. We believe that more fibrotic PDL tissues seen in aged humans might be the reason for this, and suggest that this phenomena might be due to the progressive accumulation of senescent cell populations.

Growth-related signaling in vascular smooth muscle cells is deregulated by TCDD during the G0/G1 transition

Experiments have been conducted to examine the impact of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on growth-related signaling in vascular smooth muscle cells (SMCs). A 40% reduction of peak DNA synthesis was observed in SMCs only when TCDD was added during the G0/G1 transition of the cell cycle. Enhanced phosphorylation of several endogenous proteins during this period was coincident with increased tyrosine kinase activity as early as 15 min following TCDD challenge. No changes in protein phosphorylation status occurred in cells treated with TCDD during the G1/S transition or during S phase. Cotreatment of quiescent SMCs with 10 nM TCDD and serum for 3 h reduced serum-inducible binding activity to a 12-O-tetradecanoyl phorbol 13-acetate responsive element (TRE) by approximately 40%. No alterations of constitutive TRE binding were observed in quiescent SMCs treated with TCDD for up to 5 h. These data show that mitogen-related signaling in vascular SMCs is modulated by TCDD selectively during the G0/G1 transition, and these effects influence the growth behavior of these cells.

Early phosphorylation of the retinoblastoma gene product regulates protein binding to the c-fos retinoblastoma control element during T cell activation

Function of the retinoblastoma tumor suppressor protein [pRb] is regulated by phosphorylation during the G1 and S phases of the cell cycle. pRb regulates transcription of several genes, including c-fos. However, since c-fos is regulated during exit from G0, it has remained unclear how pRb participates in c-fos regulation. We have identified a protein complex, the retinoblastoma control factor A [RCF-A] which binds to the c-fos retinoblastoma control element [RCE] and is regulated by pRb within 10 min after T cell activation. We demonstrate that pRb control of RCF-A is dependent upon the state of phosphorylation of pRb. pRb becomes hyperphosphorylated on specific peptides at 10 min after mitogenic stimulation and pRb is dephosphorylated by 30 min. This time course coincides with RCF-A DNA binding. RCF-A binds RCE DNA longer when cells are treated with okadaic acid, and okadaic acid prevents pRb dephosphorylation. Dephosphorylated pRb inhibits RCF-A binding in vitro but phosphorylated pRb does not. Thus, in addition to the described G1/S regulation of pRb, transient inactivation by phosphorylation of pRb in T cells may also be important as resting cells leave G0.

Induced PAI-1 mRNA expression and targeted protein accumulation are early G1 events in serum-stimulated rat kidney cells

Expression of plasminogen activator inhibitor type-1 (PAI-1), a member of the SERPIN gene family that functions to regulate the plasmin-based pericellular proteolytic cascade, is growth state-regulated in normal rat kidney (NRK) cells (Ryan and Higgins, 1990, J. Cell. Physiol., 155:376-384; Ryan et al., 1996, Biochem. J., 314:1041-1046). Comparative analysis of arrest states induced in NRK cells upon exposure to serum-deficient (0.5% FBS) or serum-free culture conditions served to define the kinetics of PAI-1 gene expression and fate of de novo-synthesized PAI-1 protein. While cells rendered quiescent in serum-free or serum-deficient media were equivalent with regard to the time course of PAI-1 mRNA induction, the level of expressed transcripts (27-fold vs. 12-fold) and accumulated saponin fraction PAI-1 protein (12-fold vs. 6-fold) were consistently greater in cells recruited into exponential growth phase from a serum-free as compared to a serum-deficient arrest condition. Relative PAI-1 mRNA abundance increased within 1-2 hr post-serum addition, was maximal at 4 hr, and declined rapidly thereafter; this time course of expression coupled with placement of entry into DNA synthetic phase at approximately 12 hr after stimulation indicates that PAI-1 induction is an early-to-mid G1 phase event. Induced PAI-1 protein was evident immunocytochemically within 2 hr of serum stimulation as a peripheral "rim" of accumulated protein restricted to the cellular ventral surface at the plane of the substrate. No PAI-1 was detected between individual cells suggesting that this protein may be targeted directly to the undersurface region. By 6 hr post-stimulation, the rim of PAI-1 deposition increased in intensity and broadened to occupy approximately 30 to 50% of the total undersurface area. Double-label immunocytochemistry indicated that accumulated PAI-1 was deposited in close proximity to, but not actually within, vinculin-containing focal contact structures. Potential functionality of induced PAI-1 expression to either the initiation or maintenance of the serum-stimulated phenotype was assessed using antibodies to PAI-1. The IgG fractions of two different antisera which neutralize the ability of PAI-1 to complex with and thereby inhibit the catalytic activity of urokinase plasminogen activator significantly reduced (by 25-35%) the incidence of cells displaying the serum-stimulated phenotype; antibodies that bind PAI-1 but do not block PAI-1 inhibitory activity were without effect. In view of the vagaries of antibody accessibility and in situ neutralizing activity (particularly in a region as structurally complex as the focal contact), these data may actually underestimate the importance of PAI-1 in maintaining the activated phenotype.

Induced PAI-1 mRNA expression and targeted protein accumulation are early G1 events in serum-stimulated rat kidney cells

Expression of plasminogen activator inhibitor type-1 (PAI-1), a member of the SERPIN gene family that functions to regulate the plasmin-based pericellular proteolytic cascade, is growth state-regulated in normal rat kidney (NRK) cells (Ryan and Higgins, 1990, J. Cell. Physiol., 155:376-384; Ryan et al., 1996, Biochem. J., 314:1041-1046). Comparative analysis of arrest states induced in NRK cells upon exposure to serum-deficient (0.5% FBS) or serum-free culture conditions served to define the kinetics of PAI-1 gene expression and fate of de novo-synthesized PAI-1 protein. While cells rendered quiescent in serum-free or serum-deficient media were equivalent with regard to the time course of PAI-1 mRNA induction, the level of expressed transcripts (27-fold vs. 12-fold) and accumulated saponin fraction PAI-1 protein (12-fold vs. 6-fold) were consistently greater in cells recruited into exponential growth phase from a serum-free as compared to a serum-deficient arrest condition. Relative PAI-1 mRNA abundance increased within 1-2 hr post-serum addition, was maximal at 4 hr, and declined rapidly thereafter; this time course of expression coupled with placement of entry into DNA synthetic phase at approximately 12 hr after stimulation indicates that PAI-1 induction is an early-to-mid G1 phase event. Induced PAI-1 protein was evident immunocytochemically within 2 hr of serum stimulation as a peripheral "rim" of accumulated protein restricted to the cellular ventral surface at the plane of the substrate. No PAI-1 was detected between individual cells suggesting that this protein may be targeted directly to the undersurface region. By 6 hr post-stimulation, the rim of PAI-1 deposition increased in intensity and broadened to occupy approximately 30 to 50% of the total undersurface area. Double-label immunocytochemistry indicated that accumulated PAI-1 was deposited in close proximity to, but not actually within, vinculin-containing focal contact structures. Potential functionality of induced PAI-1 expression to either the initiation or maintenance of the serum-stimulated phenotype was assessed using antibodies to PAI-1. The IgG fractions of two different antisera which neutralize the ability of PAI-1 to complex with and thereby inhibit the catalytic activity of urokinase plasminogen activator significantly reduced (by 25-35%) the incidence of cells displaying the serum-stimulated phenotype; antibodies that bind PAI-1 but do not block PAI-1 inhibitory activity were without effect. In view of the vagaries of antibody accessibility and in situ neutralizing activity (particularly in a region as structurally complex as the focal contact), these data may actually underestimate the importance of PAI-1 in maintaining the activated phenotype.

The human diploid fibroblast senescence pathway is independent of interleukin-1 alpha mRNA levels and tyrosine phosphorylation of FGFR-1 substrates

In vitro cellular senescence of human umbilical vein endothelial cells (HUVEC) may involve the intracellular activity of the signal peptide-less cytokine interleukin (IL)-1 alpha. To determine whether senescence of other human diploid cells involves the function of IL-1 alpha, we examined the steady-state expression of IL-1 alpha mRNA in IMR-90 fibroblasts. The IL-1 alpha transcript was not elevated in senescent IMR-90 cells. With the exception of the plasminogen activator inhibitor (PAI)-1 transcript, other IL-1 alpha-response gene mRNAs were not induced in senescent IMR-90, although the mRNA for each gene was induced by exogenous IL-1 alpha. The mRNA expression of cell cycle-specific genes demonstrated that Fos and ornithine decarboxylase (ODC) were induced in young and senescent cells in response to both serum and fibroblast growth factor (FGF)-1. Histone (H)3 mRNA was induced by serum in young cells, but not in senescent cells, and FGF-1 failed to induce H3 mRNA in either young or senescent cells. Further, while young IMR-90 populations were able to respond to serum as an initiator of DNA synthesis and cell growth, they did not exhibit a response to exogenous FGF-1. FGF receptor (R)-1 substrates were not tyrosine phosphorylated in either young or senescent IMR-90 cells. These data demonstrate that IL-1 alpha and FGF-1 may have different functions in HUVEC and IMR-90 fibroblast populations including distinct pathways for the regulation of cellular growth and senescence.

Regulation of growth by ACTH in the Y-1 line of mouse adrenocortical cells

Y-1 adrenal cells were cell cycle arrested by serum starvation to characterize a G0-->G1-->S transition in these cells. Cycle arrested Y-1 cells start to enter S phase 8h after serum feeding, reaching more than 90% cells synthesizing DNA by 24h. ACTH displays a dual effect in the G0-->G1-->S transition: 2h ACTH treatment stimulates DNA synthesis initiation, but longer treatments inhibit S phase entry. This dual effect of ACTH is similar to the antagonistic actions of PMA (phorbol-12-miristate-13-acetate) on the G0-->G1-->S transition. However ACTH and PMA are likely to have different mechanisms of action. ACTH inhibitory effect requires PKA, whereas PMA inhibitory effect is not dependent on PKA. ACTH induces the proto-oncogenes c-fos and c-jun, but inhibits the expression of the c-myc proto-oncogene. PMA, on the other hand, induces equally well c-fos, c-jun and c-myc. We hypothesize that ACTH promotes G0-->G1 transition by induction of c-fos and c-jun and blocks G1-->S transition by c-myc inhibition.

Change of calretinin expression in the human colon adenocarcinoma cell line HT29 after differentiation

Calretinin is a Ca(2+)-binding protein of the EF-hand family which is expressed in colon adenocarcinomas and colon-derived tumor cell lines (e.g. WiDr), but is absent from normal human enterocytes. Its function has not as yet been elucidated, but some lines of evidence lead us to postulate its involvement in cell proliferation in these cells. In order to test whether calretinin is correlated with an undifferentiated, proliferating, or with a differentiated, state of cells, its expression was studied in the human colon adenocarcinoma clonal cell line HT29-18, which can be caused to differentiate into enterocyte-like cells by replacing glucose with galactose in the culture medium (glucose starvation differentiation). Treatment of HT29-18 cells with galactose led to a drop in the calretinin mRNA level and in protein expression as evidenced by immunocytochemical staining and Western blot analysis of cytosolic cell extracts. These results suggest that calretinin is present in HT29-18 cancer cells, mostly in those which are in the undifferentiated state. The possibility that calretinin is involved in maintaining the cells in an undifferentiated (cancerous) state is discussed.

Requirement of phospholipase C gamma, the tyrosine phosphatase Syp and the adaptor proteins Shc and Nck for PDGF-induced DNA synthesis: evidence for the existence of Ras-dependent and Ras-independent pathways

We have investigated the roles of the phosphotyrosine phosphatase Syp (also called SH-PTP2), phospholipase C (PLC) gamma1, rasGTPase Activating Protein (rasGAP) and the adapter molecules Nck and Shc in the mitogenic response induced by PDGF in fibroblasts. Two separate approaches were used to inhibit the biological activity of these signalling proteins in vivo. Either glutathione S-transferase (GST) fusion proteins containing the SH2 domains of these proteins, or antibodies specific for these polypeptides, were microinjected into cells. GST-SH2 fusion proteins are expected to act as dominant inhibitors by competing for physiological SH2-mediated interactions, while microinjected antibodies can directly block protein functions. Inhibition of PLCgamma, Syp, Shc and Nck signals blocked PDGF-stimulated cells in G1 showing a requirement for these proteins for S-phase entry. Inhibition of rasGAP, in contrast, had no effect on S-phase entry. We next examined which of these signals were required for PDGF-induced cFos expression, a Ras-dependent event important for signalling. By using the same approaches with cells expressing beta-galactosidase under the control of a c-fos promoter, we showed that PLCgamma, Syp and Shc were necessary for ligand-induced cFos expression whereas Nck and phosphatidylinositol 3-kinase alpha were not. From these results we concluded that PDGF generates Ras-dependent and Ras-independent pathways important for DNA synthesis.

Local administration of antisense phosphorothioate oligonucleotides to the p65 subunit of NF-kappa B abrogates established experimental colitis in mice

Chronic intestinal inflammation induced by 2,4,6,-trinitrobenzene sulfonic acid (TNBS) is characterized by a transmural granulomatous colitis that mimics some characteristics of human Crohn's disease. Here, we show that the transcription factor NF-kappa B p65 was strongly activated in TNBS-induced colitis and in colitis of interleukin-10-deficient mice. Local administration of p65 antisense phosphorothioate oligonucleotides abrogated clinical and histological signs of colitis and was more effective in treating TNBS-induced colitis than single or daily administration of glucocorticoids. The data provide direct evidence for the central importance of p65 in chronic intestinal inflammation and suggest a potential therapeutic utility of p65 antisense oligonucleotides as a novel molecular approach for the treatment of patients with Crohn's disease.

Oligodeoxynucleotides directed to early growth response gene-1 mRNA inhibit DNA synthesis in the smooth muscle cell

Vascular smooth muscle cell proliferation plays a central role in the pathophysiology of cardiovascular diseases. The induction of the early growth response gene-1 (egr-1) mRNA is associated with different cellular processes such as cell proliferation. Antisense oligodeoxynucleotides seem to provide a promising new pharmaceutical tool for effective modification of the expression of specific genes. Hence, in the present study, the effect of 15-mer antisense oligodeoxynucleotides (targeted to the initial codon region of the egr-1 mRNA) on the angiotensin II- and platelet-derived growth factor-BB-induced growth promoting effects of aortic smooth muscle cells was evaluated. Angiotensin II- and platelet-derived growth factor-BB induced egr-1 mRNA (3.4 kb) and Egr-1 protein (80 kDa) in a time- and concentration-dependent fashion. No effects of the sense and antisense oligodeoxynucleotides on the agonist-induced elevation of the egr-1 mRNA and on the Egr-1 protein could be demonstrated. However, they effectively inhibited the angiotensin II- and the platelet-derived growth factor-BB-induced DNA synthesis. Our findings provide evidence that the oligodeoxynucleotides inhibit vascular smooth muscle cell growth via nonantisense mechanism(s).