Putative telomere-independent mechanisms of replicative aging reflect inadequate growth conditions

Ectopic AP4 expression induces cellular senescence via activation of p53 in long-term confluent retinal pigment epithelial cells

When cells are grown to confluence, cell-cell contact inhibition occurs and drives the cells to enter reversible quiescence rather than senescence. Confluent retinal pigment epithelial (RPE) cells exhibiting contact inhibition was used as a model in this study to examine the role of overexpression of transcription factor AP4, a highly expressed transcription factor in many types of cancer, in these cells during long-term culture. We generated stable inducible RPE cell clones expressing AP4 or AP4 without the DNA binding domain (DN-AP4) and observed that, when cultured for 24 days, RPE cells with a high level of AP4 exhibit a large, flattened morphology and even cease proliferating; these changes were not observed in DN-AP4-expressing cells or non-induced cells. In addition, AP4-expressing cells exhibited senescence-associated β-galactosidase activity and the senescence-associated secretory phenotype. We demonstrated that the induced cellular senescence was mediated by enhanced p53 expression and that AP4 regulates the p53 gene by binding directly to two of the three E-boxes present on the promoter of the p53 gene. Moreover, we showed that serum is essential for AP4 in inducing p53-associated cellular senescence. Collectively, we showed that overexpression of AP4 mediates cellular senescence involving in activation of p53 in long-term post-confluent RPE cells.

In Vitro Model of the Epidermis: Connecting Protein Function to 3D Structure

Much of our understanding of the biological processes that underlie cellular functions in humans, such as cell-cell communication, intracellular signaling, and transcriptional and posttranscriptional control of gene expression, has been acquired from studying cells in a two-dimensional (2D) tissue culture environment. However, it has become increasingly evident that the 2D environment does not support certain cell functions. The need for more physiologically relevant models prompted the development of three-dimensional (3D) cultures of epithelial, endothelial, and neuronal tissues (Shamir & Ewald, 2014). These models afford investigators with powerful tools to study the contribution of spatial organization, often in the context of relevant extracellular matrix and stromal components, to cellular and tissue homeostasis in normal and disease states.

Development and characterization of a new human hepatic cell line

The increasing demand and hampered use of primary human hepatocytes for research purposes have urged scientists to search for alternative cell sources, such as immortalized hepatic cell lines. The aim of this study was to develop a human hepatic cell line using the combined overexpression of TERT and the cell cycle regulators cyclin D1 and mutant isoform CDK4R24C. Following transduction of adult human primary hepatocytes with the selected immortalization genes, cell growth was triggered and a cell line was established. When cultured under appropriate conditions, the cell line expressed several hepatocytic markers and liver-enriched transcription factors at the transcriptional and/or translational level, secreted liver-specific proteins and showed glycogen deposition. These results suggest that the immortalization strategy applied to primary human hepatocytes could generate a novel hepatic cell line that seems to retain some key hepatic characteristics.

Effects of targeted nano-delivery systems combined with hTERT-siRNA and Bmi-1-siRNA on MCF-7 cells

The aim of this study was to evaluate the efficiency of a targeted siRNA nano-delivery system to silence the expression of Bmi-1 and hTERT, and to verify the toxicity of this delivery system in MCF-7 breast cancer cells. The most effective Bmi-1 siRNA and hTERT siRNA sequences were selected using RT-PCR and Western blotting. The polyethyleneimine (PEI)/siRNA nano-condensate was synthesized using PEI and modified using an NGR peptide fragment for targeting to tumor cells. The vector morphology, particle size and zeta potential were observed using an atomic force microscope and a laser particle size analyzer. The MCF-7 breast cancer cell line was transfected with the vector, and cytotoxicity was tested by MTT assays. The transfection efficiency was evaluated by qRT-PCR and Western blotting. Changes in gene expression and apoptosis rate were measured by flow cytometry. The size of LPN carrier and the condensate particle was between 100 and 200 nm and the potentials were close to neutral. There was maximum transfection efficiency and no significant increase in toxicity at 15 pmol/L. Bmi-1 and hTERT expression decreased, but the inhibition rate increased in the hTERT siRNA group, the hTERT+Bmi-1 siRNA group and the hTERT+Bmi-1 siRNA group compared with the scrambled siRNA group and the control group. Moreover, the hTERT+Bmi-1 siRNA group had the highest level of gene silencing. The complex, composed of Lipo, PEI and siRNA, is low toxicity and efficient transfection vectors. The expression level of Bmi-1 and hTERT was decreased by the gene silencing of either Bmi-1 or hTERT, but the effects were more significant when both were silenced simultaneously.

The emerging role of senescent cells in tissue homeostasis and pathophysiology

Cellular senescence is a state of permanent growth arrest and is thought to play a pivotal role in tumor suppression. Cellular senescence may play an important role in tumor suppression, wound healing, and protection against tissue fibrosis in physiological conditions in vivo. However, accumulating evidence that senescent cells may have harmful effects in vivo and may contribute to tissue remodeling, organismal aging, and many age-related diseases also exists. Cellular senescence can be induced by various intrinsic and extrinsic factors. Both p53/p21 and p16/RB pathways are important for irreversible growth arrest in senescent cells. Senescent cells secret numerous biologically active factors. This specific secretion phenotype by senescent cells may largely contribute to physiological and pathological consequences in organisms. Here I review the molecular basis of cell cycle arrest and the specific secretion phenotype in cellular senescence. I also summarize the current knowledge of the role of cellular senescence in vivo in physiological and pathological settings.

Stem cells and aberrant signaling of molecular systems in skin aging

The skin is the body's largest organ and it is able to self-repair throughout an individual's life. With advanced age, skin is prone to degenerate in response to damage. Although cosmetic surgery has been widely adopted to rejuvinate skin, we are far from a clear understanding of the mechanisms responsible for skin aging. Recently, adult skin-resident stem/progenitor cells, growth arrest, senescence or apoptotic death and dysfunction caused by alterations in key signaling genes, such as Ras/Raf/MEK/ERK, PI3K/Akt-kinases, Wnt, p21 and p53, have been shown to play a vital role in skin regeneration. Simultaneously, enhanced telomere attrition, hormone exhaustion, oxidative stress, genetic events and ultraviolet radiation exposure that result in severe DNA damage, genomic instability and epigenetic mutations also contribute to skin aging. Therefore, cell replacement and targeting of the molecular systems found in skin hold great promise for controlling or even curing skin aging.

Stable cellular senescence is associated with persistent DDR activation

The DNA damage response (DDR) is activated upon DNA damage generation to promote DNA repair and inhibit cell cycle progression in the presence of a lesion. Cellular senescence is a permanent cell cycle arrest characterized by persistent DDR activation. However, some reports suggest that DDR activation is a feature only of early cellular senescence that is then lost with time. This challenges the hypothesis that cellular senescence is caused by persistent DDR activation. To address this issue, we studied DDR activation dynamics in senescent cells. Here we show that normal human fibroblasts retain DDR markers months after replicative senescence establishment. Consistently, human fibroblasts from healthy aged donors display markers of DDR activation even three years in culture after entry into replicative cellular senescence. However, by extending our analyses to different human cell strains, we also observed an apparent DDR loss with time following entry into cellular senescence. This though correlates with the inability of these cell strains to survive in culture upon replicative or irradiation-induced cellular senescence. We propose a model to reconcile these results. Cell strains not suffering the prolonged in vitro culture stress retain robust DDR activation that persists for years, indicating that under physiological conditions persistent DDR is causally involved in senescence establishment and maintenance. However, cell strains unable to maintain cell viability in vitro, due to their inability to cope with prolonged cell culture-associated stress, show an only-apparent reduction in DDR foci which is in fact due to selective loss of the most damaged cells.

Senescence-associated secretory phenotype and its possible role in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a major disease of the lungs. It primarily occurs after a prolonged period of cigarette smoking. Chronic inflammation of airways and the alveolar space as well as lung tissue destruction are the hallmarks of COPD. Recently it has been shown that cellular senescence might play a role in the pathogenesis of COPD. Cellular senescence comprises signal transduction program, leading to irreversible cell cycle arrest. The growth arrest in senescence can be triggered by many different mechanisms, including DNA damage and its recognition by cellular sensors, leading to the activation of cell cycle checkpoint responses and activation of DNA repair machinery. Senescence can be induced by several genotoxic factors apart from telomere attrition. When senescence induction is based on DNA damage, senescent cells display a unique phenotype, which has been termed "senescence-associated secretory phenotype" (SASP). SASP may be an important driver of chronic inflammation and therefore may be part of a vicious cycle of inflammation, DNA damage, and senescence. This research perspective aims to showcase cellular senescence with relevance to COPD and the striking similarities between the mediators and secretory phenotype in COPD and SASP.

Are there roles for brain cell senescence in aging and neurodegenerative disorders?

The term cellular senescence was introduced more than five decades ago to describe the state of growth arrest observed in aging cells. Since this initial discovery, the phenotypes associated with cellular senescence have expanded beyond growth arrest to include alterations in cellular metabolism, secreted cytokines, epigenetic regulation and protein expression. Recently, senescence has been shown to play an important role in vivo not only in relation to aging, but also during embryonic development. Thus, cellular senescence serves different purposes and comprises a wide range of distinct phenotypes across multiple cell types. Whether all cell types, including post-mitotic neurons, are capable of entering into a senescent state remains unclear. In this review we examine recent data that suggest that cellular senescence plays a role in brain aging and, notably, may not be limited to glia but also neurons. We suggest that there is a high level of similarity between some of the pathological changes that occur in the brain in Alzheimer's and Parkinson's diseases and those phenotypes observed in cellular senescence, leading us to propose that neurons and glia can exhibit hallmarks of senescence previously documented in peripheral tissues.

Strategies for immortalization of primary hepatocytes

The liver has the unique capacity to regenerate in response to a damaging event. Liver regeneration is hereby largely driven by hepatocyte proliferation, which in turn relies on cell cycling. The hepatocyte cell cycle is a complex process that is tightly regulated by several well-established mechanisms. In vitro, isolated hepatocytes do not longer retain this proliferative capacity. However, in vitro cell growth can be boosted by immortalization of hepatocytes. Well-defined immortalization genes can be artificially overexpressed in hepatocytes or the cells can be conditionally immortalized leading to controlled cell proliferation. This paper discusses the current immortalization techniques and provides a state-of-the-art overview of the actually available immortalized hepatocyte-derived cell lines and their applications.

Immortalization of Human Fetal Hepatocyte by Ectopic Expression of Human Telomerase Reverse Transcriptase, Human Papilloma Virus (E7) and Simian Virus 40 Large T (SV40 T) Antigen Towards Bioartificial Liver Support

BACKGROUND

Generation of genetically stable and non-tumoric immortalization cell line from primary cells would be enormously useful for research and therapeutic purposes, but progress towards this goal has so far been limited. It is now universal acceptance that immortalization of human fetal hepatocytes based on recent advances of telomerase biology and oncogene, lead to unlimited population doubling could be the possible source for bioartificial liver device.

METHODS

Immortalization of human fetal hepatocytes cell line by ectopic expression of human telomerase reverse transcriptase (hTERT), human papilloma virus gene (E7) and simian virus 40 large T (SV40 T) antigens is main goal of present study. We used an inducible system containing human telomerase and E7, both of which are cloned into responder constructs controlled by doxycycline transactivator. We characterized the immortalized human fetal hepatocyte cells by analysis of green fluorescent cells (GFP) positive cells using flow cytometry (FACs) cell sorting and morphology, proliferative rate and antigen expression by immunohistochemical analysis. In addition to we analysized lactate formation, glucose consumption, albumin secretion and urea production of immortalized human fetal hepatocyte cells.

RESULTS

After 25 attempts for transfection of adult primary hepatocytes by human telomerase and E7 to immortalize them, none of the transfection systems resulted in the production of a stable, proliferating cell line. Although the transfection efficiency was more than 70% on the first day, the vast majority of the transfected hepatocytes lost their signal within the first 5-7 days. The remaining transfected hepatocytes persisted for 2-4 weeks and divided one or two times without forming a clone. After 10 attempts of transfection human fetal hepatocytes using the same transfection system, we obtained one stable human fetal hepatocytes cell line which was able albumin secretion urea production and glucose consumption.

CONCLUSION

We established a conditional human fetal hepatocytes cell line with mesenchymal characteristics. Thus immortalization of human fetal hepatocytes cell line by telomerase biology offers a great challenge to examine basic biological mechanisms which are directly related to human and best cell source having unlimited population doubling for bioartificial support without any risk of replicative senescence and pathogenic risks.

Phenotypic plasticity in normal breast derived epithelial cells

BACKGROUND

Normal, healthy human breast tissue from a variety of volunteer donors has become available for research thanks to the establishment of the Susan G. Komen for the Cure® Tissue Bank at the IU Simon Cancer Center (KTB). Multiple epithelial (K-HME) and stromal cells (K-HMS) were established from the donated tissue. Explant culture was utilized to isolate the cells from pieces of breast tissue. Selective media and trypsinization were employed to select either epithelial cells or stromal cells. The primary, non-transformed epithelial cells, the focus of this study, were characterized by immunohistochemistry, flow cytometry, and in vitro cell culture.

RESULTS

All of the primary, non-transformed epithelial cells tested have the ability to differentiate in vitro into a variety of cell types when plated in or on biologic matrices. Cells identified include stratified squamous epithelial, osteoclasts, chondrocytes, adipocytes, neural progenitors/neurons, immature muscle and melanocytes. The cells also express markers of embryonic stem cells.

CONCLUSIONS

The cell culture conditions employed select an epithelial cell that is pluri/multipotent. The plasticity of the epithelial cells developed mimics that seen in metaplastic carcinoma of the breast (MCB), a subtype of triple negative breast cancer; and may provide clues to the origin of this particularly aggressive type of breast cancer. The KTB is a unique biorepository, and the normal breast epithelial cells isolated from donated tissue have significant potential as new research tools.

Crosstalk between the Rb pathway and AKT signaling forms a quiescence-senescence switch

Cell-cycle arrest in quiescence and senescence is largely orchestrated by the retinoblastoma (Rb) tumor-suppressor pathway, but the mechanisms underlying the quiescence-senescence switch remain unclear. Here, we show that the crosstalk between the Rb-AKT-signaling pathways forms this switch by controlling the overlapping functions of FoxO3a and FoxM1 transcription factors in cultured fibroblasts. In the absence of mitogenic signals, although FoxM1 expression is repressed by the Rb pathway, FoxO3a prevents reactive oxygen species (ROS) production by maintaining SOD2 expression, leading to quiescence. However, if the Rb pathway is activated in the presence of mitogenic signals, FoxO3a is also inactivated by AKT, thus reducing SOD2 expression and consequently allowing ROS production. This situation elicits senescence through irreparable DNA damage. We demonstrate that this pathway operates in mouse liver, indicating that this machinery may contribute more broadly to tissue homeostasis in vivo.

The ZEB1 transcription factor acts in a negative feedback loop with miR200 downstream of Ras and Rb1 to regulate Bmi1 expression

Ras mutations are frequent in cancer cells where they drive proliferation and resistance to apoptosis. However in primary cells, mutant Ras instead can cause oncogene-induced senescence, a tumor suppressor function linked to repression of the polycomb factor Bmi1, which normally regulates cell cycle inhibitory cyclin-dependent kinase inhibitors (cdki). It is unclear how Ras causes repression of Bmi1 in primary cells to suppress tumor formation while inducing the gene in cancer cells to drive tumor progression. Ras also induces the EMT transcription factor ZEB1 to trigger tumor invasion and metastasis. Beyond its well-documented role in EMT, ZEB1 is important for maintaining repression of cdki. Indeed, heterozygous mutation of ZEB1 is sufficient for elevated cdki expression, leading to premature senescence of primary cells. A similar phenotype is evident with Bmi1 mutation. We show that activation of Rb1 in response to mutant Ras causes dominant repression of ZEB1 in primary cells, but loss of the Rb1 pathway is a hallmark of cancer cells and in the absence of such Rb1 repression Ras induces ZEB1 in cancer cells. ZEB1 represses miR-200 in the context of a mutual repression loop. Because miR-200 represses Bmi1, induction of ZEB1 leads to induction of Bmi1. Rb1 pathway status then dictates the opposing effects of mutant Ras on the ZEB1-miR-200 loop in primary versus cancer cells. This loop not only triggers EMT, surprisingly we show it acts downstream of Ras to regulate Bmi1 expression and thus the critical decision between oncogene-induced senescence and tumor initiation.

Dynamics of histone H3.3 deposition in proliferating and senescent cells reveals a DAXX-dependent targeting to PML-NBs important for pericentromeric heterochromatin organization

Oncogene-induced senescence is a permanent cell cycle arrest characterized by extensive chromatin reorganization. Here, we investigated the specific targeting and dynamics of histone H3 variants in human primary senescent cells. We show that newly synthesized epitope-tagged H3.3 is incorporated in senescent cells but does not accumulate in senescence-associated heterochromatin foci (SAHF). Instead, we observe that new H3.3 colocalizes with its specific histone chaperones within the promyelocytic leukemia nuclear bodies (PML-NBs) and is targeted to PML-NBs in a DAXX-dependent manner both in proliferating and senescent cells. We further show that overexpression of DAXX enhances targeting of H3.3 in large PML-NBs devoid of transcriptional activity and promotes the accumulation of HP1, independently of H3K9me3. Loss of H3.3 from pericentromeric heterochromatin upon DAXX or PML depletion suggests that the targeting of H3.3 to PML-NBs is implicated in pericentromeric heterochromatin organization. Together, our results underline the importance of the replication-independent chromatin assembly pathway for histone replacement in non-dividing senescent cells and establish PML-NBs as important regulatory sites for the incorporation of new H3.3 into chromatin.

SORBS2 and TLR3 induce premature senescence in primary human fibroblasts and keratinocytes

Background

Genetic aberrations are required for the progression of HPV-induced cervical precancers. A prerequisite for clonal expansion of cancer cells is unlimited proliferative capacity. In a cell culture model for cervical carcinogenesis loss of genes located on chromosome 4q35→qter and chromosome 10p14-p15 were found to be associated with escape from senescence. Moreover, by LOH and I-FISH analyses a higher frequency of allele loss of these regions was also observed in cervical carcinomas as compared to CIN3. The aim of this study was to identify candidate senescence-related genes located on chromosome 4q35→qter and chromosome 10p14-p15 which may contribute to clonal expansion at the transition of CIN3 to cancer.

Methods

Microarray expression analyses were used to identify candidate genes down-regulated in cervical carcinomas as compared to CIN3. In order to relate these genes with the process of senescence their respective cDNAs were overexpressed in HPV16-immortalized keratinocytes as well as in primary human fibroblasts and keratinocytes using lentivirus mediated gene transduction.

Results

Overall fifteen genes located on chromosome 4q35→qter and chromosome 10p14-p15 were identified. Ten of these genes could be validated in biopsies by RT-PCR. Of interest is the novel finding that SORBS2 and TLR3 can induce senescence in primary human fibroblasts and keratinocytes but not in HPV-immortalized cell lines. Intriguingly, the endogenous expression of both genes increases during finite passaging of primary keratinocytes in vitro.

Conclusions

The relevance of the genes SORBS2 and TLR3 in the process of cellular senescence warrants further investigation. In ongoing experiments we are investigating whether this increase in gene expression is also characteristic of replicative senescence.

Omeprazole blocks eotaxin-3 expression by oesophageal squamous cells from patients with eosinophilic oesophagitis and GORD

OBJECTIVE

Eosinophilic oesophagitis (EoE) and gastro-oesophageal reflux disease (GORD) can have similar clinical and histological features. Proton pump inhibitors (PPIs) are used to distinguish the disorders, with the assumption that only GORD can respond to PPIs. Oesophageal expression of eotaxin-3 stimulated by Th2 cytokines might contribute to oesophageal eosinophilia in EoE. Th2 cytokine effects on the oesophagus in GORD are not known. The objective of the authors was to explore the molecular mechanisms of Th2 cytokines on eotaxin-3 expression by oesophageal squamous cells from patients with GORD and EoE, and the effects of omeprazole on that eotaxin-3 expression.

DESIGN

Using telomerase-immortalised and primary cultures of oesophageal squamous cells from GORD and EoE patients, the authors measured eotaxin-3 protein secretion stimulated by Th2 cytokines (interleukin (IL)-4 and IL-13). Eotaxin-3 promoter constructs were used to study transcriptional regulation. Cytokine-induced eotaxin-3 mRNA and protein expression were measured in the presence or absence of omeprazole.

RESULTS

There were no significant differences between EoE and GORD primary cells in cytokine-stimulated eotaxin-3 protein secretion levels. In EoE and GORD cell lines, IL-4 and IL-13 activated the eotaxin-3 promoter, and significantly increased eotaxin-3 mRNA and protein expression. Omeprazole blocked the cytokine-stimulated increase in eotaxin-3 mRNA and protein expression in EoE and GORD cell lines.

CONCLUSION

Oesophageal squamous cells from GORD and EoE patients express similar levels of eotaxin-3 when stimulated by Th2 cytokines, and omeprazole blocks that eotaxin-3 expression. These findings suggest that PPIs might have eosinophil-reducing effects independent of effects on acid reflux and that response to PPIs might not distinguish EoE from GORD.

Mesothelial cell: a multifaceted model of aging

Human peritoneal mesothelial cells (HPMCs) dominate within the peritoneal cavity and thus play a central role in a variety of intraperitoneal processes, including the transport of water and solutes, inflammation, host response, angiogenesis, and extracellular matrix remodeling. In addition, they contribute to the development of abdominal adhesions, peritonitis, endometriosis, cancer cell metastases, and peritoneal dialysis complications. For less than a decade the primary cultures of omental HPMCs have also been used as an experimental tool in studies on cellular aging. This paper provides the first comprehensive overview of the current state of art on molecular mechanisms underlying HPMC senescence in vitro. Special attention is paid to the causes of the very fast dynamics of HPMC senescence, and in particular to the role of non-telomeric DNA damage, the autocrine activity of TGF-β1, and the causative effects of oxidative stress. In addition, some clinical manifestations of HPMC senescence will be discussed, including its interplay with organismal aging, peritoneal dialysis, and cancer progression.

Sequential inductions of the ZEB1 transcription factor caused by mutation of Rb and then Ras proteins are required for tumor initiation and progression

Rb1 restricts cell cycle progression, and it imposes cell contact inhibition to suppress tumor outgrowth. It also triggers oncogene-induced senescence to block Ras mutation. Loss of the Rb1 pathway, which is a hallmark of cancer cells, then provides a permissive environment for Ras mutation, and Ras is sufficient for invasive tumor formation in Rb1 family mutant mouse embryo fibroblasts (MEFs). These results demonstrate that sequential mutation of the Rb1 and Ras pathways comprises a tumor initiation axis. Both Rb1 and Ras regulate expression of the transcription factor ZEB1, thereby linking tumor initiation to the subsequent invasion and metastasis, which is induced by ZEB1. ZEB1 acts in a negative feedback loop to block expression of miR-200, which is thought to facilitate tumor invasion and metastasis. However, ZEB1 also represses cyclin-dependent kinase (cdk) inhibitors to control the cell cycle; its mutation in MEFs leads to induction of these inhibitors and premature senescence. Here, we provide evidence for two sequential inductions of ZEB1 during Ras transformation of MEFs. Rb1 constitutively represses cdk inhibitors, and induction of ZEB1 when the Rb1 pathway is lost is required to maintain this repression, allowing for the classic immortalization and loss of cell contact inhibition seen when the Rb1 pathway is lost. In vivo, we show that this induction of ZEB1 is required for Ras-initiated tumor formation. ZEB1 is then further induced by Ras, beyond the level seen with Rb1 mutation, and this Ras superinduction is required to reach a threshold of ZEB1 sufficient for repression of miR-200 and tumor invasion.

New insights on molecular mechanisms of renal aging

Long-term transplant outcome is importantly influenced by the age of the organ donor. The mechanisms how age carries out its pathophysiological impact on graft survival are still not understood. One major contributing factor for the observed poor performance of old donor kidneys seems in particular the age-related loss in renal regenerative capacity. In this review, we will summarize recent findings about the molecular basis of renal aging with specific focus on the potential role of somatic cellular senescence and mitochondrial aging in renal transplant outcome.

Nek4 regulates entry into replicative senescence and the response to DNA damage in human fibroblasts

When explanted into culture, normal human cells exhibit a finite number of cell divisions before entering a proliferative arrest termed replicative senescence. To identify genes essential for entry into replicative senescence, we performed an RNA interference (RNAi)-based loss-of-function screen and found that suppression of the Never in Mitosis Gene A (NIMA)-related protein kinase gene NEK4 disrupted timely entry into senescence. NEK4 suppression extended the number of population doublings required to reach replicative senescence in several human fibroblast strains and resulted in decreased transcription of the cyclin-dependent kinase inhibitor p21. NEK4-suppressed cells displayed impaired cell cycle arrest in response to double-stranded DNA damage, and mass spectrometric analysis of Nek4 immune complexes identified a complex containing DNA-dependent protein kinase catalytic subunit [DNA-PK(cs)], Ku70, and Ku80. NEK4 suppression causes defects in the recruitment of DNA-PK(cs) to DNA upon induction of double-stranded DNA damage, resulting in reduced p53 activation and H2AX phosphorylation. Together, these observations implicate Nek4 as a novel regulator of replicative senescence and the response to double-stranded DNA damage.

Resveratrol delays replicative senescence of human mesothelial cells via mobilization of antioxidative and DNA repair mechanisms

Resveratrol (3,4',5-trihydroxy-trans-stilbene; RVT) is a natural phytoestrogen known to modulate the rate of senescence in cultured cells. The mechanism by which RVT affects this process is still elusive. In this paper we used human peritoneal mesothelial cells (HPMCs) to examine the effect of RVT (0.5 and 10 μM) on their growth and senescence, with particular emphasis paid to parameters associated with oxidative stress. The results showed that RVT used at a concentration of 0.5 μM (but not at 10 μM) markedly improved HPMC growth capacity, as evidenced by elevated expression of PCNA antigen, augmented fraction of cells in the S phase of the cell cycle, and increased number of divisions achieved before senescence. These effects coincided with diminished expression and activity of senescence-associated β-galactosidase but were not associated with changes in the telomere length and an incidence of apoptosis. Moreover cells exposed to 0.5 μM RVT were characterized by increased release of reactive oxygen species, which was accompanied by up-regulated biogenesis of mitochondria and collapsed mitochondrial membrane potential. At the same time, they displayed increased activity of superoxide dismutase and reduced DNA damage (8-OH-dG and γ-H2A.X level). The efficiency of 8-OH-dG repair was increased which could be related to increased activity of DNA glycosylase I (hOgg1). As shown using RT-PCR, expression of hOgg1 mRNA in these cells was markedly elevated. Collectively, our results indicate that delayed senescence of HPMCs exposed to RVT may be associated with mobilization of antioxidative and DNA repair mechanisms.

Translational control of cell fate: from integration of environmental signals to breaching anticancer defense

Despite their genetic diversity, different cancers manifest common features at the protein pathway level. They share a core group of perturbed pathways that converge upon a few regulatory hubs linking the cellular signaling network with the basic metabolic machinery. Available evidence indicates that one such hub is the eIF4F-mediated cap-dependent mRNA translation initiation apparatus, whose integrity is required for physiological control of growth, proliferation and viability. However, when hyperactivated by upstream oncogenic signaling, eIF4F selectively stimulates the translation of a group of mRNAs required for cancer genesis and progression. Here, we describe a model that links the pro-neoplastic function of eIF4F to its ability to disable oncogene-activated tumor surveillance programs and propose a novel therapeutic strategy for cancer based upon targeting aberrant eIF4F with small-molecule antagonists.

Short hairpin RNA screen indicates that Klotho beta/FGF19 protein overcomes stasis in human colonic epithelial cells

Normal human colonic epithelial cells (HCECs) are not immortalized by telomerase alone but also require CDK4. Some human cell types growth-arrest due to stress- or aberrant signaling-induced senescence (stasis). Stasis represents the consequences of growth conditions culture that are inadequate to maintain long-term proliferation. Overexpressed CDK4 titers out p16 and allows cells to ignore the growth arrest signals produced by stasis. To identify factors contributing to the inadequate culture environment, we used a 62,000-member shRNA library to knock down factors cooperating with human telomerase reverse transcriptase (hTERT) in the immortalization of HCECs. Knockdown of Klotho gamma (KLG; also known as KLPH and LCTL) allowed hTERT to immortalize HCECs. KLG is one isoform of the Klotho family of factors that coordinate interaction between different FGF ligands and the FGF receptor. We also found that knockdown of KLG induced another member of the Klotho family, Klotho beta (KLB). Induction of KLB was maintained and could activate ERK1/2 in immortalized cells. Supplementation of the culture medium with the KLB ligand FGF19 had a similar effect on hTERT-expressing HCECs as knockdown of KLG regarding both immortalization and down-regulation of the tumor suppressor Klotho alpha. Together, these data suggest that KLB is an important regulator in the immortalization of HCECs by facilitating FGF19 growth factor signaling.

Is cellular senescence important in pediatric kidney disease?

Somatic cellular senescence (SCS) describes the limited ability of cells to divide. Normally, SCS is associated with physiological aging, but evidence suggests that it may play a role in disease progression, even in young patients. Stressors such as acute injury or chronic inflammation may induce SCS, which in turn exhausts organ regenerative potential. This review summarizes what is known about SCS in the kidney with aging and disease. As most patients with chronic kidney disease (CKD) also develop cardiovascular complications, a second focus of this review deals with the role of SCS in cardiovascular disease. Also, as SCS seems to accelerate CKD and cardiovascular disease progression, developing strategies for new treatment options that overcome SCS or protect a patient from it represents an exciting challenge.

Tumor suppressor and aging biomarker p16(INK4a) induces cellular senescence without the associated inflammatory secretory phenotype

Cellular senescence suppresses cancer by preventing the proliferation of cells that experience potentially oncogenic stimuli. Senescent cells often express p16(INK4a), a cyclin-dependent kinase inhibitor, tumor suppressor, and biomarker of aging, which renders the senescence growth arrest irreversible. Senescent cells also acquire a complex phenotype that includes the secretion of many cytokines, growth factors, and proteases, termed a senescence-associated secretory phenotype (SASP). The SASP is proposed to underlie age-related pathologies, including, ironically, late life cancer. Here, we show that ectopic expression of p16(INK4a) and another cyclin-dependent kinase inhibitor, p21(CIP1/WAF1), induces senescence without a SASP, even though they induced other features of senescence, including a stable growth arrest. Additionally, human fibroblasts induced to senesce by ionizing radiation or oncogenic RAS developed a SASP regardless of whether they expressed p16(INK4a). Cells induced to senesce by ectopic p16(INK4a) expression lacked paracrine activity on epithelial cells, consistent with the absence of a functional SASP. Nonetheless, expression of p16(INK4a) by cells undergoing replicative senescence limited the accumulation of DNA damage and premature cytokine secretion, suggesting an indirect role for p16(INK4a) in suppressing the SASP. These findings suggest that p16(INK4a)-positive cells may not always harbor a SASP in vivo and, furthermore, that the SASP is not a consequence of p16(INK4a) activation or senescence per se, but rather is a damage response that is separable from the growth arrest.

Cellular Senescence - its role in cancer and the response to ionizing radiation

Cellular senescence is a normal biological process that is initiated in response to a range of intrinsic and extrinsic factors that functions to remove irreparable damage and therefore potentially harmful cells, from the proliferative pool. Senescence can therefore be thought of in beneficial terms as a tumour suppressor. In contrast to this, there is a growing body of evidence suggesting that senescence is also associated with the disruption of the tissue microenvironment and development of a pro-oncogenic environment, principally via the secretion of senescence-associated pro-inflammatory factors. The fraction of cells in a senescent state is known to increase with cellular age and from exposure to various stressors including ionising radiation therefore, the implications of the detrimental effects of the senescent phenotype are important to understand within the context of the increasing human exposure to ionising radiation. This review will discuss what is currently understood about senescence, highlighting possible associations between senescence and cancer and, how exposure to ionising radiation may modify this.

Lessons from senescence: Chromatin maintenance in non-proliferating cells

Cellular senescence is an irreversible proliferation arrest, thought to contribute to tumor suppression, proper wound healing and, perhaps, tissue and organismal aging. Two classical tumor suppressors, p53 and pRB, control cell cycle arrest associated with senescence. Profound molecular changes occur in cells undergoing senescence. At the level of chromatin, for example, senescence associated heterochromatic foci (SAHF) form in some cell types. Chromatin is inherently dynamic and likely needs to be actively maintained to achieve a stable cell phenotype. In proliferating cells chromatin is maintained in conjunction with DNA replication, but how non-proliferating cells maintain chromatin structure is poorly understood. Some histone variants, such as H3.3 and macroH2A increase as cells undergo senescence, suggesting histone variants and their associated chaperones could be important in chromatin structure maintenance in senescent cells. Here, we discuss options available for senescent cells to maintain chromatin structure and the relative contribution of histone variants and chaperones in this process. This article is part of a Special Issue entitled: Histone chaperones and chromatin assembly.

Deoxycholic acid causes DNA damage while inducing apoptotic resistance through NF-κB activation in benign Barrett's epithelial cells

Gastroesophageal reflux is associated with adenocarcinoma in Barrett's esophagus, but the incidence of this tumor is rising, despite widespread use of acid-suppressing medications. This suggests that refluxed material other than acid might contribute to carcinogenesis. We looked for potentially carcinogenetic effects of two bile acids, deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA), on Barrett's epithelial cells in vitro and in vivo. We exposed Barrett's (BAR-T) cells to DCA or UDCA and studied the generation of reactive oxygen/nitrogen species (ROS/RNS); expression of phosphorylated H2AX (a marker of DNA damage), phosphorylated IkBα, and phosphorylated p65 (activated NF-κB pathway proteins); and apoptosis. During endoscopy in patients, we took biopsy specimens of Barrett's mucosa before and after esophageal perfusion with DCA or UDCA and assessed DNA damage and NF-κB activation. Exposure to DCA, but not UDCA, resulted in ROS/RNS production, DNA damage, and NF-κB activation but did not increase the rate of apoptosis in BAR-T cells. Pretreatment with N-acetyl-l-cysteine (a ROS scavenger) prevented DNA damage after DCA exposure, and DCA did induce apoptosis in cells treated with NF-κB inhibitors (BAY 11-7085 or AdIκB superrepressor). DNA damage and NF-κB activation were detected in biopsy specimens of Barrett's mucosa taken after esophageal perfusion with DCA, but not UDCA. These data show that, in Barrett's epithelial cells, DCA induces ROS/RNS production, which causes genotoxic injury, and simultaneously induces activation of the NF-κB pathway, which enables cells with DNA damage to resist apoptosis. We have demonstrated molecular mechanisms whereby bile reflux might contribute to carcinogenesis in Barrett's esophagus.

Immortalized cells as experimental models to study cancer

The development of cancer is a multi-step process in which normal cells sustain a series of genetic alterations that together program the malignant phenotype. Much of our knowledge of cancer biology results from the detailed study of specimens and cell lines derived from patient tumors. While these approaches continue to yield critical information regarding the identity, number, and types of alterations found in human tumors, further progress in understanding the molecular basis of malignant transformation depends upon the generation and use of increasingly sophisticated experimental models of cancer. Over the past several years, the recognition that telomeres and telomerase play essential roles in regulating cell lifespan now permits the development of new models of human cancer. Here we review recent progress in the use of immortalized human cells as a foundation for understanding the molecular basis of cancer.

Use of exogenous hTERT to immortalize primary human cells

A major obstacle to the immortalization of primary human cells and the establishment of human cell lines is telomere-controlled senescence. Telomere-controlled senescence is caused by the shortening of telomeres that occurs each time somatic human cells divide. The enzyme telomerase can prevent the erosion of telomeres and block the onset of telomere-controlled senescence, but its expression is restricted to the early stages of embryonic development, and in the adult, to rare cells of the blood, skin and digestive track. However, we and others have shown that the transfer of an exogenous hTERT cDNA, encoding the catalytic subunit of human telomerase, can be used to prevent telomere shortening, overcome telomere-controlled senescence, and immortalize primary human cells. Most importantly, hTERT alone can immortalize cells without causing cancer-associated changes or altering phenotypic properties. Primary human cells that have so far been established by the forced expression of hTERT alone include fibroblasts, retinal pigmented epithelial cells, endothelial cells, oesophageal squamous cells, mammary epithelial cells, keratinocytes, osteoblasts, and Nestin-positive cells of the pancreas. In this article, we discuss the use of hTERT to immortalize of human cells, the properties of hTERT-immortalized cells, and their applications to cancer research and tissue engineering.

Nevus senescence

Melanomas and nevi share many of the same growth-promoting mutations. However, melanomas grow relentlessly while benign nevi eventually undergo growth arrest and stabilize. The difference in their long-term growth potential may be attributed to activation of cellular senescence pathways. The primary mediator of senescence in nevi appears to be p16. Redundant, secondary senescence systems are also present and include the p14-p53-p21 pathway, the IGFBP7 pathway, the FBXO31 pathway, and the PI3K mediated stress induced endoplasmic reticulum unfolded protein response. It is evident that these senescence pathways result in an irreversible arrest in most instances; however, they can clearly be overcome in melanoma. Circumvention of these pathways is most frequently associated with gene deletion or transcriptional repression. Reactivation of senescence mechanisms could serve to inhibit melanoma tumor progression.

Human myotubes from myoblast cultures undergoing senescence exhibit defects in glucose and lipid metabolism

Adult stem cells are known to have a finite replication potential. Muscle biopsy-derived human satellite cells (SCs) were grown at different passages and differentiated to human myotubes in culture to analyze the functional state of various carbohydrate and lipid metabolic pathways. As the proliferative potential of myoblasts decreased dramatically with passage number, a number of cellular functions were altered: the capacity of myoblasts to fuse and differentiate into myotubes was reduced, and metabolic processes in myotubes such as glucose uptake, glycogen synthesis, glucose oxidation and fatty acid β-oxidation became gradually impaired. Upon insulin stimulation, glucose uptake and glycogen synthesis increased but as the cellular proliferative capacity became gradually exhausted, the response dropped concomitantly. Palmitic acid incorporation into lipids in myotubes decreased with passage number and could be explained by reduced incorporation into diacyl- and triacylglycerols. The levels of long-chain acyl-CoA esters decreased with increased passage number. Late-passage, non-proliferating, myoblast cultures showed strong senescence-associated β-galactosidase activity indicating that the observed metabolic defects accompany the induction of a senescent state. The main function of SCs is regeneration and skeletal muscle-build up. Thus, the metabolic defects observed during aging of SC-derived myotubes could have a role in sarcopenia, the gradual age-related loss of muscle mass and strength.

CDK4 and cyclin D1 allow human myogenic cells to recapture growth property without compromising differentiation potential

In vitro culture systems of human myogenic cells contribute greatly to elucidation of the molecular mechanisms underlying terminal myogenic differentiation and symptoms of neuromuscular diseases. However, human myogenic cells have limited ability to proliferate in culture. We have established an improved immortalization protocol for human myogenic cells derived from healthy and diseased muscles; constitutive expression of mutated cyclin-dependent kinase 4, cyclin D1 and telomerase immortalized human myogenic cells. Normal diploid chromosomes were preserved after immortalization. The immortalized human myogenic cells divided as rapidly as primary human myogenic cells during the early passages, and underwent myogenic, osteogenic and adipogenic differentiation under appropriate culture conditions. The immortalized cells contributed to muscle differentiation upon xenotransplantation to immunodeficient mice under conditions of regeneration following muscle injury. We also succeeded in immortalizing cryopreserved human myogenic cells derived from Leigh disease patients following primary culture. Forced expression of the three genes shortened their cell cycle to < 30 h, which is similar to the doubling time of primary cultured human myogenic cells during early passages. The immortalization protocol described here allowed human myogenic cells to recapture high proliferation activity without compromising their differentiation potential and normal diploidy.

Regulation of senescence in cancer and aging

Senescence is regarded as a physiological response of cells to stress, including telomere dysfunction, aberrant oncogenic activation, DNA damage, and oxidative stress. This stress response has an antagonistically pleiotropic effect to organisms: beneficial as a tumor suppressor, but detrimental by contributing to aging. The emergence of senescence as an effective tumor suppression mechanism is highlighted by recent demonstration that senescence prevents proliferation of cells at risk of neoplastic transformation. Consequently, induction of senescence is recognized as a potential treatment of cancer. Substantial evidence also suggests that senescence plays an important role in aging, particularly in aging of stem cells. In this paper, we will discuss the molecular regulation of senescence its role in cancer and aging. The potential utility of senescence in cancer therapeutics will also be discussed.

The role of telomeres in the ageing of human skin

Skin is a self-renewing tissue that is required to go through extensive proliferation throughout the lifespan of an organism. Telomere shortening acts as a mitotic clock that prevents aberrant proliferation such as cancer. A consequence of this protection is cellular senescence and ageing. The telomerase enzyme complex maintains telomere length in germline cells and in cancer cells. Telomerase is also active in certain somatic cells such as those in the epidermis but is almost undetectable in the dermis. Increasing evidence indicates that telomerase plays a significant role in maintenance of skin function and proliferation. Mutations in telomerase component genes in the disease dyskeratosis congenita result in numerous epidermal abnormalities. Studies also indicate that telomerase activity in epidermal stem cells might have roles that go beyond telomere elongation. Telomeres in skin cells may be particularly susceptible to accelerated shortening because of both proliferation and DNA-damaging agents such as reactive oxygen species. Skin might present an accessible tissue for manipulation of telomerase activity and telomere length with the potential of ameliorating skin diseases associated with ageing.

Cancer-related inflammation and Barrett's carcinogenesis: interleukin-6 and STAT3 mediate apoptotic resistance in transformed Barrett's cells

Cancer-related inflammation recently has been proposed as a major physiological hallmark of malignancy. Some genetic alterations known to promote cellular proliferation and induce malignant transformation also may participate in an intrinsic inflammatory pathway that produces a cancer-promoting inflammatory microenvironment. Little is known about this intrinsic inflammatory pathway in Barrett's esophagus. We have used a series of nontransformed and transformed human Barrett's epithelial cell lines developed in our laboratory to explore the potential contribution of interleukin (IL)-6 and signal transducer and activator of transcription (STAT3) (key molecules in the intrinsic inflammatory pathway) to Barrett's carcinogenesis. We determined IL-6 mRNA expression and protein secretion and protein expression of activated phospho-STAT3 and its downstream target myeloid cell leukemia (mcl)-1 (Mcl-1). We used an IL-6 blocking antibody and two JAK kinase inhibitors (AG490 and JAK inhibitor I) to assess whether STAT3 activation is IL-6 dependent. We also used small interfering RNAs (siRNAs) to STAT3 and Mcl-1 to assess effects of STAT3 pathway inhibition on apoptosis. Phospho-STAT3 was expressed only by transformed Barrett's cells, which also exhibited higher levels of IL-6 mRNA and of IL-6 and Mcl-1 proteins than nontransformed Barrett's cells. STAT3 phosphorylation could be blocked by IL-6 blocking antibody and by AG490 and JAK inhibitor I. In transformed Barrett's cells, rates of apoptosis following exposure to deoxycholic acid were significantly increased by transfection with siRNAs for STAT3 and Mcl-1. We conclude that activation of the IL-6/STAT3 pathway in transformed Barrett's epithelial cells enables them to resist apoptosis. These findings demonstrate a possible contribution of the intrinsic inflammatory pathway to carcinogenesis in Barrett's esophagus.

Four faces of cellular senescence

Cellular senescence is an important mechanism for preventing the proliferation of potential cancer cells. Recently, however, it has become apparent that this process entails more than a simple cessation of cell growth. In addition to suppressing tumorigenesis, cellular senescence might also promote tissue repair and fuel inflammation associated with aging and cancer progression. Thus, cellular senescence might participate in four complex biological processes (tumor suppression, tumor promotion, aging, and tissue repair), some of which have apparently opposing effects. The challenge now is to understand the senescence response well enough to harness its benefits while suppressing its drawbacks.

Heterogeneous activation of p19Arf in pulmonary artery smooth muscle cells

p19(ARF) is a tumor suppressor that leads to cell cycle arrest or apoptosis by stabilizing p53. p19(ARF) is not critical for cell cycle regulation under normal conditions, but loss of p19(ARF) is seen in many human cancers, and a murine p19(Arf) knockout model leads to malignant proliferation and tumor formation; its role in controlling nonmalignant proliferation is less defined. To examine this question, pulmonary artery smooth muscle cells (PASMC) were expanded in culture from a transgenic mouse in which the coding sequence of the p19(Arf) gene was replaced with a cDNA encoding green fluorescent protein (GFP), leaving the promoter intact. During the first 10 days in culture, wild-type, heterozygous, and knockout PASMC grew similarly, but, by day 14, p19(Arf)-deficient PASMC proliferated faster than p19(Arf) heterozygous or wild-type cells; reexpression of p19(Arf) prevented the increased proliferation. This time course correlated with activation of the p19(Arf) promoter, as indicated by the appearance of GFP positivity in p19(Arf)-deficient PASMC. By day 42, ∼80% of p19(Arf)-deficient cells were GFP-positive. When GFP-positive, p19(Arf)-deficient cells were sorted and subcultured separately, they remained GFP-positive, indicating that once cells had activated the p19(Arf) promoter, the promoter remained active in those and all subsequent daughter cells. In contrast, GFP-negative p19(Arf)-deficient cells gave rise to a combination of GFP-positive and -negative daughter cells over time. These results suggest that a subpopulation of PASMC are resistant to the signals that activate the p19(Arf) promoter, an event that would normally target these cells for arrest or cell death.

The essence of senescence

Almost half a century after the first reports describing the limited replicative potential of primary cells in culture, there is now overwhelming evidence for the existence of "cellular senescence" in vivo. It is being recognized as a critical feature of mammalian cells to suppress tumorigenesis, acting alongside cell death programs. Here, we review the various features of cellular senescence and discuss their contribution to tumor suppression. Additionally, we highlight the power and limitations of the biomarkers currently used to identify senescent cells in vitro and in vivo.

Malignant transformation of non-neoplastic Barrett's epithelial cells through well-defined genetic manipulations

Background

Human Barrett's cancer cell lines have numerous, poorly-characterized genetic abnormalities and, consequently, those lines have limited utility as models for studying the early molecular events in carcinogenesis. Cell lines with well-defined genetic lesions that recapitulate various stages of neoplastic progression in Barrett's esophagus would be most useful for such studies.

Methodology/Principal Findings

To develop such model cell lines, we started with telomerase-immortalized, non-neoplastic Barrett's epithelial (BAR-T) cells, which are spontaneously deficient in p16, and proceeded to knock down p53 using RNAi, to activate Ras by introducing oncogenic H-Ras^G12V, or both. BAR-T cells infected with either p53 RNAi or oncogenic H-Ras^G12V alone maintained cell-to-cell contact inhibition and did not exhibit anchorage-independent growth in soft agar. In contrast, the combination of p53 RNAi knockdown with expression of oncogenic H-Ras^G12V transformed the p16-deficient BAR-T cells, as evidenced by their loss of contact inhibition, by their formation of colonies in soft agar, and by their generation of tumors in immunodeficient mice.

Conclusions/Significance

Through these experiments, we have generated a number of transformed and non-transformed cell lines with well-characterized genetic abnormalities recapitulating various stages of carcinogenesis in Barrett's esophagus. These lines should be useful models for the study of carcinogenesis in Barrett's esophagus, and for testing the efficacy of chemopreventive and chemotherapeutic agents.

Bacterial aging: from mechanistic basis to evolutionary perspective

Aging-defined as the progressive impairment of an organism's functional capacity, resulting from deleterious changes in cells, organs, and biological systems-is one of the most fundamental features of Eukaryotes, from humans to the unicellular budding yeast Saccharomyces cerevisiae. It has recently been reported that this may also be the case for certain (if not all) types of bacteria. In this paper, the current view on the mechanistic background and evolutionary significance of bacterial kind of aging is presented, with particular emphasis on the role of asymmetric cell division, the characteristics of stationary growth phase, and the role of oxidative protein damage.

Human keratinocytes are efficiently immortalized by a Rho kinase inhibitor

Primary human keratinocytes are useful for studying the pathogenesis of many different diseases of the cutaneous and mucosal epithelia. In addition, they can form organotypic tissue equivalents in culture that can be used as epidermal autografts for wound repair as well as for the delivery of gene therapy. However, primary keratinocytes have a finite lifespan in culture that limits their proliferative capacity and clinical use. Here, we report that treatment of primary keratinocytes (originating from 3 different anatomical sites) with Y-27632, a Rho kinase inhibitor, greatly increased their proliferative capacity and resulted in efficient immortalization without detectable cell crisis. More importantly, the immortalized cells displayed characteristics typical of primary keratinocytes; they had a normal karyotype and an intact DNA damage response and were able to differentiate into a stratified epithelium. This is the first example to our knowledge of a defined chemical compound mediating efficient cell immortalization, and this finding could have wide-ranging and profound investigational and medical applications.

Acid and bile salt-induced CDX2 expression differs in esophageal squamous cells from patients with and without Barrett's esophagus

BACKGROUND & AIMS

It is not clear why only a minority of patients with gastroesophageal reflux disease (GERD) develop Barrett's esophagus. We hypothesized that differences among individuals in molecular pathways activated when esophageal squamous epithelium is exposed to reflux underlie the development of Barrett's metaplasia.

METHODS

We used esophageal squamous cell lines from patients who had GERD with Barrett's esophagus (normal esophageal squamous [NES]-B3T and NES-B10T) and without Barrett's esophagus (NES-G2T and NES-G4T) to study effects of acid and bile salts on expression of the CDX2 gene. Bay 11-705, Ad5 inhibitor kappaB(IkappaB)alpha-SR, and site-directed mutagenesis were used to explore effects of nuclear factor-kappaB (NF-kappaB) inhibition on CDX2 promoter activity; DNA binding of the NF-kappaB subunits p50 and p65 was assessed by chromatin immune-precipitation.

RESULTS

Acid and bile salts increased CDX2 messenger RNA (mRNA), protein, and promoter activity in NES-B3T and NES-B10T cells, but not in NES-G2T or NES-G4T cells. Inhibition of NF-kappaB abolished the increase in CDX2 promoter activity. Increased CDX2 promoter activity was associated with nuclear translocation of p50, which bound to the promoter. We found CDX2 mRNA in 7 of 10 esophageal squamous biopsy specimens from patients with Barrett's esophagus, but in only 1 of 10 such specimens from patients who had GERD without Barrett's esophagus.

CONCLUSIONS

Acid and bile salts induce CDX2 mRNA and protein expression in esophageal squamous cells from patients with Barrett's esophagus, but not from GERD patients without Barrett's esophagus. We speculate that these differences in acid- and bile salt-induced activation of molecular pathways may underlie the development of Barrett's metaplasia.