Transcription factor AP-1 activity is required for initiation of DNA synthesis and is lost during cellular aging

Activating mutations in JAK2 and CALR differentially affect intracellular calcium flux in store operated calcium entry

BACKGROUND

Calcium (Ca2+) signaling regulates various vital cellular functions, including integrin activation and cell migration. Store-operated calcium entry (SOCE) via calcium release-activated calcium (CRAC) channels represents a major pathway for Ca2+ influx from the extracellular space in multiple cell types. The impact of JAK2-V617F and CALR mutations which are disease initiating in myeloproliferative neoplasms (MPN) on SOCE, calcium flux from the endoplasmic reticulum (ER) to the cytosol, and related key signaling pathways in the presence or absence of erythropoietin (EPO) or thrombopoietin (TPO) is poorly understood. Thus, this study aimed to elucidate the effects of these mutations on the aforementioned calcium dynamics, in cellular models of MPN.

METHODS

Intracellular Ca2+ levels were measured over a time frame of 0-1080 s in Fura-2 AM labeled myeloid progenitor 32D cells expressing various mutations (JAK2-WT/EpoR, JAK2-V617F/EpoR; CALR-WT/MPL, CALR-ins5/MPL, and del52/MPL). Basal Ca2+ concentrations were assessed from 0-108 s. Subsequently, cells were stimulated with EPO/TPO in Ca2+-free Ringer solution, measuring Ca2+ levels from 109-594 s (store depletion). Then, 2 mM of Ca2+ buffer resembling physiological concentrations was added to induce SOCE, and Ca2+ levels were measured from 595-1080 s. Fura-2 AM emission ratios (F340/380) were used to quantify the integrated Ca2+ signal. Statistical significance was assessed by unpaired Student's t-test or Mann-Whitney-U-test, one-way or two-way ANOVA followed by Tukey's multiple comparison test.

RESULTS

Following EPO stimulation, the area under the curve (AUC) representing SOCE significantly increased in 32D-JAK2-V617F cells compared to JAK2-WT cells. In TPO-stimulated CALR cells, we observed elevated Ca2+ levels during store depletion and SOCE in CALR-WT cells compared to CALR-ins5 and del52 cells. Notably, upon stimulation, key components of the Ca2+ signaling pathways, including PLCγ-1 and IP3R, were differentially affected in these cell lines. Hyper-activated PLCγ-1 and IP3R were observed in JAK2-V617F but not in CALR mutated cells. Inhibition of calcium regulatory mechanisms suppressed cellular growth and induced apoptosis in JAK2-V617F cells.

CONCLUSIONS

This report highlights the impact of JAK2 and CALR mutations on Ca2+ flux (store depletion and SOCE) in response to stimulation with EPO and TPO. The study shows that the JAK2-V617F mutation strongly alters the regulatory mechanism of EpoR/JAK2-dependent intracellular calcium balance, affecting baseline calcium levels, EPO-induced calcium entry, and PLCγ-1 signaling pathways. Our results reveal an important role of calcium flux in the homeostasis of JAK2-V617F positive cells.

Replenishing Age-Related Decline of IRAK-M Expression in Retinal Pigment Epithelium Attenuates Outer Retinal Degeneration

Unchecked, chronic inflammation is a constitutive component of age-related diseases, including age-related macular degeneration (AMD). Here we identified interleukin-1 receptor-associated kinase (IRAK)-M as a key immunoregulator in retinal pigment epithelium (RPE) that declines with age. Rare genetic variants of IRAK-M increased the likelihood of AMD. IRAK-M expression in RPE declined with age or oxidative stress and was further reduced in AMD. IRAK-M-deficient mice exhibited increased incidence of outer retinal degeneration at earlier ages, which was further exacerbated by oxidative stressors. The absence of IRAK-M disrupted RPE cell homeostasis, including compromised mitochondrial function, cellular senescence, and aberrant cytokine production. IRAK-M overexpression protected RPE cells against oxidative or immune stressors. Subretinal delivery of AAV-expressing IRAK-M rescued light-induced outer retinal degeneration in wild-type mice and attenuated age-related spontaneous retinal degeneration in IRAK-M-deficient mice. Our data support that replenishment of IRAK-M expression may redress dysregulated pro-inflammatory processes in AMD, thereby treating degeneration.

Age-Associated Different Transcriptome Profiling in Zebrafish and Rats: an Insight into the Diversity of Vertebrate Aging

Most mammals, including humans, show obvious aging phenotypes, for example, loss of tissue plasticity and sarcopenia. In this regard, fish can be attractive models to study senescence because of their unique aging characteristics. The lifespan of fish varies widely, and several species can live for over 200 years. Moreover, some fish show anti-aging features and indeterminate growth throughout their life. Therefore, exploring the aging mechanism in fish could provide new insights into vertebrate aging. To this end, we conducted RNA sequencing (RNA-seq) assays for various organs and growth stages of zebrafish and compared the data with previously published RNA-seq data of rats. Age-associated differentially expressed genes (DEGs) for all zebrafish tissue samples reveal the upregulation of circadian genes and downregulation of hmgb3a. On one hand, a comparative analysis of DEG profiles associated with aging between zebrafish and rats identifies upregulation of circadian genes and downregulation of collagen genes as conserved transcriptome changes. On the other hand, in zebrafish, upregulation of autophagy-related genes in muscles and AP-1 transcription factor genes in various tissues is observed, which may imply fish-specific anti-aging characteristics. Consistent with our knowledge of mammalian aging, DEG profiles related to tissue senescence are observed in rats. We also detect age-associated downregulation of muscle homeostasis and differentiation-related genes in zebrafish gills, indicating a fish-specific senescence phenotype. Our results indicate both common and different aging profiles between fish and mammals, which could be used for future translational research.

Inflammatory Mediators in Oral Cancer: Pathogenic Mechanisms and Diagnostic Potential

Approximately 15% of cancers are attributable to the inflammatory process, and growing evidence supports an association between oral squamous cell carcinoma (OSCC) and chronic inflammation. Different oral inflammatory conditions, such as oral lichen planus (OLP), submucous fibrosis, and oral discoid lupus, are all predisposing for the development of OSCC. The microenvironment of these conditions contains various transcription factors and inflammatory mediators with the ability to induce proliferation, epithelial-to-mesenchymal transition (EMT), and invasion of genetically predisposed lesions, thereby promoting tumor development. In this review, we will focus on the main inflammatory molecules and transcription factors activated in OSCC, with emphasis on their translational potential.

Dysfunction of Hair Follicle Mesenchymal Progenitors Contributes to Age-Associated Hair Loss

Skin aging is accompanied by hair loss due to impairments in hair follicle (HF) epithelial progenitor cells and their mesenchymal niche. This inductive mesenchyme, called dermal papilla (DP), undergoes progressive cell loss and eventual miniaturization that contributes to HF pathogenesis. Using laser ablation and fate mapping, we show that HF dermal stem cells (hfDSCs) reconstitute the damaged DP and maintain hair growth, suggesting that hfDSC dysfunction may trigger degeneration of the inductive niche. Fate mapping over 24 months revealed progressive hfDSC depletion, and in vivo clonal analysis of aged hfDSCs showed impaired self-renewal and biased differentiation. Single-cell RNA-seq confirmed hfDSCs as a central precursor, giving rise to divergent mesenchymal trajectories. In aged skin, hfDSCs exhibited senescent-like characteristics, and senescence-associated secretory phenotypes were identified in the aging HF mesenchyme. These results clarify fibroblast dynamics within the HF and suggest that progressive dysfunction within the mesenchymal progenitor pool contributes to age-related hair loss.

Role of Resveratrol in Regulating Cutaneous Functions

Protective role of the skin is against external insults and maintenance of electrolyte homeostasis of the body. Cutaneous dysfunction can account for the development of both cutaneous and systemic disorders. Thus, improvements in cutaneous functions can benefit a number of extracutaneous and cutaneous functions. Resveratrol, a natural ingredient, displays multiple benefits for various systems/organs, including the skin. The benefits of resveratrol for cutaneous functions include stimulation of keratinocyte differentiation and antimicrobial peptide expression, inhibition of keratinocyte proliferation and cutaneous inflammation, UV protection, anticancer, antiaging, and inhibition of melanogenesis. The mechanisms of action of resveratrol include activation of sirtuin 1 and nuclear factor erythroid 2-related factor 2, and inhibition of mitogen-activated protein kinase signaling. Evidence suggests that topical resveratrol could be a valuable alternative not only for daily skin care, but also for the prevention and treatment of various cutaneous disorders. This review summarizes the benefits of resveratrol for cutaneous functions.

Stem cell paracrine actions in tissue regeneration and potential therapeutic effect in human endometrium: a retrospective study

OBJECTIVE

Determining genetic and paracrine mechanisms behind endometrial regeneration in Asherman's syndrome and endometrial atrophy (AS/EA) patients after autologous CD133⁺ bone marrow-derived stem cell (CD133⁺ BMDSC) transplantation.

DESIGN

Retrospective study using human endometrial biopsies and mouse models.

SETTING

Fundación-IVI, IIS-La Fe, Valencia, Spain.

SAMPLES

Endometrial biopsies collected before and after CD133⁺ BMDSC therapy, from eight women with AS/EA (NCT02144987) from the uterus of five mice with only left horns receiving CD133⁺ BMDSC therapy.

METHODS

In human samples, haematoxylin and eosin (H&E) staining, RNA arrays, PCR validation, and neutrophil elastase (NE) immunohistochemistry (IHQ). In mouse samples, PCR validation and protein immunoarrays.

MAIN OUTCOME MEASURES

H&E microscopic evaluation, RNA expression levels, PCR, and growth/angiogenic factors quantification, NE IHQ signal.

RESULTS

Treatment improved endometrial morphology and thickness for all patients. In human samples, Jun, Serpine1, and Il4 were up-regulated whereas Ccnd1 and Cxcl8 were down-regulated after treatment. The significant decrease of NE signal corroborated Cxcl8 expression. Animal model analysis confirmed human results and revealed a higher expression of pro-angiogenic cytokines (IL18, HGF, MCP-1, MIP2) in treated uterine horns.

CONCLUSIONS

CD133⁺ BMDSC seems to activate several factors through a paracrine mechanism to help tissue regeneration, modifying endometrial behaviour through an immunomodulatory milieu that precedes proliferation and angiogenic processes. Insight into these processes could bring us one step closer to a non-invasive treatment for AS/EA patients.

TWEETABLE ABSTRACT

CD133⁺ BMDSC therapy regenerates endometrium, modifying the immunological milieu that precedes proliferation and angiogenesis.

Thyroid hormone regulates distinct paths to maturation in pigment cell lineages

Thyroid hormone (TH) regulates diverse developmental events and can drive disparate cellular outcomes. In zebrafish, TH has opposite effects on neural crest derived pigment cells of the adult stripe pattern, limiting melanophore population expansion, yet increasing yellow/orange xanthophore numbers. To learn how TH elicits seemingly opposite responses in cells having a common embryological origin, we analyzed individual transcriptomes from thousands of neural crest-derived cells, reconstructed developmental trajectories, identified pigment cell-lineage specific responses to TH, and assessed roles for TH receptors. We show that TH promotes maturation of both cell types but in distinct ways. In melanophores, TH drives terminal differentiation, limiting final cell numbers. In xanthophores, TH promotes accumulation of orange carotenoids, making the cells visible. TH receptors act primarily to repress these programs when TH is limiting. Our findings show how a single endocrine factor integrates very different cellular activities during the generation of adult form.

Metformin induces the AP-1 transcription factor network in normal dermal fibroblasts

Metformin is a widely-used treatment for type 2 diabetes and is reported to extend health and lifespan as a caloric restriction (CR) mimetic. Although the benefits of metformin are well documented, the impact of this compound on the function and organization of the genome in normal tissues is unclear. To explore this impact, primary human fibroblasts were treated in culture with metformin resulting in a significant decrease in cell proliferation without evidence of cell death. Furthermore, metformin induced repositioning of chromosomes 10 and 18 within the nuclear volume indicating altered genome organization. Transcriptome analyses from RNA sequencing datasets revealed that alteration in growth profiles and chromosome positioning occurred concomitantly with changes in gene expression profiles. We further identified that different concentrations of metformin induced different transcript profiles; however, significant enrichment in the activator protein 1 (AP-1) transcription factor network was common between the different treatments. Comparative analyses revealed that metformin induced divergent changes in the transcriptome than that of rapamycin, another proposed mimetic of CR. Promoter analysis and chromatin immunoprecipitation assays of genes that changed expression in response to metformin revealed enrichment of the transcriptional regulator forkhead box O3a (FOXO3a) in normal human fibroblasts, but not of the predicted serum response factor (SRF). Therefore, we have demonstrated that metformin has significant impacts on genome organization and function in normal human fibroblasts, different from those of rapamycin, with FOXO3a likely playing a role in this response.

Inhibition of HSV-1 proliferation by decoy phosphodiester oligonucleotides containing ICP4 recognition sequences

Transcriptional control in eukaryotes results from the interplay between DNA sequences in promoters, enhancers, or silencers and transcription factors. Selective control of gene expression can thus be achieved by inhibiting specific transcription factor/DNA interactions. Transcriptional activity of DNA binding transcription factors can be inhibited by competition with double-stranded oligonucleotides (decoys) that contain their specific recognition sequences. The immediate early protein ICP4 of herpes simplex virus type 1 (HSV-1) is a sequence-specific DNA binding protein that is essential for viral replication. We synthesized double-stranded hairpin phosphodiester oligonucleotides carrying ICP4 sites and demonstrated their ability to specifically titrate ICP4. Upon addition to Vero cells, ICP4 hairpin decoys significantly reduced HSV-1 titers (IC50 = 0.3 microM), whereas a control hairpin oligonucleotide had no activity. Antiviral activity of ICP4 hairpin decoys was correlated to their relative binding affinities. These results show that phosphodiester oligonucleotides can compete for binding of specific transcription factors within cells, thus providing a potential therapeutic tool to control disease-causing genes.

Functional CRISPR screen identifies AP1-associated enhancer regulating FOXF1 to modulate oncogene-induced senescence

BACKGROUND

Functional characterization of non-coding elements in the human genome is a major genomic challenge and the maturation of genome-editing technologies is revolutionizing our ability to achieve this task. Oncogene-induced senescence, a cellular state of irreversible proliferation arrest that is enforced following excessive oncogenic activity, is a major barrier against cancer transformation; therefore, bypassing oncogene-induced senescence is a critical step in tumorigenesis. Here, we aim at further identification of enhancer elements that are required for the establishment of this state.

RESULTS

We first apply genome-wide profiling of enhancer-RNAs (eRNAs) to systematically identify enhancers that are activated upon oncogenic stress. DNA motif analysis of these enhancers indicates AP-1 as a major regulator of the transcriptional program induced by oncogene-induced senescence. We thus constructed a CRISPR-Cas9 sgRNA library designed to target senescence-induced enhancers that are putatively regulated by AP-1 and used it in a functional screen. We identify a critical enhancer that we name EnhAP1-OIS1 and validate that mutating the AP-1 binding site within this element results in oncogene-induced senescence bypass. Furthermore, we identify FOXF1 as the gene regulated by this enhancer and demonstrate that FOXF1 mediates EnhAP1-OIS1 effect on the senescence phenotype.

CONCLUSIONS

Our study elucidates a novel cascade mediated by AP-1 and FOXF1 that regulates oncogene-induced senescence and further demonstrates the power of CRISPR-based functional genomic screens in deciphering the function of non-coding regulatory elements in the genome.

c-Myb regulates NOX1/p38 to control survival of colorectal carcinoma cells

The c-Myb transcription factor is important for maintenance of immature cells of many tissues including colon epithelium. Overexpression of c-Myb occurring in colorectal carcinomas (CRC) as well as in other cancers often marks poor prognosis. However, the molecular mechanism explaining how c-Myb contributes to progression of CRC has not been fully elucidated. To address this point, we investigated the way how c-Myb affects sensitivity of CRC cells to anticancer drugs. Using CRC cell lines expressing exogenous c-myb we show that c-Myb protects CRC cells from the cisplatin-, oxaliplatin-, and doxorubicin-induced apoptosis, elevates reactive oxygen species via up-regulation of NOX1, and sustains the pro-survival p38 MAPK pathway. Using pharmacological inhibitors and gene silencing of p38 and NOX1 we found that these proteins are essential for the protective effect of c-Myb and that NOX1 acts upstream of p38 activation. In addition, our result suggests that transcription of NOX1 is directly controlled by c-Myb and these genes are strongly co-expressed in human tumor tissue of CRC patients. The novel c-Myb/NOX1/p38 signaling axis that protects CRC cells from chemotherapy described in this study could provide a new base for design of future therapies of CRC.

DNA-protein interaction dynamics at the Lamin B2 replication origin

To date, a complete understanding of the molecular events leading to DNA replication origin activation in mammalian cells still remains elusive. In this work, we report the results of a high resolution chromatin immunoprecipitation study to detect proteins interacting with the human Lamin B2 replication origin. In addition to the pre-RC component ORC4 and to the transcription factors USF and HOXC13, we found that 2 components of the AP-1 transcription factor, c-Fos and c-Jun, are also associated with the origin DNA during the late G1 phase of the cell cycle and that these factors interact with ORC4. Both DNA replication and AP-1 factor binding to the origin region were perturbed by cell treatment with merbarone, a topoisomerase II inhibitor, suggesting that DNA topology is essential for determining origin function.

Novel proteomic approach (PUNCH-P) reveals cell cycle-specific fluctuations in mRNA translation

Monitoring protein synthesis is required to understand gene expression regulation. Aviner et al. developed a system-wide proteomic approach for direct monitoring of translation, termed puromycin-associated nascent chain proteomics (PUNCH-P), which is based on incorporation of biotinylated puromycin into newly synthesized proteins followed by streptavidin affinity purification and LC-MS/MS analysis. Using PUNCH-P, cell cycle-specific fluctuations in synthesis for >5000 proteins were measured in mammalian cells. This approach also identified proteins not previously implicated in cell cycle processes and proteins that were not detected using other methods.

Monitoring protein synthesis is essential to our understanding of gene expression regulation, as protein abundance is thought to be predominantly controlled at the level of translation. Mass-spectrometric and RNA sequencing methods have been recently developed for investigating mRNA translation at a global level, but these still involve technical limitations and are not widely applicable. In this study, we describe a novel system-wide proteomic approach for direct monitoring of translation, termed puromycin-associated nascent chain proteomics (PUNCH-P), which is based on incorporation of biotinylated puromycin into newly synthesized proteins under cell-free conditions followed by streptavidin affinity purification and liquid chromatography-tandem mass spectrometry analysis. Using PUNCH-P, we measured cell cycle-specific fluctuations in synthesis for >5000 proteins in mammalian cells, identified proteins not previously implicated in cell cycle processes, and generated the first translational profile of a whole mouse brain. This simple and economical technique is broadly applicable to any cell type and tissue, enabling the identification and quantification of rapid proteome responses under various biological conditions.

Calorie restriction modulates redox-sensitive AP-1 during the aging process

Oxidative stress is claimed to be a major cause of aging. Recent data suggest that calorie restriction (CR) prolongs life span by its ability to retard aging, possibly by regulating the intracellular redox status through its antioxidative actions. Currently, there is little information showing the influences of age and CR on the redox-sensitive transcription factor activator protein-1 (AP-1). In the present study, we investigated how age affects the status of AP-1 and whether CR modulates the age effect. For our study, we used the kidney from male Fischer 344 rats, ages 6, 12, 18, and 24 months fed ad libitum (AL) or a CR diet. Results from our study showed that AP-1 binding activity markedly increases with age, while CR keeps this activity at the level of 6-month-old rats. We found that c-Jun and c-Fos protein levels increase during aging, and that aging induces phosphorylation of c-Jun, which might enhance AP-1 transcriptional activity. For CR's action, we found that in the nucleus of aged rats, AP-1 activation was blunted by decreasing c-Jun and c-Fos levels and inhibiting c-Jun protein phosphorylation. Results also indicated that matrix metalloproteinase-13 and heme oxygenase-1, which have an AP-1 binding site in their promoter regions, have a similar tendency toward AP-1 binding activity. Based on the data of these findings, we concluded that AP-1 activity increases in rat kidney with age and that CR reduces AP-1 activity.

Reduced expression of epidermal growth factor receptors in rat liver during aging

Proliferative responsiveness of hepatocytes to epidermal growth factor (EGF) declines during aging. The role of EGF receptors in mediating age-dependent changes of EGF-induced mitogenic signaling in liver remains incompletely understood. We assessed EGF receptor expression levels in whole liver specimens as well as in freshly isolated and cultured hepatocytes from young adult and senescent Fischer 344 male rats. Hepatic EGF receptor messenger RNA and protein levels, and the number of high- and low-affinity receptor binding sites, decreased with aging. Ligand-induced EGF receptor activation, determined by receptor dimerization and tyrosine phosphorylation, was reduced in old animals in parallel with the age-related decline in receptor expression. Stimulation of the extracellular signal-regulated kinase pathway by EGF was also attenuated in hepatocytes from old animals. Our results implicate decreased expression of EGF receptors as a key determinant of reduced mitogenic signaling responsive to EGF stimulation of liver during aging.

Gene expression changes in long-term culture of T-cell clones: genomic effects of chronic antigenic stress in aging and immunosenescence

The adaptive immune response requires waves of T-cell clonal expansion on contact with altered self and contraction after elimination of antigen. In the case of persisting antigen, as occurs for example in cytomegalovirus or Epstein–Barr virus infection, this critical process can become dysregulated and responding T-cells enter into a dysfunctional senescent state. Longitudinal studies suggest that the presence of increased numbers of such T-cells is a poor prognostic factor for survival in the very elderly. Understanding the nature of the defects in these T-cells might facilitate intervention to improve immunity in the elderly. The process of clonal expansion under chronic antigenic stress can be modelled in vitro using continuously cultured T-cells. Here, we have used cDNA array technology to investigate differences in gene expression in a set of five different T-cell clones at early, middle and late passage in culture. Differentially expressed genes were confirmed by real-time polymerase chain reaction, and relationships between these assessed using Ingenuity Systems evidence-based association analysis. Several genes and chemokines related to induction of apoptosis and signal transduction pathways regulated by transforming growth factor β (TGFβ), epidermal growth factor (EGF), fos and β-catenin were altered in late compared to early passage cells. These pathways and affected genes may play a significant role in driving the cellular senescent phenotype and warrant further investigation as potential biomarkers of aging and senescence. These genes may additionally provide targets for intervention.

The ubiquitin-proteasome system at the crossroads of stress-response and ageing pathways: a handle for skin care?

The regulation of gene expression at the transcriptional level has been considered for long as the main mechanism of cellular adaptive responses. Since the turn of the century, however, it is becoming clear that higher organisms developed a complex, sensitive and maybe equally important network of regulatory pathways, relying largely on protein interactions, post-translational modifications and proteolysis. Here we review the involvement of the ubiquitin-proteasome pathway of protein degradation at different levels of cellular life in relation with ageing, and with a special focus on skin. It comes out that the ubiquitin system plays a major role in signal transduction associated with stress and ageing, in skin in particular through the control of retinoid and NF-kappaB pathways. The understanding of specific proteolytic targeting by E3 ubiquitin-ligases paves the way for a new generation of active molecules that may control particular steps of normal and pathological ageing.

Manganese-induced apoptosis in hepatocytes after partial hepatectomy

To investigate the apoptosis induced by manganese (Mn) in hepatocytes in vivo, rats received a single injection of manganese chloride immediately after partial hepatectomy. Characteristic DNA fragmentation was observed at 4 h after partial hepatectomy with Mn-injection. The activation of caspase-3 by Mn-injection was detected as early as 30 min and peaked at 1 h after partial hepatectomy. The activity of Jun N-terminal kinase (JNK) increased to a maximal level, which was about 10-fold the maximal level of the control, at 15 min after partial hepatectomy and this increase was maintained for 4 h in Mn-injected rats, while a transient increase was observed at 1 h in the control. No effect of the Mn-injection on the activation of p38 mitogen-activated protein kinase (MAPK) was observed. Western blot analysis revealed that the injection of Mn markedly increased c-Jun and phosphorylated c-Jun protein levels at 1 h after partial hepatectomy. An increase in p53 was also observed at 30 min after the Mn-injection and followed by the upregulation of p21(WAF1/CIP1) protein expression at 2 h after partial hepatectomy. These results suggested that the activation of JNK and the upregulation of c-Jun, p53 and p21(WAF1/CIP1) were involved in the apoptosis of hepatocytes induced by partial hepatectomy with manganese.

Epidermal growth factor (EGF)-mediated DNA-binding activity of AP-1 is attenuated in senescent human epidermal keratinocytes

The proliferative responses of cells to mitogens decrease during aging, and this may result from age-related defects in signal transduction in response to mitogens. In this study, we have investigated the age-related alteration of responses to epidermal growth factor (EGF) in cultured human keratinocytes that were senesced in vitro by repeated passage. The stimulation with EGF increased the DNA-binding activity of activator protein 1 (AP-1), an important transcription factor for cell proliferation, in young keratinocytes, whereas the binding activity showed little or slight change in the senescent cells. The induced DNA-binding activity of AP-1 in young cells was inhibited by PD 98059, an inhibitor of MEK, and partially inhibited by GF 109203X, an inhibitor of protein kinase C. Western blot analysis demonstrated that EGF induced dramatic increase in the phosphorylation of EGF receptor (EGFR) and extracellular signal-regulated kinases (ERK) in young cells, while this phosphorylation was much less profound in senescent cells. Finally, the application of EGF to young cells resulted in increased phosphorylation of Fra-2, a Fos protein component of the Jun/Fos heterodimer AP-1 complex. This EGF-induced Fra-2 phosphorylation was attenuated in senescent cells. Taken together, our study suggests that the signal transduction mediated by EGF/ERK pathway is altered in senescent human keratinocytes, and this change may be attributed, in part, to the decreased AP-1 transcription activity observed in senescent keratinocytes.

Apoptosis induced by 5-(N,N-hexamethylene)-amiloride in regenerating liver after partial hepatectomy

The effects of a specific inhibitor of the Na+/H+ exchanger, 5-(N,N-hexamethylene)-amiloride (HMA), on liver regeneration after partial hepatectomy were investigated. A single injection of HMA inhibited DNA synthesis and caused apoptosis in regenerating liver. Characteristic DNA fragmentation was observed at 4 h after partial hepatectomy with HMA-injection. The activity of Jun N-terminal kinase (JNK) increased to a maximal level at 15 min after partial hepatectomy in HMA-injected rats, while it was not detected until 30 min in the control. Western blot analysis revealed that the injection of HMA markedly increased c-Jun and phosphorylated c-Jun protein levels at 30 min after partial hepatectomy. An increase in p53 was also observed at 30 min after the HMA-injection and was followed by the upregulation of p21WAF1/CIP1 protein expression at 1 h after partial hepatectomy. These results suggested that HMA induced apoptosis accompanied by the activation of JNK and the upregulation of c-Jun, p53 and p21WAF1/CIP1 expression at an early stage of liver regeneration.

Age-related alteration in hepatic acyl-CoA: cholesterol acyltransferase and its relation to LDL receptor and MAPK

The aim of this study was to evaluate changes in the regulation of lipid metabolism and mitogen-activated protein kinases (MAPK) in the liver of C57BL/6 mice as they age. This was done by assessing the status of total cholesterol content and its enzyme, acyl-CoA: cholesterol acyltransferase (ACAT), in liver microsomal preparations and the low-density lipoprotein receptor (LDLr) mRNA expression in the livers of 4-24-month-old C57B/6 mice, without exogenous cholesterol feeding. With aging, there was an increase in cholesterol content and ACAT activity in liver microsomes. Northern blot analysis and real-time quantitative polymerase chain reaction data showed that ACAT-2 mRNA increased with age as well. LDLr expression decreased significantly in an age-dependent manner. In addition, we studied the basal and activated forms of MAPK, e.g. extracellular regulatory kinase (ERK-1/2), c-jun NH2-terminal kinase (JNK-1/2) and p38 MAPK. During aging, there was a considerable decrease in phosphorylated ERK-1/2 level while JNK-1/2 and p38 MAPK levels increased with age. Our studies showed an altered LDLr expression and altered phosphorylated MAPK in the liver of C57BL/6 mice during aging. These alterations might contribute to the development of atherosclerosis, hypercholesterolemia and other cholesterol-related conditions.

Estrogen-induced proliferation of normal endometrial glandular cells is initiated by transcriptional activation of cyclin D1 via binding of c-Jun to an AP-1 sequence

To explore the mechanism of estrogen-induced growth of normal endometrium, the transactivation system of the cyclin D1 gene was analysed using cultured normal endometrial glandular cells. Estradiol (E2) treatment of cultured normal endometrial glandular cells induced upregulation of c-Jun, and then cyclin D1 proteins, followed by serial expressions of cyclins E, A and B1 proteins. Increase in the mRNA expression of cyclin D1 preceded the protein expression of cyclin D1 under E2 treatment. A luciferase assay using deletion constructs of the cyclin D1 promoter indicated that E2-induced increase in transcriptional activity was observed in reporters containing AP-1-binding site sequence, and that in the absence of E2, cotransfection of c-Jun also showed increase of transcriptional activity in the same reporters with AP-1 sequence. A gel shift assay using nuclear extract from E2-treated endometrial glandular cells and AP-1 sequences of the cyclin D1 promoter indicated specific binding between c-Jun protein and the promoter. Transfection of c-jun antisense oligonucleotides to the glandular cells resulted in the suppression of the E2-induced upregulation of cyclin D1 mRNA and protein. These findings suggest that E2-induced proliferation of normal endometrial glandular cells is initiated by transcriptional activation of cyclin D1 via binding of c-Jun to the AP-1 sequences.

Cloning and characterization of cellular senescence-associated genes in human fibroblasts by suppression subtractive hybridization

Cellular senescence marks the end of the proliferative life span of normal cells in tissue culture and occurs after cells have undergone a certain number of population doublings (PDLs). It is accompanied by alterations in the pattern of gene expression. A specific human embryonic lung diploid fibroblast cell line, 2BS, has been studied as a model of senescence in our laboratory. Here, we report a set of cellular senescence-associated genes identified from suppression subtractive cDNA libraries from senescent and young 2BS cells. They include three novel genes and six previously identified genes of unknown function. The genes whose functions are known belong to various functional pathways that have been reported to change with the onset of senescence. These include three pre-mRNA splicing factors with reduced expression in senescent cells, indicating that the regulation of mRNA splicing is altered during cell senescence. In addition, the expression of the gene TOM1 (target of Myb 1), which has not previously been associated with cellular senescence, is shown to increase in senescent cells, and we demonstrate that the expression of antisense TOM1 gene in 2BS cells can delay the progress of senescence.

Replicative senescence: a critical review

Human cells in culture have a limited proliferative capacity. After a period of vigorous proliferation, the rate of cell division declines and a number of changes occur in the cells including increases in size, in secondary lysosomes and residual bodies, nuclear changes and a number of changes in gene expression which provide biomarkers for senescence. Although human cells in culture have been used for over 40 years as models for understanding the cellular basis of aging, the relationship of replicative senescence to aging of the organism is still not clear. In this review, we discuss replicative senescence in the light of current information on signal transduction and mitogenesis, cell stress, apoptosis, telomere changes and finally we discuss replicative senescence as a model of aging in vivo.

Protein kinase C delta blocks immediate-early gene expression in senescent cells by inactivating serum response factor

Fibroblasts lose the ability to replicate in response to growth factors and become unable to express growth-associated immediate-early genes, including c-fos and egr-1, as they become senescent. The serum response factor (SRF), a major transcriptional activator of immediate-early gene promoters, loses the ability to bind to the serum response element (SRE) and becomes hyperphosphorylated in senescent cells. We identify protein kinase C delta (PKC delta) as the kinase responsible for inactivation of SRF both in vitro and endogenously in senescent cells. This is due to a higher level of PKC delta activity as cells age, production of the PKC delta catalytic fragment, and its nuclear localization in senescent but not in low-passage-number cells. The phosphorylation of T160 of SRF by PKC delta in vitro and in vivo led to loss of SRF DNA binding activity. Both the PKC delta inhibitor rottlerin and ectopic expression of a dominant negative form of PKC delta independently restored SRE-dependent transcription and immediate-early gene expression in senescent cells. Modulation of PKC delta activity in vivo with rottlerin or bistratene A altered senescent- and young-cell morphology, respectively. These observations support the idea that the coordinate transcriptional inhibition of several growth-associated genes by PKC delta contributes to the senescent phenotype.

Positional control of cell fate through joint integrin/receptor protein kinase signaling

Cells adhere to the extracellular matrix throughout most of their lifetime. This close, intimate contact with the matrix exerts an extraordinary control on the behavior of cells, determining whether they move or stay put, proliferate or remain quiescent, and even live or die. Attachment to the matrix not only enables cells to respond to soluble growth factors and cytokines but also determines the nature of the response. The integrins are a large family of receptors that attach cells to the matrix, organize their cytoskeleton, and cooperate with receptor protein tyrosine kinases to regulate cell fate. Research on integrin signaling is beginning to explain the complex and specific effects that the extracellular matrix exerts on cells.

Senescent phenotype can be reversed by reduction of caveolin status

Hyporesponsiveness to growth factors is one of the fundamental characteristics of senescent cells. We previously reported that the up-regulation of caveolin attenuates the growth factor response and the subsequent downstream signal cascades in senescent human diploid fibroblasts. Therefore, in the present experiment, we investigated the modulation of caveolin status in senescent cells to determine the effect of caveolin on mitogenic signaling efficiency and cell cycling. We reduced the level of caveolin-1 in senescent human diploid fibroblasts using its antisense oligonucleotides and small interfering RNA, and this resulted in the restoration of normal growth factor responses such as the increased phosphorylation of Erk, the nuclear translocation of p-Erk, and the subsequent activation of p-Elk upon epidermal growth factor stimulation. Moreover, DNA synthesis and the re-entry of senescent cells into cell cycle were resumed upon epidermal growth factor stimulation concomitantly with decreases in p53 and p21. Taken together, we conclude that the loss of mitogenic signaling in senescent cells is strongly related to their elevated levels of caveolin-1 and that the functional recovery of senescent cells at least in the terms of growth factor responsiveness and cell cycle entry might be achieved simply by lowering the caveolin level.

Jun N-terminal kinase activation and upregulation of p53 and p21(WAF1/CIP1) in selenite-induced apoptosis of regenerating liver

To investigate apoptosis induced by selenite in hepatocytes in vivo, rats received a single injection of sodium selenite immediately after partial hepatectomy. Characteristic DNA fragmentation in gel electrophoresis and in situ end-labeling and the increase in caspase-3 activity were observed at 4 h after partial hepatectomy with selenite injection. The activation of Jun N-terminal kinase (JNK) was observed as early as 15 min and increased to about 10-fold the maximal level of the control at 1 and 2 h after partial hepatectomy in selenite-injected rats, while a transient increase was observed at 1 h in the control. Western blot analysis revealed that the c-Jun and the phosphorylated c-Jun protein markedly increased after 30 min and reached a maximal level at 1 and 2 h after partial hepatectomy with selenite injection, although c-Jun and a faint band of the phosphorylated c-Jun were observed after 1 h in the control. The levels of c-jun mRNA and c-Fos protein and mRNA in selenite-injected rats also increased more than in the control. The rise in the p53 protein level after partial hepatectomy with selenite injection was followed by the upregulation of p21(WAF1/CIP1) mRNA and protein expression. These results suggested that selenite induced apoptosis accompanied by the activation of caspase-3 and JNK and the upregulation of c-jun, c-fos, p53 and p21(WAF1/CIP1) at the early stage of liver regeneration.

The heat shock-induced cell cycle arrest is attenuated by weak electromagnetic fields

Stress-induced effects in human acute leukaemia cells (HL-60) were studied by flow cytometry using the fluorescent dye carboxyfluorescein succinimidyl ester which allows the analysis of several successive cell generations for up to 10 days. Asynchronously cycling cells subjected to heat shock (30 min at 41 degrees C) responded in two distinct ways: while one fraction of the cell population (about 15%) re-entered the cell cycle after a short delay, other cells became arrested at different phases of the cell cycle and remained arrested for up to several days and finally underwent apoptosis. Weak electromagnetic fields (60 micro T, 50 Hz) alleviated the heat-induced block and the fraction of arrested cells was significantly smaller.

A novel transcriptional inhibitory element differentially regulates the cyclin D1 gene in senescent cells

Senescent human diploid fibroblasts are unable to initiate DNA synthesis following mitogenic stimulation and adopt a unique gene expression profile distinct from young or quiescent cells. In this study, a novel transcriptional regulatory element was identified in the 5'-untranslated region of the cyclin D1 gene. We show that this element differentially suppresses cyclin D1 expression in young versus senescent fibroblasts. Electrophoretic mobility shift assays revealed abundant complexes forming with young cell nuclear extracts compared with senescent cell nuclear extracts. Binding was maintained in young quiescent cells, showing that loss of this activity was specific to senescent cells and not an effect of cell cycle arrest. Site-directed mutagenesis within this cyclin D1 inhibitory element (DIE) abolished binding activity and selectively increased cyclin D1 promoter activity in young but not in senescent cells. Sequences with homology to the DIE were found in the 5'-untranslated regions of other genes known to be up-regulated during cellular aging, suggesting that protein(s) that bind the DIE might be responsible for the coordinate increase in transcription of many genes during cellular aging. This study provides evidence that loss of transcriptional repressor activity contributes to the up-regulation of cyclin D1, and possibly additional age-regulated genes, during cellular senescence.

Human ING1 proteins differentially regulate histone acetylation

ING1 proteins are nuclear, growth inhibitory, and regulate apoptosis in different experimental systems. Here we show that similar to their yeast homologs, human ING1 proteins interact with proteins associated with histone acetyltransferase (HAT) activity, such as TRRAP, PCAF, CBP, and p300. Human ING1 immunocomplexes contain HAT activity, and overexpression of p33(ING1b), but not of p47(ING1a), induces hyperacetylation of histones H3 and H4, in vitro and in vivo at the single cell level. p47(ING1a) inhibits histone acetylation in vitro and in vivo and binds the histone deacetylase HDAC1. Finally, we present evidence indicating that p33(ING1b) affects the degree of physical association between proliferating cell nuclear antigen (PCNA) and p300, an association that has been proposed to link DNA repair to chromatin remodeling. Together with the finding that human ING1 proteins bind PCNA in a DNA damage-dependent manner, these data suggest that ING1 proteins provide a direct linkage between DNA repair, apoptosis, and chromatin remodeling via multiple HAT.ING1.PCNA protein complexes.

The genomic organization, promoter position and expression profile of the mouse MRG15 gene

MORF4 (mortality factor on chromosome 4) and the novel related MRG (MORF4-related gene) gene family were identified when MORF4 was shown to induce senescence in a subset of tumor cell lines. The gene on chromosome 15 (MRG15) has high similarity to Drosophila MSL3, which is a component of the dosage compensation complex. MRG15 also has a chromodomain and may therefore function as a chromatin remodeling factor in a complex(es) involving a histone acetyltransferase, similar to MSL3. To complement our studies on human MRG15, we cloned and characterized the mouse MRG15 gene. Mouse MRG15 is expressed ubiquitously in adult tissues and at various embryonic stages, and expression in adult testis is higher than in other tissues. MRG15-b, which is an alternatively spliced form of MRG15-a and has a 39-amino-acid insertion in the chromodomain, is also expressed in all mouse tissues examined and localizes to the nucleus of cells. It is possible that MRG15-b may lack the function of the chromodomain because of the additional amino acids and could potentially be the equivalent of the human MORF4 in the mouse. The mouse MRG15 gene is composed of twelve exons and spans over 24 kb DNA. Using luciferase constructs we have determined that there is a functional promoter sequence 1.8 kb upstream of the ATG start codon. This region contains no TATA box but has GC-rich regions, consistent with the ubiquitous expression we have observed.

Down-regulation of receptor-mediated endocytosis is responsible for senescence-associated hyporesponsiveness

Human diploid fibroblasts (HDF) do not divide indefinitely and eventually lead to an arrest of cell division by a process termed cellular or replicative senescence. Irreversible growth arrest of senescent cells is strongly related to the attenuated response to growth factors. Recently, we reported that up-regulation of caveolin in the senescent cells is responsible for the attenuated response to growth factors. Senescent cells did not phosphorylate Erk-1/2 after EGF stimulation, whereas young cells did. In those senescent cells, we found an increased level of caveolin proteins and strong interactions between caveolin-1 and EGFR. When we overexpressed caveolin-1 in young HDF, the activation of Erk-1/2 on EGF stimulation was significantly suppressed. These results suggest that the hyporesponsiveness of senescent fibroblasts to EGF stimulation might be due to the overexpression of caveolin. In addition, the clathrin-dependent endocytosis system plays the more active and dominant role over the caveolae system. Therefore, we monitored the efficiency of clathrin-dependent receptor-mediated endocytosis in the senescent cells in order to elucidate the exact mode of the attenuated response to growth factors in the senescent cells. Using a transferrin-uptake assay and Western blot analysis of endocytosis-related proteins, we found a significant decrease of amphiphysin-1 in human diploid fibroblasts of multipassages. By adjusting the level of amphiphysin, we could modulate the efficiency of receptor-mediated endocytosis either in young or old cells toward growth factors: that is, a dominant negative mutant of amphiphysin-1 blocked the endocytosis in the young cells, while microinjection of the gene resumed its activity in the old cells. Taken together, we conclude that the loss of endocytotic activity of senescent cells is directly related to the down-regulation of amphiphysin-1 and/or up-regulation of caveolins. This opens a new field of functional recovery of the senescent cells simply through adjusting the receptor-mediated endocytosis capacity.

Methotrexate-induced apoptosis in hepatocytes after partial hepatectomy

To investigate apoptosis induced by methotrexate in hepatocytes in vivo, rats received a single injection of methotrexate immediately after partial hepatectomy and apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) and gel electrophoresis of DNA. Characteristic DNA fragmentation was obvious at 2 h and peaked at 4 h after partial hepatectomy with methotrexate injection. TUNEL-positive staining was observed in nuclei and nuclear fragments of hepatocytes in the methotrexate-injected liver (partial hepatectomy with methotrexate), with negligible background staining in the control (partial hepatectomy only) and in the methotrexate-injected normal (normal with methotrexate) rat liver. The involvement of the c-Jun N-terminal kinase (JNK) activator protein 1 (AP-1) pathway and p53 in apoptosis was also examined. The activity of JNK increased at 15 min and peaked at 1 h after partial hepatectomy. This increase was repressed by methotrexate injection. Western blot analysis showed that the levels of c-Fos and c-Jun protein expression, which increased at 1 h after partial hepatectomy, were also reduced by methotrexate. The levels of p53 protein were markedly increased after partial hepatectomy with methotrexate injection. The increase in p53 protein was followed by an up-regulation of p21(WAF1/CIP1) protein at 2 h after partial hepatectomy. These results suggested that the inhibition of the JNK-AP-1 pathway and concurrent up-regulation of p53 and p21(WAF1/CIP1) were involved in hepatocyte apoptosis induced by partial hepatectomy with methotrexate.

Growth factor regulation of uncoupling protein-1 mRNA expression in brown adipocytes

To study the effect of the mitogens epidermal growth factor (EGF), acidic and basic fibroblast growth factors (aFGF and bFGF), and vasopressin on brown adipocyte differentiation, we analyzed the expression of uncoupling protein-1 (UCP-1) mRNA. Quiescent brown preadipocytes express high levels of UCP-1 mRNA in response to triiodothyronine (T3) and norepinephrine (NE). The addition of serum or the mitogenic condition aFGF + vasopressin + NE or EGF + vasopressin + NE decreases UCP-1 mRNA. A second addition of mitogens further decreases UCP-1 mRNA. Treatment with aFGF or bFGF alone increases UCP-1 mRNA, whereas the addition of EGF or vasopressin dramatically reduces UCP-1 mRNA levels. The continuous presence of T3 increases UCP-1 mRNA levels in cells treated with EGF, aFGF, or bFGF. The effect of T3 on the stimulation of DNA synthesis also was tested. T3 inhibits the mitogenic activity of aFGF and bFGF. In conclusion, mitogens like aFGF or bFGF allow brown adipocyte differentiation, whereas EGF and vasopressin inhibit the differentiation process. T3 behaves as an important hormone that regulates both brown adipocyte proliferation and differentiation.

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.

Free radicals in the physiological control of cell function

At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, however, nitric oxide (NO), superoxide anion, and related reactive oxygen species (ROS) play an important role as regulatory mediators in signaling processes. Many of the ROS-mediated responses actually protect the cells against oxidative stress and reestablish "redox homeostasis." Higher organisms, however, have evolved the use of NO and ROS also as signaling molecules for other physiological functions. These include regulation of vascular tone, monitoring of oxygen tension in the control of ventilation and erythropoietin production, and signal transduction from membrane receptors in various physiological processes. NO and ROS are typically generated in these cases by tightly regulated enzymes such as NO synthase (NOS) and NAD(P)H oxidase isoforms, respectively. In a given signaling protein, oxidative attack induces either a loss of function, a gain of function, or a switch to a different function. Excessive amounts of ROS may arise either from excessive stimulation of NAD(P)H oxidases or from less well-regulated sources such as the mitochondrial electron-transport chain. In mitochondria, ROS are generated as undesirable side products of the oxidative energy metabolism. An excessive and/or sustained increase in ROS production has been implicated in the pathogenesis of cancer, diabetes mellitus, atherosclerosis, neurodegenerative diseases, rheumatoid arthritis, ischemia/reperfusion injury, obstructive sleep apnea, and other diseases. In addition, free radicals have been implicated in the mechanism of senescence. That the process of aging may result, at least in part, from radical-mediated oxidative damage was proposed more than 40 years ago by Harman (J Gerontol 11: 298-300, 1956). There is growing evidence that aging involves, in addition, progressive changes in free radical-mediated regulatory processes that result in altered gene expression.

Characterization of the MN/CA 9 promoter proximal region: a role for specificity protein (SP) and activator protein 1 (AP1) factors

MN/CA IX (MN) is a tumour-associated isoenzyme of the carbonic anhydrase family. Previous deletion analysis of the MN promoter established that protected regions (PRs) 1 and 2 are crucial for its transcriptional activity. Computer-assisted searching indicated putative binding sites for activator protein (AP) 2 and specificity protein (SP) 1 transcription factors, plus a CACCC box in PR1 and an AP1 site in PR2. PR1 produced four complexes in electrophoretic mobility-shift assay (EMSA) with HeLa nuclear extracts. Of these, three were completely competed with the SP1 and transforming growth factor-beta retinoblastoma control-element CACCC box (RCE) probes, whereas the AP2 probe competed against the same three complexes partially. Supershift EMSA identified SP1 in the complex 1 and SP3 in the complexes 2 and 4. Point mutations in the SP1 site abrogated the PR1 function, while mutations affecting the overlapping CACCC box/AP2 site in PR1 had minor effect on MN promoter activity. Block-replaced MN promoter mutants that had a consensus binding site (SP1 or AP2) or the RCE in place of PR1 demonstrated the stringent selectivity of the PR1 position as only the SP1 mutant reconstituted the MN promoter activity. The consensus SP1 probe generated the same SP1 and SP3 complexes as PR1 in EMSA; therefore we conclude that SP activity is both necessary and sufficient in the PR1 position. The critical role of AP1 in the PR2 position was confirmed by supershift of the PR2 complex with c-Fos antibody and markedly decreased activity of the construct with a mutated AP1 site. Detailed deletion analysis proved that PR1+PR2 account for 90% of the MN promoter activity, while neither PR1 nor PR2 on their own are sufficient for transactivation. Thus, synergistic co-operation between SP and AP1 factors bound to the adjacent PR1 and PR2, respectively, is necessary for MN transcriptional activity. The PR1+PR2 module also stimulated transcription from a heterologous promoter. The modulation of AP1 activity with PMA stimulated MN expression and activated the MN promoter, whereas inhibition of protein kinase C activity had no effect on MN expression in HeLa cells.

Altered composition and DNA binding activity of the AP-1 transcription factor during the ageing of human fibroblasts

We have investigated the expression of AP-1 transcription factor proteins during the in-vitro ageing of human fibroblasts. The numbers of these cells that are in the cell cycle gradually decreases up to 45 cumulative population doublings (cPD), thereafter the decline is steeper, until almost all cells enter a post-mitotic state by 60 cPD. We observed that a 34 kd junB species began to replace the 44 kd junB species after 41 cPD. This was followed, after 44 cPD, by a loss of fra1 and both junD species. After 49 cPD there was a gradual decline in the levels of fos and jun proteins, but disproportionately, so that the fos/jun protein ratio also declined. Although fos and jun proteins were still clearly present at 60 cPD, utilisation of the AP-1 DNA consensus sequence could not be demonstrated after 54 cPD. These data indicate that significant changes occur in the composition of the AP-1 transcription factor during ageing, but also that alterations in its DNA binding activity may involve other factors.

Phosphatidylinositol 3-kinase regulates proliferation of RAW 264.7 macrophages

Phosphatidylinositol 3-kinase (P13-kinase) is an enzyme that acts as a direct biochemical link between a novel phosphatidylinositol pathway and a number of proteins containing intrinsic or associated kinase activities. Here we demonstrate that wortmannin, P13-kinase inhibitor, decreases the proliferation of RAW 264.7 macrophages and that another structurally unrelated inhibitor of P13-kinase, LY294002. also inhibits the proliferation. These results indicate a possible involvement of P13-kinase in RAW 264.7 macrophages growth regulation. Wortmannin stimulation of RAW 264.7 macrophages is followed by sustained expression of the mRNA of c-fos and a transient expression of the mRNA of c-jun. We also show that the wortmannin and LY294002 induce a cell cycle arrest in asynchronously growing cells leading to an inhibition of cell proliferation after 12 h of treatment. In addition, wortmannin or LY294002 inhibited the phorbol 12-myristate 13-acetate-induced macrophages proliferation potently. These results suggest that P13-kinase plays an important role in growth regulation of RAW 264.7 macrophages and that protein kinase C is a down stream effector of P13-kinase.

Prolonged Jun N-terminal kinase (JNK) activation and the upregulation of p53 and p21(WAF1/CIP1) preceded apoptosis in hepatocytes after partial hepatectomy and cisplatin

Cisplatin induced apoptosis in regenerating liver after partial hepatectomy (PH). Apoptosis was determined by in situ end-labeling and gel electrophoresis of DNA fragmentation. Characteristic DNA fragmentation was obvious at 4 h and peaked at 8 h after PH. The activity of Jun N-terminal kinase (JNK) transiently increased at 1 h after PH. However, in cisplatin-injected rats, the JNK activity increased at 30 min and the increased level was maintained up to 4 h after PH. The in vivo activation of JNK was confirmed by the increased level of the phosphorylated c-Jun protein. Western blot analysis showed that the phosphorylated c-Jun level increased at 1 h and reached more than 30-fold the control level at 2 h after PH with cisplatin. The c-jun mRNA levels also markedly increased at 1 h after PH with cisplatin. The protein level of p53 increased after 1 h on cisplatin injection, but no significant change in the mRNA level was observed. The rise in the p53 protein level was followed by the upregulation of p21(WAF1/CIP1) mRNA and protein levels. These results suggested that the enhanced and sustained JNK activation and the upregulation of p53 and p21(WAF1/CIP1) were involved in hepatocyte apoptosis induced by PH with cisplatin.

Gene profile of replicative senescence is different from progeria or elderly donor

In vitro cellular senescence of human diploid fibroblast has been a good model for aging research, which shows similar phenotypes to in vivo aging. Gene expression profiling would provide an insight to understand the mechanism of senescence. Using cDNA microarray containing 384 known genes, we compared the expression profiles of three different types of aging models: replicative senescence, fibroblasts from progeria or from elderly donor. Although all of them showed senescence phenotypes, distinct sets of genes were altered in each group. Pairwise plots or cluster analysis of activation fold of gene expression revealed closer relationships between fibroblasts from progeria or from old individual, but not between replicative senescence fibroblasts and either models. Differential expression pattern of several genes were confirmed by RT-PCR. We suggest that the replicative senescence model might behave differently to other types of aging models due to the distinct gene expression.

Loss of functional caveolae during senescence of human fibroblasts

Primary human fibroblasts have a finite replicative lifespan in culture that culminates in a unique state of growth arrest, termed senescence that is accompanied by distinct morphological and biochemical alterations. Senescent cell responses to extracellular stimuli are believed to be altered at a point after receptors are bound by ligand, leading to improper integration of the signals which initiate DNA replication. In this study we demonstrate that one of the key organizing membrane microdomains for receptor signaling, caveolae, are absent in senescent cells. A comparison of young and senescent cells indicated that senescent cells contained a higher total amount of caveolins 1 and 2 but had significantly less of both proteins in the caveolar fraction. Additionally, caveolar fractions from senescent cells completely lacked the tyrosine-kinase activity associated with functional caveolae. Furthermore, old cells had little caveolar protein exposed to the outer plasma membrane as estimated by using an in vivo biotinylation assay and no detectable caveolin 1 on the cell surface when processed for immunofluoresence and confocal microscopy. Together, these data suggest that a fundamental loss of signal integration at the plasma membrane of senescent cells is due to the loss of signaling competent caveolae.

The mammalian Jun proteins: redundancy and specificity

The AP-1 transcription factor is composed of a mixture of homo- and hetero-dimers formed between Jun and Fos proteins. The different Jun and Fos family members vary significantly in their relative abundance and their interactions with additional proteins generating a complex network of transcriptional regulators. Thus, the functional activity of AP-1 in any given cell depends on the relative amount of specific Jun/Fos proteins which are expressed, as well as other potential interacting proteins. This diversity of AP-1 components has complicated our understanding of AP-1 function and resulted in a paucity of information about the precise role of individual AP-1 members in distinct cellular processes. We shall discuss recent studies which suggest that different Jun and Fos family members may have both opposite and overlapping functions in cellular proliferation and cell fate.

Effects of prolonged wakefulness on c-fos and AP1 activity in young and old rats

Recent studies have demonstrated that the immediate-early gene c-fos is induced in neuronal populations responsible for specific sleep-wake states. The induction of this gene may be functionally relevant to sleep homeostasis since without the gene mice (c-fos null) take longer to fall asleep and have a selective reduction in slow-wave sleep. This suggests that a build-up of c-fos during wakefulness increases the drive to sleep and lack of c-fos is associated with reduced sleep. Sleep also has an effect on c-Fos serving to eliminate the protein rapidly. Waxing and waning of transcription factors such as c-Fos may influence slow, oscillating events such as sleep and wakefulness. To further examine what role c-Fos may play in regulating sleep, the present study examined the effects of prolonged wakefulness on c-Fos and AP-1 activity in young (3.5 months old) and old (21.5 months old) Sprague--Dawley rats. Previously we found that old rats slept less even after prolonged wakefulness, and other investigators have found that aging is also associated with a decline in c-Fos. In the present study, we reasoned that prolonged wakefulness would also fail to increase c-Fos in old versus young rats. The baseline levels of c-Fos and AP-1 activity were not different between young and old rats. However, in response to 6 or 12 h of prolonged wakefulness, old rats demonstrated significantly less c-Fos and AP-1 activity compared to young rats. These findings suggest that in old rats the mechanism responsible for c-Fos induction in response to wakefulness is deficient. Such a decline at the molecular level could contribute to the decline in sleep that typically occurs with age.

Attenuation of EGF signaling in senescent cells by caveolin

One of the characteristics of senescent cells is unresponsiveness to external stimuli like EGF. Although they have a normal level of receptors and downstream signaling molecules, EGF cannot induce the activation of Erk kinases and DNA synthesis in senescent cells as much as in young cells. Caveolin proteins directly interact with signaling molecules including EGF receptor and suppress the activation of EGFR upon EGF stimulation. We found that Erk activation after EGF stimulation in senescent human diploid fibroblasts was down-regulated. Those senescent cells showed an increased level of three isoforms of caveolin proteins. This change seems to lie in transcriptional control in senescent cells. We also demonstrated up-regulated caveolin proteins were co-localized with EGFR proteins in detergent-insoluble fractions. From these results, we suggest that the up-regulated expression of caveolin might explain the unresponsiveness of senescent fibroblasts to EGF stimulation.

Organ-specific distribution of AP-1 in AP-1 luciferase transgenic mice during the maturation process

Activator protein-1 (AP-1), a dimeric complex consisting of proteins encoded by the jun and fos gene families, is a transcription factor induced by a variety of signals including those eliciting proliferation, differentiation, and neoplastic transformation. Although AP-1 has been widely studied in the last decade, physiological levels of AP-1 in different tissues are unclear. In the present study, we analyzed AP-1 activity in several organs (liver, kidney, brain, lung, spleen, heart, skin) of AP-1-luciferase transgenic mice of various ages. Results of these studies indicate that the level of AP-1 in young mice is much higher than that in older mice, and, second, that the skin contains considerably higher levels of AP-1 than other organs. The level of phosphorylated extracellular signal-regulated protein kinase (ERK) in skin was higher in 1- and 2-day-old mice than in mice of other ages. In addition, phosphorylated p38 kinase was high in 2-day-old and 1-wk-old mice, but phosphorylated c-Jun NH(2)-terminal kinase was not detected at any age. AP-1 activity and level of phosphorylated ERKs declined with maturation. These results imply that AP-1 activity mediated through an ERKs-dependent pathway may be involved in skin development.