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Mitochondrial autophagy (or mitophagy) is essential for mitochondrial quality control, which is critical for cellular and organismal health by attenuating reactive oxygen species generation and maintaining bioenergy homeostasis. Previously, we showed that mitophagy is activated in human cells through SIRT1 activation upon treatment of nicotinamide (NAM). Further, mitochondria are maintained as short fragments in the treated cells. In the current study, molecular pathways for NAM-induced mitochondrial fragmentation were sought. NAM treatment induced mitochondrial fission, at least in part by activating dynamin-1-like protein (Drp1), and this was through attenuation of the inhibitory phosphorylation at serine 637 (S637) of Drp1. This Drp1 hypo-phosphorylation was attributed to SIRT1-mediated activation of AMP-activated protein kinase (AMPK), which in turn induced a decrease in cellular levels of cyclic AMP (cAMP) and protein kinase A (PKA) activity, a kinase targeting S637 of Drp1. Furthermore, in NAM-treated cells, cytosolic Ca2+ was highly maintained, and, as a consequence, activity of calcineurin, a Drp1-dephosphorylating phosphatase, is expected to be elevated. These results suggest that NAD+-mediated SIRT1 activation facilitates mitochondrial fission through activation of Drp1 by suppressing its phosphorylation and accelerating its dephosphorylation. Additionally, it is suggested that there is a cycle of mitochondrial fragmentation and cytosolic Ca2+-mediated Drp1 dephosphorylation that may drive sustained mitochondrial fragmentation.

Mitochondrial autophagy (or mitophagy) is essential for mitochondrial quality control, which is critical for cellular and organismal health by attenuating reactive oxygen species generation and maintaining bioenergy homeostasis. Previously, we showed that mitophagy is activated in human cells through SIRT1 activation upon treatment of nicotinamide (NAM). Further, mitochondria are maintained as short fragments in the treated cells. In the current study, molecular pathways for NAM-induced mitochondrial fragmentation were sought. NAM treatment induced mitochondrial fission, at least in part by activating dynamin-1-like protein (Drp1), and this was through attenuation of the inhibitory phosphorylation at serine 637 (S637) of Drp1. This Drp1 hypo-phosphorylation was attributed to SIRT1-mediated activation of AMP-activated protein kinase (AMPK), which in turn induced a decrease in cellular levels of cyclic AMP (cAMP) and protein kinase A (PKA) activity, a kinase targeting S637 of Drp1. Furthermore, in NAM-treated cells, cytosolic Ca2+ was highly maintained; and, as a consequence, activity of calcineurin, a Drp1-dephosphorylating phosphatase, is expected to be elevated. These results suggest that NAD+-mediated SIRT1 activation facilitates mitochondrial fission through activation of Drp1 by suppressing its phosphorylation and accelerating its dephosphorylation. Additionally, it is suggested that there is a cycle of mitochondrial fragmentation and cytosolic Ca2+-mediated Drp1 dephosphorylation that may drive sustained mitochondrial fragmentation.

Under glucose deprivation, cells heavily mobilize oxidative phosphorylation to maintain energy homeostasis. This leads to the generation of high levels of ATP, as well as reactive oxygen species (ROS), from mitochondria. In nutrient starvation, autophagy is activated, likely to facilitate resource recycling, but recent studies suggest that autophagy flux is inhibited in cells undergoing glucose deprivation. In this study, we analyzed the status of autophagic flux in glucose-deprived human fibroblasts. Although lysosomes increased in quantity due in part to an increase of biogenesis, a large population of them suffered low acidity in the glucose-deprived cells. Autophagosomes also accumulated due to poor autolysis in these cells. A treatment of antioxidants not only restored lysosomal acidity but also released the flux blockade. The inhibition of ataxia telangiectasia mutated (ATM) serine/threonine kinase, which is activated by ROS, also attenuated the impairment of lysosomal acidity and autophagic flux, suggesting an effect of ROS that might be mediated through ATM activation. In addition, the activity of extracellular signal-regulated kinase (Erk) increased upon glucose deprivation, but this was also compromised by a treatment of antioxidants. Furthermore, the Erk inhibitor treatment also alleviated the failure in lysosomal acidity and autophagic flux. These together indicate that, upon glucose deprivation, cells undergo a failure of autophagy flux through an impairment of lysosomal acidity and that a high-level ROS-induced activation of Erk and ATM is involved in this impairment.

Nicotinamide (NAM) is a form of vitamin B3 that, when administered at near-gram doses, has been shown or suggested to be therapeutically effective against many diseases and conditions. The target conditions are incredibly diverse ranging from skin disorders such as bullous pemphigoid to schizophrenia and depression and even AIDS. Similar diversity is expected for the underlying mechanisms. In a large portion of the conditions, NAM conversion to nicotinamide adenine dinucleotide (NAD+) may be a major factor in its efficacy. The augmentation of cellular NAD+ level not only modulates mitochondrial production of ATP and superoxide, but also activates many enzymes. Activated sirtuin proteins, a family of NAD+-dependent deacetylases, play important roles in many of NAM’s effects such as an increase in mitochondrial quality and cell viability countering neuronal damages and metabolic diseases. Meanwhile, certain observed effects are mediated by NAM itself. However, our understanding on the mechanisms of NAM’s effects is limited to those involving certain key proteins and may even be inaccurate in some proposed cases. This review details the conditions that NAM has been shown to or is expected to effectively treat in humans and animals and evaluates the proposed underlying molecular mechanisms, with the intention of promoting wider, safe therapeutic application of NAM. NAM, by itself or through altering metabolic balance of NAD+ and tryptophan, modulates mitochondrial function and activities of many molecules and thereby positively affects cell viability and metabolic functions. And, NAM administration appears to be quite safe with limited possibility of side effects which are related to NAM’s metabolites.

The quality of mitochondria is a key determinant of mitochondrial ATP production and reactive oxygen species generation; therefore, it plays critical roles in energy homeostasis and cellular health. Mitochondrial quality is governed by mitochondrial turnover, which involves autophagic removal of old mitochondria and biogenesis of new ones. Both activities are critically modulated by sirtuin proteins, in particular, SIRT1 and SIRT3. These proteins activate mitophagy and mitochondrial biogenesis through deacetylation-mediated activation of factors participating in key steps of autophagy and mitochondrial protein expression. They also control other factors involved in maintenance of mitochondrial integrity and in damage prevention. At the same time, the activities and protein levels of SIRT1 and SIRT3 decline during aging, contributing to mitochondrial dysfunction associated with tissue aging and many degenerative diseases. However, recent studies suggest that the activity of the sirtuin proteins can be elevated through modulation of nicotinamide adenine dinucleotide (NAD⁺) and in physiological settings. An understanding of the underlying molecular pathways is actively sought and practical strategies are proposed based on basic research; nevertheless, their applicability at the clinical and subclinical levels could be better recognized and understood in the field of medicine. To this end, this review discusses the recent understanding of the biochemistry underlying the NAD+-redox mediated modulation of cellular sirtuin activity.

The current statistic data on the open access (OA) journals and institutional repositories show some successes and increased awareness on OA in Asian countries. There are several concerns, however, in regards to the access and use of articles by researchers together with the continued increase of libraries’ expenditure for journals. In the present article we introduce five solutions in the global and local perspectives. OA2020 initiative is a global initiative to transform existing journals to OA. Although the practical process of OA2020 remains a challenge, the transformation will increase OA without significant increase of journals and budgets for publishing. The promotion of the local and Asian journals is the second big challenge. Because these local or Asian journals still have important roles in the local research community, they should keep current publishing model of OA at the low cost but with high quality and the better access. The restructuring of the current library budget is the third challenge. The budget for periodicals should be reduced and the saved budget can be used to pay articles processing charge for OA and for purchasing monographs. The fourth important issue is ‘the digital blind spot at the young unemployed and retired elderly’. These groups of poorly supported and potentially important researchers have to be considered as a priority issue to the policies on OA and scholarly knowledge. Lastly, we believe there should be different needs for other activities: optimization of the searchable database, governmental policy on open science and international cooperation on OA.

Nicotinamide (NAM) plays essential roles in physiology through facilitating NAD+ redox homeostasis. Importantly, at high doses, it protects cells under oxidative stresses, and has shown therapeutic effectiveness in a variety of disease conditions. In our previous studies, NAM lowered reactive oxygen species (ROS) levels and extended cellular life span in primary human cells. In the treated cells, levels of NAD+/NADH and SIRT1 activity increased, while mitochondrial content decreased through autophagy activation. The remaining mitochondria were marked with low superoxide levels and high membrane potentials (Δψm); we posited that the treatment of NAM induced an activation of mitophagy that is selective for depolarized mitochondria, which produce high levels of ROS. However, evidence for the selective mitophagy that is mediated by SIRT1 has never been provided. This study sought to explain the mechanisms by which NAM lowers ROS levels and increases Δψm. Our results showed that NAM and SIRT1 activation exert quite different effects on mitochondrial physiology. Furthermore, the changes in ROS and Δψm were not found to be mediated through autophagy or SIRT activation. Rather, NAM suppressed superoxide generation via a direct reduction of electron transport, and increased Δψm via suppression of mitochondrial permeability transition pore formation. Our results dissected the effects of cellular NAD+ redox modulation, and emphasized the importance of the NAD+/NADH ratio in the mitochondria as well as the cytosol in maintaining mitochondrial quality.

Humanities and social sciences studies in Korea have remarkably low rates of co-authorship between professors and students. We chose a bibliometrics-based approach to characterize changes in the ratio of joint authorship between professors and students. Articles classified in the humanities and social sciences sectors that were published in journals registered in the Korean Citation Index during 2 phases over a 10-year period—2004 to 2006 (phase 1) and 2011 to 2013 (phase 2)—were used as the main source for the analysis. The study results can be summarized as follows: first, the overall number of co-authored articles drastically increased from phase 1 to phase 2; the percentage of co-authorship articles increased from 34.8% to 47.7%, and the percentage of co-authorship between students and professors rose from 9.9% to 20.7%. This trend was particularly noticeable in the social sciences, such as accounting, social welfare, and economics/business administration. Second, papers written by scholars from Seoul National University, Yonsei University, and Korea University were often published in high-impact factor journals. Among those articles, the rate of professor-student co-authorship increased by 21.6% for 7 years. Third, the increase in professor-student co-authored articles published in high- impact factor journals was even sharper. These findings indicate that perceptions of professor-student co-authorship have changed in the humanities and social sciences. In the near future, positive perceptions toward joint research and joint authorship between professors and students are expected to become more widespread.

Nicotinamide (NAM) is a dietary source of nicotinamide adenine dinucleotide (NAD+). Gram doses of NAM have long been used to treat diverse disease conditions, such as inflammatory diseases and dementia, in humans and animal models. Recent studies have elucidated some of the mechanisms underlying the therapeutic effectiveness of NAM; these appear to be predominantly mediated by its conversion to NAD+. By increasing the amount of NAD+ and the NAD+/NADH ratio, NAM administration alters mitochondrial physiology and ROS generation. It also modulates the activity of many proteins. For example, SIRT1 activation plays important roles by exerting cytoprotection, antiinflammation, and antimetabolic syndrome effects. However, SIRT1 activity in cells can be either positively or negatively regulated by NAM treatment depending on various conditions. In this chapter current understandings of the biochemistry and function of NAM and NAD+ are presented with the aim of promoting wider and safer applications of NAM as a pharmaceutical.

During T cell activation, mitochondrial content increases to meet the high energy demand of rapid cell proliferation. With this increase, the level of reactive oxygen species (ROS) also increases and causes the rapid apoptotic death of activated cells, thereby facilitating T cell homeostasis. Nicotinamide (NAM) has previously been shown to enhance mitochondria quality and extend the replicative life span of human fibroblasts. In this study, we examined the effect of NAM on CD8(+) T cell activation. NAM treatment attenuated the increase of mitochondrial content and ROS in T cells activated by CD3/CD28 antibodies. This was accompanied by an accelerated and higher-level clonal expansion resulting from attenuated apoptotic death but not increased division of the activated cells. Attenuation of ROS-triggered pro-apoptotic events and upregulation of Bcl-2 expression appeared to be involved. Although cells activated in the presence of NAM exhibited compromised cytokine gene expression, our results suggest a means to augment the size of T cell expansion during activation without consuming their limited replicative potential.

Nicotinamide (NAM) at doses far above those recommended for vitamins is suggested to be effective against a wide spectrum of diseases and conditions, including neurological dysfunctions, depression and other psychological disorders, and inflammatory diseases. Recent increases in public awareness on possible pro-longevity effects of nicotinamide adenine dinucleotide (NAD+) precursors have caused further growth of NAM consumption not only for clinical treatments, but also as a dietary supplement, raising concerns on the safety of its long-term use. However, possible adverse effects and their mechanisms are poorly understood. High-level NAM administration can exert negative effects through multiple routes. For example, NAM by itself inhibits poly(ADP-ribose) polymerases (PARPs), which protect genome integrity. Elevation of the NAD+ pool alters cellular energy metabolism. Meanwhile, high-level NAM alters cellular methyl metabolism and affects methylation of DNA and proteins, leading to changes in cellular transcriptome and proteome. Also, methyl metabolites of NAM, namely methylnicotinamide, are predicted to play roles in certain diseases and conditions. In this review, a collective literature search was performed to provide a comprehensive list of possible adverse effects of NAM and to provide understanding of their underlying mechanisms and assessment of the raised safety concerns. Our review assures safety in current usage level of NAM, but also finds potential risks for epigenetic alterations associated with chronic use of NAM at high doses. It also suggests directions of the future studies to ensure safer application of NAM.

Nicotinamide (NAM) has been shown to suppress reactive oxygen species (ROS) production in primary human fibroblasts, thereby extending their replicative lifespan when added to the medium during long-term cultivation. Based on this finding, NAM is hypothesized to affect cellular senescence progression by keeping ROS accumulation low. In the current study, we asked whether NAM is indeed able to reduce ROS levels and senescence phenotypes in cells undergoing senescence progression and those already in senescence. We employed two different cellular models: MCF-7 cells undergoing senescence progression and human fibroblasts in a state of replicative senescence. In both models, NAM treatment substantially decreased ROS levels. In addition, NAM attenuated the expression of the assessed senescence phenotypes, excluding irreversible growth arrest. N-acetyl cysteine, a potent ROS scavenger, did not have comparable effects in the tested cell types. These data show that NAM has potent antioxidative as well as anti-senescent effects. Moreover, these findings suggest that NAM can reduce cellular deterioration caused by oxidative damage in postmitotic cells in vivo.

Modernization projects are actively underway to replace conventional logistics equipment for the development of the 21st century logistics management system. The modernized logistics system is expected to expand to each troops on future. In this paper, we deal with simulation of automated logistics center to analyse the current system. Especially, the alternative to the same scale is designed based on needs of military distinctiveness. As a result, it can be effectively compared the current system. The result obtained in this design process is comprehensively analyzed by the AHP(Analytic Hierarchy Process). The proposed method in this study is allowed to cost-effectively evaluate current and future automated logistics center. And, that is expected to contribute to modernization projects of the military logistics system. Key Words : AHP(Analytic Hierarchy Process), AS/RS(Automated Storage & Retrieval System), Automated logistics center, Simulation * Corresponding Author : Seung-Won Baik(Korea Military Academy)Tel: +82-2-2197-2951 email: gem853@kma.ac.krReceived October 8, 2013 Revised (1st November 28, 2013, 2nd December 5, 2013) Accepted February 5, 2013

Nicotinamide (NAM), a form of vitamin B3, plays essential roles in cell physiology through facilitating NAD+ redox homeostasis and providing NAD+ as a substrate to a class of enzymes that catalyze non-redox reactions. These non-redox enzymes include the sirtuin family proteins which deacetylate target proteins while cleaving NAD+ to yield NAM. Since the finding that NAM exerts feedback inhibition to the sirtuin reactions, NAM has been widely used as an inhibitor in the studies where SIRT1, a key member of sirtuins, may have a role in certain cell physiology. However, once administered to cells, NAM is rapidly converted to NAD+ and, therefore, the cellular concentration of NAM decreases rapidly while that of NAD+ increases. The result would be an inhibition of SIRT1 for a limited duration, followed by an increase in the activity. This possibility raises a concern on the validity of the interpretation of the results in the studies that use NAM as a SIRT1 inhibitor. To understand better the effects of cellular administration of NAM, we reviewed published literature in which treatment with NAM was used to inhibit SIRT1 and found that the expected inhibitory effect of NAM was either unreliable or muted in many cases. In addition, studies demonstrated NAM administration stimulates SIRT1 activity and improves the functions of cells and organs. To determine if NAM administration can generate conditions in cells and tissues that are stimulatory to SIRT1, the changes in the cellular levels of NAM and NAD+ reported in the literature were examined and the factors that are involved in the availability of NAD+ to SIRT1 were evaluated. We conclude that NAM treatment can hypothetically be stimulatory to SIRT1.

Cell therapies using mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) are increasing in regenerative medicine, with applications to a growing number of aging-associated dysfunctions and degenerations. For successful therapies, a certain mass of cells is needed, requiring extensive ex vivo expansion of the cells. However, the proliferation of both MSCs and EPCs is limited as a result of telomere shortening-induced senescence. As cells approach senescence, their proliferation slows down and differentiation potential decreases. Therefore, ways to delay senescence and extend the replicative lifespan these cells are needed. Certain proteins and pathways play key roles in determining the replicative lifespan by regulating ROS generation, damage accumulation, or telomere shortening. And, their agonists and gene activators exert positive effects on lifespan. In many of the treatments, importantly, the lifespan is extended with the retention of differentiation potential. Furthermore, certain culture conditions, including the use of specific atmospheric conditions and culture substrates, exert positive effects on not only the proliferation rate, but also the extent of proliferation and differentiation potential as well as lineage determination. These strategies and known underlying mechanisms are introduced in this review, with an evaluation of their pros and cons in order to facilitate safe and effective MSC expansion ex vivo.

Transforming growth factor β1 (TGF β1) induces Mv1Lu cell senescence by persistently producing mitochondrial reactive oxygen species (ROS) through decreased complex IV activity. Here, we investigated the molecular mechanism underlying the effect of TGF β1 on mitochondrial complex IV activity. TGF β1 progressively phosphorylated the negative regulatory sites of both glycogen synthase kinase 3 (GSK3) α and β, corresponding well to the intracellular ROS generation profile. Pre-treatment of N -acetyl cysteine, an antioxidant, did not alter this GSK3 phosphorylation (inactivation), whereas pharmacological inhibition of GSK3 by SB415286 significantly increased mitochondrial ROS, implying that GSK3 phosphorylation is an upstream event of the ROS generation. GSK3 inhibition by SB415286 decreased complex IV activity and cellular O 2 consumption rate and eventually induced senescence of Mv1Lu cell. Similar results were obtained with siRNA-mediated knockdown of GSK3. Moreover, we found that GSK3 not only exists in cytosol but also in mitochondria of Mv1Lu cell and the mitochondrial GSK3 binds complex IV subunit 6b which has no electron carrier and is topologically located in the mitochondrial intermembrane space. Involvement of subunit 6b in controlling complex IV activity and overall respiration rate was proved with siRNA-mediated knockdown of subunit 6b. Finally, TGF β1 treatment decreased the binding of the subunit 6b to GSK3 and subunit 6b phosphorylation. Taken together, our results suggest that GSK3 inactivation is importantly involved in TGF β1-induced complex IV defects through decreasing phosphorylation of the subunit 6b, thereby contributing to senescence-associated mitochondrial ROS generation.

Active autophagy coupled with rapid mitochondrial fusion and fission constitutes an important mitochondrial quality control mechanism and is critical to cellular health. In our previous studies, we found that exposure of cells to nicotinamide causes a decrease in mitochondrial content and an increase in mitochondrial membrane potential (MMP) by activating autophagy and inducing mitochondrial fragmentation. Here, we present evidence to show that the effect of nicotinamide is mediated through an increase of the [NAD+]/[NADH] ratio and the activation of SIRT1, an NAD+-dependent deacetylase that plays a role in autophagy flux. The [NAD+]/[NADH] ratio was inversely correlated with the mitochondrial content, and an increase in the ratio by the mobilization of the malate-aspartate shuttle resulted in autophagy activation and mitochondrial transformation from lengthy filaments to short dots. Furthermore, treatment of cells with SIRT1 activators, fisetin or SRT1720, induced similar changes in the mitochondrial content. Importantly, the activators induced mitochondrial fragmentation only when SIRT1 expression was intact. Meanwhile, MMP did not increase when the cells were treated with the activators, suggesting that the change in MMP is not induced by the mitochondrial turnover per se and that elevation of the [NAD+]/[NADH] ratio may activate additional mechanisms that cause MMP augmentation. Together, our results indicate that a metabolic state resulting in an elevated [NAD+]/[NADH] ratio can modulate mitochondrial quantity and quality via pathways that may include SIRT1-mediated mitochondrial autophagy.

Cellular senescence is characterized by cell-cycle arrest accompanied by various cell biological changes. Although these changes have been heavily relied on as senescence markers in numerous studies on senescence and its intervention, their underlying mechanisms and relationship to each other are poorly understood. Furthermore, the depth and the reversibility of those changes have not been addressed previously. Using flow cytometry coupled with confocal microscopy and Western blotting, we quantified various senescence-associated cellular changes and determined their time course profiles in MCF-7 cells undergoing DNA damage-induced senescence. The examined properties changed with several different kinetics patterns. Autofluorescence, side scattering, and the mitochondria content increased progressively and linearly. Cell volume, lysosome content, and reactive oxygen species (ROS) level increased abruptly at an early stage. Meanwhile, senescence associated β-galactosidase activity increased after a lag of a few days. In addition, during the senescence progression, lysosomes exhibited a loss of integrity, which may have been associated with the accumulation of ROS. The finding that various senescence phenotypes matured at different rates with different lag times suggests multiple independent mechanisms controlling the expression of senescence phenotypes. This type of kinetics study would promote the understanding of how cells become fully senescent and facilitate the screening of methods that intervene in cellular senescence.

Human sirtuin 1 (SIRT1) is a NAD(+)-dependent deacetylase that participates in cell death/survival, senescence and metabolism. Although its substrates are well characterized, no direct regulators have been defined. Here, we show that SIRT1 associates with SKI-interacting protein (SKIP) and modulates its activity as a coactivator of retinoic acid receptor (RAR). Binding assays indicated that SKIP interacts with RAR in a RA-dependent manner, through a region that overlaps the binding site for SIRT1. SKIP augmented the transcriptional activation activity of RAR by cooperating with SRC-1, and SIRT1 suppressed SKIP/SRC-1-enhanced RAR transactivation activity. The suppression was dependent on the deacetylase activity of SIRT1 and was enhanced by a SIRT1 activator, resveratrol. In contrast, the suppression was relieved by SIRT1 knockdown, overexpression of SKIP and treatment with a SIRT1 inhibitor, splitomicin. Upon SKIP overexpression, the recruitment of SIRT1 to the endogenous RARbeta2 promoter was severely impaired, and SKIP was recruited to the promoter instead. Finally, resveratrol treatment inhibited RA-induced neuronal differentiation of P19 cells, accompanied by reductions in the neuronal marker nestin and a RAR target gene, RARbeta2. This inhibition was relieved by either knockdown of SIRT1 or overexpression of SKIP. These data suggest that SIRT1 and SKIP play reciprocal roles in the regulation of RAR activity, which is implicated in the regulation of RA-induced neuronal differentiation of P19 cells.

Nicotinamide (NAM) treatment causes a decrease in mitochondrial respiration and reactive oxygen species production in primary human fibroblasts and extends their replicative lifespan. In the current study, it is reported that NAM treatment induces a decrease in mitochondrial mass and an increase in membrane potential (DeltaPsim) by accelerating autophagic degradation of mitochondria. In the NAM-treated cells, the level of LC3-II as well as the number of LC3 puncta and lysosomes co-localizing with mitochondria substantially increased. Furthermore, in the NAM-treated cells, the levels of Fis1, Drp1, and Mfn1, proteins that regulate mitochondrial fission and fusion, increased and mitochondria experienced dramatic changes in structure from filaments to dots or rings. This structural change is required for the decrease of mitochondrial mass indicating that NAM accelerates mitochondrial autophagy, at least in part, by inducing mitochondrial fragmentation. The decrease in mitochondria mass was attenuated by treatment with cyclosporine A, which prevents the loss of mitochondrial membrane potential by blocking the mitochondrial permeability transition, suggesting autophagic degradation selective for mitochondria with low DeltaPsim. All these changes were accompanied by and dependent on an increase in the levels of GAPDH, and are blocked by inhibition of the cellular conversion of NAM to NAD(+). Taken together with our previous findings, these results suggest that up-regulation of GAPDH activity may prolong healthy lifespan of human cells through autophagy-mediated mitochondria quality maintenance.

Various intracellular organelles, such as lysosomes, mitochondria, nuclei, and cytoskeletons, change during replicative senescence, but the utility of these changes as general markers of senescence and their significance with respect to functional alterations have not been comprehensively reviewed. Furthermore, the relevance of these alterations to cellular and functional changes in aging animals is poorly understood. In this paper, we review the studies that report these senescence-associated changes in various aging cells and their underlying mechanisms. Changes associated with lysosomes and mitochondria are found not only in cells undergoing replicative or induced senescence but also in postmitotic cells isolated from aged organisms. In contrast, other changes occur mainly in cells undergoing in vitro senescence. Comparison of age-related changes and their underlying mechanisms in in vitro senescent cells and aged postmitotic cells would reveal the relevance of replicative senescence to the physiological processes occurring in postmitotic cells as individuals age.

Normal somatic cells proliferate for a limited number of doublings in culture and then enter an irreversible growth-arrest state called replicative senescence. Replicative senescence has been believed a reason for the limited cellular turnover and deterioration of tissue function in aged animals. However, there is no experimental evidence supporting this assumption. Furthermore, cells from aged person have been poorly characterized with an exception of the cases of T cells. In this study, we examined cell biological changes occurring in replicative senescence of fibroblast strains originated from a new-born (NHF-NB) and a 87 year old man (NHF-87). NHF-87 (and the cells from a 75-year old) proliferated to smaller population doublings and with longer doubling times than NHF-NB did. At early passages, NHF-87 exhibited a low senescence-associated (SA ) activity and lipofuscin level, typical markers for cellular senescence. Furthermore, they maintained low levels of lysosome and reactive oxygen species (ROS). All of these levels increased dramatically in the late passage NHF-87 quite similarly as those in the late passaged NHF-NB did. These results indicate that most cells originated from the aged maintain a phenotype of the cells originated from new-born donors and undergo replicative senescence with the same kinetics as that of the cells from new-born. It is also indicated that not SA activity but cell proliferation rate may be qualified as a biomarker for cells aged in vivo.

We found that an ongoing application of nicotinamide to normal human fibroblasts not only attenuated expression of the aging phenotype but also increased their replicative lifespan, causing a greater than 1.6-fold increase in the number of population doublings. Although nicotinamide by itself does not act as an antioxidant, the cells cultured in the presence of nicotinamide exhibited reduced levels of reactive oxygen species (ROS) and oxidative damage products associated with cellular senescence, and a decelerated telomere shortening rate without a detectable increase in telomerase activity. Furthermore, in the treated cells growing beyond the original Hayflick limit, the levels of p53, p21WAF1, and phospho-Rb proteins were similar to those in actively proliferating cells. The nicotinamide treatment caused a decrease in ATP levels, which was stably maintained until the delayed senescence point. Nicotinamide-treated cells also maintained high mitochondrial membrane potential but a lower respiration rate and superoxide anion level. Taken together, in contrast to its demonstrated pro-aging effect in yeast, nicotinamide extends the lifespan of human fibroblasts, possibly through reduction in mitochondrial activity and ROS production.

2-Deoxyglucose (2-DG), a non-metabolizable glucose analogue, blocks glycolysis and inhibits protein glycosylation. It has been tested in multiple studies for possible application as an anticancer or antiviral therapeutic. The inhibitory effect of 2-DG on ATP generation made it a good candidate molecule as a calorie restriction mimetic as well. Furthermore, 2-DG has been utilized in numerous studies to simulate a condition of glucose starvation. Because 2-DG disrupts glucose metabolism, protein glycosylation, and ER quality control at the same time, a cellular or pathologic outcome could be easily misinterpreted without clear understanding of 2-DG's effect on each of these aspects. However, the effect of 2-DG on protein glycosylation has rarely been investigated. A recent study suggested that 2-DG causes hyperGlcNAcylation of proteins, while low glucose supply causes hypoGlcNAcylation. In certain aspects of cellular physiology, this difference could be disregarded, but in others, this may possibly cause totally different outcomes.

Objective. E6 and E7 oncoproteins of high risk type HPV modulate activities of host components in cell cycle regulation. Many of these factors are also involved in the regulation of telomerase activity or the expression of hTERT, the catalytic subunit. Transcription of E6 and E7 is inhibited by the papillomavirus E2 protein, and ectopic expression of E2 in HeLa cells has been shown to cause activation of the p53-growth inhibitory pathway and downregulation of the hTERT gene. In this study, using E2 transduction in HeLa cells, the relative importance of host and viral factors in the maintenance of hTERT and telomerase activity in cervical carcinoma cells was investigated. Methods. Depletion of E6/E7 proteins, concomitant upregulation of p53, p21WAF1, and hypophosphorylated Rb, and downregulation of E2F1, c-Myc, and hTERT were achieved in HeLa cells through SV40-mediated E2 transduction. And, through gene transduction, E6 and E7 proteins were separately re-expressed in HeLa cells that were devoid of these proteins. As well, E2F1, c-Myc, and p53 were ectopically expressed in HeLa cells to ascertain their effect on the level of hTERT expression through RT-PCR, Western blotting, and TRAP assays. Results. Continued expression of E2F1 and c-Myc could not prevent hTERT downregulation caused by E2 transduction, but re-expression of either E6 or E7 individually reactivated hTERT expression. Finally, p53 overexpression caused repression of the hTERT gene in the presence of E6 and E7. Conclusion. HPV E6 plays an important role in the induction and maintenance of high levels of hTERT in cervical carcinoma cells through direct stimulation of hTERT promoter and prevention of the inhibitory effects of p53. E7, but not E2F1, may contribute to high telomerase activity in cancer cells.

2-Deoxyglucose (2-DG), a nonmetabolizable glucose analogue, blocks glycolysis at the phosphohexose isomerase step and has been frequently used as a glucose starvation mimetic in studies of a wide variety of physiological dysfuctions. However, the effect of 2-DG on protein glycosylation and related signal pathways has not been investigated in depth. In HeLa, an HPV18-positive cervical carcinoma line, 2-DG treatment down-regulates human papillomavirus early gene transcription. This down-regulation was also achieved by low glucose supply or hypoxia, suggesting that this is a response commonly modulated by cellular glucose or energy level. We investigated how 2-DG and low glucose affect transcriptional activity. Human papillomavirus gene transcription was only marginally affected by the inhibition of ATP synthesis or the supplementation of pyruvate to 2-DG-treated cells, suggesting that poor ATP generation is involved only to a limited extent. 2-DG treatment also inhibited activation of p21 WAF1 promoter, which is controlled by p53 and/or Sp1. In a reporter assay using p21 WAF1 promoter constructs, 2-DG exerted a strong inhibitory effect on Sp1 activity. DNA binding activity of Sp1 in 2-DG-treated HeLa cells was intact, whereas it was severely impaired in cells incubated in a low glucose medium or in hypoxic condition. Unexpectedly, Sp1 was heavily modified with GlcNAc in 2-DG-treated cells, which is at least partially attributed to the inhibitory effect of 2-DG on N-acetyl-beta-D-glucosaminidase activity. Our results suggest that 2-DG, like low glucose or hypoxic condition, down-regulates Sp1 activity, but through hyper-GlcNAcylation instead of hypo-GlcNAcylation.

Recent animal and clinical studies report promising results for the therapeutic utilization of stem cells in regenerative medicine. Mesenchymal stem cells (MSCs), with their pluripotent nature, have advantages over embryonic stem cells in terms of their availability and feasibility. However, their proliferative activity is destined to slow by replicative senescence, and the limited proliferative potential of MSCs not only hinders the preparation of sufficient cells for in vivo application, but also draws a limitation on their potential for differentiation. This calls for the development of safe and efficient means to increase the proliferative as well as differentiation potential of MSCs. Recent advances have led to a better understanding of the underlying mechanisms and significance of cellular senescence, facilitating ways to manipulate the replicative lifespan of a variety of primary cells, including MSCs. This paper introduces a class of proteins that function as senescence suppressors. Like tumor suppressors, these proteins are lost in senescence, while their forced expression delays the onset of senescence. Moreover, treatments that increase the expression or the activity of senescence suppressors, therefore, cause expansion of the replicative and differentiation potential of MSCs. The nature of the activities and putative underlying mechanisms of the senescence suppressors will be discussed to facilitate their evaluation.

Objective. E6 and E7 proteins of high-risk-type human papillomavirus are major etiological agents for cervical carcinomas and are continuously expressed in those cancer cells. They inhibit cell cycle control functions by inactivating p53 and Rb proteins and also immortalize cells through the induction of telomerase activity. Expression of E6 and E7 genes in HeLa, an HPV18-positive cell line, has been shown to be inhibited by the E2 protein of bovine papillomavirus (BPV1), and this resulted in the activation of the p53-mediated growth inhibitory pathway followed by an inhibition of cell proliferation. In this study, the effect of BPV1 E2-mediated inhibition of E6 and E7 expression was examined in HPV16-positive cervical carcinoma cell lines recently established from Korean patients. Methods. BPV1 E2 was expressed in the test cells through acute infection of an SV40–BPV1 recombinant virus. Its effect on cell proliferation was assessed through MTT and DNA synthesis assays, and the status of factors involved in cell cycle control was examined through Western blotting and reverse transcription-polymerase chain reaction. Results. BPV1 E2 expression caused a significant decrease in E6/E7 transcription in all three cell lines. This was accompanied by an increase in the levels of p53 protein and activity and a decrease in the expression of Cdc25A, a Cdk2-activating phosphatase. Concomitantly, E2F1 activity and cellular DNA synthesis capacity were significantly reduced. Conclusions. These results indicate that inhibition of E6/E7 gene expression in the HPV16-positive cervical carcinoma cells induces suppression in cell proliferation by activating the growth inhibitory factors, p53 and Rb, and also by downregulating the cell cycle stimulatory factor, Cdc25A.

In studying biological roles of interferon regulatory factor (IRF)-1 tumor suppressor in cervical carcinogenesis, we found that HPV E7 is functionally associated with IRF-1. Binding assays indicate a physical interaction between IRF-1 and HPV E7in vivo and in vitro. The carboxyl-terminal transactivation domain of IRF-1 was required for the interaction. Transient co-expression of E7 significantly inhibits the IRF-1-mediated activation of IFN-β promoter in NIH-3T3 cells. Co-transfection of E7 mutants reveals that the pRb-binding portion of E7 is necessary for the E7-mediated inactivation of IRF-1. It was next determined whether histone deacetylase (HDAC) is involved in the inactivation mechanism as recently suggested, where the carboxyl-terminal zinc finger domain of E7 associates with NURD complex containing HDAC. When trichostatin A, an inhibitor of HDAC, was treated, the repressing activity of E7 was released in a dose-dependent manner. Furthermore, the mutation of zinc finger abrogates such activity without effect on the interaction with IRF-1. These results suggest that HPV E7 interferes with the transactivation function of IRF-1 by recruiting HDAC to the promoter. The immune-promoting role of IRF-1 evokes the idea that our novel finding might be important for the elucidation of the E7-mediated immune evading mechanism that is frequently found in cervical cancer.

Retinoids and interferons have been implicated in the growth regulation of cervical cancer cells. However, the molecular mechanisms are not fully defined. To analyze detailed mechanisms, HPV-positive (HeLa, CaSki), HPV-negative (C33A, HT-3) and non-cervical Cos-1 cell lines were treated with I microM all-trans-retinoic acid (RA) and/or 10 ng/ml interferon-gamma (IFN-gamma). The growth of RA-treated HeLa cells was less effectively suppressed than that of IFN-gamma-treated ones. A combination of RA and IFN-gamma leads to an additive antiproliferative effect on the cell growth. CaSki cell growth was also inhibited by IFN-gamma but was little stimulated by RA treatment, and the IFN effect was attenuated when IFN-gamma was combined with RA. HPV-negative C33A and HT-3 cells, which are defective in p53 and Rb, and Cos- 1 cells were weakly or not responsive to all combined treatments. The molecular mechanism underlying the differential effects of RA/IFN on HeLa and C33A cells was investigated. Combined RA/IFN-gamma treatment caused a marked increase in the level of IFN regulatory factor-1 (IRF-1) in HeLa, whereas no induction of IRF-1 was observed in C33A, consistent with the findings that IFN signaling is functional in HeLa but is defective in C33A cells. The increase of p53 in HeLa cells might account for the down-regulation of HPV-18 E6 gene expression by RA/IFN-gamma. Furthermore, RA/IFN-gamma treatment resulted in the concurrent induction of p21WAF1 CDK inhibitor and dephosphorylation of Rb protein. Transient co-expression of IRF-1 and p53 led to the cooperative activation of the p21WAF1 promoter. Our results indicate that 2 transcription factors, increased in response to RA/IFN-gamma, cooperate functionally to regulate the cell cycle through the activation of a common p21WAF1 gene in HeLa cells.

Human papillomavirus (HPV) DNAs are often found to be integrated into the human genome in high-grade cervical intraepithelial neoplasia (CIN) as well as in invasive cervical cancers. Investigation of the relationship between the genomic status of specific HPV genes and their antibody responses to the virus-like particles (VLPs) of HPV-16 L1/L2 proteins and the in vitro translated HPV-16 E6 and E7 proteins may help to illustrate the mechanism of HPV-related cervical carcinogenesis and host immune response. Cervical cancer tissues obtained from 39 patients were studied to evaluate the physical status of HPV genes by Southern blotting, DNA-PCR, and RT-PCR of E2. The antibody response against the HPV-16 L1/L2 VLPs of serum specimens were tested by ELISA and the antibody response against the HPV-16 E6 and E7 proteins were tested by radioimmunoprecipitation assay (RIPA), respectively. Integrated forms of HPV-16 DNA were found in 23 of the 38 patients (60.5%). The HPV-16 positive cervical cancer patients showed a significantly higher prevalence rate (39.5%; 15/38) of antibodies to HPV-16 L1/L2 VLPs than that of the control group (8.7%; 2/28) (P0.05). Antibodies to HPV-16 L1/L2 VLPs were more commonly detectable in cervical cancer patients having the episomal form of HPV-16 DNA (pure episomal and mixed forms) (60%; 9/15) than in those who had only the integrated forms of HPV-16 DNA (26.1%; 6/23) (P0.05). Antibodies to E6 and E7 proteins were positive in 36.8% (14/38) and 50% (19/38) of the patients with HPV-16 positive cervical cancer, respectively. These were significantly higher than the positive rates for the control group (8.3% and 2.8%) (P0.05). The differences between sero-reactivities to E6 and E7 proteins in the patients with episomal forms of HPV-16 DNA and those with integrated forms of HPV-16 DNA were not statistically significant (P0.05). Integrated forms of HPV-16 DNA were prevalent in most patients with cervical cancer in Korea. Antibodies to HPV-16 L1/L2 VLPs, in vitro translated HPV-16 E6 and E7 proteins, appeared in a significantly larger proportion of the HPV-associated cervical cancer patients than in the controls. Antibodies to HPV-16 L1/L2 VLPs were more often detected in cervical cancer patients having the episomal form of HPV-16 DNA than in those having only integrated forms of HPV-16 DNA. Antibody responses to HPV-16 E6 and E7 proteins were not influenced by the different viral states.

Hwang ES, Kim J, Kim JS, Kao C, Ko S-C, Chung L, Lee J-H. The effects of the adenovirus-mediated wild-type p53 delivery in human epithelial ovarian cancer cell lines in vitro and in vivo. Int J Gynecol Cancer 1998; 8: 27-36. The effect of p53 overexpression on the proliferation of various ovarian cancer cell lines was tested by using an adenovirus vector, Avp53, that expresses wild-type human p53. Cell lines SKOV3, 2774, and OVCAR3, which bear mutations in the endogenous p53 gene, were all affected by Avp53 treatment, undergoing growth suppression and apoptosis at a dose that had little effect on the growth of normal fibroblasts. In these cells, p21WAF1/CIP1 was readily induced and the hypophosphorylated pRb protein accumulated by the treatment of Avp53, suggesting that the growth inhibitory pathway can be activated in these cells by the expression of wild-type p53. However, in PA-1 cell line which endogenously expresses wild-type p53, p21WAF1/CIP1 was not induced by p53 transduction, although p53 was found transcriptionally active. These results indicate that the tested ovarian cancer cell lines bear defects either in p53 itself or in the responsiveness to p53. The cytocidal effect of Avp53 was also examined in vivo against tumors developed in the peritoneal cavity of nude mice. Avp53 administered intraperitoneally eradicated microscopic and small-sized tumor nodules, demonstrating that the intraperitoneal administration of Avp53 may serve as an effective adjuvant therapy for ovarian cancers.

It is known that E2 protein of oncogenic human papillomavirus (HPV) inhibits the expression of E6 and E7 genes from their major promoters in vitro and suppresses the proliferation of cervical cancer cells. This suggests that the loss of functional E2 gene may provide selective advantages in the development of cervical cancer. Investigation of the relationship between the disruption of HPV-16/18 E2 genes by DNA integration and clinical outcome of cervical cancer may not only help to understand the mechanism of HPV-related cervical carcinogenesis, but may also provide novel management of cervical cancer. It was noted that integrated HPV-16/18 DNA was predominant in most patients with cervical cancers, marking 51 of a total of 68 cases (75%); episomal HPV DNAs were found in 5 cases (7.4%), and finally mixed forms of HPV DNAs with episome and integration were found in 12 cases (17.6%). Whole portions of E2 DNA of HPV-16 could be amplified by PCR in 19 (36.5%) of 52 cases of cervical intraepithelial neoplasia. It was shown that there was not statistically significant association with the different stages, but integrated HPV DNAs were detectable only in the patients with far-advanced stage of cervical cancers, which also means no episomal forms were detected. Episomal forms of HPV DNA were detectable in 14 (25.9%) of 54 squamous cell carcinomas (4 pure episomal forms and 10 mixed forms), whereas only 1 (8.3%) of 12 adenocarcinomas and adenosquamous cell carcinomas contained episomal viral DNA. When HPV DNA forms were compared with initial tumor size, lymphovascular space involvement, and frequency of nodal metastasis, statistically significant relationships were not found. The association of DNA integration with invasive cervical cancers was seen regardless of HPV type; however, there were differences between the integration profiles of HPV-16 and HPV-18 DNA. Of the 51 HPV-16-containing cancers, 36 (70.6%) revealed purely integrated HPV DNA, and another 10 cases (19.6%) displayed both integrated and episomal HPV DNAs. However, 5 (9.8%) cases showed only episomal copies of the HPV-16 genome. In contrast, all 17 HPV-18-containing cancers (5 cases positive for HPV-18 and 12 cases positive for both HPV-16 and -18) revealed only the integrated form of HPV-18 DNA. The expression of E6 and E7 transcripts of HPV-16/18 is uniformly correlated with the physical status of HPV DNAs. HPV E2 mRNAs were constantly expressed in the presence of the intact virus in cases with episome and mixed forms of HPV DNA. In general, amplified signals from HPV E2 RT-PCR are more intensive than those from DNA-PCR in the same patients. It is suggested that RT-PCR is a valuable method to evaluate dynamic expression of the specific gene and seems to be more sensitive than the DNA-PCR method in detecting intact E2 gene because of the gene copy numbers.

The human papillomavirus-16 (HPV16) E5 gene is able to induce stable growth transformation and transient mitogenic stimulation in a variety of cultured cell systems. To characterize the biochemical properties of the hydrophobic HPV16 E5 transforming protein, we have constructed vectors expressing the wild-type HPV16 E5 gene and have generated antipeptide antisera. The 10-kDa E5 protein was readily detectable in transfected COS monkey cells by using these antisera either for immunoprecipitation of metabolically labeled cells or for immunoblotting. Coimmunoprecipitation analysis of cells coexpressing the viral protein and various growth factor receptors demonstrated stable complex formation between the E5 protein and the epidermal growth factor receptor, platelet-derived growth factor β receptor, colony stimulating factor-1 receptor, and p185 neu . The E5 protein also formed a stable complex with the vesicular stomatitis virus glycoprotein. These experiments indicated that the HPV16 E5 protein was able to participate in complex formation with a variety of transmembrane proteins, a property which may contribute to the biological activities of the viral protein. In addition, the expression vectors and antibodies described here will be useful reagents in examining various aspects of HPV16 E5 expression and function.

SA β-Gal activity is a key marker of cellular senescence. The origin of this activity is the lysosomal β-galactosidase, whose activity has increased high enough to be detected at suboptimal pH. SA β-Gal is also expressed in the cells in quiescence driven by serum-starvation or a high confluency, and it has been hypothesized that SA β-Gal positivity is rather a surrogate marker of high lysosome content or activity. In this study, it was determined how SA β-Gal activity is expressed in quiescence and how lysosome content and activities are differently maintained in senescence and quiescence using DNA damage-induced senescence and serum starvation-induced quiescence as study models. Lysosome content increased to facilitate SA β-Gal expression in both the conditions but with a big difference in the levels of the change. Lipofuscins whose accumulation leads to an increase in residual bodies also increased but with a smaller difference between the two conditions. Meanwhile, lysosome biogenesis was actively ongoing only in senescence progression, indicating that the difference in the lysosome contents may largely be due to lysosome biogenesis. Further, the cells undergoing senescence progression but not the ones in quiescence maintained high mTOR and low autophagy activities. Overall, the results indicate that, although SA β-Gal is expressed due to the elevated lysosome content in both cellular senescence and quiescence, senescence differs from quiescence with high lysosome biogenesis and low autophagy activity, and mTOR activity might be involved in these differences.

The E5 proteins are short, hydrophobic transforming proteins encoded by many of the papillomaviruses. The 44 amino acid E5 protein of bovine papillomavirus efficiently transforms cultured fibroblasts and interacts with a variety of cellular proteins, Considerable evidence implicates the PDGF β receptor as an important mediator of the transforming activity of the BPV E5 protein in fibroblasts. Other potential targets of the BPV E5 protein include the EGF receptor, a subunit of the vacuolar H + -ATPase, and a protein related to α-adaptin. The E5 transforming proteins of the human papillomaviruses may interact with similar cellular targets in keratinocytes.

Cellular senescence is a spontaneous organismal defense mechanism against tumor progression which is raised upon the activation of oncoproteins or other cellular environmental stresses that must be circumvented for tumorigenesis to occur. It involves growth-arrest state of normal cells after a number of active divisions. There are multiple experimental routes that can drive cells into a state of senescence. Normal somatic cells and cancer cells enter a state of senescence upon overexpression of oncogenic Ras or Raf protein or by imposing certain kinds of stress such as cellular tumor suppressor function. Both flow cytometry and confocal imaging analysis techniques are very useful in quantitative analysis of cellular senescence phenomenon. They allow quantitative estimates of multiple different phenotypes expressed in multiple cell populations simultaneously. Here we review the various types of fluorescence methodologies including confocal imaging and flow cytometry that are frequently utilized to study a variety of senescence. First, we discuss key cell biological changes occurring during senescence and review the current understanding on the mechanisms of these changes with the goal of improving existing protocols and further developing new ones. Next, we list specific senescence phenotypes associated with each cellular trait along with the principles of their assay methods and the significance of the assay outcomes. We conclude by selecting appropriate references that demonstrate a typical example of each method.

Cellular senescence is a spontaneous organismal defense mechanism against tumor progression which is raised upon the activation of oncoproteins or other cellular environmental stresses that must be circumvented for tumorigenesis to occur. It involves growth-arrest state of normal cells after a number of active divisions. There are multiple experimental routes that can drive cells into a state of senescence. Normal somatic cells and cancer cells enter a state of senescence upon overexpression of oncogenic Ras or Raf protein or by imposing certain kinds of stress such as cellular tumor suppressor function. Both flow cytometry and confocal imaging analysis techniques are very useful in quantitative analysis of cellular senescence phenomenon. They allow quantitative estimates of multiple different phenotypes expressed in multiple cell populations simultaneously. Here we review the various types of fluorescence methodologies including confocal imaging and flow cytometry that are frequently utilized to study a variety of senescence. First, we discuss key cell biological changes occurring during senescence and review the current understanding on the mechanisms of these changes with the goal of improving existing protocols and further developing new ones. Next, we list specific senescence phenotypes associated with each cellular trait along with the principles of their assay methods and the significance of the assay outcomes. We conclude by selecting appropriate references that demonstrate a typical example of each method.

Human papillomavirus (HPV) E6 and E7 oncogenes are expressed in the great majority of human cervical carcinomas, whereas the viral E2 regulatory gene is usually disrupted in these cancers. To investigate the roles of the papillomavirus E2 genes in the development and maintenance of cervical carcinoma, the bovine papillomavirus (BPV) E2 gene was acutely introduced into cervical carcinoma cell lines by infection with high-titer stocks of simian virus 40-based recombinant viruses. Expression of the BPV E2 protein in HeLa, C-4I, and MS751 cells results in specific inhibition of the expression of the resident HPV type 18 (HPV18) E6 and E7 genes and in inhibition of cell growth. HeLa cells, in which HPV gene expression is nearly completely abolished, undergo a dramatic and rapid inhibition of proliferation, which appears to be largely a consequence of a block in progression from the G1 to the S phase of the cell cycle. Loss of HPV18 gene expression in HeLa cells is also accompanied by a marked increase in the level of the cellular p53 tumor suppressor protein, apparently as a consequence of abrogation of HPV18 E6-mediated destabilization of p53. The proliferation of HT-3 cells, a human cervical carcinoma cell line devoid of detectable HPV DNA, is also inhibited by E2 expression, whereas two other epithelial cell lines that do not contain HPV DNA are not inhibited. Thus, a number of cervical carcinoma cell lines are remarkably sensitive to growth inhibition by the E2 protein. Although BPV E2-mediated inhibition of HPV18 E6 and E7 expression may contribute to growth inhibition in some of the cervical carcinoma cell lines, the BPV E2 protein also appears to exert a growth-inhibitory effect that is independent of its effects on HPV gene expression.

Nicotinamide at millimolar concentrations affects cell survival in various conditions, and is being utilized therapeutically in many human diseases. However, the effect of an acute treatment of nicotinamide at such high dose on gene expression and cellular metabolism has rarely been determined previously. In this study, we found that levels of O -N-acetylglucosamin(O-GlcNAc)ylated proteins including Sp1 acutely decreased upon treatment of 10 mM nicotinamide. Concomitantly, Sp1 protein level decreased rapidly through accelerated proteasome-mediated proteolysis. Co-treatment of glucosamine or 2-deoxyglucose, which inhibits protein deGlcNAcylation, effectively blocked the decrease induced by nicotinamide. Interestingly, the decline in the levels of Sp1 and protein O-GlcNAcylation was only transient lasting for two days post treatment, and this pattern matched closely the rapid fluctuation of the cellular [NAD+]. Our results suggest a possible link between cellular nicotinamide metabolism and protein O-GlcNAcylation, and an existence of cellular [NAD+] homeostasis.

Nicotinamide at mM concentration is a potent inhibitor of certain key molecules involved in cell survival, such as SIRT1 and PARP-1, and affects cell survival in various conditions in vivo and in vitro . However, the effect of an acute treatment of nicotinamide on gene expression has rarely been closely examined. In our study, the treatment of 10 mM nicotinamide downregulated p21WAF1 expression in various human cells including p53-negative or SIRT1-knockdown cells indicating gene regulation not mediated by p53 or SIRT1. Meanwhile, in the nicotinamide-treated cells, Sp1 activity and protein level was substantially reduced due to increased proteasome-mediated degradation. Our results indicate that nicotinamide treatment attenuates p21WAF1 expression through Sp1 downregulation, and suggest a possible involvement of nicotinamide metabolism in cellular gene expression.

The specific DNA-binding protein integration host factor (IHF) of Escherichia coli stimulates the site-specific recombination reaction between the attP site of bacteriophage HP1 and the attB site of its host, Haemophilus influenzae, in vitro and also appears to regulate the expression of HP1 integrase. IHF interacts specifically with DNA segments containing the att sites and the integrase regulatory region, as judged by IHF-dependent retardation of relevant DNA fragments during gel electrophoresis. The locations of the protein-binding sites were identified by DNase I protection experiments. Three sites in the HP1 attP region bound IHF, two binding sites were present in the vicinity of the attB region, and one region containing three partially overlapping sites was present in the HP1 integrase regulatory segment. The binding sites defined in these experiments all contained sequences which matched the consensus IHF binding sequences first identified in the lambda attP region. An activity which stimulated the HP1 site-specific integration reaction was found in extracts of H. influenzae, suggesting that an IHF-like protein is present in this organism.

We found that the protein level of Sp1 transcription factor decreases as normal human fibroblasts undergo replicative aging. Sp1 also undergoes a rapid decrease in the protein level and activity in MCF-7 cells that are induced to a state of cellular senescence. In the cells treated with other DNA damaging chemicals such as actinomycin D and H(2)O(2), the Sp1 level decreased progressively as well. Inhibition of ATM/ATR kinases prevented this downregulation, suggesting that DNA damage signaling is involved in the regulation of the Sp1. This decrease in Sp1 protein level is due to the accelerated proteasomal degradation since a proteasome inhibitor, ALLN, blocked this downregulation. Therefore, the global decrease in gene transcription frequently reported in aging cells and tissues could be attributed at least in part to the decrease in Sp1 level.

Replicative senescence limits the proliferation of somatic cells passaged in culture and may reflect cellular aging in vivo. The most widely used biomarker for senescent and aging cells is senescence-associated beta-galactosidase (SA-beta-gal), which is defined as beta-galactosidase activity detectable at pH 6.0 in senescent cells, but the origin of SA-beta-gal and its cellular roles in senescence are not known. We demonstrate here that SA-beta-gal activity is expressed from GLB1, the gene encoding lysosomal beta-D-galactosidase, the activity of which is typically measured at acidic pH 4.5. Fibroblasts from patients with autosomal recessive G(M1)-gangliosidosis, which have defective lysosomal beta-galactosidase, did not express SA-beta-gal at late passages even though they underwent replicative senescence. In addition, late passage normal fibroblasts expressing small-hairpin interfering RNA that depleted GLB1 mRNA underwent senescence but failed to express SA-beta-gal. GLB1 mRNA depletion also prevented expression of SA-beta-gal activity in HeLa cervical carcinoma cells induced to enter a senescent state by repression of their endogenous human papillomavirus E7 oncogene. SA-beta-gal induction during senescence was due at least in part to increased expression of the lysosomal beta-galactosidase protein. These results also indicate that SA-beta-gal is not required for senescence.

Inhibition of human papillomavirus (HPV) E6 and E7 transcription by means of the E2 protein of bovine papillomavirus 1 (BPV1) has been shown to induce acute growth arrest in HPV-positive cervical carcinoma cells. This state of arrest is marked by the expression of senescence phenotypes including SA beta-Gal activity and lipofuscin accumulation. In this study, we examined the reversibility of these phenotypes by exogenously expressing the E6 and E7 genes into HeLa cells growth-arrested by the depletion of E6/E7. Re-expression of E7 (but not E6) in 2 days following E2 transduction induced the cells to resume growth. The proliferating cells manifested the phenotype of untreated HeLa cells, suggesting that E7 is the major factor responsible for the continued proliferation and the suppression of the senescence phenotype in cervical carcinoma cells. However, E7 in 5 days following E2 transduction did not prevent HeLa cells from entering the senescent state, indicating that the arrested state becomes irreversible. Our results suggest that, upon depletion of the viral oncoproteins, a senescent state is irreversibly induced in HeLa cells after a period of commitment. The status and cellular location of certain factors involved in signal transduction and cell cycle control was altered as well along with this irreversibility transition.

Studies on the replicative senescence and premature senescence induced by various stresses in normal somatic cells have provided important clues on the role of telomere shortening and mechanisms involved in aging processes and carcinogenesis. Recent work revealed that cancer cells also are induced to undergo replicative senescence state via telomere shortening as well as to enter a senescence-like state by the activation of cell cycle inhibitory pathways. Although less relevant in terms of aging physiology, studies on these phenomena in cancer cells have yielded important information on telomerase regulation and the roles of tumor suppressors in senescence and immortalization, and are expected to generate valuable anti-cancer strategies. Several features of the phenotypes specific for the senescent and senescence-like states induced in cancer cells are discussed.

The E6 and E7 oncoproteins of human papillomavirus (HPV) play a major role in the development of cervical carcinoma. In this study, a recombinant adenovirus that expresses the bovine papillomavirus (BPV) E2, which has been shown to inhibit HPV early gene expression, was delivered to two HPV-immortalized cell lines as well as CaSki, a cervical carcinoma cell line. We tested whether the carcinoma and the immortal cells were equally affected by the expression of BPV E2. In all cell lines, BPV E2-mediated inhibition of HPV E6/E7 expression caused a dramatic suppression of cell growth, being preceded by the activation of the p53–Rb growth-inhibitory pathway, and a decrease in hTERT mRNA expression and telomerase activity. This suggests that the HPV E6 and E7 proteins are required not only for induction of the proliferative phenotype and telomerase activity, but also for their maintenance. In both the carcinoma and the immortal lines, the number of cells with enlarged cytoplasm and senescence-associated β-galactosidase activity, which are markers for cellular senescence, was significantly increased. These results suggest that a senescence program exists in cells immortalized by HPV DNA as well as in cervical carcinoma cells.